How to Repair a Flat Roof


Water runs right off of sloped roofs, but flat ones must maintain a watertight seal to prevent leaking. When you have a crack or blister in the shingles, water can get underneath and wreak all sorts of havoc.

Things You'll Need

  • Roofing Cement
  • Brooms
  • Utility Knives
  • Putty Knives
  • Roofing Nails

Treating a Cracked or Peeled Area

  • Sweep the roof to get any dust or dirt away from your work area. The roofing cement you'll be using won't stick if the surface is dirty.

  • Cut out around any cracked or peeling areas with a razor knife and remove each bad section. Make it a uniform shape such as a square or rectangle.

  • Use the cutout piece as a pattern and cut a replacement piece of shingle in the same size and shape. If you cut out more than one bad layer, you'll need to cut enough pieces to bring the new section up to the same level as the area around it.

  • Cut another patch of shingle about 2 inches larger all the way around.

  • Slip a putty knife under the edges around the cutout area. Apply roofing cement under the edges.

  • Put a layer of roofing cement down in the entire cutout area with the putty knife.

  • Press the new shingle into the hole.

  • Tack down the shingle(s) with roofing nails. You should cement only the bottom one; the other layers can just be nailed down.

  • Lay the larger patch over the one you just applied and nail it down.

  • Go around the edges of this top patch with cement to form a seal.

Treating a Bubble or a Split Shingle

  • Treat a bubble by cutting a line in just that layer with a razor knife.

  • Pry the cut open and force roofing cement in both sides of the cut. This is also what to do with a split in the shingle.

  • Tack down both sides of the cut or split with roofing nails, and cover it with a patch as described in "Treating a Cracked or Peeled Area."

Tips & Warnings

  • Use a straightedge when cutting the shingles. This will make it easier to match the size and shape.
  • Be careful when walking on the roof.
  • Step lightly. You can do a lot of damage stomping around in work boots.

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