Roof Repair: How to Find and Fix Roof Leaks

Overview: The roof leak problem

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Roof leak damage

A small leak caused the roof sheathing and rafters of this home to rot. Mold grew in the insulation as well.

If you have water stains that extend across ceilings or run down walls, the cause is probably a roof leak. Tracking down the leak is the hard part; the fixes are usually pretty easy. We’ll show you some simple tricks for finding and repairing most of the common types of roof leaks. But if you live in the Snow Belt and in the winter you have leaks only on warm or sunny days, you probably have ice dams. We won’t go into those fixes in this story.

Minor leaks can cause major damage
If you have a roof leak, you’d better fix it immediately, even if it doesn’t bother you much or you’re getting a new roof next year. Even over a short time, small leaks can lead to big problems, such as mold, rotted framing and sheathing, destroyed insulation and damaged ceilings. The flashing leak that caused an expensive repair bill (Photo) 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.

How to find roof leaks

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Search for leak signs

If running water doesn't reveal the exact location of the leak, don’t be timid. Start removing shingles in the suspect area. With them removed, there'll be evidence of the leak and you'll be able to track it down right to the source. You'll see discolored felt paper or water-stained or even rotted wood directly below and around it.

When you’re trying to track down a leak, start by looking at the roof uphill from the stains. The first thing to look for is any roof penetrations. 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 the right or left 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 the 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 and examine the suspect(s).

If the problem still isn’t obvious, enlist a helper and go up on 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.

Frosty shank of a nail that protrudes several
inches through the roof sheathing

Solution for a Small Leak

Some roof leaks are tough to locate. Sometimes the water shows up at a ceiling spot distant from the leak. If your ceiling has a plastic vapor barrier between the drywall and the attic insulation, push the insulation aside and look for flow stains on the plastic. Often water runs to openings in the vapor barrier, such as at ceiling light fixtures.

If you can’t see any telltale flow marks, and since the stain is fairly small, look at the underside of the roof for “shiners.” A shiner is a nail that missed the framing member, in this case when the carpenter nailed the roof sheathing to the rafters. Moisture that escapes into the cold attic from the rooms below often condenses on cold nails. Sometimes you can spot this if you climb up into your attic on a cold night. The nails will look white because they’re frosted. When the attic heats up a bit during the day, the frost melts and drips, then the nails frost up at night again and so on. The solution is to simply clip the nail with a side-cutting pliers.

Fix common leaks: Plumbing vent boots

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Photo 1: Vent boot problem

When gasket-type plumbing vent flashing leaks, the culprit is usually a cracked gasket or missing or loose nails.

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Photo 2: Vent boot solution

Replace the old boot. Screw the base to the roof with rubber-washered screws. Don’t use nails. They'll only 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. But 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. 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.

Fix common leaks: Roof vents

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Photo 1: Roof vent problem

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

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Photo 2: Roof vent 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 pulled or missing nails at the base’s bottom edge. 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 in 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 renailing the shingles.

Fix common leaks: Walls and dormers

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Photo 1: Wall/dormer problems

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

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Photo 2: Wall/dormer solutions

Recaulk 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 a siliconized latex 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.

Soffit of one roof meeting another roof

Complex Roof Problem

This roof leaks during the snowy part of winter and during storms in the summer, certainly due to poor flashing. The soffit that meets the roof is one of the toughest areas to waterproof. In the photo, you can still see signs of an ice dam. An ice dam occurs when snow melts and the water freezes when it hits the colder edges of your roof. Eventually, water pools behind the dam and works its way back up under the shingles and under the soffit until it finds an opening through the roof.

The solution begins with good flashing, since this should stop leaks from rainfall and might stop the leaks from ice dams as well. Begin by removing the shingles down to the wood sheathing and slip a strip of adhesive ice-and-water barrier (available where roofing products are sold) under the soffit/main roof joint. Depending on how the roofs join, you may have to cut a slot to work it in far enough. It should overlap another piece of ice-and-water barrier laid below, all the way down to the roof edge. This should cover the most leak-prone areas. Then reshingle, sliding metal step flashing behind the fascia board (the trim behind the gutter). The valley flashing, laid over the joint where the two roofs meet, should overlap the step flashing at least 2 in.

If leaks continue to occur from ice dams, consider installing roof edge heating cables. (Find them locally at hardware stores or home centers.) Improved attic insulation and ventilation are usually the best ways to prevent ice dams, but they might not be effective in this complicated roof situation.

Fix common leaks: Step flashing

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Photo 1: Step flashing problem

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

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Photo 2: Step flashing solution

Push a loose piece of step flashing right back in 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 in place and it eventually slips down to expose the wall.

Fix common leaks: Small holes

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Photo 1: Small hole problem

Leftover mounting holes can let in vast amounts of water.

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Photo 2: Small hole 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 or just about anything. And exposed, misplaced roofing nails should be pulled and the holes patched. Small holes are simple to fix, but the fix isn't to inject caulk in the hole. You'll fix this one with flashing.

Chimney flashing is complicated

Leaks Around 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. Get complete instructions on how to install chimney flashing here.