NC 2009 SSc7.2: Heat Island Effect—Roof

Shriram Bhide replied Jan 18 2010

Bill,
Thank you so much for your response.

Mara Baum replied Sustainability Coordinator, Anshen + Allen Architects Jan 22 2010

This is a great question, and one that has been on my mind as well. SRIThe solar reflectance index (SRI) is a measure of a material's ability to reject solar heat, as shown by a small temperature rise. Standard black (reflectance 0.05, emittance 0.90) is 0 and standard white (reflectance 0.80, emittance 0.90) is 100. For example, a standard black surface has a temperature rise of 90_F (50_C) in full sun, and a standard white surface has a temperature rise of 14.6_F (8.1_C). Once the maximum temperature rise of a given material has been computed, the SRI can be calculated by interpolating between the values for white and black. Materials with the highest SRI values are the coolest choices for paving. Because of the way SRI is defined, particularly hot materials can even take slightly negative values, and particularly cool materials can even exceed 100. is calculated using solar reflectance (albedoAlbedo is synonymous with solar reflectance.) and emissivityEmissivity is the ratio of the radiation emitted by a surface to the radiation emitted by a black body at the same temperature. (emittance). If you have these two values, you can use a calculator like the one at http://www.arkema-inc.com/index.cfm?pag=986. If you don't have these values, you're in for some big excitement (so to speak).

Although I've never had to measure this myself, I have heard that it's a big pain -- and now I know why. I took a look at a slide show on this topic at the Lawrence Berkeley National Labs Cool Roofs website http://eetd.lbl.gov/HeatIsland/CoolRoofs/Overview/. This LBL group developed much of the leading research and research methods on this topic. To summarize, you need a combination of the following instrumentation, depending on the situation: UV-VIS-NIR Spectrometer with integrating sphere, a solar spectrum reflectometer, and a Fourier-Transform Infra-Red (FTIR) spectral emissometer and/or an emissometer. The protocols must comply with specific ASTMVoluntary standards development organization which creates source technical standards for materials, products, systems, and services standards for each type of measurement.

If your project is local and presents a scientific question that might pique LBL interest, perhaps you should contact them for advice or assistance. (A note to other readers, Lauren is lucky to be practically in LBL's back yard.) Paul Berdahl is the primary contact for SRI info, see http://eetd.lbl.gov/HeatIsland/STAFF/.

Although I didn't see a specific discussion on the question of roof vs. hardscape measurement procedures, it makes sense that they would be the same.

Have any other readers undertaken these measurements themselves?

Dave Intner replied Firmitas Architecture & Planning Jan 25 2010

It may be more cost effective to send a sample to a lab, instead of bringing the equipment on-site. We researched this for a project where we were filling the cells of pervious pavers with gravel; we had manufacturer SRIThe solar reflectance index (SRI) is a measure of a material's ability to reject solar heat, as shown by a small temperature rise. Standard black (reflectance 0.05, emittance 0.90) is 0 and standard white (reflectance 0.80, emittance 0.90) is 100. For example, a standard black surface has a temperature rise of 90_F (50_C) in full sun, and a standard white surface has a temperature rise of 14.6_F (8.1_C). Once the maximum temperature rise of a given material has been computed, the SRI can be calculated by interpolating between the values for white and black. Materials with the highest SRI values are the coolest choices for paving. Because of the way SRI is defined, particularly hot materials can even take slightly negative values, and particularly cool materials can even exceed 100. values for the pavers themselves, but not the gravel. It ended up not being necessary because the USGBC reviewers accepted the paver value for 60% of the area (excluding the 40% voids filled with gravel), which put us over the 50% area threshold. The lab we received quotes from for testing was Atlas Material Testing in Phoenix, www.atlaswsg.com.

Mara Baum replied Sustainability Coordinator, Anshen + Allen Architects Jan 27 2010

Great idea, Dave, thanks. That approach is a little tougher for an existing roof, though.

Lauren Glasscock replied Sr. Sustainability Professional, KEMA Services, Inc. Jan 28 2010

Thanks Dave for your comments

Tristan Roberts replied Editor – LEEDuser, BuildingGreen, LLC Mar 17 2010

Is this a situation where it will make a difference in terms of credit compliance, whether you use one method or another? I would say that for simplicity's sake it would make the most sense to simply count the full area of both roofs—including the part that has the overhang over it.

In some situations (like with balconies) the overhead method is used so it could probably be justified, but to counter that, when the sun is at an angle, it would hit an overhung portion.

