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