Schools-2009 IEQc8.1: Daylight and Views—Daylight

  • Schools IEQc8.1 action steps and doc diagram

  • Use a collaborative design process

    Access to daylight inside buildings makes for healthier and more comfortable occupants—and is also linked with greater productivity. When designed with proper glare control and minimized solar heat gain, daylighting provides high-quality light while reducing energy use for lighting and for cooling. Increased daylight through increased vision glazing can help projects earn IEQc8.2 for access to views. Realizing the benefits of daylighting requires a collaborative design process.

    Balance other design goals

    Keep in mind that daylighting strategies must balance with other design goals. For example, you will want to provide enough glazing area for lighting, and plan for open spaces that allow for light transfer, but not at the expense of too much heat gain, glare, or loss of privacy. Incorporating daylighting goals into the early planning stages will help project teams avoid design conflicts at more advanced stages. Daylighting goals should be laid out explicitly in the Owners Project Requirements document required for EAp1: Fundamental Commissioning.

    Documentation can be cumbersome

    This credit is easy to achieve for projects with large windows, open floor plates, and most occupied areas near the perimeter, but the documentation may be cumbersome for some large projects, depending on the chosen compliance path.

  • FAQs for IEQc8.1

    What spaces are considered regularly occupied and must be included in the calculations?

    The USGBC's IEQ Space Matrix has detailed guidance that is helpful for any spaces you aren't sure about.

    When should daylight measurements be taken?

    LEED does not prescribe the date or time, but it is recommended that they be taken close to noon under clear sky conditions, and, if possible, on or near one of the two equinoxes.

    Do I need to have glare control devices?

    Yes.

    Where can I find the Supplemental Views and Daylight Calculator?

    On LEED Online, in the credit, under credit resources.

    Do I need to submit the Supplemental Views and Daylight Calculator?

    You must submit a spreadsheet which contains all the information required on the calculator, and submitting the LEED Online calculator is recommended, but some teams have preferred to create their own, and have had them accepted.

    Can I average the compliant square footage between 9 a.m. and 3 p.m. for a space and use the average as the compliant square footage?

    No, the compliant square footage would be the worst-case scenario between the two times. For example, a 900 ft2 space located on the western side of a building is 100% compliant at 9 a.m. but only 50% compliant at 3 p.m. The compliant square footage in this case is 450 ft2.

    What daylight simulation software can I use for LEED compliance?

    LEED doesn’t require certain software to run the compliance calculation. However, the simulation should be able to run under “clear sky” conditions and calculate illuminance levels at 2’-6” above finished floor (AFF).

    Can I use Option 2: Prescriptive method if I have:

    • Windows with different Tvis values within the same wall width?

    • Windows with different head heights within the same wall width?

    • Windows with different sill heights (and above 30”) within the same wall width?

    • Windows with permanent shading devices?

    • Skylights with different Tvis values within the same ceiling area?

    • Clear skylights?

    • Light that is transferred between one room to the next through an interior wall opening—glazed or unglazed?

    • A Tvis/WFR value above 0.180?

    • Rooms that borrow light from an atrium?

    • Clerestory windows?

    • Roof monitors?

    • Tubular daylighting devices such as Solatube?

    • Roof overhangs?

    • Shared daylighting scenarios?

    No. The only option in any of these cases will be the simulation or the measurement methods.

Legend

  • Best Practices
  • Gotcha
  • Action Steps
  • Cost Tip

Pre-Design

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  • Focus on optimizing building orientation. Look for opportunities to optimize the glazing on each orientation to account for varying heat gain and lighting angles. When selecting a site, look for potential obstacles to daylight such as neighboring buildings, vegetation, and topography.

  • To reduce heating loads, use daylighting strategies in tandem with passive solar heating strategies, such as using materials with greater thermal mass and orienting the building for maximum solar gain.

  • To reduce cooling loads, use overhangs, lightshelves or fins, courtyards, and lightwells to block high-angle summer sun and low-angle morning and afternoon sun. These strategies also reduce glare and can improve daylighting by reflecting it deeper into the building.

  • Glare can become a problem if you have too much glass, or east- and west-facing glass. Using shading devices can allow projects to combat glare and still have large expanses of glazing. Daylighting from the north is consistent and high quality, while daylighting from the south is abundant and comparatively easy to control.

  • Large areas of glazing may cause unwanted heat gain and compromise energy efficiency. However, daylighting may require less glazing than you think—about 40% window-to-wall ratio may be more than you need. Glazing closer to the ceiling will have a greater daylight benefit than glazing near the floor—anything below 30 inches is considered to have no daylight benefit.

  • When programming, identify occupant lighting needs that could be met with daylight. The Illuminating Engineering Society of North America (IES) has prescribed footcandle levels for project types, occupant types, and tasks.

  • Set daylighting goals at the initial goal-setting workshop and incorporate them into the Owners Project Requirements document required for EAc1: Fundamental Commissioning.

  • Having two different sources of daylight in a space will help minimize contrast and shadows.

Schematic Design

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  • Identify regularly occupied spaces that need to be included in the LEED daylight calculation. Locate these spaces near perimeter glazing, courtyards, or other daylight sources.

  • Your project's regularly occupied spaces should be defined consistently across other LEED credits, especially IEQc8.2: Daylight and Views—Views.

  • Some applicable spaces may be exempt from the daylighting calculation if their uses are daylight-sensitive. Examples include museum or gallery spaces, auditoriums and high-security areas. If you have daylight-sensitive spaces in your project that you would like to exempt from the calculation, you must provide a detailed narrative explanation and exemption request along with the credit documentation. This requests are scrutinized carefully, however, and may not be successful.

  • Find out the Visual Light Transmittance (VLT) value of the glazing and enter it on the LEED credit form for each occupied space. The VLT is usually included with the glazing specifications.

  • Take the VLT of the whole window, not just the glazing, to account for shading from mullions.

  • More natural light is transmitted through glazing with higher VLT values, but higher VLT values tend to correlate with higher solar heat gain coefficients (SHGC). Assess the optimal balance of these values, along with U-value, based on the project’s climate and heating and cooling needs. These values are available on manufacturers’ specifications.

  • Hold an integrated design meeting with the architect, interior designers, mechanical engineer, lighting designer and the end users to discuss daylighting-related tradeoffs.   Optimize glazing area while preventing excessive heat gain and glare; and use open space planning that allows for greater light transfer while preserving privacy.

  • Consider designing spaces with narrow floor plates so that most spaces are near windows and have access to daylight.

  • Daylit classroomA Chartwell schools classroom with abundant daylight and electric light controlled by a photo sensor. Photo – EHDDLocate classrooms and other regularly occupied spaces near perimeter glazing, courtyards, or other daylight sources. Support areas such as restrooms, storage, and areas that do not require or would be hindered by windows, such as restrooms, storage areas, and transitions can be located near the building core.

  • Prescriptive compliance paths for EAc1 (other than energy modeling) do not allow window-to-wall ratios greater than the relevant reference standard. Projects using these compliance paths are limited in the amount of allowable glazing area.

  • Designing for daylighting will allow you to reduce the number of ambient light fixtures and their frequency of use, reducing the cost of electric lighting both upfront and in operations.

  • Retailers may see increased sales linked with daylighting, according to studies showing a correlation between sales and natural lighting. Additional savings may be seen by employers through increased employee retention/satisfaction as well as productivity and reduced absenteeism.

  • Choose a LEED compliance path to verify that the daylighting meets the footcandle requirements of 25–500 footcandles for 75%–90% of regularly occupied spaces.

    • Option 1:  Computer daylight simulations can be the most effective design tool, but hiring a modeler will be an upfront cost.
    • Option 2: Prescriptive LEED calculations can help inform design, but not as accurately as a daylight simulation. The calculations can be time-consuming for large buildings, but do not require expert help.  The prescriptive calculations will only take window, wall, ceiling and floor areas, and glazing type into account, so other methods that help daylighting such as lightshelves and light-colored finishes won’t be factored in.
    • Option 3: Daylight metering can be an inexpensive way to measure actual footcandles, but won’t be accurate until construction is complete, when the results cannot help to inform design.

Design Development

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  • Explore a combination of daylight strategies such as space planning techniques, glazing selection, lightshelves and more.

