Project Guide

How to Fix a Leaky Roof

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How to Find a Roof Leak
A garden hose is used to spray water on a roof.

Learning how to find a roof leak is easy but accomplishing the task can be frustrating. And fixing a leaky roof can be less time-consuming than locating where the water is coming in.

Water frequently enters the house near things that go through the roof. Projections or penetrations such as vents, dormers and chimneys are frequent places for leaks. Locating the exact source can be tricky because visible signs of a leak on the inside might be several feet away from – either to the left, right or below – the actual source.

To find the source of a roof leak:

  • Look in the attic with a flashlight for evidence like water stains, trhen trace them up the roof and rafters to the entry point.
  • If the leak isn’t obvious, have a helper watch in the attic while you get on the roof with a garden hose.
  • Begin soaking low on the roof, just above where the leak is visible inside the house.
  • Use enough water to mimic heavy rains.
  • Run water over the low side of the penetration for several minutes while the helper watches for any water droplets.
  • If none appear, move to the right or left side of the penetration and let the water run over the area for several minutes before moving to the other side.
  • Work your way up the roof, isolating areas around each penetration until the helper yells that a drip is visible.
  • That will be the vicinity of the leak. 
Plumbing Vent Boots and Roof Vents
A plumbing vent penetrates the roof of a house and could cause leaks if not properly secured.

Check plumbing vent boots and roof vents if water is entering from that area to cause the leaking roof.

Look for cracks in the base of flexible rubber flashing or broken seams in metal varieties of vent pipe flashing. The rubber gasket that surrounds the vent pipe could be rotted. Either of these situations could allow water to find its way into the house.

Replace the plumbing vent boot if necessary and use washer-head roofing screws to secure the base to the roof. If the boot is in good condition but fasteners are missing, replace them with washer-head roofing screws.

Similarly, roof vents with cracked or otherwise damaged housings should be replaced to prevent water entering at the base.

Old Mounting Holes
Roofing material on a house appears damaged or improperly installed.

Small nail holes left behind from old vents, satellite dish brackets or anything previously attached to the roof can allow water to enter and cause damage for years before leaking is noticed.

Patch the nail or screw holes by slipping a piece of roof flashing underneath the shingle. Add a bead of caulk or roof cement to the top and bottom edge of the flashing to keep it in place.

Step Flashing
Step flashing is used around the chimney on a roof to conceal the seam between the brick and the roof surface.

Step flashing is found around the chimney and on walls that intersect a shingle roof. Short sections of overlapping L-shaped flashing are arranged to channel water over the shingle downhill from it. If one of the steps has become loose or rusted through, water can creep behind it, underneath the others and into the house.

Replace a damaged piece of step flashing by carefully loosening the shingle and siding to remove it. Push the new flashing into place and secure the repair with roofing cement.

Dormers and Walls
Dormers on the second story of a residence give architectural interest to the home.

Water doesn’t always enter a home directly through the roof surface. Dormers provide a number of vertical places for water to dribble in, such as walls with cracks between its siding and the corner boards or windows.

  • Dig out any cracked or dry caulking that isn’t properly sealing adjoining surfaces and replace with silicone caulk.
  • Replace any missing or rotted siding above the step flashing on dormers.
  • Recaulk the corner flashing if any areas have hardened caulk.
Tree Damage
A damaged roof with an exposed hole is in need of repair.

If your home has sustained roof damage from a tree or other falling debris that has made a visible hole in the roof, it’s better to have a professional roofing contractor make the roof leak repair. In some cases, a roof replacement might be necessary.

Meanwhile, tarp the roof to prevent additional water damage.

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