How To Handle A Leaky Roof

Finding out where a leak is on your roof isn’t always as easy as it would appear to be. When trying to locate a leak, use the following guidelines to assist you. NOTE: whenever you see the words "the leak area," it refers to an area within a 10 foot (3 meter) diameter of the leak.

Flat or Low-Slope Roofs

Inspect any roof drains near the leak area. If they are plugged or draining slowly, then there is a strong chance that they are the reason for the leaks. Drains are rarely waterproof if they are plugged. They are generally designed and constructed for water to flow in one direction only...down.

Inspect any material seams in the area of the leak. Just because you see "tar" or adhesive sticking out under a lap, it doesn’t mean that the material is adhered properly. Take a flat blade about 2 inches (5 cm) long (like a pocketknife blade), and gently run it along under the lap. If it slides in more than 1 inch (2.5 cm), then the seam should be sealed. If it slides in for the length of the 2 inch blade, it’s a good suspect for a leak.

Look carefully at all penetrations for signs of problems. Problems include holes in the metal flashings, shrunken pitch pan filler, deteriorated caulking, curled flashing flanges that are sticking up through the roof membrane, or any other visible defects.
Look for blisters that have been punctured.

Look closely at expansion joint seams. These are often faulty.
Check for splits in the area. Do this by walking the area with your feet close together and taking many small steps, turning in all directions. If there is a split, you’ll see the roof separate between your feet.

If the leak occurs near the edge of the building, check the edge metal. It can separate at the seams and tear the roof membrane in the process.

Check under debris. A lot times, if debris has been sitting on a roof for a long period of time, then it can hold water which will expedite roof deterioration. Bird, rodent, and other vermin nests have been found under piles of debris on roofs.

If you get a freak rain storm that dumps horrendous amounts of water on your roof in a short period of time, and all of a sudden you have half a dozen leaks where before there were none, don’t get overly excited. Most roofs are not designed or constructed to handle that much water all at once.

If you look carefully, and find nothing on the roof, then check your attic or ceiling space. What is mistaken for a roof leak can sometimes be a problem with the plumbing, especially with commercial buildings because fire sprinkler lines usually run along the attic space. This is often identified by a leak occurring when it isn’t raining.

Another problem that is frequently mistaken for a roof leak is a poorly designed roof-mounted HVAC unit. HVAC units can have faulty pans in them which will permit water to enter the building during a rain storm.

Steep Slope Roofs

Look at all roof penetrations in the leak area closely for holes and/or damage.

Look for "shiners." Shiners are nails that were not covered by the following course of roofing material. If left exposed too long, many nails will rust, leaving a hole and causing leaks.

Look at the mortar on chimneys and parapet walls. It’s rare, but damaged mortar can cause leaks.

If your building has a stucco facade, then cracks in the stucco, especially along the tops of walls, can be the source of leaks.

Check to make sure that all drain details are functioning and that your gutter is not full of debris. If your edge details and gutter details are not done correctly, water can back up over the top of the fascia, run along the soffit, and down the inside of the wall where it enters your building.

If you look carefully, and find nothing on the roof, then check your attic or ceiling space. What looks like a roof leak can be a problem with the plumbing, especially with commercial buildings because fire sprinkler lines usually run along the attic space. This is often identified by a leak occurring when it isn’t raining.

Another problem frequently mistaken for a roof leak is a poorly designed roof-mounted HVAC unit. HVAC units can have faulty pans in them which can permit water to enter the building during a rain storm.

Look for areas where there is a lot of debris such as leaves and branches that have gathered. Piles of debris can block water flow which can cause the water to back up under the roofing. This commonly occurred behind chimneys and in valleys.


If you are calling a Seattle Roofing contractor to take care of your leaks. Here are some questions that he may want to ask you.

Q: Has anyone been on your roof doing work? An electrical contractor, HVAC mechanic, someone installing a heat pump or evaporative unit? And if so, were they anywhere near the leak area?

This question is important because people can often drop tools which can penetrate the roof and cause a leak.

Q: Does it leak only when there’s a wind-driven rain? Only when it snows?

A lot of times wind will drive rain up under overhangs where it can get into the building where it normally couldn’t. Or if there is a turbine vent that is frozen in place, the wind will drive the rain into it and cause a leak. Snow is tricky because it can cause ice dams which will allow water to back up under shingles, or it can be deep enough to go over the tops of curbs. When it starts melting, it starts leaking.

Q: How long after precipitation starts does the leaking begin? How long after the precipitation quits does the leak quit?

This will give the contractor an idea of how far the water has to travel before it actually shows up.

Q: Has anyone been up in your attic recently?

A lot of times when plumbers, electricians, HVAC mechanics, etc. are working in attics, they can knock a flashing loose, break a seam along a condensation line, or even accidentally put a hole in the roof system by puncturing it in the spaces between decking. None of this is purposefully done, it’s just something that happens because attic spaces are usually very cramped and difficult to work in.

If you are looking for a GAF roofing contractor in the Seattle area please call us today at 425-290-7827 or complete our online request form.