Built-up roofs are the traditional approach to flat commercial or industrial roofing in North America. Multiple layers of felt with interply moppings of asphalt or coal tar are assembled in the field to "build up" a finished roof assembly. These type of roofs are classed by the number of plies of felt that is used in their construction. Ex. "Three ply roof" or a "four ply roof". Coal tar built up roofs are best used when roof areas have a very low slope and ponding water is probable. Coal tar is completely impervious to ponding water, one of the few roofing materials that has that attribute. Coal tar also has a low melting point, which means in the summer months, the coal tar becomes fluid and will "self-heal". Asphalt built up roofs are best used when roof areas have significant slope where the low melting point of coal tar might cause "slippage" of the membrane. Normally any roof system which has in excess of 1/4" per running foot of slope should utilize asphalt if the building owner wishes to utilize a built-up system. These type roof assemblies have a good life expectancy, normally in the range of 15 to 25 years. To get a good life span out of these systems, a protective surface must be applied to the top of the roof. The typical surfaces to protect the roof from solar radiation are embedding gravel in the asphalt/coal tar, applying a surface coating, or applying a granular-surfaced "cap" sheet.
Built-up roofing is formed on site from two or more layers of roll roofing. The vast majority of materials available consist of a reinforcement base of glass or polyester coated with oxidised or modified bitumen.Rag, wood or asbestos fibre were originally used to form the base reinforcement for all built-up roofing. They achieved only limited success and are not now recommended for commercial built-up roofing. They have been withdrawn from British Standards, other than for underslating felt. Glass tissue reinforcement was introduced during the 1950’s. It is still used as a component in specifications to provide improved dimensional stability.
High Performance Roofing Today
Most high performance membranes are made on a polyester fibre base which has a high elongation at break which exceeds all likely demands to be met in service.
Polyester roofing has been in regular service for some 25 years and there appears to be no report of failure through ageing. Reported defects have been due to design faults or workmanship faults, for example at outlets or pipes.The addition of a polymer to the bitumen improves its properties as a roofing material in almost all respects, and in particular the flexibility, strength and fatigue
Full Bond 2 layers high performance roofing bonded to substrate
Partial Bond 2 layers high performance roofing
Nailed First Layer 2 Layers high performance roofing fully bonded
A premium-performing fiberglass Type VI roofing felt. The proprietary Micro-Weave™ core provides superior tensile strength and dimensional stability, for greater resistance to splitting and cracking. Coverage: 500 sq./ft. per roll
SBS rubber modified, asphaltic base sheet that is designed to be used as a base ply in built-up roofing systems and as a base or intermediate ply in modified bitumen systems. Coverage: 300 sq./ft. per roll
This sheet can be mechanically fastened or hot-asphalt applied and is designed for use as a base sheet for use over nailable decks or insulation prior to the SBS-modified cap sheet of BUR systems. Coverage: 200 sq./ft. per roll
A heavyweight, venting base sheet that is intended to relieve vapor pressure over lightweight insulating concrete or gypsum decks. It is also specified in modified roofing systems installed over existing roofing systems. Coverage: 100 sq./ft. per roll
Consists of a TAMKO fiberglass mat coated on both sides with SBS-rubber-modified asphalt. Can be used as an alternate for Organic Base Sheet or Glass-Base® and also serves as a good vapor retarder when set in hot asphalt or between layers of insulation. Coverage: 150 sq./ft. per roll
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