Built-Up Roofing
Built-Up Roofing
Built-Up Roofing (BUR) is a traditional and time-tested flat roofing system composed of multiple layers of reinforcing fabric and bitumen (asphalt or coal tar), topped with a protective surface layer such as gravel or a reflective coating. BUR systems are most commonly found in commercial and industrial applications, particularly on low-slope and Flat Roofs.
With a history of over 100 years in use across North America, built-up roofs are known for their durability, multi-layer protection, and ability to withstand foot traffic and extreme weather.
Key Components of Built-Up Roofing
A typical BUR system includes the following layers:
- Base Sheet: Attached directly to the roof deck, often mechanically fastened or adhered.
- Ply Sheets: Layers of reinforcing felt (fiberglass or organic) embedded in hot asphalt or cold adhesive.
- Bitumen: Asphalt or coal tar applied between plies to create a waterproof barrier.
- Surfacing Layer: Options include gravel (ballast), reflective coatings, or mineral cap sheets for UV and weather protection.
These layers combine to form a seamless, multi-ply membrane that is highly resistant to water intrusion and mechanical damage.
Benefits of Built-Up Roofing
BUR systems offer several distinct advantages:
- Durability: Multi-layer construction provides excellent protection against leaks, punctures, and impact.
- Water Resistance: Redundant waterproofing layers minimize risk of moisture intrusion.
- UV and Fire Resistance: Surface gravel or coatings protect from sun exposure and can improve fire ratings.
- Longevity: Lifespans typically range from 20–30 years, or more with proper maintenance.
- Thermal Performance: Optional insulation layers and surfacing options improve Energy Efficiency.
Types of Built-Up Roofing Systems
Asphalt BUR
Uses hot asphalt to adhere layers. Most common type in modern commercial applications.
Coal Tar BUR
Less common due to environmental concerns, but provides excellent chemical and moisture resistance.
Cold-Applied BUR
Avoids the use of kettles or torches by using cold adhesives, safer for occupied buildings or tight work areas.
Modified Bitumen Hybrid Systems
Combine BUR layers with Modified Bitumen membranes for enhanced flexibility and performance.
Ideal Applications
BUR is ideal for:
- Warehouses, factories, and office buildings with flat or low-slope roofs.
- Roofs exposed to foot traffic or heavy mechanical equipment.
- Structures in climates with wide temperature ranges or high precipitation.
BUR vs Other Roofing Systems
BUR vs Single-Ply Membranes (like TPO Roofing and EPDM Roofing)
- BUR provides multiple waterproofing layers; single-ply systems rely on one.
- Single-ply systems are generally lighter and faster to install.
- BUR systems are heavier and require more labor but often offer better resistance to damage.
BUR vs Modified Bitumen
- Modified bitumen is a factory-produced membrane; BUR is assembled on-site.
- Modified bitumen may be easier to install with fewer layers.
- BUR is still preferred in many legacy and heavy-duty commercial projects.
Maintenance and Repairs
Like all roof systems, BUR roofs require regular care:
- Inspect flashings, seams, and gravel surfacing annually.
- Look for signs of ponding water, blistering, or cracks in the membrane.
- Maintain consistent gravel coverage or recoating to extend the system’s life.
- Small repairs can often be made by patching over affected layers.
Environmental and Energy Considerations
- BUR systems can incorporate insulation to enhance thermal performance.
- Reflective coatings improve solar reflectance and qualify for Cool Roofs status.
- While BUR systems are durable, they are not typically recyclable at end-of-life.
- Cold-applied systems reduce emissions and are better suited for sensitive environments.
