Roof Contractor | Tampa | If you have ever had a roof leak you know how frustrating it can be to try and find the source of the leak. More often than not you will find that the leak is due to a problem with flashing. As you can see in the photo, flashing problems (usually due to improper installation) can cause serious damage. Unfortunately, this damage is often hidden until it becomes severe or a roof contractor notices it. In this article I’ve asked Michael Chotiner who works for Home Depot to weigh in on some summarized tips to consider when inspecting asphalt shingle roofs for leaks.
CHECK THE FLASHING
Joints between the roof deck and any feature that changes or interrupts the roof slope need flashing. A large majority of roof leaks are caused by missing, improperly installed or failed flashing in the following areas:
The most effective protection for joints where a chimney passes through a roof deck are joints crafted with sheet metal step flashing. There are a number of good ways to construct chimney flashing, and all require skilled craftsmanship.
But even the best are vulnerable to weathering, freeze-thaw cycles, normal expansion and contraction caused by temperature fluctuations, and settling or sagging of a house foundation and roof structure. If you see evidence that a leak has its origin from a point high up on a roof-that is, if water stains appear on ceilings well away from exterior walls-suspect the chimney flashing. A chimney flashing probably needs replacement or repair if:
Visible metal is bent or twisted;
The sheet metal isn’t in continuous contact with the chimney;
There are signs of rust or other oxidation;
Roof cement or caulk has been applied over the metal flashing, especially if it’s dried and/or cracked;
If you find loose brick or bad mortar joints in a masonry chimney, they may also be the source of leaks.
Plumbing vents that come up through a roof deck should be protected with sheet metal / rubber boot flashing with a bead of roof cement applied at the top joint where the flashing meets the pipe. The source of a leak could be around the vent stack penetrating the roof if:
A flashing boot isn’t present;
The flashing material is damaged;
The flashing / boot assembly hasn’t been properly installed-for example, if the metal base isn’t covered by shingles at the sides and above the stack
Nail heads securing the boot flashing to the roof deck are visible
The boot is coated with roof cement or caulk, particularly if the coating is dried and/or cracked
Joints where two different roof planes meet are particularly vulnerable to leaks. There are a number of acceptable ways to flash valleys on asphalt shingle roofs, including applying extra layers of felt underlayment or a layer of self-adhering asphalt membrane where the roof planes join. Valley construction without flashing will use asphalt shingles from each of the adjoining roof planes. They are applied over the underlayment and run past the joint, overlapping to provide extra layers of protection.
A much better approach for the roof contractor is to place a wide strip of sheet metal flashing over underlayment at the valley joint; shingles from the adjoining roof planes are trimmed so that a swath of metal is exposed. Unless the valley flashing is the open metal type, it may be a little difficult to tell how a valley was flashed without removing a few shingles and investigating.
Roof valley flashing may be the source of a leak if the leak appears in proximity below a valley. Here are a few conditions that might cause problems:
Flashing underlayment was not adequately overlapped-lower sheets should be overlapped by higher sheets at least 12 in. at the top and 8 in. along the sides
Underlayment was nailed too close to the joint of the roof sheathing-should be at least 8 in. from valley center.
Buckled or otherwise damaged metal flashing
Dormers / Adjoining Sidewalls:
Joints between a sloping roof deck and a vertical surface such as a house wall, dormer sidewall or chimney should be protected with metal step flashing. Some roof shingles and siding may need to be removed to inspect the flashing.
Flashing at the Eaves:
In cold winter climates you will find that leaks occurring within 2 feet or so of exterior walls are usually caused by inadequate eave flashing. This condition is exacerbated by inadequate roof ventilation which together can cause serious ice dam damage. To protect against leaks caused by ice dams, roof sheathing should be waterproofed with self-adhesive rubber membrane up to 4 ft. within the roof edge
Roof Contractor | If you see evidence of leaks close to exterior walls, gently lift the edges of a couple shingles (when they are warm) at the eaves to see if there’s a thick black rubber membrane beneath it. If the membrane is missing that could be contributing to the problem.