Tar-and-Gravel (Built-Up) Roofs: Repair, Recover, or Replace?
| # | Table of Contents |
|---|---|
| 1 | What a Built-Up Roof Is |
| 2 | How They Fail |
| 3 | When Repair Makes Sense |
| 4 | Can a New Roof Go Over It? |
| 5 | Test for Asbestos Before Tear-Off |
| 6 | Replacement Options |
| 7 | FAQ |
What a Built-Up Roof Is
NRCA describes a built-up roof (BUR) as a membrane of "multiple plies of saturated felts, coated felts, fabrics or mats assembled in place with alternate layers of bitumen." The top is surfaced with gravel (aggregate), a coating or a granule-surfaced cap sheet.
Each layer has a job. In the EPA's description, "The bitumen is used as an adhesive as well as a waterproofing layer," "The roofing felts stabilize and reinforce the system," and "The aggregate protects the membrane from the effects of sunlight and weathering." The gravel is set into a flood coat of bitumen, so when it wears thin or washes away, the felts underneath start to bake.
Built-up roofs are common on older commercial buildings, strip centers and mid-century homes with flat sections across Central Texas.
How They Fail
- Bare spots. Gravel washes into drains or gets scraped away, exposing the bitumen to UV, which dries and cracks it.
- Alligatoring and cracking of the exposed bitumen surface.
- Blisters and splits where layers have come unstuck or the membrane has been stressed by movement.
- Flashing failures at parapet walls, curbs and penetrations, often the first leaks on an older BUR.
- Ponding in low areas that keeps the membrane wet.
- Wet insulation underneath, which shows up as soft spots and leaks that move around.
For two of these in detail, see flat roof blisters and ponding water on a flat roof.
When Repair Makes Sense
| Usually repairable | Usually points to replacement |
|---|---|
| One or a few open blisters or splits | Bare, cracked felts over large areas |
| A failed flashing at a wall, curb or drain | Leaks in many places, or leaks that keep moving |
| Small areas of lost gravel | Spongy or wet insulation across the roof |
| A puncture from equipment or foot traffic | Repairs that keep failing next to earlier patches |
Repairs on a built-up roof should use compatible materials. A quick patch with an incompatible product can fail where it meets the old bitumen. An inspection that checks for wet insulation, not just surface damage, is what separates a sensible repair from money spent on a roof that is wet underneath.
Can a New Roof Go Over It?
Putting a new roof over the existing one (a recover) can save tear-off cost, but the building code limits it. The 2024 International Residential Code (section R908.4, which the City of Austin now enforces) and the International Building Code (section 1512.3) say a recover is not permitted where:
- the existing roof is "water soaked or has deteriorated to the point that the existing roof or roof covering is not adequate as a base for additional roofing";
- the existing roof covering is slate, clay, cement or asbestos-cement tile; or
- "the existing roof has two or more applications of any type of roof covering."
Both codes also allow a new protective coating over an existing built-up roof without tear-off, which can be an option for a roof that is dry and sound but weathered. Loose gravel is normally removed before work on the old membrane; the EPA notes that "Loose, surface gravel is often removed from the existing roof membrane before removal begins."
Test for Asbestos Before Tear-Off
Older built-up roofs deserve one extra step. The EPA notes that asbestos was used as a reinforcing material in roofing felts until about the early 1980s, and that "you can't tell whether a material contains asbestos simply by looking at it, unless it is labeled." It recommends that "a trained and accredited asbestos professional should take samples for analysis." Felts, base flashings, mastics and coatings on an older roof are worth sampling before a tear-off is scheduled, so the work can be planned correctly.
Replacement Options
When a built-up roof is replaced, the main choices are another built-up or modified bitumen system, or a single-ply membrane such as TPO. The decision usually comes down to the building's drainage, rooftop traffic, equipment, budget and how long the owner plans to hold the property. A replacement is also the right time to fix slope and drainage with tapered insulation, add overflow scuppers where required, and replace wet insulation.
If you own or manage a building with an older tar-and-gravel roof, our commercial roofing and flat roofing teams can inspect it, tell you whether it is a repair, coating or replacement candidate, and document what we find with photos.
Sources: NRCA Roofing Guidelines glossary ("Built-up roof"); U.S. EPA roofing manual (1994) and EPA asbestos guidance pages (2026); 2024 International Residential Code R908.4 and 2024 International Building Code 1512.3 (R908.3.1.1 in the 2021 IRC).
Frequently Asked Questions
How long does a tar and gravel roof last?
It depends heavily on installation, drainage and maintenance. The gravel layer protects the felts from sun; once it wears away and the bitumen is exposed, deterioration speeds up. An inspection of the surface and the insulation underneath tells you more than the roof’s age.
Can you put a new roof over tar and gravel?
Sometimes. Building codes do not allow a recover if the existing roof is water-soaked or deteriorated, or if there are already two or more roof coverings. A dry, sound built-up roof may be recoverable or coatable.
Does an old tar and gravel roof contain asbestos?
It can. The EPA notes asbestos was used in roofing felts until about the early 1980s and that it cannot be identified by sight. Have an accredited professional take samples before tear-off.
Is it worth repairing a built-up roof?
Yes, when problems are isolated and the insulation is dry. Widespread bare spots, brittle felts, many leaks or wet insulation usually make replacement the better value.
What replaces a tar and gravel roof?
Common replacements are modified bitumen, a new built-up system or a single-ply membrane such as TPO, chosen for the building’s drainage, traffic and budget.
