How to fix a leaky flat roof

Updated February 21, 2017

A leaky roof is a serious problem. Belongings get wet, mould begins to develop and before you know it you need a very expensive replacement. Flat roofs are particularly susceptible to leaking and when they do, fixing them is a priority. The job, which can be fairly messy and labour-intensive, involves climbing a ladder and getting onto the roof. If the roof only needs a repair or maintenance, it is easy enough for the average homeowner to accomplish.

Choose a warm, dry day to make your repairs. The temperature should be at least 10 degrees C, but 70 or above will make the tar will flow easier.

Sweep the area to be repaired clear of debris or dirt. If the spot is particularly dirty, wash it and allow the area to dry thoroughly. Use the shovel as a dustpan.

Use a hammer to seat nails that have popped through the roofing material.

Spread repair tar over cracks and seams that might be leaking with a wide putty knife. Remember that water may travel a considerable distance before showing itself through a ceiling, so the leak could be far from a wet spot on the ceiling. Work the tar into the cracks and cover them completely. Wide coverage is desired for each crack.

Repair any cracks that could leak in the future following the steps above. On a day with the temperature above 10 degrees C, bring your repair materials up to the roof.

Mix the roofing tar thoroughly before pouring it. Pour out 1/2 to 1 gallon at a time and spread with the squeegee or applicator brush. Don't push the tar over the edge of the roof or it will create a mess on the fascia that you won't be able to remove. Allow the tar to pool slightly in low areas; it will harden later.

Work one area a time until you have covered the entire roof. Pay special attention to places where the flat roof joins a sloped section; go about a foot up the slope with the tar.

Pour out the final area near the ladder and take the bucket down. From the ladder, spread the last of the tar with the squeegee or brush. Let the tar harden before walking on the roof.

Things You'll Need

  • Broom and square shovel
  • Bucket of roofing tar
  • Applicator brush or squeegee
  • Hammer
  • Wide putty knife
  • Roof repair tar
  • Ladder
  • Large garbage bags
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About the Author

Michael Logan is a writer, editor and web page designer. His professional background includes electrical, computer and test engineering, real estate investment, network engineering and management, programming and remodeling company owner. Logan has been writing professionally since he was first published in "Test & Measurement World" in 1989.