How To Find and Fix Roof Leaks

Roof leaks can occur in many locations and can cause major problems down the road if not immediately. Learn how to locate and fix leaks here.

Diagram showing potential spots for roof leakage | Construction Pro Tips

If a house has water stains that extend across ceilings or run down walls, the there's a good chance it's a leaky roof. Tracking down the leak can be hard; the fixes are usually pretty easy. We’ll show you simple tricks for finding and repairing the most common types of roof leaks.

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Spraying a roof with a hose to find leaks | Construction Pro Tips

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Find the leaks

When you’re trying to track down a leak, start by looking at the roof uphill from the stains. Roof penetrations are the first thing to look for. Items that penetrate the roof are by far the most common source of leaks. In fact, it’s rare for leaks to develop in open areas of uninterrupted shingles, even on older roofs. Penetra­tions can include plumbing and roof vents, chimneys, dormers or anything else that projects through the roof. They can be several feet above the leak or to either side of it.

If you have attic access, the easiest way to track down a leak is to go up there with a flashlight and look for evidence. There will be water stains, black marks or mold. But if access is a problem or you have a vaulted ceiling, you’ll have to go up onto the roof to examine the suspect(s). The photos on the following pages will show you what to look for.

If the problem still isn’t obvious, enlist a helper and go up onto the roof with a garden hose. Start low, soaking the area just above where the leak appears in the house. Isolate areas when you run the hose. For example, soak the downhill side of a chimney first, then each side, then the top on both sides. Have your helper stay inside the house waiting for the drip to appear.

Let the hose run for several minutes in one area before moving it up the roof a little farther. Tell your helper to yell when a drip becomes visible. You’ll be in the neighborhood of the leak. This process can take well over an hour, so be patient and don’t move the hose too soon. Buy your helper dinner.

Water stains can also indicate condensation or ice dam issues. Condensation problems can often be caused from bath, cooking or even dryer vents exhausting into attics rather than through the roof.

Ice dams usually happen in cold climates in the spring or on mild winter days. Have a big chunk of ice along the eaves during winter? That’s an ice dam.


Rotted framing caused by a leaky roof | Construction Pro Tips

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Minor leaks can cause major damage

Discover a roof leak? Well, you’d better fix it, even if it doesn’t bother you much or you’re getting a new roof next year. Over time, even small leaks can lead to big problems, such as mold, rotted framing and sheathing, destroyed insulation and damaged ceilings. The flashing leak that caused this expensive repair bill was obvious from the ceiling stains for over two years. If the homeowner had dealt with it right away, the damage and subsequent repairs would have been minimal.

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Leaky walls & dormers

Problem:Water that sneaks behind walls and dormers dribbles down into your house just like a roof leak

Fixing flashing with caulk | Construction Pro Tips

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Leaky walls and dormers

Solution: Re-caulk the corner flashing. Lift the overlapping section, clean it thoroughly and add a generous bead of fresh caulk underneath. Make sure the gap at the corner is filled with caulk.

Water doesn’t always come in at the shingled surface. Often, wind-driven rain comes in from above the roof, especially around windows, between corner boards and siding, and through cracks and knotholes in siding. Dormer walls provide lots of spots where water can dribble down and enter the roof. Caulk can be old, cracked or even missing between the corner boards and between window edges and siding. Water penetrates these cracks and works its way behind the flashing and into the house. Even caulk that looks intact may not be sealing against the adjoining surfaces. Dig around with a putty knife to see if the area is sealed. Dig out any suspect caulk and replace it with an exterior grade caulk. Also check the siding above the step flashing. Replace any cracked, rotted or missing siding, making sure the new piece overlaps the step flashing by at least 2 in. If you still have a leak, pull the corner boards free and check the overlapping flashing at the corner. Often, there’s old, hardened caulk where the two pieces overlap at the inside corner. Slipping in as strip of self adhering roofing underlayment behind the siding and overlapping the flashing is also a good idea.<

Duct tape as a non-viable solution for roof leaks | Construction Pro Tips

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Roof vents

Problem: Plastic roof vents can crack and leak. Duct tape is not the solution this time!

