Modified Bitumen is a rolled roofing material that was developed in Europe in the 1970’s and has been manufactured in this country since the 1980’s. Often referred to as a ‘torch-down’ roof, it is applied over nailed base sheets and heat-welded in place with a hand-held torch fueled by propane. Modified bitumen consists of asphalt-based tar products applied to polyester or fiberglass mats, and bonded with modifiers added to provide flexibility and improve aging and curing after heat application. The ease of installation and relatively low-cost of this material has enabled it to supplant built-up (tar & gravel) as the most ubiquitous low-slope roofing membrane in residential applications in this country. Various forms are available; typically a mineral surface is presented to the weather, with several choices of color available.
LIFE: 20-30 years
THERMO PLASTIC (TPO)
Thermoplastic Polyolefin is another rolled roof product with seams. It can be nailed to the roof deck over base sheets, or simply glued down. This product was introduced in the mid-1990’s and over the past several years has become very popular. It’s worth noting that no fumes or off-gassing occurs while this system is being applied and is therefore well liked by both installers and environmentalists. Noted for its seam strength, resistance to puncture and tear, and the UV-reflective qualities of the white membrane, TPO is increasingly specified by designers and architects. It is expected to soon become the most common flat roof membrane in the country. It is also available in various shades of grey.
LIFE: 25-30 years
POLYVINYL CHLORIDE (PVC)
Vinyl roofs have been around for over 40 years. It is another seamed rolled roof product that can be fully adhered to the base sheets, or nailed down with the seam of the second sheet covering the nails of the first. The seams are heat-welded and are reputed to be several times stronger than the field of the product. Like TPO, the associated flashings (edge-flashings, pipe and vent-flashings etc.) are proprietary. In this case they have to be vinyl-clad to bond into the membrane. PVC roofing is usually bright white in color and is considered energy efficient. Due to its long life and durability, this system is often used as the base for a Green Roof or growing roof assembly with the addition of various drain-mats and growing medium. Interestingly, some Green builders object to the use of PVC due to the chemicals used in the manufacturing process and the potential for toxic release in a fire. PVC products are also available as deck coverings. These walkable membranes are typically applied over smooth-surfaced plywood on a deck or patio area, making pavers, tiles or decking unnecessary. They tend to have a slightly textured (non-skid) surface reminiscent of linoleum.
LIFE: 25-35 years
METAL SHINGLES AND STANDING SEAM
Galvanized (corrugated) steel, aluminum and steel with (or without) powder-coated paint finish, zinc, and copper are all available as roofing materials, either as shingles or as roof panels. The conductive properties of metal usually require that a heat resistive base sheet be installed. In hotter areas a gypsum heat barrier may be worth considering. Standing seam roofs have become increasingly popular over the last few years. They provide a clean modern look and are relatively simple to install. As they have become more widespread, they are one of the very few assemblies that have actually come down in price!
LIFE: 40-90 years
COST: $500-$1,100 Standing Seam: $700-$1,000