Flat Roofing Systems
Built-up roofing, modified bitumen, torch-applied membranes, cold process adhesives, and ballasted systems.
- Describe the components and minimum slope of built-up roofing systems
- Explain the advantages of modified bitumen roofing
- Identify the differences between torch-applied and cold process adhesive membranes
- Describe mechanical attachment and ballasted roofing methods
- Explain the purpose and design of tapered insulation systems
Lección 1
Built-Up Roofing (BUR) Systems
BUR Components
Built-up roofing (BUR) is a traditional flat roofing system consisting of alternating layers of bitumen and reinforcing felts. The "built-up" name comes from building up multiple plies to create a waterproof membrane.
A standard BUR system includes:
- Base sheet - mechanically fastened or adhered to the insulation
- Interply felts (2-4 layers) - saturated with hot asphalt between each ply
- Flood coat - final heavy layer of hot asphalt
- Surfacing - gravel, cap sheet, or mineral coating
The minimum slope for a built-up roof (BUR) system is 1/4 inch per foot (2%). This minimum slope is necessary to ensure positive drainage and prevent ponding water. Dead-flat installations are not recommended because standing water degrades the bitumen and surfacing.
Hot-Mopped Asphalt
The material used for hot-mopped built-up roofing is heated asphalt (bitumen). Asphalt is heated in a kettle to between 200 and 260 degrees Celsius and mopped between felt layers. The hot asphalt acts as both adhesive and waterproofing agent.
Flash Point Safety
Never exceed the flash point of roofing asphalt. Overheating causes the asphalt to ignite. The kettle operator must monitor temperature continuously and maintain a fire extinguisher at the kettle.
Gravel Surfacing
The function of gravel on a built-up roof is to protect the bitumen from UV degradation and provide ballast against wind uplift. Gravel also improves fire resistance by protecting the combustible bitumen layer. Aggregate must be clean, dry, and embedded in the flood coat at a rate of approximately 400 lbs per square.
The minimum slope for BUR is 1/4 inch per foot (2%). BUR consists of alternating layers of hot asphalt and reinforcing felts. Gravel surfacing protects bitumen from UV, provides ballast, and improves fire resistance.