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Built-Up (Flat) Roof Repair

Expert advice on how to repair built-up and tar-and-gravel roofs, including DIY tips on patching torn roofing and repairing blisters on a flat roof.

Although built-up roofs are durable, leaks can develop. These are most often found where flashing is located, such as at connections between the roof and the chimney, the eaves, or another roof plane. They may also develop where wind has blown the gravel away and exposed the surface to sun, heat, and cold. An older roof may also develop leaks where the asphalt has blistered or where the layers of roofing felt and bitumen have separated.[GARD align=”left”]

To keep built-up roofs in good shape, be sure that there are no bare patches in the gravel. Keeping the roof surface covered with gravel will also keep your house cooler in the summer and warmer in the winter.

If simple repairs do not remedy leaks, the roof surface may need to be replaced. This is a job for professionals; rolling out layers of roofing felt and hot mopping asphalt is more than most homeowners will want to take on.

Modified bitumen or “torch-down” roofing is a popular alternative to classic tar-and- gravel built-up roofs. Easier and faster to install, it consists of a single rubber membrane that is heated with a torch and then bonded to a fiberglass mat that is attached to the roof sheathing.

Repairing Blisters on a Flat Roof

Blisters on an almost flat roof may be caused by heat and sun, but they often signify moisture under the surface. The chances are good that water has penetrated the roof membrane through a nearby hole or flashing.

If there are several blisters or the blisters are quite large, consider calling a roofing contractor to handle the work. Otherwise, follow the steps below:[GARD align=”right”]

1Sweep gravel and dirt away from the blister.


2Using a utility knife, slice through the top layer, releasing the pressure from the bubble.

Apply roofing cement into slit with putty knife.

3Feel inside the hole for moisture. If it feels wet, look for possible sources of leaks along the flashing or in the same general area as the blister, and fix those leaks.

4With a putty knife, work plastic roofing cement into the pocket and around the surface of the cut (see illustration at left). Apply cement beyond the damaged area at least 2 inches in all directions.

Cover hole with patch and seal with roofing cement.

5Cut a patch from an asphalt shingle or a piece of roll roofing that’s about 2 inches larger than the hole, and slide it into the slit. Press it into the roofing cement, making certain to cover as much of the area inside the cut as possible. Cover the blister or hole with roofing cement to seal the patch, and then apply cement about 2 inches beyond the edges. When the cement begins to set up, sweep the gravel back over the top of the patch.

Featured Resource: Find Pre-Screened Local Built-up Roofing Repair Help

Call for free estimates from roofing pros now:
[telnumlink] 1-866-342-3263[/telnumlink]

Built-Up (Tar-and-Gravel) Roofing Systems

Parts and composition of tar-and-gravel, built-up, and flat roofing systems, with a helpful tar-and-gravel roof construction diagram.

Built-Up (Tar-and-Gravel) Roofing Diagram   ©HomeTips

Most houses with flat or nearly-flat roofs are topped with built-up roofing, or “tar-and-gravel” roofing, made from fiberglass-based asphalt sheeting that is applied in layers, with hot bitumen mopped on between each layer.

The surface is coated with bitumen and a layer of gravel or crushed rock to hold the roofing material down and minimize damage from the sun and from abrasion. The light-colored gravel also reflects the sun’s heat. Built-up roofs can last from 10 to 20 years, depending on the severity of the weather.[GARD align=”left”]

Similar to built-up roofing is roofing made from a single layer of asphalt-impregnated material, called asphalt roll roofing. This is used more often on garages and outbuildings than on houses because of its relatively short life span (5 to 15 years). It is generally the least expensive roofing material available.


Featured Resource: Find a Pre-Screened Local Built-up Roofing Contractor

Call for free estimates from roofing pros now:
[telnumlink] 1-866-342-3263[/telnumlink]

Built-Up Roofing

Expert advice on working with tar-and-gravel, built-up, flat and roll roofing materials, with tips on installation, construction diagrams and repairs.

Flat or almost-flat roofs can collect a tremendous amount of water, especially if their outlets or downspouts become plugged with leaves and debris.

For this reason, they must be designed to seal against standing water that may pool on the roof. Ordinary roof shingles won’t seal-out standing water–they are designed to overlap one another and shed rain downward and so are intended for sloped roofs. “Flat” roofs (which usually have a very slight slope) utilize roofing that is completely sealed and therefore impervious to leaking. The standard roofing for this situation is built up from layers of hot tar and thick roofing felt and topped with a layer of gravel; this is called built-up roofing.

This section of HomeTips discusses the basics of built-up roofing and offers help for basic do-it-yourself repairs. Installing a built-up roof is not a DIY project; if you need a new or replacement built-up roof, contact a licensed built-up roofing contractor in your area.


• Built-Up (Tar-and-Gravel) Roofing Systems
• Built-Up (Flat) Roof Repair

Featured Resource: Find a Pre-Screened Local Built-up Roofing Contractor

Call for free estimates from roofing pros now:
[telnumlink] 1-866-342-3263[/telnumlink]

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