The Science of a Waterproof Roof

By Dymon BradyWe all know that a well installed roof keeps water out. But have you ever wondered why? Why don’t those roofing nails put holes in the roof that cause more leaks? Why do you need shingles if there is a waterproof layer (underlayment) installed on every roof? Just for fun, I wanted to answer a few of those questions today.

You are right, underlayment is installed on every roof. Some contractors, including Brady Roofing, actually install a thick underlayment called ice shield on the outer edges of the roof for extra protection. But why do we need such a strong waterproof installed beneath shingles? Aren’t shingles supposed to keep water out?The truth is, even brand new shingles can get water under them. Especially in situations with ice dams or heavy rains, water can seep up and under the shingles. In case of this situation, the underlayment provides a perfect backup, and in the end you never have to know that your shingles can’t do their job all on their own.  (Learn more about your roof's underlayment)This brings up the question: why do we need shingles? If water regularly gets under the shingles anyways, why do we even need them?While underlayment is a great backup, it is no match for the strength and resistance offered against the elements by your shingles, metal panels, etc. These roof coverings stand up against impact from hard rain and hail, extreme temperatures and stress from UV rays. Without shingles, your underlayment would fail pretty quickly.As we install shingles, and underlayment, we must use nails. Roofing nails have disproportionately large heads and thick shafts, and when they are installed flush, they expertly keep water from working down around them and into your home below. Also, it is important to realize that the nails are installed on a strip above the shingle that never shows once the roof is completed, this protects the nails from being exposed to water and rusting.

Another element of your roof that can often be overlooked is the flashings. Flashings are metal pieces installed around pipes, chimneys and walls. If we didn’t use flashings, it wouldn’t matter how well the rest of your roof was installed. Water would continuously leak around your chimney walls, swamp cooler, and pipes, slowly destroying your roof’s rafters and home interior. Flashings help to direct water away from these areas and seal them so that they do not collect water.As the experts at HGTV Remodel put it “The home's exterior isn't a continuous surface. It has intersections, penetrations and abrupt terminations. Roofs have chimneys, dormers, ridges and valleys. Exterior walls have windows, doors and adjoining roofs. Porches and decks interrupt the flow of rain and melted snow as they move down the home. Wherever water moving down the exterior or the drainage plane has to change direction, it needs the help of flashing to keep it moving down and away from the home.”Do you have any more questions for us? Email us at dbrady@bradyroofing.net or request a free estimate today.