Lee Dingemans replied LEED AP, Wightman & Assoc. Jul 30 2010

How should I handle Parapet walls? Include or exclude? If I include parapet walls should I tread them as a separate roof in the fillable forms in "LEED On-Line"?

Thank you

Tristan Roberts replied Editor – LEEDuser, BuildingGreen, LLC Aug 03 2010

Lee, we had this discussion in the CS forum for SSc7.2—I would check that out and post back here with further thoughts.

Lee Dingemans replied LEED AP, Wightman & Assoc. Aug 03 2010

Thank you for referring me to CS forum for SSC7.2, this answered my questions for this particular credit (for now).

Thanks again.

Lee

Tristan Roberts replied Editor – LEEDuser, BuildingGreen, LLC Apr 16 2010

Unfortunately, the roof system you describe does not meet the Exemplary PerformanceIn LEED, certain credits have established thresholds beyond basic credit achievement. Meeting these thresholds can earn additional points through Innovation in Design (ID) or Innovation in Operations (IO) points. As a general rule of thumb, ID credits for exemplary performance are awarded for doubling the credit requirements and/or achieving the next incremental percentage threshold. However, this rule varies on a case by case basis, so check the credit requirements. requirements described in the LEED Reference Guide.

The Reference Guide specifies a 100% green (vegetated) roof, not an SRIThe solar reflectance index (SRI) is a measure of a material's ability to reject solar heat, as shown by a small temperature rise. Standard black (reflectance 0.05, emittance 0.90) is 0 and standard white (reflectance 0.80, emittance 0.90) is 100. For example, a standard black surface has a temperature rise of 90_F (50_C) in full sun, and a standard white surface has a temperature rise of 14.6_F (8.1_C). Once the maximum temperature rise of a given material has been computed, the SRI can be calculated by interpolating between the values for white and black. Materials with the highest SRI values are the coolest choices for paving. Because of the way SRI is defined, particularly hot materials can even take slightly negative values, and particularly cool materials can even exceed 100.-compliant roof. You could submit a 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 to argue this point, but it doesn't seem likely to succeed.

David Koons replied Apr 21 2010

Yes, contact your roof manufacturer for samples. Johns Manville (JM) does have certain colors besides white that will meet your requirement.

Tristan Roberts replied Editor – LEEDuser, BuildingGreen, LLC Apr 20 2010

Tysa, in this situation you can comply by performing a "weighted average calculation." For details on how to do that please see the Getting It Done tab above, as well as a calculator you can use in the Documentation Toolkit.

Tristan Roberts replied Editor – LEEDuser, BuildingGreen, LLC Apr 28 2010

Tysa, that's a pretty broad question! What are you seeing as the key pros and cons, and considerations for your project?

Tristan Roberts replied Editor – LEEDuser, BuildingGreen, LLC Apr 29 2010

Wow, this is really frustrating! It basically seems like GBCI/USGBC are treating this credit as a construction submittal, despite its being offically labeled a design submittal.

Looks like to be on the safe side, teams should wait to submit till construction. Hopefully USGBC will either clarify this in the future, or remove the requirement for installed equipment info.

Tristan Roberts replied Editor – LEEDuser, BuildingGreen, LLC Apr 26 2010

Richard, to duplicate what you're seeing I would need to know what the SF of the respective roof areas is.

However, my guess is that what's throwing you for a loop is the "Weighted compliant rooftop SRIThe solar reflectance index (SRI) is a measure of a material's ability to reject solar heat, as shown by a small temperature rise. Standard black (reflectance 0.05, emittance 0.90) is 0 and standard white (reflectance 0.80, emittance 0.90) is 100. For example, a standard black surface has a temperature rise of 90_F (50_C) in full sun, and a standard white surface has a temperature rise of 14.6_F (8.1_C). Once the maximum temperature rise of a given material has been computed, the SRI can be calculated by interpolating between the values for white and black. Materials with the highest SRI values are the coolest choices for paving. Because of the way SRI is defined, particularly hot materials can even take slightly negative values, and particularly cool materials can even exceed 100." number that's calculated by the LEED Online credit form. As the title implies, this is a weighted number that gives you extra credit for extra compliance (beating the required SRI number). It's designed to allow you to offset poor performance in one area with really good performance in another. Since you are exceeding the compliance requirements for both slope types, you've earned a lot of extra credit, which is likely to give you a % well over 100.

