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Cool roof basics
This credit provides a variety of options for using your project’s roof to reduce your contribution to the urban heat islandA densely populated area in which pavement and buildings absorb, store, and release solar energy, making the vicinity warmer than it would be if the pavement and buildings were not present. effect, while also potentially reducing your building’s cooling load.
- Option 1: A light-colored roof with a high solar reflectance index (SRIThe solar reflectance index (SRI) is a measure of a material's ability to reject solar...
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8 Comments
SRI compliant paints
What if we apply a paint, for instance lets say we apply White color paint which is not a specific reflective coating on our roof. Will we able to claim the credit?
If not, do we specifically need to make the roof by a compliant 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. material or by a specific reflective coating to meet the credit needs?
Please forward your ideas....Thanks
Tristan Roberts replied Editor – LEEDuser, BuildingGreen, LLC Mar 25 2010
Rashid, you will need documentation showing that the paint or whatever else you apply is actually 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.. You can't simply claim the credit by using a white color, since SRI values vary so much even with materials that may appear to be simlar colors. Also, keep in mind that SRI factors in emissivityEmissivity is the ratio of the radiation emitted by a surface to the radiation emitted by a black body at the same temperature. which is different than reflectivity. Polished aluminum, for example, is highly reflective but very poorly emissive.
RASHID HAMEEN replied Mar 26 2010
Thanks tristan for your comments. In case if we couldn't find a coating which has data sheets to show compliance of that having a suitable 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. will it be sufficient if we check a sample with lab and show the compliance or does our test has to be done to a sample of the roof material which is after applying the paint..please post your comments.
Ballasted Roofs SRI?
Has anyone had luck getting a good 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. rating out of existing ballasted roofs? Apart from sending this to a lab, are there any charts or other information to use? Has anyone successfully gotten this credit when their building has a majority of light-colored ballasted roofs?
Tristan Roberts replied Editor – LEEDuser, BuildingGreen, LLC May 28 2010
Cara, I don't have definite answers to any of your very good questions, but I did find some interesting resources. A fairly recent note in the Cool Roofs Rating Council newsletter that makes it sound like ballasted roofs are gaining acceptance as "cool" roofs. Also, a study from ORNL that may be behind some of this recognition.
I'm not sure where this leaves you, except perhaps with some encouragement that you're on a reasonable path.
BKSK Architect replied BKSK Architects Jun 01 2010
Just to clarify a bit further, while white ballasted roofs are showing evidence of performing as well as other "cool roof" systems, the USGBC does not recognize any flat roof material under a 78 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 SScr7.2 LEED credit. This is because the intention of the credit for micro-climate development is not met by materials that do not meet this threshold.
What if the roof doesn't requiring replacing?
Our project's roof does not meet the credit requirements. The owner is willing to spec a compliant roofing system; however, the roof is in good conditions and still has 7 years left on its warranty. Is a commitment to purchase a compliant roofing system once the roof requires replacement a valid compliance path? I'm guessing based on Kim's experience above that this is not likely a possibility. It seems a bit 'counter-green' to replace a roofing system that is still in good working order.
Natalie Bodenhamer replied Green Building Consultant, CTG Energetics, Inc Jun 01 2010
A commitment to purchase a compliant roof system does not meet the credit requirements of SSc7.2. This is a great opportunity to integrate the roof replacement into the LEED EB Recertification plan/strategy. The replacement may impact energy efficiency (EAc1), in addition to SSc7.2.
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