How to Repair Flat Roof

Written by lacy enderson
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A roof is not generally maintenance free. Ice and water can accumulate on a flat roof causing damage. Nails can and do work themselves loose, flashings rust and mildew and moss grow on roofs; especially flat roofs where water congregates. Occasionally, a flat roof needs repairs. The most common repair is due to leaks. Follow a few simple repair procedures and your flat roof will be as good as new.

Skill level:

Things you need

  • Razor Knife
  • Broom
  • Roof Cement
  • Towels
  • Nails
  • Nail Gun

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    Repairing a Flat Roof

  1. 1

    Look for the leak when the flat roof is dry. Because water puddles and then travels to different areas, by the time the leak is located, the water might have wandered to a different spot. Searching for a leak when the roof is dry enhances visibility.

  2. 2

    Look first around flashings. A flashing, often metal, is used as a barrier between the roof and the chimney or a plumbing stack. Check them for cracks. Make sure the flashing overlaps the roofing material. The edge of the roof also uses flashing. Check these areas for little cracks or openings.

  3. 3

    Brush off all extra debris and gravel. Make sure the roof is clean so any possible damage is visible. If the top layer of your flat roof has separated, there might be a crack or a large blister. This damaged area will need repair.

  4. 4

    Cut a slice down the middle of the blister using a sharp razor knife. Cut clear through the top layer without damaging the felt underneath. Soak up any water found inside of the blister. Open up the edges and let the roofing material dry out.

  5. 5

    Spread a thick coat of roof cement on the bottom edges of any loose felt. Firmly press down the edges of the blister.

  6. 6

    Nail each side of the blister slit with 6d galvanised roofing nails. Spread roof cement over the entire repaired area. All nail heads should be covered.

Tips and warnings

  • Fill in puddling areas on your flat roof with an asphalt lightweight cement or an acrylic based product. This will prevent future problems.
  • Use a fibreglass seam tape to reinforce any edge where a patch was applied. As the roof cement dries, the tape helps prevent cracking.
  • If you attempt to repair your flat roof when it's cold and your roof isn't drying out, use a propane torch with a flame-spreader nozzle to dry out the felt. Roofing felt and tar are flammable, so be careful not to let the layers get to hot.

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