Built up roofs are one of the oldest and most reliable low slope roof systems. These systems have been used for over 100 years and are proven to perform well in extreme temperatures. Built up roofs consists of multiple layers of roof felts laminated together with asphalt. The hot asphalt is the bonding and waterproofing agent used between the layers. The felts (polyester or fiberglass) reinforce the asphalt and prevent it from cracking. Built up roofs are typically installed as 3, 4, or 5 ply systems.
The built up roof systems are laid up one section at a time. The asphalt is heated in a kettle and applied by large mops or a mechanical spreader. Approximately 25-30 lbs. of hot asphalt is used between each ply per 100 square feet. The first coat of hot asphalt is applied onto the base sheet and is followed by a layer of felt. The process of laying down hot asphalt and felt is repeated to build up to the desired amount of layers/ply. Then a surface coat is applied to protect and preserve the roof components from weathering and UV exposure.
There are numerous surfacing options for built up roof systems including hot asphalt mopped over the entire surface, mineral surfaces, gravel surfaces, cap sheets, and “cool roof” coatings, which are highly reflective coatings that can help save on cooling costs.
These durable roofs can carry manufacturers’ warranties from 10 to 30 years.