Flat roof built up, commonly called built-up roofing (BUR), is a time-tested roofing system that layers asphalt or coal tar with reinforcing fabric and a protective surface. It remains popular for its durability, waterproofing, and versatility in various climates. This article explains how BUR works, typical materials and configurations, installation steps, maintenance needs, and practical considerations for homeowners and property managers in the United States.
What Is Built-Up Roofing (BUR) For Flat Roofs
Built-up roofing combines multiple plies, or layers, of waterproofing materials with a bituminous adhesive to create a durable, moisture-resistant surface. A protective cap sheet or granulated surface is installed on top to shield the system from UV exposure and weathering. BUR systems are known for their long track record, excellent waterproofing, and ability to withstand foot traffic when used as a walking surface on flat roofs.
Common Materials And Layer Configuration
A typical BUR assembly includes three main components: plies, adhesive or cold-process glue, and the surfacing layer. The exact configuration varies by climate and manufacturer, but common arrangements include:
- First Ply: Roofing felt or fiberglass mat embedded in asphalt or coal tar.
- Middle Plies: Additional plies of felt or fabric sealed with bitumen to build thickness and resistance.
- Cap Sheet: A final layer, often asphalt-saturated felt or a fire-rated cap sheet, that provides UV protection and wind uplift resistance.
- Surfacing: Mineral granules, gravel, or a reflective coating to protect against sun exposure and improve curb appeal.
Common bitumen types include traditional coal tar or asphalt, with asphalt being more prevalent in modern BUR installations. In some designs, fiberglass or organic felts reinforce the layers, offering strength and tear resistance. The choice of materials affects longevity, maintenance, and compatibility with underlayment and insulation.
Advantages And Disadvantages
Built-up roofing offers several advantages for flat or low-slope roofs. It provides excellent waterproofing, proven durability, and a robust surface for foot traffic. The layered system helps distribute loads and resist hail damage, while the cap sheet offers UV protection and wind uplift resistance. However, BUR can be heavier than single-ply systems, requires skilled installation, and may involve higher initial costs. Some climates demand regular maintenance to preserve flexibility and prevent cap-sheet degradation.
Installation Process: Steps And Timelines
Installing BUR is a specialized process that involves careful surface preparation and multiple application stages. Typical steps include:
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- Roof Evaluation: Inspect deck integrity, flashings, and penetrations; repair as needed.
- Deck Preparation: Clean, dry, and smooth the surface; install or repair insulation and vapor barriers.
- Base Plywood Or Felt: Apply the first ply with hot asphalt or coal tar adhesive and embed roofing felt.
- Additional Plies: Add subsequent plies, each sealed with bitumen, to reach desired thickness and durability.
- Cap Sheet: Install a cap sheet for UV protection and wind uplift resistance.
- Surfacing: Apply mineral granules or a reflective coating to finish the surface.
The process often requires weather windows, especially for hot-applied asphalt. A typical BUR installation spans several days for larger roofs, with curing times and inspection milestones along the way. Repairs or patching may be needed between plies if moisture intrusion is detected during installation.
Maintenance, Repairs, And Longevity
Proper maintenance extends BUR life, which commonly ranges from 15 to 30 years depending on climate, installation quality, and maintenance. Key maintenance practices include:
- Regular Inspections: Check for blisters, pooled water, cracking, or exposed cap sheet after heavy storms.
- Clean Gutters And Drains: Prevent water buildup near parapets and penetrations.
- Prompt Repairs: Seal blisters, replace damaged cap sheets, and re-secure loose flashing as needed.
- Avoid Excessive Foot Traffic: Limit traffic to designated walkways to reduce wear.
- Professional Maintenance: Schedule periodic assessments by a licensed contractor to assess adhesion, insulation, and membrane integrity.
Damaged BUR often shows as bubbling, cracking, or exposed layers. Left unchecked, moisture intrusion can lead to rot, mold, and structural problems. Repair methods may include re-sealing blisters, re-laying plies, or applying new cap sheets, depending on damage extent.
Climate, Energy, And Environmental Considerations
BUR performs well in diverse climates, offering dependable waterproofing in rain-prone regions and resilience against hail. Energy performance can be improved with reflective or white cap sheets, reducing cooling loads in hot southern regions. Some older BUR systems may contain asphalt or coal tar with higher volatile emissions; modern installations often use low-odor, environmentally friendlier materials and improved cap sheets. Local code requirements, fire ratings, and warranty terms influence material selection and installation practices.
Code Compliance, Insurance, And Warranty
Flat roof BUR installations must comply with local building codes, fire ratings, and wind uplift requirements. Many jurisdictions require a fire-rated membrane and proper detailing at edges, penetrations, and parapets. Insurance policies may have specific clauses about BUR systems, particularly regarding fire safety and maintenance records. Warranties vary by manufacturer and contractor, typically covering membrane integrity, adhesion, and workmanship for specified periods. Homeowners should obtain comprehensive, transferable warranties and ensure documentation of maintenance and repairs.
Cost Considerations And Budgeting
Initial BUR installation costs are influenced by roof size, thickness (number of plies), material choice, insulation needs, and the complexity of detailing. Roughly, BUR can range from moderate to higher pricing relative to other flat roofing options, with long-term durability often offsetting upfront expenses. Ongoing maintenance and occasional patching contribute to lifetime costs. For budgeting, request detailed quotes that itemize plies, cap sheet type, insulation, flashing, and labor. Consider lifecycle costs, not just initial price, to assess value.
DIY Versus Professional Installation
Flat roof BUR installation requires specialized equipment, safety protocols, and knowledge of roofing temperatures and adhesives. Improper installation can lead to leaks, poor adhesion, and premature failure. Hiring licensed roofing professionals with BUR expertise is highly recommended. For minor repairs, trained homeowners can perform blister patching or edge sealing after consultation with a contractor to avoid compromising the system.
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Typical Maintenance Checkpoints And Best Practices
To maximize performance, establish a maintenance schedule with these checkpoints:
- Annual inspections focusing on seams, flashings, and perimeter edges.
- Post-storm assessments for punctures or hail damage.
- Seasonal cleaning of debris from parapet walls and drainage outlets.
- Documentation of all repairs and warranty information for future claims.
Adherence to these practices helps identify issues early, preserving waterproofing and extending the life of the BUR system.