Lee Dingemans replied LEED AP, Wightman & Assoc. Jul 30 2010

Credit 7.2 Heat Island EffectHeat island effect refers to the absorption of heat by hardscapes, such as dark, nonreflective pavement and buildings, and its radiation to surrounding areas. Particularly in urban areas, other sources may include vehicle exhaust, air-conditioners, and street equipment; reduced airflow from tall buildings and narrow streets exacerbates the effect. – Roof
I am following Option No. 3 (Combination) and full documentation path. I have a roof plan depicting roof areas depicting location and quantity of roof materials (this is not uploaded yet).
I have entered the following:
Total roof area = 10,110 sf (Low Slope)
Curved mtl. roof = 5,310 sf has a SRIThe solar reflectance index (SRI) is a measure of a material's ability to reject solar heat, as shown by a small temperature rise. Standard black (reflectance 0.05, emittance 0.90) is 0 and standard white (reflectance 0.80, emittance 0.90) is 100. For example, a standard black surface has a temperature rise of 90_F (50_C) in full sun, and a standard white surface has a temperature rise of 14.6_F (8.1_C). Once the maximum temperature rise of a given material has been computed, the SRI can be calculated by interpolating between the values for white and black. Materials with the highest SRI values are the coolest choices for paving. Because of the way SRI is defined, particularly hot materials can even take slightly negative values, and particularly cool materials can even exceed 100. 84.75 (Low Slope)
Tpo roof (flat)= 3,327 sf has a SRI 102.23 (Low Slope)
Vegetated roof (flat) = 1,473 don’t know the SRI for this one (Low Slope).

Questions:
How do I handle the green roof if I don’t know and don’t have a SRI value for it? Or don’t I need one and should I eliminate this line from the “Material Description/ID” list? It is again listed below as “Total Vegetated Roof Area (sf):”.

Why does this roof not comply “Total weighted roof area in compliance: (must be greater than or equal to total roof area)” it is not. Even if I arbitrary enter an SRI value it won’t bring square footage number in compliance with “greater than or equal to” rule as described above.

Bottom line: The way I see this roof is that the different parts is some way or another do comply but the calcs in LEED Online don’t agree. Is there any place where I can get quick help in filling out forms like this, or sample forms for me to look at??

Thanks!!

Tristan Roberts replied Editor – LEEDuser, BuildingGreen, LLC Aug 03 2010

You shouldn't need to enter an SRIThe solar reflectance index (SRI) is a measure of a material's ability to reject solar heat, as shown by a small temperature rise. Standard black (reflectance 0.05, emittance 0.90) is 0 and standard white (reflectance 0.80, emittance 0.90) is 100. For example, a standard black surface has a temperature rise of 90_F (50_C) in full sun, and a standard white surface has a temperature rise of 14.6_F (8.1_C). Once the maximum temperature rise of a given material has been computed, the SRI can be calculated by interpolating between the values for white and black. Materials with the highest SRI values are the coolest choices for paving. Because of the way SRI is defined, particularly hot materials can even take slightly negative values, and particularly cool materials can even exceed 100. for the vegetated roof. Just enter it below.

It looks like this form is in "beta" on LEED Online, and thus there's always the chance it's not working right. I entered your numbers for Option 3, and the SRI-compliant roof didn't seem to be counted as much as it should have been. I then entered the same numbers for Option 1, ignored the green roof, and it seemed to add up correctly and you got full credit. Since you get full credit using that option, it might simply be worth doing that?

Bottom line: you're not crazy. I hope that helps, at least.

LEED Online v3 sample forms and guidance are not really available anywhere, with the exception of about 10 key forms that we've created tipsheets for on LEEDuser.

Tristan Roberts replied Editor – LEEDuser, BuildingGreen, LLC May 03 2010

Seems to me that this is a roof, or at least 80% of it is. The only reason that makes me think twice is the fact that it's at grade, but plenty of roofs are at grade.

It seems like a vegetated roof—can you argue for that?

Mara Baum replied Sustainability Coordinator, Anshen + Allen Architects May 06 2010

The part of the roof that is over occupied space is definitely a roof, not hardscape. If the pavers themselves do not meet the roof SRIThe solar reflectance index (SRI) is a measure of a material's ability to reject solar heat, as shown by a small temperature rise. Standard black (reflectance 0.05, emittance 0.90) is 0 and standard white (reflectance 0.80, emittance 0.90) is 100. For example, a standard black surface has a temperature rise of 90_F (50_C) in full sun, and a standard white surface has a temperature rise of 14.6_F (8.1_C). Once the maximum temperature rise of a given material has been computed, the SRI can be calculated by interpolating between the values for white and black. Materials with the highest SRI values are the coolest choices for paving. Because of the way SRI is defined, particularly hot materials can even take slightly negative values, and particularly cool materials can even exceed 100. requirement, then you might consider an alternate calculation method in which you borrow the method from the non-roof credit and apply that to the roof credit -- but this is just a suggestion; I don't know exactly how GBCI would respond. I don't think you should count the pavers as a green roof, although if you have exposed soil/vegetation (at the roof level, not the tree canopy) that should qualify as a green roof.

