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.
Shingle of felts is a common installation of built up roofs. Overlapping the felts to develop an achieved minimal thickness characterized by 2-ply, 3-ply and 4-ply. It is said that each ply represents 5 years of service, so a 3-ply would indicate a 15-year roof system and a 4-ply would signify a 20-year roof system. This is only if the roof system is properly installed and maintained over its life span.
Advantages of BUR
- Built-up roofing systems have had a long-standing popularity, due in large part to the success and proven reliability of BUR. The stock of 20, 30 and 40-year-old BUR roofs still in excellent condition attests to this fact. Specifically, BUR roofs offer.
- Multi-Layer Protection–the multiple layers of bitumen and bitumen saturated “felts” make a water tight barrier capable of providing many years of reliable protection from the elements.
- Thermal Performance –Built-up roofing systems exhibit exceptional resistance to the conduction of heat between the exterior and interior of a building, resulting in noticeable reductions in heating and cooling costs.
- Fire and Uplift Resistance –Built-up roofing systems are tested through Factory Mutual Research Corporation to meet very strict fire resistance requirements and ensure adequate uplift resistance under extreme wind conditions.
Disadvantages of BUR
- Not the best looking, although good applications with careful roofers can help the aesthetics.
- If application is not installed properly possible future problems such as, blistering, splitting, ridging/wrinkling and slippage can occur.
- Requires hot tar, which is not only hot but has quite an odor when being applied. That can influence customers, employees, etc.…
- Requires hot tar kettle and the mess and danger they can represent.
- Needs regular maintenance and occasional re-coats (usually commercial applications without a covering of rock or cap sheet.)
- Compared to other high performance commercial roofing systems, built-up roofing is one of the highest priced investments on the market due.