Last year I had two friends help me put new asphalt shingles on my house roof. Our roof has two levels, one second-storey gable roof above a lower gable roof. Now I have leaks at a plumbing vent and where the lower roof meets the gable stucco wall of the second storey upper roof. This is a brand new roof. Why is it leaking?

It is probably not the new shingles that are causing you this aggravation. More likely the problem is inadequate and leaky flashing details. Often when people replace their roof shingles they don’t bother to replace the existing flashings. Unfortunately, they forget that the pipes, chimneys and joints of rooflines to vertical walls are the most vulnerable locations on any roof. In other words, if there is anywhere that water will find its way in to your home, it is most likely to leak at places where the shingles are penetrated and not adequately flashed and counter flashed. Flashings are your first line of defense against leaks at these penetrations and joints so they should be in very good condition throughout when you install new roofing. However, most often they are as old and deteriorated as the shingles you are replacing

For instance, where your lower roof shingles come up to the second storey wall it’s quite likely there are no step flashings under the shingles. This is a difficult place to install flashings because the stucco coat you mentioned does not permit a person to slip the vertical part of the step flashing under the siding (stucco). So people often just caulk a continuos metal strip on to the wall and over the shingles. This half measure usually leaks. Other folks just caulk the shingle joint to the wall. Over time this will also fail because the caulking will deteriorate. The best solution is to saw-cut a groove in the stucco about 3 inches up the wall and parallel to the plane of the roof. Install the metal lip of custom bent step flashings into the grove as you lay the shingles up the roof. Then grout the groove once all the step flashings have been installed.

As for plumbing pipe penetrations, replace the old flashings with new EDPM rubber “boots”. They are inexpensive and much easier to replace when re-roofing than after the fact when the old flashings leak. If your chimney flashings are bent and worn, it is also worth the effort to remove the old ones and re-grout new metal flashings in as you go. If you have made the extra effort to re-flash the shingles properly you can rest assured that your new roof will be water tight even at these vulnerable locations.

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This article was written by Steven Cannon, a Registered Building Official and partner in Lynch Building Inspection Services Ltd. of Nelson, British Columbia. It originally appeared in The Nelson Express.

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