Leaky roof? Check flashing
Q: During the heavy rains recently, a leak developed in one of our second-floor bedrooms. I can’t find the source of the leak, and it’s in an improbable place. The only thing that might have happened is that the leak is near enough to the chimney that it ran along the outside of the chimney to the ceiling and then pooled above the bedroom. But I can’t see any damage from the attic, and the shingles on the roof look all right. Do you have any suggestions on resolving this? — Dan L., Medford, Mass.
A: My first thought is that a leak has developed in the flashing around the chimney. Flashing is a soft metal (aluminum or copper) used to seal joints between the roof sheathing and things jutting through the sheathing, like chimneys or vent stacks, as well as the joints where the sides of the roof meet. It is tapped into place with a hammer or mallet so that it conforms tightly to the materials next to the joint, overlapping by a few inches. Then a weather-resistant sealing compound is applied to the flashing to hold it in place and provide additional protection from water and debris.
The trouble is, housing materials, sealants and soft metal all expand and contract and deteriorate over the years, and even the most flexible of materials eventually cannot cover the little gaps that appear. Sometimes these gaps are not easily seen; sometimes, in heavy, wind-driven rains, water is forced into crevices one never thought of, causing a little bit of damage that becomes bigger with each rain, wind or snowstorm.
Check the flashing around the chimney, looking for cracks, gaps, warping of the metal or other damage. Visually inspect the outside of the chimney as well for cracks in the masonry or gaps in the mortar (another serious issue that needs immediate attention if discovered, due to the risk of house fires). Make your way along the joints of the roof — anywhere two sides meet — to inspect the flashing and sealants.
Damaged flashing can be temporarily patched if another long period of rain is forecast, but this patch will fail quickly. So plan on replacing the metal flashing in the damaged area completely, as soon as a couple of warm, sunny days are expected. You can do this yourself, with the correct materials and tools, or if extensive damage is noted, contact a roofing contractor.