Know-How: Roofing
Jun 1, 2005 12:00 PM, by Mike Kennedy
As schools and universities build and renovate facilities at a robust pace, administrators can choose from many types of roofs to cover their multi-million-dollar investments:
Built-up roofing (BUR). According to the Collaborative for High-Performance Schools Best Practices Manual, a built-up roof is the most common type of low-slope roofing. It consists of layers of waterproofing bitumen (asphalt or coal tar) alternating with layers of felt. They “provide good strength and protection from environmental conditions and have a low life-cycle cost,” the manual says.
Single-ply roofing. A system in which the principle roof covering is a single-layer flexible membrane, according to the National Roofing Contractors Association. The Single-Ply Roofing Industry association (SPRI) identifies three main categories of single-ply roofs: thermosets, thermoplastics and modified bitumens.
Thermoset membranes are compounded from rubber polymers, says the SPRI. The most commonly used polymer is EPDM.
Thermoplastic membranes are based on plastic polymers, according to the SPRI. The most common thermoplastic is PVC (polyvinyl chloride) that has been made flexible by including ingredients called plasticizers.
Modified bitumen roofing systems, the SPRI says, are factory-fabricated layers of asphalt, “modified” using a rubber or plastic ingredient for increased flexibility.
Metal roofing, according to the CHPS Best Practices Manual, may consist of galvanized steel, aluminum or copper. Standing-seam metal roofs often are used to replace school roofs in retrofit projects. To install this type of roof, metal panels are locked in place by clips inside a raised seam standing 2 to 3 inches above the roof surface.
Polyurethane foam roofing (PUF). Another type commonly used for re-roofing, it is lightweight and has a high insulation value.
Garden or green roofing. The CHPS manual says a green roof consists of a waterproof barrier, a drainage layer, a filter membrane, growing medium and vegetation. These roofs can reduce energy consumption and limit stormwater runoff.
NOTABLE
Solar reflectance is a measure of a material's ability to reflect sunlight:
0.0
The solar reflectance level at which a surface absorbs all solar radiation.
1.0
The solar reflectance level that represents total reflectivity.
0.6 TO 0.7
The solar reflectance level of a highly reflective roof.
0.10 TO 0.35
The solar reflectance level of a brown or red tile roof.
0.03 TO 0.18
The solar reflectance level of a tar and gravel roof.
Source: U.S. Environmental Protection Agency
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