If you are considering a roofing project on your building that involves going over the existing roofing membrane (rather than completely replace the current membranes) section 1510 of the NYC Code provides guidance. There are 2 key take aways:
1. If the area to be re-covered is less than 50 percent of the roof area and less than 500 square feet then the requirements of section 1504.9 shall NOT apply. (Section 1504.9 covers Reflectance and Thermal Emittance
2. Re-roofing over the existing membrane is NOT allowed where any of the following conditions occur:
If the existing roof is water soaked;
If the existing roof covering is wood shake, slate, clay, cement or asbestos-cement tile;
If the existing roof has two or more applications of any type of roof covering.
The standard to avoid switching to a ‘white’ roof is very high. As item 1 states, other than re-roofing a very small area, your new overlay must be white.
Item 2 is important. Many Owners are unaware of the multiple layers of various systems in place on their roofs. Many wood framed structures have several layers in place, the accumulated load from which can reach a level detrimental to the structure. The statement of ‘two or more applications’ is interpreted to mean two separate membrane applications – the quantity of layers per installation is incidental.
Code section 1504.9 is shown below – for reference.
Roof coverings on roofs or setbacks with slope equal to or less than two units vertical in 12 units horizontal (17 percent) shall have:
- A minimum initial solar reflectance of 0.7 in accordance with ASTM C 1549 or ASTM E 1918, and a minimum thermal emittance of 0.75 as determined in accordance with ASTM C 1371 or ASTM E 408; or
- A minimum SRI of 78 as determined in accordance with ASTM E 1980.
- Terraces on setbacks comprising less than 25 percent of the area of the largest floor plate in the building.
- Any portion of a roof covered by a green roof system, including such a system with agricultural plantings, in compliance with Section 1507.16.
- Any portion of a roof used as outdoor recreation space by the occupants of the building that is landscaped, covered by wood decking or covered with a walking surface or other protective surface, provided that such walking surface or protective surface has a minimum initial solar reflectance of 0.3 as determined in accordance with ASTM C 1549 or ASTM E 1918.
- Ballasted roofs, provided that the ballast has a minimum initial solar reflectance of 0.2 as determined in accordance with ASTM C 1549 or ASTM E 1918.
- Any portion of a roof that is under mechanical equipment, flush mounted solar panels lying directly on the roof surface, duckboarding, decking, platform, roof tank, cooling tower or any other rooftop structure or equipment exempted by rule by the commissioner.
- Any roof or portion of a roof composed of glass, metal, clay or concrete tile or plastic/rubber intended to simulate clay or concrete tile, wood, or slate.
- Any portion of a roof used by a school or daycare center as a playground for children.
- Any roof, if the amount of rooftop space not subject to exceptions 1 through 7 is in the aggregate less than 100 square feet