Regarding your article (Roofs so cool, they gotta wear shades, Sustainable Life, May 15): This article makes the suggestion that Portland never met a LEED point they didn’t like, but every LEED point is not created equal.

The voluntary green building certification system, LEED (Leadership in Energy and Environmental Design), was intended to have new construction, as well as existing buildings undergoing renovation, quantify the level of commitment to the system by achieving points and attaining various threshold levels that would certify the building as a silver, gold or platinum building.

The problem with this approach is not every building uses the same points or even all the same categories. So comparisons from building to building are difficult. 

Some LEED points are designed for special situations that do not affect all buildings being built or renovated. If you build a new building on a property that has never been used for buildings (greenfield), you will not qualify for the credits for building a new building on a previously occupied site (brownfield). If you re-use parts (walls, floors, etc.) or most of your existing building in your renovation project, you will achieve points, but if you tear most of it down, you will not. This is pretty straightforward for some credits.

On the other hand, under the sustainable sites credit category, there is a credit for mitigation of the heat island effect for both roofs and parking areas. LEED adopted the California Title 24 model of highly reflective surfaces as a mitigation strategy for urban heat island effect. This applies to roofs, covered parking areas and sidewalks.

The theory is that sunlight and heat would be deflected off these horizontal surfaces and travel back into the atmosphere. If you use these “cool roofs” or “cool surfaces” in southern climates such as Florida, Texas and Southern California, you also would benefit from reduced cooling costs in the summer due to this deflection.

As you move up into the more northern climates, this energy benefit is reduced significantly or negated entirely, since levels of insulation are increased due to colder winters, and the use of cooling goes down while heating goes up. Having a “cool roof” in the winter has a negative effect on heating, allowing more heat to transfer from the inside of the building out of the roof, due to the higher temperature differential. 

So using the LEED credit for urban heat island reduction may have some effect on your local heat island during the summer, but during the winter the increased energy use needed while using a cool roof will cause more carbon emissions due to the increased use of the heating fuel source (i.e. electric, natural gas, wood, etc.).

Portland should examine all the LEED points and use the appropriate ones for their buildings, but make sure they also understand what the

tradeoffs are for using a cool roof. Don’t be surprised when you have increased energy bills even though you have a LEED-certified building with a “cool roof.”

Craig A. Tyler is an architect and specification developer at Carlisle SynTec Systems, a roofing products company in Carlisle, Pa.

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