  • Interior finishes can enhance or hinder daylight levels. Specify light-colored ceiling and wall paint to bounce light further into the room.

  • A common misconception is that a design needs to have more glass for effective daylighting. But effective daylighting can also be achieved with smaller apertures and glazing designed for specific indirect light, located high in a space to bounce light on to a ceiling.

  • Daylight sensors that adjust lamp brightness based on the presence of natural light can greatly reduce lighting energy loads. On average, commercial buildings use 25% of their energy for lighting. Dimming ballasts are more expensive and complicated to specify than stepped ballasts. Stepped lighting is considered less attractive because the dimming is not gradual  but can do an excellent job reducing energy use.

  • Daylight controls, sensors, integrated blinds, and lighting controls come with moderate first costs but will bring energy savings over the long run.

  • Integrate glare control into the design.

  • Identify designs that combine glazing and building elements for optimum daylighting, such as window frames with integrated overhangs or light shelves. However, make sure that there is a thermal break (insulation) between the interior and the lightshelves, or these could become large-scale radiators of interior heat.

  • Glare can hinder the use of a space and be unpleasant for occupants. Daylight modeling can help project teams anticipate problem areas due to sun angles as they interact with the architecture. Exterior and interior shading along with associated controls can greatly reduce the effects of glare.

  • Fill out the LEED credit form with the names of the regularly occupied spaces and their square footage.

  • Option 1:  Computer Simulation

  • Use daylight simulation software to adjust daylight design as needed before it is finalized.

  • Coupling daylight modeling with energy modeling can help project teams make effective decisions about daylighting as it relates to other strategies like thermal massing, window area, window efficiency, and shading.

  • Simulation makes documentation easy by clearly indicating compliant areas.

  • Simulation is the only way to account during the design phase for daylight designs that have many variables such as the use of lightshelves and light-colored interior finishes. The prescriptive  compliance path (Option 2) takes into account only walls, windows, floor and ceiling areas, and the measurement path (Option 3) will not help inform design

  • Daylight simulations may add an upfront cost but they offer fast payback in the form of effective daylighting strategy selection resulting in reduced energy costs.

  • Option 2:  Prescriptive Design

  • Run prescriptive design calculations to verify that the required percentage of floor area meets the required levels.

  • This compliance path does not require modeling and can still help inform decisions during the design phase. However, the documentation and calculations can be complicated and time-consuming.

  • Option 3:  Measurement

  • Measuring daylighting with handheld light meters can be time-consuming for large areas. Also, you are likely to need to defer this credit to the construction phase LEED submittal so that accurate light readings can be taken with interior walls in place.

  • Measurement can account for complex daylight designs but does not help inform the design process. It can only confirm compliance once the space has already been constructed.  At that late phase, it may be too costly to make design changes to bring more floor area into compliance.

  • Measurement is a low-cost compliance method but may not help to optimize daylight during the design phase. An optimized daylight design can cut down substantially on lighting costs over the long run.

  • Option 4: Combination

  • A hybrid compliance path may be the best solution for some projects. For example, if most of the regularly occupied spaces pass the calculation criteria in the prescriptive path, and a portion of the spaces fall short very narrowly or use strategies like lightshelves not accounted for by the prescriptive path, measurement of those spaces after finishes are complete could demonstrate that they are sufficiently daylit after finishes are complete.

Construction Documents

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  • For Options 1 and 2, enter square footage for the portions of the regularly occupied areas that meet the daylight requirements in the LEED credit form and upload all required documents to LEED Online.

  • Incorporate daylight-related items such as lightshelves, daylight sensors, and light-colored paint into specifications.

  • During the value engineering process, ensure that components critical to the daylight design, such as high-performance glazing and internal shading devices, are not removed from the project.

Construction

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  • For Option 3, take daylight measurements with a hand-held light meter and record the values on a 10x10 grid plan. Enter square footage for the portions of the regularly occupied areas that meet the daylight requirement in the LEED credit form and upload all required documents to LEED Online.

  • Measuring daylight levels can be a time-consuming process in large buildings. Measurements are taken on a 10-foot by 10-foot grid, with four measurement points for each 10 ft2 section. Taking and recording each measurement takes about 30 seconds—not including setting up the grid—for a total of about two minutes per grid section.

  • Daylight sensors and other daylight controls should be added to commissioned systems for lighting for EAp1: Fundamental Commissioning.

Operations & Maintenance

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  • Cleaning plans need to integrate the maintenance of interior and exterior shading and control dust so that reflectivity is not compromised.

  • Daylighting controls can be set and tailored for each space. The facility manager or another designated person should be in charge of adjusting the settings to meet the needs of occupants.

  •  Educate staff and occupants on daylight-related and glare-control technologies. Some daylighting controls such as shades or blinds may require occupant operation, and without instruction, may not be used properly, resulting in the building not operating as designed.

  • USGBC

    Excerpted from LEED 2009 for Schools New Construction and Major Renovations

    COPYRIGHT © 2009 BY THE U.S. GREEN BUILDING COUNCIL, INC. ALL RIGHTS RESERVED

    IEQ Credit 8.1: Daylight and views - daylight

    1–3 Points

    Intent

    To provide building occupants with a connection between indoor spaces and the outdoors through the introduction of daylight and views into the regularly occupied areas of the building.

    Requirements

    Option 1. Simulation

    Demonstrate through computer simulation that the applicable spaces achieve daylight illuminance levels of a minimum of 10 footcandles (fc1. A footcandle (fc) is a measure of light falling on a given surface. One footcandle is defined as the quantity of light falling on a 1-square-foot area from a 1 candela light source at a distance of 1 foot (which equals 1 lumen per square foot). Footcandles can be measured both horizontally and vertically by a footcandle meter or light meter. 2. The non-metric measurement of lumens per square foot, one footcandle is the amount of light that is received one foot from a light source called a candela, which is based on the light output of a standardized candle. A common range for interior lighting is 10 to 100 footcandles, while exterior daytime levels can range from 100 to over 10,000 footcandles. Footcandles decrease with distance from the light source. The metric equivalent of a foot candle is 10.76 lux, or lumens per square meter.) (108 luxMeasurement of lumens per square meter.) and a maximum of 500 fc (5,400 lux) in a clear sky condition on September 21 at 9 a.m. and 3 p.m.

    Provide glare control devices to avoid high-contrast situations that could impede visual tasks. However, designs that incorporate view-preserving automated shades for glare control may demonstrate compliance for only the minimum 10 fc (108 lux) illuminance level.

    Option 2. Prescriptive

    For sidelighting zones:

    • Achieve a value, calculated as the product of the visible light transmittance (VLT) and window-to-floor area

      ratio (WFRWindow-to-floor ratio (WFR) is the total area of the window (measured vertically from 30 inches above the finished floor to the top of the glass, multiplied by the width of the glass) divided by the floor area.) between 0.150 and 0.180.

      • 0.150 < VLT x WFR < 0.180


    • The window area included in the calculation must be at least 30 inches (0.8 meters) above the floor.
    • In section, the ceiling must not obstruct a line that extends from the window-head to a point on the floor that is located twice the height of the window-head from the exterior wall as measured perpendicular to the glass (see diagram on the next page).



    • Provide glare control devices to avoid high-contrast situations that could impede visual tasks. However, designs that incorporate view-preserving automated shades for glare control may demonstrate compliance for only the minimum 0.150 value.

    For toplighting zones:

    • The toplighting zone under a skylight is the outline of the opening beneath the skylight, plus in each direction the lesser of (see diagram below):

      • 70% of the ceiling height
      • 1/2 the distance to the edge of the nearest skylight
      • The distance to any permanent partition that is closer than 70% of the distance between the top of the partition and the ceiling.

    • Achieve skylight coverage for the applicable space (containing the toplighting zone) between 3% and 6% of the total floor area.
    • The skylight must have a minimum 0.5 VLT.
    • A skylight diffuser, if used, must have a measured haze value of greater than 90% when tested according to ASTMVoluntary standards development organization which creates source technical standards for materials, products, systems, and services D1003.
    Option 3. Measurement

    Demonstrate through records of indoor light measurements that a minimum daylight illumination level of 10 fc (108 lux) and a maximum of 500 fc (5,400 lux) has been achieved in the applicable spaces. Measurements must be taken on a 10-foot (3-meter) grid and shall be recorded on building floor plans.

