Cool Roofs: How a White Roof Lowers Building Temperature

What is a cool roof and does it actually work?

A cool roof is a roof surface that reflects most of the sunlight hitting it instead of absorbing it as heat. On a commercial low-slope building, that is usually a white reflective coating or membrane. The effect is measurable: a dark roof can run well over 150 degrees on a summer afternoon, while a reflective white surface on the same building stays far closer to ambient air temperature.

The symptom: the top floor never gets comfortable

The complaints show up before the roof does. Upper floors that the HVAC cannot hold. Rooftop units running nearly nonstop through July and August. Cooling bills that climb faster than the weather explains. On a warehouse, workers on the floor feeling the heat come down all afternoon.

The problem: a dark roof is a heat collector on your deck

Every degree of roof surface temperature is heat pushing into the building envelope, and heat your cooling system has to remove. It is also heat stressing the roof itself. That daily expansion and contraction is what opens seams, works fasteners loose, and ages the membrane.

And the rooftop units are pulling their intake air off the hottest surface on the property, which is exactly the wrong condition for a condenser.

The solution: reflect the load instead of paying to remove it

A white reflective acrylic coating applied over the existing roof does several things at once:

• Cuts peak surface temperature, often by dozens of degrees, which lowers the cooling load through the deck.
• Reduces thermal cycling, which extends the life of the roof system underneath.
• Lowers intake air temperature for rooftop HVAC, so the equipment runs shorter cycles.
• Seals the roof at the same time, because the coating is a waterproofing system, not paint.

The EPA's work on cool roofs and heat islands covers the building science if you want the underlying research.

An honest caveat

Savings depend on your climate, your insulation, and how your building is used. A well-insulated building in a northern climate sees less benefit than an under-insulated warehouse in the South. Anyone who quotes you a fixed percentage without looking at your building is making it up.

What is consistent everywhere: lower surface temperature, less thermal stress on the roof, and a sealed membrane out of the same job. Related reading: white roof coating energy savings and how roof color affects HVAC lifespan.

Talk to a Conklin-trained contractor near you

No article can tell you what your roof needs. How much a cool roof saves depends on your building, not on an average. A contractor has to walk it, check the seams and penetrations, and look at the deck before anyone gives you a real answer.

White Roofing Systems coordinates Conklin-trained commercial roofing crews across the country. Call (309) 303-3128 or request a free roof inspection and we will route you to the contractor who covers your city. You can also browse the contractor directory by city and state or look through real before-and-after projects.