Date
Inquiry

Many CIRs address the fact that you can use the weighted average method outlined in the SSc7.1 CIR dated 12/5/2001 for SSc7.2. That CIR outlined a baseline which assumed 30% of the site met the 0.3 reflectance requirement, and 70% did not. However, the NCv2.2 Reference Guide for SSc7.2 outlines a weighted average calculation which differs from the SSc7.1 method in two ways. The first is that the outlined baseline (75% w/ SRI of 78 & 25% w/ SRI of 30) requires that 100% of the roof area is compliant with the SRI requirements. Also, the outlined baseline assumes that 75% of the roof area is low sloped, and 25% is steep sloped. If a project has a low slope for 64% and a steep slope for 36% of the roof area, can we use a baseline weighted average which reflects our ratio of steep to low sloped roof? Also, can we use a baseline weighted average calculation which requires 75% of the roof area to be compliant instead of 100% of the roof area? I\'ve outlined an example below: If 75% of the low sloped roof is compliant, for our project this would mean 48% (64%x0.75) of the total roof area should have an SRI of at least 78. If 75% of the steep sloped roof is compliant, this would mean 27% (36%x0.75) of the total roof area should have an SRI of at least 29. Since 48% + 27% = 75% of the total roof area, this method reflects credit requirements and is consistent with the weighted average methodology outlined in the SSc7.1 CIR. Therefore, the weighted average baseline would be: 27% x 29 + 48% x 78 = 45.27 Can this calculation methodology be used to calculate the baseline for the weighted average option for SSc7.2?

Ruling

Can a project use a weighted average calculation to show credit compliance? Yes, projects may use a weighted average calculation to achieve compliance equivalent to the required 75% threshold. As noted in v2.2 SSc7.2 CIR Ruling dated 6/19/2008, if the project applies for this credit under v2.2, the project may use the following formula to calculate credit compliance for multiple materials: [(Area of Roof A*(SRI of Roof A/Required SRI)) + (Area of Roof B*(SRI of Roof B/Required SRI)) / 0.75] + [ Area of Vegetated Roof/0.5] >= Total Roof Area In order for a project registered for v2.1 to apply for this credit using the v2.2 requirements, the project team must submit through LEED Online and follow the process outlined in the Credit Substitution Memo dated 12/19/2006 which can be found on the USGBC\'s website at: www.usgbc.org/ShowFile.aspx?DocumentID=1704 Applicable Internationally.

Internationally Applicable
On
Campus Applicable
Off
Credits