    Provide glare control devices to avoid high-contrast situations that could impede visual tasks. However, designs that incorporate view-preserving automated shades for glare control may demonstrate compliance for only the minimum 10 fc (108 lux) illuminance level.

    Option 4. Combination

    Any of the above calculation methods may be combined to document the minimum daylight illumination in the applicable spaces.

    Potential Technologies & Strategies

    Design the building to maximize interior daylighting. Strategies to consider include building orientation, shallow floor plates, increased building perimeter, exterior and interior permanent shading devices, high-performance glazing, and high ceiling-reflectance values; additionally, automatic photocell-based controls can help to reduce energy use. Predict daylight factors via manual calculations or model daylighting strategies with a physical or computer model to assess footcandle levels and daylight factors achieved.

Technical Guides

Whole Building Design Guide—Guidance for Daylight Design

This is an excellent resource for researching how to apply different daylight strategies and the implications the design strategies may have.  Includes information on materials and methods of construction as well as calculation tools and software resources.

IESNA Recommended Practice of Daylighting—Daylight Design Guidance

This is the American industry authority on lighting levels and energy use.  The Illumination Engineering Society of North America (IESNA) publishes several design guides for recommended lighting levels, daylighting and much more.

Window 5.2 computer program—The Lawrence Berkeley National Laboratory

This is a database of window brands, VLT and U-values for different glazing manufacturers.  The program provides a versatile heat transfer analysis method.     

IEQ Space Matrix

This spreadsheet categories dozens of specific space types according to how they should be applied under various IEQ credits. This document is essential if you have questions about how various unique space types should be treated.

Software Tools

AGi32—Lighting Design Software

This is one of the most frequently used daylight modeling computer simulation programs.  AGi32 offers lighting analysis software for calculations and renderings of electric lighting and daylighting systems.

Virtual Environment Apache Thermal Analysis Software

A simple modeling tool for preliminary light and energy analysis.  Virtual Environment software, or VE-Ware, gives you instant feedback on a building's energy consumption and carbon emissions, as well as benchmarking it against the Architecture 2030 Challenge if it is located in the US.  You can access the carbon and energy calculator through the Revit and SketchUp plug-ins.  

Building Lighting System Software Tools Directory

This is a comprehensive list of modeling tools compiled by the U.S. Department of Energy.

Radiance—Lighting Design Software

This daylight modeling tool is widely accepted in the lighting industry.

SketchUp

SketchUp is used to create 3-D graphic models that can help in your daylighting analysis and documentation.

Organizations

Heschong-Mahone Group

This is a lighting group that has published research on the effects of daylighting.

IES—Illumination Engineering Society of North America

This is the organization that sets lighting standards.  The IES also works directly with ASHRAE to develop energy standards.

Publications

Daylighting in Schools: Reanalysis Report

This is a case study for the effects of daylighting on productivity in schools.  Prepared by Heschong Mahone Group for the California Energy Commission.

Psychosocial Value of Space—Whole Building Design Guide

This is a study exploring the relationship of daylighting and other design features on human psychological well being.  By Judith Heerwagen -
J.H. Heerwagen & Associates, Inc.

Windows and Classrooms: A Study of Student Performance and the Indoor Environment

This is a case study for the effects of daylighting on productivity in schools.  Prepared by Heschong Mahone Group.

Daylight Measurement

Option 3

Take daylight measurements with a handheld light meter and record the values on a 10x10 grid. Enter square footage for the portions of the regularly occupied areas that meet the daylight requirement in LEED Online.

Prescriptive Compliance

Option 2

To use the prescriptive compliance path, follow a process like the one in this example, which achieves the credit using a combination of side and top lighting.

LEED Online Forms: Schools-2009 IEQ

The following links take you to the public, informational versions of the dynamic LEED Online forms for each Schools-2009 IEQ credit. You'll need to fill out the live versions of these forms on LEED Online for each credit you hope to earn.

Version 4 forms (newest):

Version 3 forms:

These links are posted by LEEDuser with USGBC's permission. USGBC has certain usage restrictions for these forms; for more information, visit LEED Online and click "Sample Forms Download."

Design Submittal

PencilDocumentation for this credit can be part of a Design Phase submittal.

100 Comments

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Gabriela G
Jan 09 2013
Guest
8 Thumbs Up

Option 3 - Measurement

We are now trying to achieve this point by the measurement option.
There is no mention in the book at what time the daylight measurement should be taken.
Would someone be familiar as to what time the measurement needs to be taken, or can it be taken at any time?
Also, for this credit do all the windows require glare controls? And if so, do they need to be manually operated...such as roll down curtains?

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Todd Reed Daylight Designer, 7group Jan 09 2013 LEEDuser Expert 3438 Thumbs Up

There is not specific time to take the measurements. However, to get the most out of the measurements it is suggested that the measurements be taken under clear sky conditions as close to noon as possible.

All windows in all spaces being included in the calculations require some form glare control device such as roller shades. These need to be controlled either manually or automatically.

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Gabriela G
Dec 13 2012
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8 Thumbs Up

Zone Floor Area ...Help!!!!!

Can someone please confirm the following.
If my window has a head height of 10 feet, then my zone floor area would be:
Twice the head height (20) times the length of the 60 degree line?
In this case if the 60 degree line was 20 feet long.....would the zone floor area be:
20x20=400 square feet?????

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Todd Reed Daylight Designer, 7group Dec 14 2012 LEEDuser Expert 3438 Thumbs Up

The depth of your zone is established by either twice the window height or if you have an overhang or interior obstruction then you must use the 60 degree angle which would intersect the lowest point of the overhang or interior obstruction. The length of the zone, side to side would be from wall to wall.

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Jill Dalglish President & Senior Engineer, Dalglish Daylighting Dec 14 2012 LEEDuser Expert 2744 Thumbs Up

Gabriela, Are you the same Gabriela who posted a similar question under the NC board? If not, please see that board for a good discussion of this question. http://www.leeduser.com/credit/NC-2009/IEQc8.1

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Gabriela G
Dec 13 2012
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8 Thumbs Up

Glare Control Type Question

For the "glare control type"....can it be an overhang of a second floor, or a canopy that is used for glare control?

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Todd Reed Daylight Designer, 7group Dec 14 2012 LEEDuser Expert 3438 Thumbs Up

No, a glare control device must be able to be manually operated by the occupants or automatically controlled. If you have implemented exterior shading or other architectural elements to help control glare and provide good daylighting, i would suggest that you use the simulation option.

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Jill Dalglish President & Senior Engineer, Dalglish Daylighting Dec 14 2012 LEEDuser Expert 2744 Thumbs Up

I disagree. I don't see any reason why you can't used fixed features for glare control. However, these features must shield the window from all direct glare for all occupied hours. Technically, even an extremely low TvisVisible light transmittance (VLT) (Tvis) is the ratio of total transmitted light to total incident light (i.e., the amount of visible spectrum, 380–780 nanometers of light passing through a glazing surface divided by the amount of light striking the glazing surface). The higher the Tvis value, the more incident light passes through the glazing. (usually accomplished with window obscuration) could block glare altogether.

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Todd Reed Daylight Designer, 7group Dec 14 2012 LEEDuser Expert 3438 Thumbs Up

I have had some long discussions about what is considered glare and glare control devices. I agree that overhangs or exterior shading devices can control some forms of glare, but in regards to someone using the prescriptive method, which is not orientation or climate based, how can it be proven that said devices do what it does. It can't. Therefore, with the prescriptive method, and even the other options, glare control devices are basically manual or automatic shades. The other reason GBCI consider shading devices shades is that many project probably do not take into account the effects of reflections, such as off facades of neighboring buildings and even windshields off cars in the parking lots. So a building may have exterior sun shades designed based on the sun path, but what do the occupants do when the sun is reflecting off a neighboring building or even off snow and they can;t block it?

I haven;t bought into the whole extreme low VLT solution to solve issues like these. The relation of the quality of view and the spectrum of light that the eye receives is very much connected to ones circadian rhythms and health. I will have to look for the study that i read awhile ago about the effects of the quantity of light that young adults are exposed to and its effects upon sleep. There is a part of the light spectrum which effects this. So if you were to use an extremely low VLT or obscure the view, this spectrum could be removed.

