What's the Best Fix for a Leaky Roof?
Ask This Old House general contractor Tom Silva suggests a fix for a roof that’s letting rain in
When wind and rain comes from the northeast, water is getting under the asphalt roof shingles and inside the house. I know this because twice the dampness has reached the newly-installed ceiling in our master bedroom, leaving water stains in the first instance and a bloom of gypsum efflorescence in the second instance. At least it was not mold, yet.
A roofing contractor diagnosed the problem: there aren’t any drip edges along the rakes on the gable ends, one of which faces east. But the roof is fairly new and I’d rather find a fix that doesn’t involve tearing it off and starting again.
So I’m thinking about nailing right-angle copper flashing over the shingles, not slipped under them. A Band-Aid, yes, but copper will look better than white metal, I think. What do you think?
—John Marks, Lincoln, RI
I agree with your contractor that there should be a drip edge along the rake. But your proposed fix probably isn’t the best idea. For one thing, when flashing is placed on top of the shingles, water can still sneak under it, particularly when the wind is blowing from a direction opposite the one your gable faces. Also, nailing the flashing to the existing shingles can create an avenue for water to reach the sheathing. Then there’s the problem that copper is expensive and liable to dissolve whatever aluminum it touches through galvanic action.)
Try this approach instead. On a warm day, when the shingles are pliable, slip a taping knife under the side of the shingle located in the corner where the rake meets the eave and above the roofing underlayment. Pry up the shingle slightly to expose its underside and the underlayment. (A flat prybar may come in handy if you have any nails that need to be lifted slightly, too.) Then squeeze a fat bead of roofing cement onto the underlayment near the edge of the roof along the rake.
The bead should extend from the shingle’s lower edge to its upper edge. Press the shingle into the bead, tap down any lifted nails, then lift the side edge of the next shingle overhanging the rake. Apply the next bead to the underside of this second shingle from its bottom edge to its top edge, making sure that the bead is far enough in that it will land on the underlayment. Continue in this same way with all the other rake-side shingles up to the roof ridge. Now work your way up the rake from other side of the roof.
This method of applying the roofing cement to one shingle at a time, in what amounts to overlapping beads, provides much better protection than simply running a single bead from eave to ridge.
When the roofing cement loses its resiliency and needs to be replaced, the rest of the roofing will probably have to be replaced, too, but this time with a proper drip edge (see Tom’s related video).
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