Man replacing an old roof vent | Construction Pro Tips

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Roof vents

Solution: Replace the old vent. If you’re careful, you won’t have to remove any shingles to slip out the old one and slide the new one into place.

Check for cracked housings on plastic roof vents and broken seams on metal ones. You might be tempted to throw caulk at the problem, but that solution won’t last long. There’s really no fix other than replacing the damaged vents. Also look for any pulled or missing nails at the base’s bottom edge and replace them with rubber-washered screws.

In most cases, you can remove nails under the shingles on both sides of the vent to pull it free. There will be nails across the top of the vent too. Usually you can also work those loose without removing shingles. Screw the bottom into place with rubber-washered screws. Squeeze out a bead of caulk beneath the shingles on both sides of the vent to hold the shingles down and to add a water barrier. That’s much easier than re-nailing the shingles.

Potential leak spots in old plumbing vents | Construction Pro Tips

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Plumbing vent boots

Problem: When the source of a leak is gasket-type vent flashing, the culprit is usually a cracked gasket or missing or loose nails.

Man repairing an old plumbing vent boot | Construction Pro Tips

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Plumbing vent boots

Solution: Replace the old boot. Screw the base to the roof with rubber-washered screws. Don’t use nails. They’ll just work loose over time.

Plumbing vent boots can be all plastic, plastic and metal, or even two-piece metal units. Check plastic bases for cracks and metal bases for broken seams. Then examine the rubber boot surrounding the pipe. That can be rotted away or torn, allowing water to work its way into the house along the pipe. With any of these problems, you should buy a new vent boot to replace the old one. You’ll have to work neighboring shingles free on both sides. If you don’t have extra shingles, be careful when you remove shingles so they can be reused. Use a flat bar to separate the sealant between the layers. Then you’ll be able to drive the flat bar under the nail heads to pop out the nails.

However, if the nails at the base are missing or pulled free and the boot is in good shape, replace them with the rubber-washered screws used for metal roofing systems. You’ll find them at any home center with the rest of the screws.

Small holes in a roof | Construction Pro Tips

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Small holes

Problem: Leftover mounting holes can let in vast amounts of water.

Fixing small roof holes with a piece of sheet metal and caulk | Construction Pro Tips

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Small holes

Solution: Seal nail holes forever. Slip flashing under the shingle and add a bead of caulk under and over the flashing to hold it in place.
Tiny holes in shingles are sneaky because they can cause rot and other damage for years before you notice the obvious signs of a leak. You might find holes left over from satellite dish or antenna mounting brackets. And exposed, misplaced roofing nails should be pulled and the holes patched. Small holes are simple to fix, but the fix isn’t to just inject caulk in the hole.

Flashing that has slipped from its proper spot | Construction Pro Tips

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Step flashing

Problem: Unnailed step flashing can slip down and channel water into the wall.

Repairing stepped flashing | Construction Pro Tips

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Step flashing

Solution 1: Push a loose piece of step flashing right back into place and then secure it with caulk above and below.
Step flashing is used along walls that intersect the roof. Each short section of flashing channels water over the shingle downhill from it. But if the flashing rusts through, or a piece comes loose, water will run right behind it, and into the house it goes. Rusted flashing needs to be replaced. That means removing shingles, prying siding loose, and then removing and replacing the step flashing. It’s that simple. But occasionally a roofer forgets to nail one into place and it eventually slips down to expose the wall.

Brick chimneys are a major potential leak zone | Construction Pro Tips

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Brick chimneys

All kinds of bad things can happen around brick chimneys. In fact, there are far too many to cover in this story. Flashing around chimneys can rust through if it’s galvanized steel, especially at the 90-degree bend at the bottom. A quick but fairly long-term fix is to simply slip new flashing under the old rusted stuff. That way any water that seeps through will be diverted. The best fix, though, is to cut a saw kerf into the mortar and install new flashing.

Next, read our story on how to set roof trusses the right way.