I'm a firm believer in providing as clear of glass and highest VLT possible. Make the inside as connected to the exterior as possible.

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Jill Dalglish President & Senior Engineer, Dalglish Daylighting Dec 14 2012 LEEDuser Expert 2744 Thumbs Up

I didn't see "prescriptive option" listed in the question. True, you should not be using the prescriptive option if you are using fixed glare control.

Daylighting for quality and daylighting for LEED are two different discussions as much as you and I would like that it wasn't. I agree for quality daylighting that visual spectrum should be preserved as much as possible, but there are quality low VLT glazings that will do this. Personally, I would not recommend this for a majority of windows in a buliding, but if you can't locate blinds on, for example, a window in an overhead door, a low VLT could be an option and an energy-efficient one.

Applying a "highest VLT as possible" policy in all situations ignores the complexity of the human visual system especially in different space types and reduces options for energy-efficient glazing.

Having a view is addressed in the Views credit. An option such as low VLT glazing should not be eliminated in the daylighting credit when daylighting for LEED, especially if the views credit is not being attempted.

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Todd Reed Daylight Designer, 7group Dec 14 2012 LEEDuser Expert 3438 Thumbs Up

Gabriel G has been the one asking all about the prescriptive path, therefore the response was towards that option.

I agree on areas such as doors and other areas like that where harvesting views and daylight through is not critical, one needs to look more at the thermal performance. ie, glass stair towers.

To clarify, i wouldn;t recommend a VLT of 70% on a glass box in Dallas and also recommend that they not install blinds. But if by some chance they wanted a glass box and no blinds, then yes, i would say to balance the energy side and the daylighting side, that you have to go dark. But there are now some really good high VLT low U value and SHGCSolar heat gain coefficient (SHGC): The fraction of solar gain admitted through a window, expressed as a number between 0 and 1. glazings on the market.

Yes in LEED the views and daylight are separated, and if you design a to scorecard, well then you;ll look at them as separate elements and not as a whole as they should be. You can use a low VLT if you want but i won;t say that a certain level of VLT takes the place of a glare control device. By glare control device, i mean one that has the ability for all types of glare. I also think that there is a certain level of VLT where the view is not what is considered a quality view (the discussion of quality is a long one and has many opinions) I look at this way, the view you get wearing sunglasses is not the same you get without them. Same with the amount and quality of daylight.

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Gabriela G
Dec 13 2012
Guest
8 Thumbs Up

Excel Spreadsheet

I have a couple of questions concerning the prescriptive method for achieving LEED credit 8.1. We are doing LEED for schools.
*If my space has two windows, how do I add that to the excel sheet?
When I added a row for the additional window I need to add the square footage of the space again…..which means it doubles the area of the space for the total “total regularly occupied area”….right now its highlighting the cell as “red” because I am not repeating the square footage of the space.
*My VLTxWFR is greater than .18….so now I need to fill out three additional columns, my questions are:
-What is noted on the “glare control type column”
-For the “View preserving automated shades”….what I noticed is that when I mark this category as “yes” it takes into consideration the “zone floor area” under the “sidelighted area subtotal”…..my questions is when should I mark this column as “yes”.

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Lauren Fakhoury Research Assistant, Sustainable Design Consulting, LLC Dec 13 2012 LEEDuser Member 551 Thumbs Up

Gabriela,

For rooms with multiple windows, I normally just add up the window areas and put the total in just one row. GBCI won't question it when reviewing and it is the easiest way to go about including all windows.

If your VLTxWFR is great than 0.18, LEED 2009 now requires that automated view-preserving shades be installed to control daylight. You can only choose "yes" if the project actually has these. In some cases, daylight modeling helps to show the compliant space vs. non-compliant space, because the prescriptive method does not really allow this.

I only fill out the "glare control type column" if there is a "yes" in the automated shade column, or you can just write in "blinds" or whatever type of shading device the space has.

Hope this helps!

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Todd Reed Daylight Designer, 7group Dec 13 2012 LEEDuser Expert 3438 Thumbs Up

Group all you windows together on an orientation that have the same characteristics, VLTand height. This will give the glazing area. The daylight zone is then established, by either twice the head height or using the 60 degree angle. That gives you the depth of the zone. This will establish your VLTxWFR. Which i bet once you combine all your window together may not be over the 0.18.

Glare control is the type of shading and only check yes for automated shades when you actually have them in your project.

Personally, every space used in the daylight calculations should have some type of glare control, especially if the prescriptive path is being used. The prescriptive path cannot tell you if you have any glare conditions or even when they do happen. The prescriptive path cannot show direct sun penetration. So if you just follow the requirements as noted in the prescriptive path, you won;t put blinds in a space. Not good daylight design. Even spaces on the north side of building may experience a condition where shades are needed. How can you say your space or building is well daylit when only the prescriptive path is used? You can;t.

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Todd Reed Daylight Designer, 7group Dec 13 2012 LEEDuser Expert 3438 Thumbs Up

Lauren, you should group all your windows together if they are same, but if not, that is a different zone and you should not group them together. For example, you have six windows on the south wall. All six have the same head height, but the three on the left have a sill height of 12" and the other three have a sill height of 32". Technically, that is two zones, one for each group of three. Why, because the one half the space has more glazing than the other half, and if the same VLT, could actually be overdaylit, and therefore your VLTxWFR is over the 0.18 and therefore you need shades according to the the spreadsheet, well only for half the windows.

This is the stuff that I believe alot of people don;t do and it is hard for a reviewer to determine whether it has been done properly or not. I would question a space that only had one zone for the south facade and was shown two different types of windows.

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Gabriela G Dec 13 2012 Guest 8 Thumbs Up

Tod,
My dilema is that I have a room that has two windows one on the north and one on the south (this happens for most of my rooms)....how do I then divide the area for that room if I can group the windows together on the south side.....I wish i could upload PDF's to this website....eeekk!

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Todd Reed Daylight Designer, 7group Dec 14 2012 LEEDuser Expert 3438 Thumbs Up

Technically you would have a zone on the north and a zone on the south. The zones can overlap. If you have alot of these rooms you could just do one and then extrapulate the info. Our do what i do, and just create your own so that you can easily manipulate the spreadsheet.

I'd have to see exactly what you have to help you further.

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Lauren Fakhoury Research Assistant, Sustainable Design Consulting, LLC Dec 14 2012 LEEDuser Member 551 Thumbs Up

Thanks, Todd, for the tip. We haven't been questioned on this yet for a review but it is helpful to know for the future. I have been splitting up the zones if the TvisVisible light transmittance (VLT) (Tvis) is the ratio of total transmitted light to total incident light (i.e., the amount of visible spectrum, 380–780 nanometers of light passing through a glazing surface divided by the amount of light striking the glazing surface). The higher the Tvis value, the more incident light passes through the glazing. is different, although for most projects so far the windows have been located at the same height, with same area and all, so there wasn't a need to separate them.

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Jill Dalglish President & Senior Engineer, Dalglish Daylighting Dec 14 2012 LEEDuser Expert 2744 Thumbs Up

In my opinion, twice the head height and/or the 60 or 63 degree line are not used to establish the daylight zone. They are only used to establish the applicable window head height. After that, similar windows dictate where you draw your zone lines. If your results are outside of the 0.150 and 0.180 parameters, a second evaluation needs to be done of the zone area. You can check out the NC board for more detail on this.

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BWBR Architects BWBR Architects
Nov 09 2012
LEEDuser Member
178 Thumbs Up

LEED Excel spreadsheet protected?

I'm trying to update the LEED daylight spreadsheet but it seems to be protected. I'm resubmitting after design review comments and I only want to make chnages to what I already submitted, not make an all-new spreadhseet. Any ideas?

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Todd Reed Daylight Designer, 7group Nov 09 2012 LEEDuser Expert 3438 Thumbs Up

Have you tried doing a save as to another file name? I have not seen it where it says file protected, but i usually just do my own so i don;t have to deal with issues like this.

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Eddy Santosa Sustainable Design Coordinator, HMC Architects Nov 09 2012 LEEDuser Expert 2101 Thumbs Up

I agree with Todd. It is probably because the file is still in read only mode when you downloaded. You need to download and save as with different name to ensure that you can edit.

