Ten Common Reasons for Roof Leaks

Written by duane craig
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Ten Common Reasons for Roof Leaks
Roof leaks hide but investigating common sources reveals the causes. (Roof image by Gonçalo Carreira from Fotolia.com)

Roof leaks are no fun and because of the way roofs are built, finding a leak can be a challenge. Fortunately, there are common places to look for exterior signs that water may be getting below the roof covering.

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Bad Chimney Flashing Seal

Chimney flashing uses a series of metal flashing sections (steps) resting on top of a base flashing, and tucked beneath the shingles. Each step in the flashing must be sealed against the chimney. Typically each one is bent at its top and inserted between the chimney bricks. The bricks are then re-grouted. If the step flashing is not well sealed, water gets behind it and makes its way into the roof framing.

Chimneys are notorious for leaks.
Chimneys are notorious for leaks. (chimney image by hazel proudlove from Fotolia.com)

Damaged or Missing Eave Flashings

This metal flashing is normally installed directly against the roof sheathing. The vapour barrier goes over it and then the shingles overhang it by a half inch. When it is missing or damaged, water will run backward on the underside of the shingles and make its way behind the fascia, or beneath the sheathing.

Damaged or Missing Rake Flashings

This metal flashing follows the pitch of the roof at the gables and is installed the same as the eave flashing. A particular problem area is where this flashing overlaps the eave flashing.

Faulty Valley Flashings

The flashing where two roofs meet (open valley) must be wide enough to prevent water from finding its way to the vapour barrier and ultimately to the roof sheathing. It's the lower parts of this flashing that is most subject to water intrusion. The shingles that overlap the flashing should be sealed to the flashing.

Gutters Not Draining

If the gutters are not pitched slightly, they will not drain, or will drain slowly. Plugged downspouts will cause the same problem. Water fills up the gutters and then runs behind them. Moisture then causes problems to the fascia and soffit.

Improperly Sealed Step Flashing

Besides its use on chimneys, this flashing is also used where a pitched roof meets a sidewall like those on a dormer. The flashing must extend upward and beneath the siding in these locations.

Exposed Fasteners

Along the ridge and at other places where shingles overlap, there will undoubtedly be some fastener heads that are not covered. These need to be sealed with roofing cement.

Unsealed Pipe Flashing

A common place for leaks is wherever a vent pipe or flue pipe extends through the roof. The flashing, or roof jack, should be beneath the shingles that are above and at the sides of the pipe and on top of them below the pipe.

Unsealed Skylights

Skylights come in a wide variety of styles, and manufacturers of skylights specify the way the skylight should be sealed to prevent roof leaks. On old installations, the seals may have deteriorated. On newer installations there may have been mistakes made in the sealing process.

Ice Dams

In cold climates, the temperature differential at roof overhangs causes ice to form all along the edge of the roof. The warmer temperatures further up on the surface of the roof cause a constant process of freezing and thawing to repeat. The ice build-up holds water back which eventually finds its way below the roofing where it infiltrates the building's framing.

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