How to Repair a Flat Roof

You can repair a hot tar built-up flat roof with just a few materials. It's time to check this task off your to-do list!

Roofs come in all kinds of shapes, sizes and materials. However, with each unique look, comes unique problems and repairs. For homeowners dealing with a flat roof, it may be common to see small bubbles or tears in the roofing material. 

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. Follow our steps below to learn how to fix it yourself without hiring professional help.

  • Start to Finish 2 Hours
  • Difficulty         Projects Kind of Hard

What you need

Tools

  • Utility knife
  • Trowel
  • Squeegee/broom for applying aluminum coating
  • Hammer

Materials

  • Roofing cement
  • Fiber-mesh patching
  • EPDM or other flat-roofing material
  • Roofing nails

How to do it

Part 1 Patching a Small Hole or Bubble

Step 1 Fill Hole With Cement

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.

Step 2 Cover With Cement

Spread roofing cement over an area that is six 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.

Part 2 Patching a Large Area

Step 1 Remove Damage

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.

Step 2 Apply Cement

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

Step 3 Cut Patch and Coat

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.

RectangleCreated with Sketch. Rectangle Copy 3Created with Sketch.

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