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Adam Rustige Energy Analyst FDH Engineering, Inc.
Oct 03 2012
LEEDuser Member
7 Thumbs Up

Daylight Option 3-Measurement

If I use the daylight measurement method for IEQ 8.1, is there a certain time of day the measurements must be taken?

Thanks

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Todd Reed Daylight Designer, 7group Oct 03 2012 LEEDuser Expert 3438 Thumbs Up

There is no required or specific time to take measurements to document this option. I would suggest to get the most out of taking the measurements other than for just documentation, that you take measurements under clear sky conditions at noon, as close to an equinox as possible.

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kelly ryan
May 17 2012
LEEDuser Member
23 Thumbs Up

Pre-School Questions; Height, "bay area", and interior windows

Hello all! I do believe my questions have yet to be touched upon but apologize if i just missed a comment in this section.
1. I am currently attempting to use option 2 Prescriptive method and am curious if anyone has been able to submit different "work heights" for their calculations? As our rooms are mostly used by toddlers, infants and teachers working and sitting on the floor, it seems 30" is too high of work height. Has anyone made a similar argument and it has been accepted by LEED?
2. This idea of the bayA bay is a component of a standard, rectilinear building design. It is the open area defined by a building element such as columns or a window. Typically, there are multiple identical bays in succession. floor area slightly confuses me. Looking at the LEEDuser sample, it seems that through sort of arbitrary denotations of space, one can determine what windows light where and then these areas can be adjusted to have a compliant square footage and an uncompliant square footage. This is better than the all or nothing i was initially using to calculate each room but i'm still not sure this would apply to smaller classrooms that are only 600sq ft? I guess i dont see why not, just that it will be extremely time consuming to do this for each classroom.
3. In our design we use a lot of borrowed light through other spaces with interior windows. How would the VLT be calculated for that?

Thanks so much for any information,
The DW Arthur Team

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Eddy Santosa Sustainable Design Coordinator, HMC Architects May 17 2012 LEEDuser Expert 2101 Thumbs Up

Hi Kelly,
Here is my opinion on your questions:
1. If you use prescriptive, there is no different in calculation for lower work plane. If you use simulation, it should be OK because that is actually the correct way.
2. In LEED calculation, the width is arbitrary. There is no requirement on that. The depth is actually the projection of your window head.
3. You can't use prescriptive for your case.

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Jill Dalglish President & Senior Engineer, Dalglish Daylighting May 17 2012 LEEDuser Expert 2744 Thumbs Up

Hi Kelly,

1.Where do you find work heights in the prescriptive option? They call out a height for the minimum window area as 30", is this what you mean. In that case, I can see an argument for lowering that to the seated height of your toddlers, but I don't know that it will make a huge difference in your calculations.
2. The "bayA bay is a component of a standard, rectilinear building design. It is the open area defined by a building element such as columns or a window. Typically, there are multiple identical bays in succession." stuff is confusing but the LEEDuser sample can be used in any type of space and space size.
3. You cannot use the prescriptive method for borrowed light. You do have the option of using the prescriptive method for the other areas and then using simulations for the borrowed light areas under Option 4. Combination.

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Nanechka Pagan Architect, LEED GA Bayside Contractors, Inc.
May 02 2012
Guest
25 Thumbs Up

School Daylighting - more than one type of VLT

I am currently using the prescriptive method supporting LEED calculator. Each classrooms have two types of VLT. One side window with 53% VLT that is located at one side of the room and another with 75% VLT located at the other side of the room. Right know since I just put only the windows with 53%, the classrooms doesn't not comply with the 75% daylit. I'm pretty sure if I add the windows that have the 75% VLT the classroom will comply with the requirement. My problem is that I don't know how to put the information in the spreedsheat. I though about taking an average between the VLT and sum all window areas but don't know if that approch will be accepted. My other alternative was to put first the room area, the window area with the correspondent VLT and add another row with the same room but changing the window area and VLT (the issue is that I will be duplicating room area) any thoughts, anyone?
Will appreciate any comment

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Lauren Fakhoury Research Assistant, Sustainable Design Consulting, LLC May 02 2012 LEEDuser Member 551 Thumbs Up

I haven't run into this problem yet (it was easier to document the different VLTs in v2.2!) but maybe you can put them on separate lines. Instead of putting the same room area on each line, you can divide it based on what percentage of the room will receive daylight from one kind of window, and what percentage will receive daylight from the other kind. You can't know this for sure so it would have to be a good estimate. I wonder if that would work? Otherwise you might just have to do a daylight simulation.

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Todd Reed Daylight Designer, 7group May 02 2012 LEEDuser Expert 3438 Thumbs Up

The divide the room in half if you can. If the depth of the daylight zone from both sides is halfway, or even if they overlap, use the midpoint. Separate the classroom on two different lines but only for half the square footage. Label it accordingly and definitely provide a narrative on what you are doing. If the two zones do not touch at midpoint, i believe you can increase the depth of the zone, not decrease, increase the one until the two zones cover the total area.

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Eddy Santosa Sustainable Design Coordinator, HMC Architects May 02 2012 LEEDuser Expert 2101 Thumbs Up

The depth of the zone is driven by the height of the windows. Except they overlap, we cannot adjust the depth.

If they do not overlap, it will be easier. You can split into two floor area in any middle point in the area outside the zone floor areas. Each floor area has its own zone floor area. Because the zone floor area (a.k.a. daylight zone area) is always smaller or equal than the floor area, there will be no issue to split the rooms into two inputs.

I agreed with Todd for the midpoint if the daylight zones or zone floor areas overlap.

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Elizabeth Thompson LEED Specialist USGBC
Jan 03 2012
Guest
190 Thumbs Up

Gyms & inclusion in credit requirements - New USGBC guidance

Does your project have a gymnasium that is used only for athletic, auditorium or stage uses? If so, your project may be able to exclude the gym from the credit requirements for IEQc8.1.

The USGBC released new space type classifications, available here: http://www.usgbc.org/DisplayPage.aspx?CMSPageID=220 under the Rating System page. Scroll down to the first item under IEQ, and open the excel spreadsheet. Read the Overview statement, and then click on the second tab at the bottom, "BD+C and ID+C Table". Look under Column X, Rows 48-49.

If the gym is also used as an assembly space, please also see Column X, Rows 10-13 to see if the assembly use would necessitate inclusion in the credit requirements. Gyms used for assembly purposes or social activities must be included in the credit requirements.

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Lauren Fakhoury Research Assistant Sustainable Design Consulting, LLC
Oct 12 2011
LEEDuser Member
551 Thumbs Up

Supplemental Calculator

This supplemental calculator Excel file only seems to create problems every time I used it! Right now, I'm trying to document the prescriptive method for toplighting, but the floor area isn't registering and summing in the total. I put in the floor area the skylight covers, the area of the skylight, and the TvisVisible light transmittance (VLT) (Tvis) is the ratio of total transmitted light to total incident light (i.e., the amount of visible spectrum, 380–780 nanometers of light passing through a glazing surface divided by the amount of light striking the glazing surface). The higher the Tvis value, the more incident light passes through the glazing. but nothing is happening. The spreadsheet caclulates the skylight coverage percentage, but nothing happens in the "toplighted area subtotal" column. Anyone know what else I need to do for this? I have used the calculator before using the simulation and sidelighitng prescriptive options, so I'm not sure what is wrong this time.

Thanks!

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Todd Reed Daylight Designer, 7group Nov 17 2011 LEEDuser Expert 3438 Thumbs Up

Sounds like a download issue, or an error in the script. Down load it again and save it some where else. I personally create my own spreadsheets that do the same thing as the one's available. This way it can be modified and i can correct any issues.

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Eddy Santosa Sustainable Design Coordinator, HMC Architects Nov 17 2011 LEEDuser Expert 2101 Thumbs Up

Lauren, if you can send me the spreadsheet, I can take a look on that.

Todd is correct that it may be the macros from the excel. I didn't have any problem using their spreadsheet last time but there was a formula error last time in one of them. I agree with Todd, if you can make your own, it's much better.

