|
Built Up Roofing (BUR)
Built up roof is a generic term for a roof system that is literally built by adding layers. This is by far the oldest of the "modern methods" of roofing dating back to the early 1800's. Formerly, the built up roof membrane was the waterproofing agent and the bitumen was the adhesive. With the advent of synthetic fibers, the rolls of the two principle elements have been reversed. Now, the bitumen is the waterproofing agent and the membrane is used to hold the bitumen in place. Built up roofs can be installed using different waterproofing materials including coal tar pitch, asphalt, cold application adhesive, and modified asphalt. All systems will utilize either base sheet, ply sheets (felts), or cap sheets in some combination. The roof has a variety of surfacing options ranging from gravel, asphalt, coatings, to mineral surfaced.
The most common built up roofs:
Bitumen asphalt - Bitumen's are heavy and black or very dark brown. Asphalt is the dense residue left behind from petroleum distillation. There are several versions of bitumen asphalt ranging from type I (dead level) to type IV (special steep). Generally, a type II is used on the field of the roof system and type III is used on the penetration and base flashings.
Coal Tar Pitch - Coal tar is derived from the distillation of high temperature coke oven tar, which is produced during refining of bituminous coal. It has a natural resistance to temperature changes, water, moisture, and vapor transmission. Its low melt point makes it naturally "self-healing." Coal tar does have an odor associated with its heating and can cause some discomfort to the nose, eyes, skin. Coal tar roofs must be surfaced with gravel in order to keep the bitumen in place. It is not recommended for roofs with slopes over 1/2" in 12".
Cold process - An inexpensive tar/asphalt based, semi-liquid material commonly called cold process. Used mainly for smaller jobs that by cost, or other restriction, does not require a more substantial roof (this material/application is being changed to create a better roofing system). Application similar to hot, but applied with a long handled brush or roller.
|
