Built-up roofing (BUR) is a multi-ply, low-slope roof assembled on site from layers of reinforcing felt and bitumen, then finished with gravel, a cap sheet or a coating. It suits roofs that take heavy foot traffic, carry a lot of equipment or need redundancy against punctures. It is a strong choice when the structure can carry the weight and the building can tolerate hot work or odor.
Strong Contractors installs, replaces and repairs built-up roofing systems for commercial, industrial and institutional facilities. Built-up roofing, commonly called BUR, uses multiple reinforcing plies bonded with hot asphalt or an approved cold-applied adhesive and finished with aggregate, a cap sheet or another protective surfacing. It is commonly selected for its puncture resistance, traffic tolerance and long history of performance on demanding low-slope roofs. ‘
Common Applications:
Built-up roofing develops its strength through multiple reinforcing plies bonded with bitumen and protected by a finished surfacing. Strong controls each layer as it is installed because deficiencies in asphalt application, ply placement or adhesion can become concealed as the assembly is built.
A built-up roof goes together one ply at a time, in the field, with crews, kettles and weather all in play. This is the usual sequence.
| Spec | Typical Value |
|---|---|
| Plies | Typical: 3 to 4 reinforcing plies over a base sheet |
| Bitumen | Hot-mopped asphalt or an approved cold-applied adhesive |
| Surfacing | Aggregate (gravel), mineral cap sheet or coating |
| Roof slope | Typical: low-slope, minimum 1/4 in. per ft for new roofs |
| Added weight | Typical: about 4 to 6 lb per sq ft with gravel surfacing |
| Service life | Typical: 20 to 30 years with routine maintenance |
| Warranty | No Dollar Limit (NDL) manufacturer warranties, typically 10 to 20 years depending on the system |
Built-up roofing is labor-intensive, so the price follows how much has to come off, how many plies go on and how hard the roof is to reach. These factors move it most.
Wet insulation, rotted deck or multiple old roof layers all add removal and replacement work. Core samples tell us early, before the bid is final.
A four-ply gravel roof uses more material and crew hours than a three-ply cap sheet roof. The specification and the traffic on the roof decide which one fits.
Hot asphalt needs kettles, fuel and fume control. Cold-applied adhesives avoid that but cost more per gallon and cure more slowly in cool weather.
Crane or hoist access, building height, limited laydown space and work around occupied areas all change how fast material moves to the roof.
Every curb, pipe, drain and wall needs flashing by hand. A roof crowded with mechanical units is priced higher per square foot than a clear, open field.
| Built-Up Roofing (BUR) | Modified Bitumen Roofing | Spray Foam (SPF) Roofing | ||
|---|---|---|---|---|
| How it is built | 3 to 4 plies bonded in the field | Factory-made sheets, usually 2 plies | Foam sprayed in place, then coated | |
| Seams | Staggered laps through every ply | Side and end laps per ply | Seamless | |
| Tear-off | Usually, for a full replacement | Usually, for a full replacement | Often not, over a dry, sound roof | |
| Traffic and puncture | High, especially with gravel | High with a granule cap sheet | Good; walkways for heavy traffic | |
| Insulation | Separate insulation board | Separate insulation board | Foam adds insulation value | |
Yes, a gravel-surfaced built-up roof is what most people call tar and gravel. Modern BUR is usually built with asphalt rather than coal tar, and it can be finished with a mineral cap sheet or a coating instead of loose gravel. The structure underneath is the same: several reinforcing plies bonded into one membrane.
A well-installed built-up roof typically lasts 20 to 30 years with routine maintenance. The number of plies, the surfacing, drainage and how well flashings are kept up all change that range. Ponding water and neglected flashings shorten it fastest. A core sample and inspection tell you where your roof sits today.
Often, yes, when the plies are well bonded and cores show dry insulation. On our Eglin Air Force Base work, the existing built-up roof stayed in place: the crew cleared off loose gravel, then sprayed foam and a granule-surfaced urethane coating over it. Wet insulation has to come out first, so we take cores before recommending this route.
It can be. Gravel surfacing typically adds about 4 to 6 pounds per square foot, and older buildings were not always designed with a margin for more. If a new roof would add layers or weight, have the structure reviewed first. A cap sheet or coated surface is a lighter BUR option.
They can if the work is not planned for it. We place kettles downwind and away from air intakes, coordinate with facility staff on HVAC settings and schedule work around sensitive areas. Where fumes are not acceptable, such as some hospital or lab settings, a cold-applied BUR system is an option.
Repair if the problems are local and the insulation underneath is dry. Replace when moisture has spread through the assembly, the plies are blistering or splitting widely, or repairs keep failing in the same areas. Between those two, a restoration over the existing BUR can add service life while the plies stay in place.