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Lauren Fakhoury Research Assistant, Sustainable Design Consulting, LLC Nov 17 2011 LEEDuser Member 551 Thumbs Up

Thanks, Eddy. I figured out what is going on with the template. I am trying to get the toplighting percentage between 3 and 6 to comply, and am reducing the zone floor area to reach that number. The calculator is using the actual floor area, but I think that it should be using the zone floor area to calculate the toplighted area. Someone from GBCI has been helping me, but it's still not working! At least I know what is wrong now. Thank you!

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Eddy Santosa Sustainable Design Coordinator, HMC Architects Nov 22 2011 LEEDuser Expert 2101 Thumbs Up

It's good, Lauren.. You may need to double check though.. as I remember, the new amendment define that the zone floor area is the daylit area.

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Felix Hunziker
Sep 23 2011
LEEDuser Member
39 Thumbs Up

Zones, bay floor area

Trying to use Option 2 and I'm confused about Zone Floor Area in the spreadsheet. Isn't the ZFA for sidelighting the same as the bayA bay is a component of a standard, rectilinear building design. It is the open area defined by a building element such as columns or a window. Typically, there are multiple identical bays in succession. floor area? And if that's the case, why does the top lighting zone have a different definition, one driven by ceilng height and distance to obstructions?

Is there a tutorial that shows how Option 2 areas are calculated? I'm kinda scratching my head here.

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Todd Reed Daylight Designer, 7group Oct 04 2011 LEEDuser Expert 3438 Thumbs Up

Felix you are correct with the ZFA. The reason for the difference between sidelighting and the toplighting calculations is because there is a big difference between how sidelighting and toplighting actually works. If such a method were to have the same means of calculating sidelighting and toplighting, it would be invalid. The view, or access to the sky vault is completely different between the two scenarios.

I do not know of any tutorials that show you how the areas are calculated. I suggest you personally consult with someone who knows how to correctly document this credit.

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Felix Hunziker Oct 04 2011 LEEDuser Member 39 Thumbs Up

Thanks Todd. After I posted that I signed up as a LEEDuser member and the resource materials posted here helped me quite a bit. I ended up calculating each room in its entirety.

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David Posada Sustainability Manager, GBD Architects Oct 04 2011 LEEDuser Expert 11332 Thumbs Up

Felix,
The "Sample Prescriptive Compliance Calculation and Path" file in the Documentation Toolkit tab above may help answer some of your questions.

The graphics show how the floor area zones are set up and then adjusted to first determine how much daylight coverage you get from side lighting. You may want to do all the side lighting calcs first for all the rooms to see how close you are to 75% of your regularly occupied spacesRegularly occupied spaces are areas where one or more individuals normally spend time (more than one hour per person per day on average) seated or standing as they work, study, or perform other focused activities inside a building..

Then, look at any areas in a room that don't have enough daylight and assess whether you have toplighting over those areas. If you do, analyze the additional daylight provided by skylights for those top-lit areas that are below the skylight as defined by the footnote #5 (using ceiling height, distance to next skylight or partition, etc.)

Since it would be possible to over-estimate daylight provided if you add the lighting provided by sidelight and toplight for the same floor area, there's a note at the top saying "only one daylight method may be selected for a space." I think most users assume that Prescriptive section in columns M-Z is one "method," but my understanding is that this spreadsheet can only analyze the light hitting an area of the floor from one source - either all from the side or all from the top.

This might be clear as mud... if you're confused, look at the graphic for Step 6 in the LEEDUser sample above. This example doesn't use the 2009 spreadsheet - it uses a simpler scenario to manually calculate the areas being day lit. Notice in the example how an area that has both side light and top light doesn't get double counted since they are looking at the % of the space that is not-day lit - 550 sf. But in the spreadsheet, I don't think there's a way to distinguish in one space (one row of the spreadsheet) the areas that are have only top light, only sidelight, or a mixture of the two.

The work around might be to define smaller spaces or zones based on what kind of day lighting they receive- say, a perimeter zone of a class room that only gets sidelight, and an interior area that's all top lit.

This prescriptive method has used different calculation methods in several different LEED versions, and has always been an imperfect tool. To make it more accurate would make it even more complicated... so for some situations it just won't give an accurate assessment of the daylight. If that's the case, you'll have to use either the Simulation path or the Measurement path.
Hope that helps,

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Dana Murdoch
Aug 09 2011
Guest
540 Thumbs Up

Solatubes (tubular skylights) and Option 2 prescriptive method

We're having difficulty getting Solatubes to calculate correctly for the prescriptive (option 2) method. The required ratio of top-lighting aperture sf to floor area inaccurately reflects the performance of the Solatube (we feel). We contacted the Solatube company and they agree. They have never used the prescriptive method to assist with LEED applications; they said they usually use simulation method (option 1). Solatube said they have been on projects that submitted a combination of Option 1 and 2 - Option 2 for the windows and Option 1 for the Solatubes. Is this possible?? What I really would like to know is if there any way that anyone knows of to calculate Solatubes with the prescriptive method more accurately.

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Todd Reed Daylight Designer, 7group Aug 10 2011 LEEDuser Expert 3438 Thumbs Up

The prescriptive method is a means to provide projects some type of guidelines that will get them some daylighting scenarios that would be better if they had not even considered daylight. It is method of formulas and rules. It is not a method that can effectively or accurately provide projects teams information about the performance of their daylighting scenarios.It is not meant for anything other than punched openings in a building envelope.

Your not going to get the actual performance of the solartube using the prescriptive method. You will need to use a combination of methods as Solar tube had mentioned. When simulating soar tubes you will actually simulate them as electric lights. You can get the IES file from Solar Tube to do this.

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Matt Nolan LEED AP, Belay Architecture Aug 10 2011 Guest 124 Thumbs Up

Dana,

I'm working on a project which will also attempt to earn the daylighting credit with the prescriptive approach, and is also using Solatube skylights. I would be interested in what your outcome was if you have had your project reviewed- and how you chose to document the Solatubes.

We have an approach we used during design - allowing us to decide how many we needed, how to space them, and we expected it to comply with the LEED requirements, but it hasn't been submitted yet. I don't want to post our idea on the forum in-case it's incorrect- (then it will just confusion), but we can compare notes if you haven't submitted yet. Here is my contact mnolan (at) BelayArchitecture (dot) com -thanks!

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Susan M Kaplan Director of Specifications and Sustainability HLW
Aug 03 2011
LEEDuser Member
562 Thumbs Up

Modeling advice

We are trying to evaluate the best way of meeting this requirement through Option 1 - Simulation according to the latest (May 2011) Addenda changes (min. 10 fc1. A footcandle (fc) is a measure of light falling on a given surface. One footcandle is defined as the quantity of light falling on a 1-square-foot area from a 1 candela light source at a distance of 1 foot (which equals 1 lumen per square foot). Footcandles can be measured both horizontally and vertically by a footcandle meter or light meter. 2. The non-metric measurement of lumens per square foot, one footcandle is the amount of light that is received one foot from a light source called a candela, which is based on the light output of a standardized candle. A common range for interior lighting is 10 to 100 footcandles, while exterior daytime levels can range from 100 to over 10,000 footcandles. Footcandles decrease with distance from the light source. The metric equivalent of a foot candle is 10.76 lux, or lumens per square meter. on Sept. 21 at 9 am and 3 pm under clear sky conditions).

We have the project modeled in Sketchup.

My initial thought was to export from Sketchup into Daysim, but I understand there will be a problem with the sensor file and we'll need to create a text file (?). We have Ecotect and can import the .3ds file from the Sketchup Model and then export into Daysim.

I've also learned that Radiance will do the same analysis as Daysim.

Thoughts? What are other design teams using to meet this credit? Thanks in advance.

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Todd Reed Daylight Designer, 7group Aug 04 2011 LEEDuser Expert 3438 Thumbs Up

Susan,
What you need to simulate is footcandles to meet the credit requirements. Daysim provides daylight autonomy ratios, which are based upon a whole year worth of sky conditions and not just one time step. Radiance does not simulate daylight autonomy like Daysim, but Daysim does use a Radiance engine.

