Built-Up Roofs
Built-Up Roofs (BURs) consist of multiple plies of roof felts laminated together with bitumen. BUR material can consist of bitumen-saturated felt, coated felt, polyester felt or other fabrics. A surfacing is generally applied and can be asphalt, aggregate (gravel or slag), emulsion or a granule-surfaced cap sheet.
BUR is one of the oldest and most reliable ways of installing a new roof. It was first known as composition roofing and started in the 1840's. BURs come in two basic types - asphalt and coal tar - and three basic components – (1) the waterproofing component, (2) the reinforcing component, and (3) the surfacing component which is used to protect the other components from the elements. There are many different types of materials used in Built-Up Roofing. Some are:
Base Sheets:
- Asphalt-Coated Organic Base Sheet – Perforated and Non-Perforated
- Asphalt-Coated Glass Fiber Base Sheet
- Asphalt-Coated Glass Fiber Venting Base Sheet, Types I and II
Felts and Fabrics:
- Asphalt-Saturated Organic Felt – Type I ( aka No. 15) and Type II ( aka No. 30)
- Coal Tar-Saturated Organic Felt
- Smooth-Surfaced Asphalt Roll Roofing – Types I, II, III, and IV
- Asphalt- or Coal Tar-Saturated Cotton Fabrics
- Asphalt- or Coal Tar-Saturated Woven BUR Lap Fabrics
- Asphalt-Impregnated Glass Felt – Types III, IV, and VI
- Coal Tar-Impregnated Glass Felt – Type I
- Thermoplastic Fabrics for Built-Up Roofing – Types I, II, III, and IV
Bitumens:
- Asphalt – Types I, II, III, and IV
- Coal Tar – Types I, II, and III
- Lap Cement – aka Cold-Applied Liquid Adhesive, aka Solvent Based (Cutback)
- Asphalt – Type I (Grades 1 and 2), and Types II and III
Surfacings:
- Gravel or Slag
- Asphalt Roof Coatings – Asbestos and Non-Asbestos
- Aluminum-Pigmented Asphalt Roof Coatings – Non-Fibered, Asbestos Fibered, and Fibered without Asbestos
- Emulsified Asphalt – Fibered and Non-Fibered
- Mineral-Surfaced Asphalt Roll Roofing (Organic)
- Mineral-Surfaced Asphalt Roll Roofing (Glass Felt)
Other items not listed are flashing materials, mastics, caulking materials, fasteners, and roof insulations, to name a few.
The service life of a flat roof is dependent on many factors: geographical location & weather conditions, foot traffic, materials used, conditions under which the roof was installed, slope of roof, type of surfacing material, etc. Under ideal conditions, a 3-ply built-up roof should last at least fifteen years, a 4-ply should last at least 20 years, and a 5-ply should last at least 25 years. We have seen ten year old 4-ply roofs that needed to be replaced and twenty year old 3-ply roofs that were still functioning.
