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Advice provided by: Maia Kumari Gilman, AIA, LEED AP, Maia Gilman Architect PLLC
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Rawan asks: By using a tubular skylight or Solatube product in a project, will Solatube flashings that are installed at roof affect the credit related to green roofs if we decide to pursue both?

Answer:Dear Rawan, I’m happy to hear you are installing a green roof in your project – this is a fantastic way to reduce the heat island effect, to increase insulation values in your building and to offer an attractive educational opportunity to visitors. By introducing a Tubular Skylight system, you also bring daylight into areas of the building that would otherwise receive low natural light, thereby reducing the need for electric lighting.

According to the LEED handbook, the credit you are referencing is SS 7.2. In order to be eligible for this credit, you need to calculate the area of green roofing and deduct the area that the Solatube and its associated flashing will occupy. You can use the following calculations provided by USGBC to determine the necessary square footage. Note that the abbreviation SRI stands for Solar Reflectance Index and refers to a material’s ability to reject solar heat. This is a factor that is available from the product manufacturer and you will need it in order to complete these calculations.

Step 1

Calculate the total roof surface area of the project building in square feet.

Step 2

Calculate the area of the roof covered by mechanical equipment, solar energy panels, Solatubes, etcetera. Subtract this number from the total roof surface area.

Step 3

Use the following Equation 1 to determine if you have enough green roof area left in order to qualify for credit SS7.2.

Equation 1

[area of low-slope SRI material/(78x0.75/SRI value) + area of steep-slope SRI material/(29x0.75/SRI value) + vegetated roof area/0.5] ≥ [total roof area – deducted area]

The Solatube product itself can contribute to LEED credits. According to Solatube’s ‘LEED Contribution Matrix’, you can gain additional points under the LEED categories of Sustainable Sites (SS8.1, Light Pollution Reduction), Energy and Atmosphere (EA Prerequisite 1, Minimum Energy Performance ; EA 1, Optimize Energy Performance; EA4, Windows), Indoor Environmental Quality (IEQ6.1, Controllability of Systems-Lighting; IEQ8.1 Daylight & Views: Daylight), and Innovation in Design (ID1, Innovation in Design-Exemplary Performance). You may also be eligible for Materials and Resources (MR5, Regional Content) and Innovation in Design (ID3, School as a Teaching Tool).

Again, I commend you on making these sustainable choices in your building project and I look forward to seeing photos of the finished result!