My suggestion to you, and this is if you have Sketchup Pro, export the model into a dxf or other compatible format. Import into Ecotec, and then run the lighting analysis with the export to Radiance. You can then import the Radiance file back into Ecotec. The numbers will be in LuxMeasurement of lumens per square meter., so in the import data table, you will have to revise the equation to convert the incoming lux to footcandles. You can also leave it at lux and explain to the reviewer in narrative the lux levels which meet the requirement.

Hope that helps

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Caroline Kilbane Project Manager Lesko Associates
Jun 22 2011
LEEDuser Member
88 Thumbs Up

Weather file for September 21 not typical

I am using sketchup and Daysim for daylight simulation for a school project. My results give me daylight levels for every hour, every day of the year. The results are abnormally low on Sept 21 and 22 compared with most of the days in September. It looks as though Sept 21 and 22 must have been very dark cloudy days when the weather file I am using was created. Should I use the results for Sept 23 and explain my reason for doing so as an alternative compliance path?

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Todd Reed Daylight Designer, 7group Jun 22 2011 LEEDuser Expert 3438 Thumbs Up

Caroline,
What is your step set to in Daysim? In Daysim you can set the time step to have the program look at the weather from every 5 minutes up to every 60 minutes. By setting it to 60 minutes you'll decrease your simulation time and you may get results that are closer to clear sky conditions.

You may need to really explain your methodology to the reviewer on this. Just stating that you got better results on those days will not cut it. The reviewer may not be as familair with how Daysim works as you so you will need to justify the results. I would dig in the weather file and look for those 3 days, pull out the sky illuminance for those days. Use that information to show the reviewer that clear sky conditions for the projects location has an illuminance of ( ) and typical cloudy conditions have an illuminance of ( ). Based on the average illuminance of those days, the date you use is closer to clear sky conditions for the site. You may have to add some fcs to your calcs since how daysim is looking at weather conditions and there are times in there which are cloudy. State that those days are closer to clear sky conditions than the 21st.

For this version of LEED it requires clear sky conditions to demonstrate compliance, this is because it requires projects to consider direct solar impacts. If the 2012 daylight credit were a pilot credit, you would have an easier time. The reviewer could deny it because the calculations where not done under true clear sky conditions.

I have only played with Daysim plugin for Sketchup and not sure if it allows you to run radiance and import the radiance results. This would be better for this version of LEED.

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Tyler Barter Architect Oak Point Associates
May 31 2011
LEEDuser Member
395 Thumbs Up

Too much daylight?!?!

Hello, I am in the process of working on collecting information for LEED certification on 3 different schools that all have large amounts of glass in the cafeteria, gym, and Library, as well as a few other classrooms. Has anyone had any experience in getting this situation to work with the daylighting credit? I have been working on getting a simulation going but still have to change the window square footage in order for the room to pass the credit.
Any help would be appreicated!
Thanks
Tyler

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Todd Reed Daylight Designer, 7group Jun 01 2011 LEEDuser Expert 3438 Thumbs Up

Tyler,
Not sure as to exactly what you are asking. So you are saying that the rooms you are simulating will only meet the credit requirements if the amount of glazing is changed? What program are you using? Is your VLT correct? Are all your input parameters correct? Is it only meeting at one time and not the other?

Lots of unknowns to your question so if you could be more specific it would help in providing you an answer that will help.

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Tyler Barter Architect, Oak Point Associates Jun 01 2011 LEEDuser Member 395 Thumbs Up

Sorry for the lack of info.
I am using IES ve with a sketch up model.
I am working with a 5000 sf cafeteria that has just under 2000 sf of glazing..
the room is meeting the 9am simulation but not the 3pm.
I have my parameters in to the best of my knowledge with the IES ve Program.
It seems that we have a few rooms with large amounts of glass that go over the maximum threshold for this credit. Does anyone know how to work around this?
Thank you!

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Todd Reed Daylight Designer, 7group Jun 02 2011 LEEDuser Expert 3438 Thumbs Up

There is no work around for this. There have been complaints about the 500fc limit at these times in trying to meet the requirements. I think the next addenda may be addressing this issue.
If you have this submit this soon, this is what i would do. Run a simulation with binds half way down the window and all the way down. You can do this two ways to simulate blinds. Actually create a blind in the model and give it an opacity of 10%. Or you can take half the window area and make it translucent with a 10% VLT. Assuming then that you meet the requirement, make the argument that blinds will be in all those spaces and they will be used. People use blinds to reduce direct sun, especially in schools and an assumption that occupants would not lower the blinds is not accurate. DAYSIM, which is yearly daylight simulation program and calculates daylight autonomy uses blinds in the calculations. The reason that the blind option is there is that we know people use blinds. The trick is figuring out at what level of illuminance do people pull the blinds down. Anyway, state the argument that it is not possible for space with easterly or westerly facing spaces to meet the 500 limit. Automated shades are costly, and again, shades will be installed and used.

Have you modeled all exterior buildings and other natural features? There is no barren sight. So if you have buildings or terrain that would help use it. I would on a project that was located very close to the north side of a very large mountain. The sun never impacted the east elevation till late in the morning in the summer time. Without actually modelling the terrain, the project would have issues meeting the 500fc limit even with exterior shading.

Good luck

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Tyler Barter Architect, Oak Point Associates Jun 15 2011 LEEDuser Member 395 Thumbs Up

Do you know when the next addenda may be coming out?

This is a school in Falmouth, Maine. there are no other buildings around just lots of trees along the outside of the site.

Thank you!

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Eddy Santosa Sustainable Design Coordinator, HMC Architects Jun 20 2011 LEEDuser Expert 2101 Thumbs Up

Tyler,
the new addenda may help you. It said "Identify the area of the room that has daylight illumination between 10 footcandles and 500 footcandles at both times (9:00 am and 3:00 pm).Spaces that do not meet the daylight illumination levels at both times do not qualify."

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Diana Hernandez Admin. Assistant SSOE, Group
May 25 2011
Guest
34 Thumbs Up

VLT

Hello,
If the window looks like sandwich, a piece of glass( VLT1) , air gap, another piece of glass(VLT2) , how to define the VLT of that window? Can we use VLT1 x VLT2 as the window's VLT?

Thanks

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Todd Reed Daylight Designer, 7group Jun 01 2011 LEEDuser Expert 3438 Thumbs Up

Diana,
The manufacturers data will provide the VLT of the Window. Depending on how the unit is built, such as thickness of glass one, location of any films or coatings, and the thickness of glass two, will determine the center of glass VLTs.

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Eddy Santosa Sustainable Design Coordinator, HMC Architects Jun 07 2011 LEEDuser Expert 2101 Thumbs Up

Diana,
you can also use Window6 software to calculate by inputting each glass type and the thickness of the gap.

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John Drigot Design/LEED Specialist The Neenan Company
Apr 12 2011
Guest
1443 Thumbs Up

Excluding Casework from IEQc8.1 & IEQc8.2

On a previous LEED for Schools 2009 project I was sucessful in not including the space occupied by built-in casework in the occupied square footage of a space. I am on another LEED project and would like to have something to stand behind in case I am challenged. Is anyone aware of documentation which would support excluding the square footage of built-in casework from the occupied square footage of the space?

Xie xie

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Jill Dalglish President & Senior Engineer, Dalglish Daylighting Apr 13 2011 LEEDuser Expert 2744 Thumbs Up

There is a LEED interpretationLEED Interpretations are official answers to technical inquiries about implementing LEED on a project. They help people understand how their projects can meet LEED requirements and provide clarity on existing options. LEED Interpretations are to be used by any project certifying under an applicable rating system. All project teams are required to adhere to all LEED Interpretations posted before their registration date. This also applies to other addenda. Adherence to rulings posted after a project registers is optional, but strongly encouraged. LEED Interpretations are published in a searchable database at usgbc.org. Inquiry number 5748 from 4/18/05 that states that areas with movable furnitureMovable furniture and partitions are those that can be moved to provide access to the view by the user without the need for tools or assistance from special trades and facilities management. cannot be excluded but storage areas can. I could see this being used to justify exclusion of built-in cabinetry. That space, obviously, cannot be occupied so it stands to reason it cannot be regularly occupied.

