Four-Ply Roofing Alternatives

Two and Three Ply

• A four-ply roof is a type of built-up roofing system that involves sandwiching four layers of roofing felt between the black asphalt used to cover roads. It is possible to make three- and two-ply roofing finishes instead of four plies. Two-ply roofs only last between eight and 11 years, according to Tenant Improvement Construction, while adding the third layer only increases it to 15 years. Using less layers of felt does reduce the installation cost and time.

Single-Ply Membranes

• Three main single-ply membranes can be used in place of a four-ply roof. These single layers use materials like polyvinyl chloride, PVC; thermo plastic olefin, TPO; and ethylene propylene diene monomer rubber, EDPM, to create a watertight roof, states the Cool Flat Roof website. EDPM rubber requires only adhesives and seam sealing during installation, while the other two membranes must be sealed to the deck with a heat welding tool, making EDPM easier for a homeowner to install.

Modified Bitumen

• The modified bitumen roofing material is a single-ply material as well; however, it is coated with a layer of mineral bits that help the roof resist wear and water. A torch is required to melt it to the roof deck, making it potentially hazardous to install on an occupied building, warns This Old House. The self-adhesive bitumen rolls don't last as long as other flat roofing materials. The mineral coating won't handle being walked on, making roof maintenance tricky.

Ballasted

• Ballasted roofs use a single-ply membrane but do not involve adhering the membrane to the roofing deck with adhesives or heat and torch welding. The loose layer of membrane is secured with ballasts or heavy objects like large pieces of gravel and concrete pavers, explains the Whole Building Design Guide. These weights keep the membrane from flying away in high winds but must be regularly replaced. Ballasts can wear holes in the membrane and cause leaks.