Class A Built-Up Roofs combine layers of roofing felts and hot-applied asphalt or coal tar to create a durable, fire-resistant membrane widely used on low-slope commercial and multifamily buildings in the United States.
| Feature | Typical Range / Value |
|---|---|
| Fire Rating | Class A (highest for roof coverings) |
| Common Materials | Asphalt or Coal Tar, Roofing Felts, Gravel or Mineral Surfacing |
| Typical Life Expectancy | 20–30+ Years With Proper Maintenance |
| Suitable Slopes | Low-Slope Roofs (≤ 3:12) |
What Is A Class A Built-Up Roof?
A Class A Built-Up Roof (BUR) is a multi-ply membrane assembled on-site using alternating layers of bitumen (asphalt or coal tar) and reinforcing felts, finished with a protective surfacing such as gravel or mineral granules to achieve a Class A roof covering fire performance rating.
The Class A rating reflects the roof covering’s resistance to severe fire exposure, determined by standardized tests such as ASTM E108/UL 790, making it one of the most fire-protective options for flat and low-slope roofs.
Why The Class A Rating Matters
The Class A designation indicates a roof covering’s performance against exterior fire exposure, burning brand tests, and lateral flame spread, which can influence insurance premiums, code compliance, and occupant safety.
A building owner selecting a Class A built-up roof typically seeks higher fire resistance, improved acceptance by local building officials, and potentially lower insurance costs compared with Class B or C roof coverings.
Components And Construction Of Built-Up Roofs
A typical built-up roof uses three primary components: bituminous adhesive (hot-applied asphalt or coal tar), reinforcing felts (organic or fiberglass), and a surfacing layer such as gravel, slag, or mineral cap sheets.
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Construction is sequential: the deck is prepared, flashings installed, multiple plies of felt embedded in hot bitumen are applied, and the surface is finished with loose-laid gravel or bonded mineral surfacing to protect against UV and mechanical damage.
Types Of Bitumen And Felts
Hot-applied asphalt and coal tar are the most common bitumens for BUR systems, each with distinct properties; asphalt offers versatility and availability while coal tar has superior chemical resistance and aging characteristics.
Reinforcing felts vary between organic felts and fiberglass mats; the choice affects durability, dimensional stability, and compatibility with the bitumen used in the built-up roof system.
Surfacing Options And Their Roles
Surfacing protects the membrane from sunlight, weather, and mechanical wear. Common finishes include loose-laid pea gravel, crushed stone, slag, and mineral-surfaced cap sheets embedded in bitumen.
Gravel surfacing adds ballast and fire resistance, while mineral cap sheets provide a factory-controlled surface with color options and enhanced UV protection.
Performance Characteristics
Class A built-up roofs provide excellent fire resistance, good waterproofing, and strong resistance to foot traffic and mechanical damage, making them a preferred choice for commercial and industrial low-slope roofs.
These roofs also deliver thermal mass and sound-dampening benefits, but they are heavier than single-ply membranes and require roofs and structures to be engineered for the additional dead load.
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Code Compliance And Testing
Building code acceptance of a roofing system as Class A depends on test results from ASTM E108 or UL 790, which evaluate burning brand exposure, flame spread, and deck contribution under controlled laboratory conditions.
Manufacturers and contractors must ensure that the exact assembly tested is used in the field because substitutions or changes can void the tested classification and affect code compliance.
Installation Best Practices
Proper installation is essential for longevity. A qualified roofing contractor should perform substrate inspection, ensure proper substrate venting, detail flashings and parapets carefully, and follow manufacturer specifications for bitumen temperatures and ply orientation.
Key installation checkpoints include ensuring even bitumen coverage, removing moisture from the deck prior to application, using the correct number of plies for the specified assembly, and final surfacing placement while the bitumen is still receptive.
Common Problems And How To Prevent Them
Typical issues include ponding water, blisters, seam failures, and surfacing displacement. Many failures are related to improper installation, poor drainage, or neglected maintenance.
Prevention strategies include designing adequate slope or tapered insulation, installing effective roof drains and scuppers, ensuring proper flashing details, and scheduling regular inspections to catch small problems early.
Maintenance And Repair Strategies
Routine maintenance preserves a Class A built-up roof lifespan: biannual inspections, debris removal, ensuring drains are clear, and repairing punctures or seam failures quickly will extend service life.
Repair actions are typically localized patching or overlay systems. When damage is widespread or the deck is compromised, full replacement or reroofing with a new BUR assembly should be considered.
Life Expectancy And Cost Considerations
With proper specification and regular maintenance, a built-up roof often lasts 20 to 30 years or longer. Costs vary by region, materials, roof complexity, and surfacing choice.
Initial installation costs for BUR tend to be higher than some single-ply membranes, but long-term durability and lower life-cycle maintenance can make Class A built-up roofs cost-effective over decades.
Comparing Built-Up Roofs To Other Low-Slope Options
Compared with single-ply membranes (EPDM, TPO, PVC), BUR systems offer superior fire performance and puncture resistance but are heavier and less reflective unless surfaced with light-colored materials.
Modified bitumen systems borrow from BUR technology but come factory-assembled in sheets for faster installation and potentially more uniform quality control while still achieving Class A assemblies in many cases.
When To Specify A Class A Built-Up Roof
Architects and specifiers commonly select a Class A built-up roof when seeking maximum fire protection, durable roof coverings for high-traffic mechanical areas, or proven multi-ply performance on large low-slope buildings.
Insurance requirements, local building codes, or tenant safety expectations also frequently dictate Class A specifications for commercial, institutional, and multifamily properties.
Selecting A Contractor And Warranties
Choose a contractor with BUR-specific experience, strong references, and verified insurance. Request documentation showing installation meets the tested Class A assembly rather than relying solely on material labels.
Warranties vary: manufacturer system warranties, contractor workmanship warranties, and extended guarantees should be reviewed for coverage limits, maintenance obligations, and required inspection schedules.
Environmental And Energy Considerations
Bursting into modern performance goals, BUR systems can be surfaced with reflective coatings or light-colored cap sheets to improve albedo and reduce cooling loads, aligning with energy code incentives and rebates.
Recycling options are limited compared with single-ply membranes, but BUR systems can be resurfaced or recovered in some reroofing scenarios, reducing tear-off waste and lifecycle environmental footprint.
Key Takeaways For Building Owners
Class A built-up roofs remain a robust, fire-resistant choice for low-slope commercial and multifamily buildings, offering long-term durability when installed and maintained properly.
Owners should prioritize selecting an assembly tested to ASTM E108/UL 790, hire experienced contractors, plan for routine maintenance, and weigh upfront costs against lifecycle performance and insurance benefits.
How to Get the Best Roofing Quotes
- Prioritize Workmanship
A roof is one of your home’s most important investments. Always choose a contractor based on experience and reputation — not just price. Poor installation can lead to expensive problems down the road. - Compare Multiple Estimates
Don’t settle for the first quote you receive. It’s always a smart move to compare at least three bids from local roofing professionals. You can 877-801-4315 to get local quotes from roofing contractors in your area, available across the United States. - Use Negotiation Tactics
After selecting a trusted roofer, be sure to use our proven tips — How to Negotiate with Roofing Contractors — to secure the best possible final price without cutting corners.