How is solar radiation control installed?
If radiation control is achieved by replacing the existing roof membrane by a new membrane with radiation control characteristics, roofing industry-accepted low-slope roof installation procedures are followed. An excellent guide to specifications and construction details for low-slope roof installation is the National Roofing Contractor's Association Roofing and Waterproofing Manual, Fifth Edition, Volumes 1 and 2, published in 2001.
Cleanliness is a special concern during installation of new membranes with radiation control characteristics. These membranes are light-colored and they are easily and permanently soiled by asphaltic materials. Foot traffic that tracks such materials from other areas on the roof must be avoided. Materials used to adhere insulation before the new membrane is installed may also have the potential to stain the top of the new membrane. If so, they must dry thoroughly before the new membrane is laid out on the roof. Besides being unsightly on a light-colored roof, every spot of asphaltic material lowers the solar reflectance of the affected area to less than 0.1.
Coating an existing roof to achieve radiation control is a less complicated procedure. For any coating process, the key to success is thorough cleaning and drying of the substrate. Roof coatings are especially formulated to adhere to a variety of roof membranes. They are not the same as paint. The final coating thickness for white latex or acrylic coatings is usually about 0.015 in. (0.38 mm) and is less for many aluminum coatings. Only minor surface defects can be bridged without compromising the integrity of the coating. Defects in the coating are potential sites for cracking and peeling. Many coating products are intended to seal the area they cover against leaks in the original membrane. Coating defects compromise this function before cracking or peeling becomes apparent .
The large area of most low-slope roofs rules out brush-coating as a means to apply the coating. Even so, brushing is often used near flashings and edges to precoat for additional sealing. On large areas of a smooth-surfaced roof, roller application of coatings is possible. A typical roller application is shown in Figure 1. On a rough-surfaced roof or for the most uniform application on any substrate, spray application of coatings is done. See Figure 2 where an airless sprayer is being used to apply a white coating to a gravel-topped built-up roof.
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Figure 1
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Figure 2
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