Tristan Roberts replied Editor – LEEDuser, BuildingGreen, LLC May 03 2010

Like your other question, seems like roof to me. Encloses a conditioned, functional space. What is the argument for its not being roof?

Ben Koenig replied Gensler May 04 2010

The intent of the credit is that it doesn't heat up spaces inside the building through sunshine and causing more cooling energy, correct?
So, the water is absorbing the solar heat and it doesn't go into the space below. Also the space below is not being cooled at all. Anyway, I could argue that all spaces are a roof, but because of water and tree shading, it should be considered as being excluded much like mechanical equipment on the roof can be excluded. I think Water is also reflective, but not sure if it meets SRI78.

Ben Koenig replied Gensler May 17 2010

A follow up on if water features are roofs: CIRs dated 2/7/2006 and 5/23/2005 are for LEED NC2.1 and deals with the non-roof credit, but it's feasable that it would also apply to NC2.2 and apply to roofs as well. it says that water feature are excluded from calculations for non-roofs:
http://www.usgbc.org/LEED/Credit/CIRDetails.aspx?RequirementID=13

Thought this might help for people that may have the same question. Obviously things are subject to change, but it's certainly something to go by.

Tristan Roberts replied Editor – LEEDuser, BuildingGreen, LLC May 20 2010

To document this credit, LEED Online requires you to upload SRIThe solar reflectance index (SRI) is a measure of a material's ability to reject solar heat, as shown by a small temperature rise. Standard black (reflectance 0.05, emittance 0.90) is 0 and standard white (reflectance 0.80, emittance 0.90) is 100. For example, a standard black surface has a temperature rise of 90_F (50_C) in full sun, and a standard white surface has a temperature rise of 14.6_F (8.1_C). Once the maximum temperature rise of a given material has been computed, the SRI can be calculated by interpolating between the values for white and black. Materials with the highest SRI values are the coolest choices for paving. Because of the way SRI is defined, particularly hot materials can even take slightly negative values, and particularly cool materials can even exceed 100. documentation AND/OR emissivityEmissivity is the ratio of the radiation emitted by a surface to the radiation emitted by a black body at the same temperature. and reflectance percentages) for each material. You will also have to enter material data, and you can enter SRI, and again, you have the choice of entering the emissivity and reflectance data. The LEED Online form does a quick calculation to come up with its own SRI value.

In short, you should be fine getting an SRI value and entering that. You don't also need the other values.

Erik Bergstrom replied Green Building Associate Jun 24 2010

Is it not then possible to cover a roof with 100% SRIThe solar reflectance index (SRI) is a measure of a material's ability to reject solar heat, as shown by a small temperature rise. Standard black (reflectance 0.05, emittance 0.90) is 0 and standard white (reflectance 0.80, emittance 0.90) is 100. For example, a standard black surface has a temperature rise of 90_F (50_C) in full sun, and a standard white surface has a temperature rise of 14.6_F (8.1_C). Once the maximum temperature rise of a given material has been computed, the SRI can be calculated by interpolating between the values for white and black. Materials with the highest SRI values are the coolest choices for paving. Because of the way SRI is defined, particularly hot materials can even take slightly negative values, and particularly cool materials can even exceed 100.-59 material?

Tristan Roberts replied Editor – LEEDuser, BuildingGreen, LLC Jun 24 2010

Yes, you are right in principle. However, I just checked your math on the SRIThe solar reflectance index (SRI) is a measure of a material's ability to reject solar heat, as shown by a small temperature rise. Standard black (reflectance 0.05, emittance 0.90) is 0 and standard white (reflectance 0.80, emittance 0.90) is 100. For example, a standard black surface has a temperature rise of 90_F (50_C) in full sun, and a standard white surface has a temperature rise of 14.6_F (8.1_C). Once the maximum temperature rise of a given material has been computed, the SRI can be calculated by interpolating between the values for white and black. Materials with the highest SRI values are the coolest choices for paving. Because of the way SRI is defined, particularly hot materials can even take slightly negative values, and particularly cool materials can even exceed 100.-59 question using the Excel calculator we offer in the Documentation Toolkit above, and it doesn't seem to be compliant.

