Flat Roof Repairs

You can repair a hot tar built-up flat roof with fiber-mesh patching or an aluminum fiber coating.


A flat roof is usually slightly sloped. It may be covered with a granular roll roofing, EPDM (which is smooth surfaced), or modified bitumen (which may be smooth or mineral surfaced). Some flat roofs have hot tar built-up roofing, which may have a gravel surface. If you live in an arid region or an older urban area, you may have a large flat roof. Suburban homes sometimes have small flat sections.

Where the roofing curves to meet a wall or chimney, the material may loosen along its topmost edges. Apply plenty of roofing cement to fill the void and smooth the cement so water can run off unimpeded.

An application of aluminum fiber coating quickly seals many small leaks and can prolong the life of a roof. It cannot be applied over a gravel-topped or mineral surfaced roof however.

Prestart Checklist

1 to 2 hours for most repairs

Utility knife, trowel, squeegee/broom for applying aluminum coating, hammer

No special skills required

Inspect the roof for bubbles, cracks, and voids.

Roofing cement, fiber-mesh patching, EPDM or other flat-roofing material, roofing nails

Patching a small hole or bubble: Step 1

Use a utility knife to cut a slit in a bubble or lift up the two sides of a crack. You may need to cut out a narrow strip so the two sides can lie flat. Use a trowel to slip some roofing cement under the damaged area.

Patching a small hole or bubble: Step 2

Spread roofing cement over an area that is 6 or more inches wider than the damage. Embed fiberglass mesh in the cement, then apply another layer of cement. Use a trowel to feather the edges.

Patching a larger area: Step 1

Use a utility knife and straightedge to cut a rectangle around the damage. Cut just deep enough that you can remove the piece. Use the piece as a template to cut a patch.

Patching a larger area: Step 2

Spread roofing cement onto the cutout area and work it under the surrounding roofing as well. Set the patch into the wet cement.

Patching a larger area: Step 3

Cut a patch that is about 6 inches longer and wider than the first patch. Spread roofing cement, set the patch into the cement, and spread another layer of cement over the patch. Once it has dried coat the area with aluminum-fiber coating.

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