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Built-up roofing

Built-up roofing (BUR) is a membrane assembled on the roof from several plies of reinforcing felt, each set in hot asphalt, coal tar pitch or a cold adhesive. The top is finished with gravel or slag, a mineral-surfaced cap sheet or a coating. It is a field-built system for flat and low-slope commercial and industrial roofs.

Warranty available
Up to 20 to 25 years, by manufacturer and plies
Plies
3 to 5, or 2 to 4 under a cap sheet
Seams
Lapped plies set in bitumen or adhesive
Surface
Gravel, slag, a cap sheet or a coating
Attachment
Hot-mopped or cold-applied over insulation

How it's installed

What the plies are set in decides the method: hot asphalt, coal tar pitch or a cold adhesive. Insulation goes down first, fastened to the deck or adhered in hot asphalt or adhesive; on nailable decks such as wood, a nailed base sheet starts the membrane.

Hot-applied asphalt

Each ply is rolled into a solid mopping of hot asphalt, with the asphalt grade (ASTM D312 Type I to IV) picked for the roof slope and climate. A gravel roof then gets a hot flood coat with the aggregate set into it while it is still fluid.

Coal tar pitch

Coal tar pitch (ASTM D450) takes the place of asphalt in some gravel-surfaced specifications, and existing tar roofs can be resurfaced with tar-based cold flood coats. JM keeps coal tar out of its systems and guarantees and notes that IARC classifies coal tar as carcinogenic to humans.

Cold-applied

Plies are set in a cold adhesive instead of hot asphalt, so no kettles run on site. JM limits cold-applied BUR to slopes of 3 inches per foot or less and calls for fully coated, non-porous felts.

Pros and cons

Where built-up wins

  • Several plies set in bitumen, not a single sheet: manufacturers describe the layers as redundant waterproofing.
  • A gravel surface makes the roof somewhat less likely to be damaged by hail than a smooth one.
  • Cold-applied systems avoid kettles and asphalt fumes, which can suit buildings that stay occupied, such as schools and hospitals.
  • Reflective finishes exist: white aggregate in white adhesive, or cap sheets with reflective granules.

Where it falls short

  • Hot-applied jobs run asphalt kettles on site, with fumes and a fire risk if the asphalt overheats.
  • Gravel is heavy: JM and Garland call for about 400 lb per 100 sq ft, on top of the flood coat.
  • The membrane is made on the roof, so asphalt grade and temperature, dry conditions and finishing each day's work all decide the result.
  • Loose gravel can blow off in high winds; the federal guide specification for BUR doesn't allow it where the basic wind speed is 100 mph or more.

Built-up roofs and hail

Gravel helps a built-up roof in hail: it spreads the impact, so gravel-surfaced roofs are somewhat less likely to be damaged than smooth ones. In 1969 tests by the National Bureau of Standards, built-up roofs also resisted hail better over dense substrates than over soft ones, and coarse aggregate improved resistance. When hail does get through, it cracks the bitumen and can fracture the felts, and that damage is harder to find under gravel.

Hail ratings belong to the whole assembly: FM 4470 tests the roof cover over its substrate and rates it for moderate, severe or very severe hail (MH, SH or VSH). NRCA's summary of the 2018 edition of FM Global Data Sheet 1-34 says FM accepts SH-rated built-up roofs in very severe hail zones where VSH systems aren't available. If you're replacing in hail country, ask for the FM listing of the exact assembly and whether the warranty covers hail; JM, for one, offers hail riders by hailstone size.

Back to all roof systems

Sources

  1. FM Approvals, Approval Standard 4470: Single-Ply, Polymer-Modified Bitumen Sheet, Built-Up Roof (BUR) and Liquid Applied Roof Assemblies (April 2022)
  2. Johns Manville, Asphalt-Applied and Cold Application Built-Up Roofing Application Guide (RS-4927 2-14)
  3. USACE / NAVFAC / AFCEC (via WBDG), UFGS 07 51 13 Built-Up Asphalt Roofing (August 2025)
  4. National Bureau of Standards (now NIST), Hail Resistance of Roofing Products, Building Science Series 23 (1969)
  5. Johns Manville, JM Peak Advantage Guarantee Charges and Requirements – JM BUR (RS-1671 5-25)
  6. Elevate (Amrize Building Envelope), Elevate Domestic U.S. Warranty Pricing Guide (6/9/2026)
  7. Johns Manville, BUR Roofing Systems
  8. Johns Manville, Section 075113 Built-Up Asphalt Roofing (BUR), 3-Part Master Specification
  9. The Garland Company, Black-Knight/Black-Stallion Cold Technical Data Sheet
  10. Tremco Roofing, Cold Applied Built-Up Roofing Systems
  11. Tremco Roofing, BURmastic Built Up Roofing System
  12. National Roofing Contractors Association (Professional Roofing), Standing up to hail (Ric Vitiello, June 2007)
  13. National Roofing Contractors Association (Professional Roofing), Designing for hail resistance (Mark S. Graham, May 2018)

Updated October 2026.