Erik Bergstrom replied Green Building Associate Jun 25 2010

The calculator works when you enter 100% low sloped roof. You have to remove the 25% steep sloped line, since in this situation the building has a flat roof. The reason I bring up this question is that in version 2.2, this approach was not allowed. The roofing had to have a minimum of SRI78 (low-sloped roof) to count it as high-SRI roofing (see 2.2 template). In the 2009 version, the approach is implied to be allowed by the calculation, but not directly mentioned.

Mara Baum replied Sustainability Coordinator, Anshen + Allen Architects Jun 28 2010

The rating system requirements for Option 1 say, "Roofing materials having a lower SRIThe solar reflectance index (SRI) is a measure of a material's ability to reject solar heat, as shown by a small temperature rise. Standard black (reflectance 0.05, emittance 0.90) is 0 and standard white (reflectance 0.80, emittance 0.90) is 100. For example, a standard black surface has a temperature rise of 90_F (50_C) in full sun, and a standard white surface has a temperature rise of 14.6_F (8.1_C). Once the maximum temperature rise of a given material has been computed, the SRI can be calculated by interpolating between the values for white and black. Materials with the highest SRI values are the coolest choices for paving. Because of the way SRI is defined, particularly hot materials can even take slightly negative values, and particularly cool materials can even exceed 100. value than those listed below [78 for low slopes] may be used if the weighted rooftop SRI average meets the following criteria: [75% calculation]". (See page 118 of the BD+C Reference Guide 2009 Edition). So yes, you should be able to use a lower SRI value on a higher percentage of roof, and yes, this is a change from NC v2.2.

Tristan Roberts replied Editor – LEEDuser, BuildingGreen, LLC Jul 01 2010

No, I don't know of any, although in principle it seems like it should be possible, if red clay tiles can have an SRIThe solar reflectance index (SRI) is a measure of a material's ability to reject solar heat, as shown by a small temperature rise. Standard black (reflectance 0.05, emittance 0.90) is 0 and standard white (reflectance 0.80, emittance 0.90) is 100. For example, a standard black surface has a temperature rise of 90_F (50_C) in full sun, and a standard white surface has a temperature rise of 14.6_F (8.1_C). Once the maximum temperature rise of a given material has been computed, the SRI can be calculated by interpolating between the values for white and black. Materials with the highest SRI values are the coolest choices for paving. Because of the way SRI is defined, particularly hot materials can even take slightly negative values, and particularly cool materials can even exceed 100. >29. I can't even find a typical SRI value for cedar shingles. What have you been able to come up with?

Elliot Powers replied LEED AP BD+C Jul 02 2010

So far, nothing. Anyone else?

Tristan Roberts replied Editor – LEEDuser, BuildingGreen, LLC Jul 12 2010

You will need to use the Roof Weighted Average Calculator (discussed above under the Getting It Done tab, and in the Documentation Toolkit) to calculate how to comply.

I would use geometry to divide the roof up into at least two (or maybe more, if it seems appropriate) areas based on the approximate pitch—greater or less than 2:12.

Tristan Roberts replied Editor – LEEDuser, BuildingGreen, LLC Aug 16 2010

What's the building official's reasoning? I don't have experience in this situation, but I don't think edge guards are standard practice.

Tristan Roberts replied Editor – LEEDuser, BuildingGreen, LLC Aug 04 2010

From the LEED perspective, mechanical systems and appurtenances including PV are not included in the SSc7 credit calculations.

From a general perspective, PV panels are dark-colored and would most likely contribute to the heat-island effect, compared with a high-SRIThe solar reflectance index (SRI) is a measure of a material's ability to reject solar heat, as shown by a small temperature rise. Standard black (reflectance 0.05, emittance 0.90) is 0 and standard white (reflectance 0.80, emittance 0.90) is 100. For example, a standard black surface has a temperature rise of 90_F (50_C) in full sun, and a standard white surface has a temperature rise of 14.6_F (8.1_C). Once the maximum temperature rise of a given material has been computed, the SRI can be calculated by interpolating between the values for white and black. Materials with the highest SRI values are the coolest choices for paving. Because of the way SRI is defined, particularly hot materials can even take slightly negative values, and particularly cool materials can even exceed 100. roofing material.

Jean Marais replied b.i.g. Bechtold INGENIEURGESELLSCHAFT MBH Aug 05 2010

Bang on!