Heating versus cooling a flat roof in New England has always been a hotly contested debate. I have been to countless seminars on this subject, and have heard the following arguments:
In New England, we are heating our buildings more often than cooling them.
On the average building in New England, it’s undeniable that we are heating our buildings more often than cooling them. Air conditioning typically runs consistently from June to August (3 months). On the other hand, heating typically runs consistently from October to April (7 months). As a result, the argument is that we are better off installing a black roof system that heats the roof than a white roof system that cools the roof. The heating benefit lasts for 7 months compared to the cooling benefit, which lasts for only 3 months.
The strongest argument that I have heard against this theory is that during the winter, once the snow falls, the roof is white regardless. The black membrane may help melt a small amount of snow, but much like your driveway, once snow builds up, you have a snowy white surface instead of a black surface. This doesn’t happen during the summer, so the cooling benefit is there during the entire season.
Rooftop equipment benefits from a cooler surface.
During the hottest points of the summer, a black roof system is about double the outside temperature because it absorbs the heat. A white roof system is roughly the same temperature because it reflects the heat. The argument here is that during the hottest days, when your rooftop equipment is working the hardest, a black roof system will make cooling even more difficult, whereas a white roof system makes cooling easier. Your rooftop equipment can pull in cooler air instead of warmer air. Most HVAC contractors I have spoken to say the rooftop equipment is designed to handle any type of roof system and heat difference either way, but it never hurts to put less stress on the roof system.
With the amount of insulation on the roof, it doesn’t matter.
The argument that I personally believe in the most is that with the amount of insulation we are putting on the roof, it doesn’t really make a difference. The high “R” value insulation that we are installing on our roof systems not only helps keep heating and cooling in the building, but it also helps keep it out of the building, especially with heat, which rises.
My personal opinion is that when deciding on a roof system, heating versus cooling doesn’t make a big difference especially if you are completing a tear-off and installing code-compliant insulation, which has a high “R” value. When deciding on which roof system to install, my recommendations are typically based on the use of the building versus the benefits and drawbacks of each roof system. Whether your roof system has heavy foot traffic, grease and oil output, extensive rooftop equipment, unique details, or a variety of other unique circumstances where one type of membrane would benefit over the other is far more important to the longevity and usefulness of the roof system than any heating or cooling benefits.