Cool roofing may not be as “cool” as we think!
Beginning in the 1980’s research on the benefits of cool roofs was conducted by the Department of Energy in hopes to find a way to save on energy costs and reduce our carbon footprint on the environment. The widely accepted belief that has developed from this research is that white roofs are the most environmentally friendly and energy efficient choice when it comes to roofing. This “cool roof” solution has become a quick and low cost solution in hopes to reduce carbon emission which is known to effect climate change. However, it has been said that cool roofs are not a “quick fix” to save on energy costs and that in certain climates they may actually increase energy consumption.
Due to the belief that reflective roofing is the easiest solution to lowering energy costs and reversing the effects of climate change, there has not been much consideration of geographic location . Although roofing professionals know that depending on geographic location and weather conditions there is a roofing system required for each roof.
Reflective, or what is known as “cool roofs” have been proven to reduce air conditioning costs during hot summer months, which in return provides home and building owners a great deal on energy savings. However, take into consideration colder, northern climates where people must spend more money heating a building rather than cooling them, the cool roof solution may not be a smart choice for them. In return, a reflective roof may actually increase carbon emissions due to increased energy consumption.
Effects of Cool Roofing in Cool Climates
Aside from inefficiency, reflecting roofing systems can have negative consequences in cool climates. The roof cover only concept regarding white reflective roofing implements only changing the color of the roof top from black to white. However, this concept ignores the components that are underneath the surface and how they are effected by the transition from black to white. One issue that can arise from cool roofs being installed in cooler climates is condensation. During the summer surfaces stay cooler, however when temperatures are colder the surface remains cooler for a longer period of time. In return it will fall below the dew point and remain there longer compared to darker membranes, which leads to condensation formation.
Condensation is one of the most potentially hazardous consequences of cool roofing. How does condensation occur? Warm air begins to rise toward the roof when temperatures outside drop. With no air or vapor retarder the warm air that rises makes contact with a surface that has dropped below the dew point and forms condensation.
There are several signs that can reveal the presence of condensation. One way to tell is when you walk on top of the roof, if there is a crackling noise below your feet it is a dead give away that there is frozen moisture in your roofing system. You can come across this situation typically when a roofing system is insulated with a single layer opposed to multiple layers. When multiple layers of insulation are implemented in a roofing system, the joints end up staggered which in turn makes warm, moist air to reach the underside of the roof membrane. Therefore, using multiple layers to insulate your roof, although not foolproof, can help to decrease the level of moisture collecting beneath a roof membrane. Another issue that can arise from the use of a single layer of insulation is that moisture can free between the insulation joints, which causes it to expand as it begins to freeze and pushes the edges of insulation boards apart. Moisture will also lead to the insulation warping. Therefore, when frozen inflation experiences warmer temperatures, the frozen moisture will begin to drip inside the building. Another unfortunate result of condensation is adhesion loss. When moisture accumulates and does not have the opportunity to dry, insulation facers can weaken, and therefore the membrane can detach from the insulation which causes reduced wind uplift resistance.
How to avoid condensation
When choosing a roofing membrane color make sure you take into consideration the climate in which the roof will be installed. Typically in northern and colder climates, a dark membrane is used, where in warmer southern climates, a white more reflective membrane is used. However, if you are to implement a reflective membrane in a cooler climate, one way to try and avoid condensation is to use a continuos air or vapor retarder, as well as using the multi layer insulation method.
Although reflective roofs are installed with good intentions, in hopes to reduced energy costs as well as our carbon footprint. Do not forget that these benefits are typically seen in warmer, southern climates. Therefore, if you are going to install reflective roofs in cooler climates make sure you implement certain design modifications to help reduce the presence of condensation, because when installed cautiously and correctly, cool roofs can perform quite well in cooler climates!
Chase NW Roofing is factory trained and certified with GAF, IKO, Versico and Custom-Bilt Metals to install almost every roofing application. We specialize in composition shingles, torchdown, single ply, metal roofing, wood shakes, slate and concrete tile. We have been providing quality re-roofs in the North West for over a decade. If you are planning to re-roof your house, need an inspection give us a call at 253-445-8950, or fill out our free estimate form!