How to Waterproof Your Roof

Roof work

Photo credit: E E Solar

If you live in an area with frequent rain, like Washington State, you know that there’s not much point in having a roof over your house unless it is waterproof. Fortunately, there are several ways to waterproof your roof and keep it from leaking. This brief guide will show you: 1) how to troubleshoot potential roof problems and 2) how to waterproof your roof both before and after putting on new shingles or other roofing materials. This roof waterproofing guide is for do-it-yourselfers as well as homeowners who are about to hire a roofing contractor.

Troubleshoot Your Roof

The most important part of roof waterproofing is troubleshooting and checking over the roof. Look all over the roof for damaged, loose or missing shingles. Gaps in the shingles can leave the underlayment exposed to wind and sun, which can rapidly deteriorate it. Next, check the flashing, another name for the metal seals between the roof and the chimney, vents or skylights. Seal or replace any flashing that has gaps, cracks or holes. Some experts say the flashing causes 90 percent of roof leaks, so without checking the flashing, you won’t know how to waterproof your roof and prevent leaks.

Waterproof Under the Shingles

When you are replacing an old roof or working on new construction, you will need to know how to waterproof your roof from the start. Shingles are the most common roofing material, and all shingle roofs should have a solid waterproof material, such as tar paper or roofing felt, between the rafters and shingles. A newer, lighter and stronger option for waterproofing your roof under the shingles is thermoplastic polyolefin. There are also breathable TPO membranes that allow water vapor to pass through. This may not seem to be how to waterproof your roof, but the permeability actually reduces condensation in the attic.

Waterproof Over the Shingles

If wood shingles are getting old enough to show wear but not old enough to replace, here’s how to waterproof your roof and get a few more years of use out of the shingles. Spray, roll or brush a waterproofing compound directly on to the shingles. The oil- or water-based compounds basically restore the original waterproofing oils and resins in shingles. Oil-based compounds tend to last longer, but the water-based compounds are more environmentally sound. Of course, these compounds will not help waterproof your roof if you don’t have a waterproof underlayment, as discussed in the previous paragraph.

Updated February 11, 2018.

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