Here's How: Find Leak and Fix Flat Roof

James Dulley on Nov 27, 2025

Dear James: There is a small leak from the asphalt roll garage roof. It's not very old, so I prefer to just repair it. How can I locate to leak and fix it? -- Mindy F.

Dear Mindy: Although a flat roll roof is more prone to leaks than a typical pitched roof, there certainly are many leak-free flat roofs. It is wise to inspect a flat roof at least twice each year and preferably four times (once each season). Rainwater tends to puddle on a flat roof.

First, here are several safety tips when using your extension ladder to climb on to the roof. Lay the ladder on the ground and step on each rung to check for damage. Extend the ladder at least three rungs over the roof eaves. Tilt the ladder at a slope of one-quarter its height from the side of the house.

It helps to understand the components of a flat roof when diagnosing a leak. It consists of multiple layers of roofing felt, building paper or roll roofing. A heavy layer of roofing cement is applied between each layer. The top layer is covered with a stone/gravel mixture to block the damaging effect of the sun's rays.

The key areas to check for leaks are flashing or where roofing has pulled away from a chimney or vents. Look for exposed roof nailheads and drains where the water flows to the gutters. Seams where two pieces of roofing lap and any spots devoid of the stone/gravel covering are also likely sources.

Pay particular attention to areas where the stone/gravel covering appears to be a different color. These are often slightly lowered areas where the water puddles after a rain and can eventually leak. As you walk around, be aware of any bubbles and blisters where the roofing has pulled away from the decking.

You will no doubt find an exposed nailhead or two, but don't worry, this is simplest repair to make yourself. Brush away any loose stone/gravel mixture around the nailhead. Using a scraper, carefully remove any remaining gravel mixture from a spot a little larger than the nailhead.

Dip a putty knife into a can of roofing cement and spread a generous coating over the nailhead and an inch or so all around it. Throw some of the stone/gravel over the repair spot. Put it on thick enough so you cannot see the cement through it. Using the scraper, just press the stone/gravel slightly into the cement so it will stay in place. Don't work it in too much.

Patching a blister or bubble is another repair you can probably handle yourself. Brush away the stone/gravel and clean off the area with the scraper. Cut through the blister area so it lays flat against the roof decking.

Cut a patch piece of roll roofing so it overlaps the blister area by 6 inches. Spread a thick layer of cement over the blister and place the patch over the blister. Nail it in place and coat it with more cement. Cover it with stone/gravel, pressing it down lightly.

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Send your questions to Here's How, 6906 Royalgreen Dr., Cincinnati, Ohio, 45244 or visit www.dulley.com. To find out more about James Dulley and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.