Reflective roofs are often chosen to lower the temperature of a home or office building. Particularly in the Los Angeles basin, everyone is trying to figure out how to save money on cooling bills.
I have seen this debated just about everywhere and very often. I am asked this question virtually weekly. In SoCal, we have a unique combination of architecture and sunny days which conspire to make some homes unbearably hot during the summer. This may not be a major issue in someplace like Seattle, but around here – it’s the topic de jour. In some cases, the thermal transfer is so significant that even an appropriately sized AC system cannot keep up. These usually involve homes that have no attic space (cathedral ceilings or open beam architecture), lots of windows, and so on, all of which is pretty popular around here.
There is clearly a disadvantage that many don’t immediately understand with such open architecture. The airspace created by a normal attic acts as a buffer between the roof and the interior of a dwelling. This thermal dynamic can be seen with something even more simple and perhaps well known, such as dual pane glass. The airspace helps prevents heat from radiating into the dwelling and with good ventilation, can prevent it entirely.
But will an ultra reflective roof, which reflects more of the suns energy, actually translate into cooler temperature inside a home?
The short answer is yes, it usually will. Circumstances will produce larger or smaller effects, as in the case mentioned above with an open beam ceiling. In this case, where the ceiling of a home might actually be the wood deck upon which the roof is attached, it can produce a dramatic difference. In cases where a black/dark shingle is used on an open beam ceiling, the heat radiating through is massive. When a lighter shingle is introduced, the temps go down.
Where the roof is flat and there is a minimal airspace between the roof and the ceilings inside (usually about 1 to 2 feet) a reflective roof can produce beneficial results.
The reason why is fairly simple. When a roof surface heats up, it will radiate/transmit that heat inside. If there is an attic space, this can, and should be controlled with ventilation.
The point is that, in my experience, having an expensive, ultra reflective shingle on a normal home, with sloped roofing and a normal attic (the sort that at it’s highest points, at least 4 ft high), does not produce as much of an effect as can be achieved by simply having effective ventilation. If you have good ventilation, even though the roofing may be transmitting a higher than ambient temperature into the attic, if proper/rapid air exchanges are happening, the ventilation will keep the airspace in the attic close to ambient temps. Along with good insulation (critical), this is your best defense against a hot house.
If you have a flat roof or open beam architecture (where in many cases insulation isn’t practical) an ultra reflective roof can make a big difference and is probably worth the money. There are some shingles made that are considered ultra reflective but which also don’t cost a lot more or cost the same as ordinary shingles – many manufacturers have them.
My next segment will cover insulation and ventilation which in many cases can be as much or more important in reducing the heat in your home than ultra reflective shingles.