A built-up roof consists of plies of reinforcing material (organic felts, fiberglass mats or polyester), inter-ply layers of bitumen (asphalt or coal tar) and a finish surfacing, such as gravel or decorative rock, mineral surface cap sheets, or coatings. Owing to energy concerns, many built-up systems today incorporate rigid board insulation as well. Built-up roofing is one of the oldest and most durable systems available. Introduced during the 1840s, built-up ("tar and gravel") roofing remains the predominant system installed on low-slope ("flat") roofs. They are ideally suited for applications requiring a high level of redundancy.
Built-up Roofing System advantages:
- Surfacing materials can be coated with paint or other reflective materials to reduce the effects of UV radiation
- Coatings can help reduce heating and cooling costs
- Highly resistant to wind and hail
- Easy to repair
The repetitiveness of a built-up roofing system -- its layer upon layer nature -- provides both flexibility and durability. The number of plies and the materials used for surfacing can be varied to adapt the system to virtually any environmental or aesthetic concerns. For the same reason, a built-up roof is more forgiving of abuse after application than are many other roofing systems.