DIY advice: repairing a flat roof

Blisters, cracks and tears can spell big trouble for flat roofs, so they should be fixed promptly to keep your home dry and safe. Check out this DIY advice for how to effectively and safely repair your flat roof.

The steps you'll need to take to repair a flat roof will depend upon the type of roofing material and the nature of the damage.

• Heat bakes the oils out of unprotected tar roofs and makes them brittle. You can protect your flat roof from damaging ultraviolet rays by using a topcoat of fiberglass (white) or aluminum (silver), which you can apply yourself with a squeegee or mop.
• Inspect a flat roof at least once a year for blisters, cracks, tears and storm damage. Make repairs promptly. A hot-tar built-up roof will need more attention than a modified bitumen roof.
• Wherever the roofing curves upward at a vertical wall or chimney, make sure the top edge is tightly sealed against the surface. Apply a liberal amount of roofing cement, perhaps using a caulking tube, and smooth it so that water has no opportunity to puddle.
• For large areas with lots of small cracks, the solution may be to apply a silver or white topcoat. If there are numerous problem spots, or if an area larger than 1.2 metres (4 feet) square is cracked or blistered, have the roof resurfaced by a roofing company.

Blisters indicate that roofing felt has separated from the underlying layers or from the wood sheathing. For blisters that seem likely to break open, fix them using the steps below. You can also repair tears and cracks using steps 2 and 3.

1. Sweep away dirt and loose gravel. Slice the blister open lengthwise with a utility knife. (If there is water under the blister, it may be coming from an open spot nearby.) Use a putty knife to smear roofing cement under both sides of the cut.
2. Press the layers of roofing material flat. Nail each side with roofing nails, spaced 7.5 centimetres (3 inches) apart. Cut a piece of fiberglass mesh 15 centimetres (6 inches) or longer and 6.0–7.5 centimetres (2–3 inches) wider than the patch. Apply roofing cement to the sealed blister and place the patch on the cement.
3. Gently press the mesh into the cement, smoothing out any wrinkles with a spreading tool at least 7.5 centimetres (3 inches) wide. Cover the patch with another coat of roofing cement, smoothing the surface so water cannot collect on it.

When buying fiberglass mesh, make sure that it is specifically designed for roof repairs.

When it comes to roof repair work, safety should always come first.

• Anytime you're working on your roof or gutters, be sure that the ladder is securely footed on the ground at least a quarter of its length away from the house and that it extends at least 0.6 metres (2 feet) above the eaves for maximum stability.
• Always wear slip-resistant shoes.
• Never work on a wet or cold roof – it's dangerous for you and can harm the roof.
• Don't use an aluminum ladder near electrical wires; use a wooden or fibreglass ladder instead.

While some homeowners are well equipped do their own minor repair work on flat roofs, you should always seek help from a professional roofer if you are unsure or uncomfortable with carrying out the repairs yourself.