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John Drigot Design/LEED Specialist, The Neenan Company Apr 13 2011 Guest 1443 Thumbs Up

Jill,

Thanks for the advice. I looked a little closer at this CIRCredit Interpretation Ruling. Used by design team members experiencing difficulties in the application of a LEED prerequisite or credit to a project. Typically, difficulties arise when specific issues are not directly addressed by LEED information/guide and one statement makes me a little nervous - 2) The areas to be categorized as "regularly occupied" should include all spaces that an occupant would utilize in the course of their daily work. Though I can't apply this CIR to my project I will use it if challenged by the reviewer but I'm not expecting it to carry much weight with the new LEED Interpretations process.

Thanks again & best of luck,

John Drigot

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Rebecca Griffith
Feb 22 2011
LEEDuser Member
240 Thumbs Up

Too much Window Area (WA)?

Is it possible to have too much window area, therefore disqualifying a room from being included in the total daylit area? I am using the prescriptive calculation and the spreadsheet from the resources area of LEED Online v3.

My example:

Corner Office: 198 SF Gross Floor AreaGross floor area (based on ASHRAE definition) is the sum of the floor areas of the spaces within the building, including basements, mezzanine and intermediate‐floored tiers, and penthouses wi th headroom height of 7.5 ft (2.2 meters) or greater. Measurements m ust be taken from the exterior 39 faces of exterior walls OR from the centerline of walls separating buildings, OR (for LEED CI certifying spaces) from the centerline of walls separating spaces. Excludes non‐en closed (or non‐enclosable) roofed‐over areas such as exterior covered walkways, porches, terraces or steps, roof overhangs, and similar features. Excludes air shafts, pipe trenches, and chimneys. Excludes floor area dedicated to the parking and circulation of motor vehicles. ( Note that while excluded features may not be part of the gross floor area, and therefore technically not a part of the LEED project building, they may still be required to be a part of the overall LEED project and subject to MPRs, prerequisites, and credits.)
2 Windows: 133 SF of total window area
Window to Floor Ratio (WFRWindow-to-floor ratio (WFR) is the total area of the window (measured vertically from 30 inches above the finished floor to the top of the glass, multiplied by the width of the glass) divided by the floor area.): 0.67
VLT: 0.69
VLT x WFR: 0.463 (needs to be between 0.15 and 0.18 - would need more gross floor area or less window area to acheive this)

If I would decrease the window area, which I would rather not do, then I could acheive optimal daylit area in this room. This would increase my overall daylight percentage. This does not seem to follow the purpose of the credit.

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Eddy Santosa Sustainable Design Coordinator, HMC Architects Feb 24 2011 LEEDuser Expert 2101 Thumbs Up

I agree with you. The calculation method is not a robust method. I will suggest to use simulation method. I think if there is no direct light in the room, the room will comply easily.

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Tyler Barter Architect, Oak Point Associates Apr 19 2011 LEEDuser Member 395 Thumbs Up

Do you have any program suggestions for the simulation method? I have been trying to figure out a couple different ones but would like some input from others that have done this before.
Thank you!

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John Drigot Design/LEED Specialist, The Neenan Company Apr 19 2011 Guest 1443 Thumbs Up

Tyler,

At our company we have used two software packages, Autodesk's 3d Studio Max and AGI. It seems like AGI has less of a learning curve than 3d Studio Max. What we haven't found yet is a daylighting simulation software that takes the results from 9am and 3pm and gives you the net percentage which is compliant. Any ideas anyone?

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Eddy Santosa Sustainable Design Coordinator, HMC Architects Apr 19 2011 LEEDuser Expert 2101 Thumbs Up

Tyler, I use Ecotect as GUI and run the calculation in Radiance engine. Additionally, I heard AGI is a good tool as well.

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Jill Dalglish President & Senior Engineer, Dalglish Daylighting Apr 19 2011 LEEDuser Expert 2744 Thumbs Up

Carol,
To address your initial question of too much window area: from your description it does sound like you have too much window area and quite a high VLT.

In what way do you think that reducing your window area does not follow the purpose of the credit? A lot more information about your project is needed to assess this, for example, what is the use of the room (a classroom) ? What are the hours of the room? Is the building heating load or cooling load dominant? Are the windows on the same wall or two different walls with two different orientations? What is the height of the window head height? What is the height of the ceiling?

Glare and over-glazing are the two main enemies of good daylighting. What type of shading devices are being provided?

To answer the software question, first a question in reply: What kind of resources do you have to commit to purchasing, learning and using daylighting software? If you do not have roughly $1,000/2 years, at least 40-80 training hours and roughly 4-8 hours per room simulation, you are probably better off hiring a daylighting consultant or simulationist on an as-needed basis. Daylighting simulations are like any other computer software, garbage in-garbage out, so you need someone who is experienced with the output to make sure that it is accurate.

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Jean Marais b.i.g. Bechtold DesignBuilder Expert Aug 15 2011 LEEDuser Member 5201 Thumbs Up

I have a similar situation. My project has a large overhang external shading, but with big windows. Simulation results show all the perimeter rooms with almost no light at Sep 21 09:00 and 15:00. However, when I attempt with the prescriptive method, my WTF ratios are too large for compliance! My TvisVisible light transmittance (VLT) (Tvis) is the ratio of total transmitted light to total incident light (i.e., the amount of visible spectrum, 380–780 nanometers of light passing through a glazing surface divided by the amount of light striking the glazing surface). The higher the Tvis value, the more incident light passes through the glazing. is 0.83.

Something is wrong here. And also is the "Daylit zone" deturmined from the 62º rule (or is that only for internally dropped ceilings), or is it 2H where H is the allowable window height for calculations, OR is it the bayA bay is a component of a standard, rectilinear building design. It is the open area defined by a building element such as columns or a window. Typically, there are multiple identical bays in succession. depth to the back wall of the zone?

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Todd Reed Daylight Designer, 7group Aug 15 2011 LEEDuser Expert 3438 Thumbs Up

Jean,
What simulation program are you running? Something appears to be wrong if simulation is showing nothing with a TVISVisible light transmittance (VLT) (Tvis) is the ratio of total transmitted light to total incident light (i.e., the amount of visible spectrum, 380–780 nanometers of light passing through a glazing surface divided by the amount of light striking the glazing surface). The higher the Tvis value, the more incident light passes through the glazing. of 0.83 (This TVIS is typical for interior glazing or single glazing. Seems high for an exterior glazing component) and your WFRWindow-to-floor ratio (WFR) is the total area of the window (measured vertically from 30 inches above the finished floor to the top of the glass, multiplied by the width of the glass) divided by the floor area. is too big. I would say you have an input error or you modeled something incorrectly. I have done projects were the WFR was too small to meet compliance, yet, both simulation and actual measurements show the project meeting the daylight requirements with a 63% VLT in north facing glazing.

It is actually 63 degrees, and is used to determine your daylight zone if there is a drop ceiling that would intersect the glazing if continued across the space. If there is no ceiling that would interfere with the glazing then the depth of your daylight zone is twice the window head height.

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Jean Marais b.i.g. Bechtold DesignBuilder Expert Aug 15 2011 LEEDuser Member 5201 Thumbs Up

Thanks for the reply,
Actually, in my prescriptive method, I discovered a meter to foot conversion error. I just, just get 75%, but I've not limited it to 2H (we don't have any dropped ceilings under the top of the window height). That means if I recalculate with 2H...it's dead. Also, at the moment I am using a bayA bay is a component of a standard, rectilinear building design. It is the open area defined by a building element such as columns or a window. Typically, there are multiple identical bays in succession. area that starts on the interior side of a glass vestibule (on x2 occasions)...which makes it even more dead, if this is not accepted.

As for the simulation, I have simulated with energy plus using fullexterior reflections (and am rerunning with fullinterior and exterior reflections to see if it improves things), and got the same result when running the model in the new DesignBuilder v3 Daylighting simulation which uses Radiance.

There are public picture up of the building here: http://www.schloss-geister.de/nachricht/items/baufortschritt-28-juni-2011/

The funny thing is, is when you look at the model and try to tell someone that it doesn't have "good enough" daylighting, they will laugh in your face.

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Jean Marais b.i.g. Bechtold DesignBuilder Expert Aug 15 2011 LEEDuser Member 5201 Thumbs Up

It looks like I used the 62º Rule on the lighting through the glass vestibules which gave 0ft² conforming square meter. So I'm still in there with a chance.

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