I’ve inspected thousands of shingle roofs
In my years as a roofing contractor, I’ve inspected, literally, thousands of shingle roofs on all types of buildings and in all manner of disrepair.
During those visits, I’ve noticed that most problems people are having related to their asphalt shingles are related to just a few common installation mistakes.
I’m going to show you what these mistakes are and how to avoid them.
For more information on the correct installation techniques, please refer to the appropriate section in my video on installing asphalt shingles on our site
Wrong nail pattern
The number one mistake people make when installing shingles is using the wrong nail pattern or not using enough nails. Most common among these mistakes is placing the nails too high on the shingle. When you do this, you miss the top edge of the shingle below and leave too few nails in that shingle.
For most asphalt shingle profiles, the nail needs to have at least eight nails holding it on. When you place your four nails in the face of the shingles too high, the shingle below is left with only four nails instead of eight. This can lead to big problems down the road, as this shingle is now vulnerable to pulling off those nails and just falling off the roof. Make sure to follow the exact manufacturer’s instructions on how many nails to use and on where to place them in the shingle.
Use on Flat Roofs
One of the other more common mistakes that I see with shingled roofs are using them on roofs that are too flat. Shingles are designed to be installed on roofs with a pitch greater than 2/12. That’s nine and a half degrees, and they really perform best on roofs with a 4/12 pitch or greater; that’s 18 and half degrees.
While you can get away with installing shingles down to a 2/12 pitch with special precautions, I’d strongly advise you to avoid any applications below a 4/12. The fact is, the slower the water is moving off your roof, the more likely you are to have problems. Especially important to take into consideration is the design of the lower slope roof. If the roof is cut up with many valleys and weird angles or there are a good many penetrations, like pipes, or, God forbid, a skylight, please steer clear of installing shingles on that section of roof. Trust me, you’re just asking for trouble.
Flashing Pipes Cause Leaks
Another common mistake that I see all the time involves flashing pipes. I bet that 50% of all the leaks that I have ever looked at have come from around a pipe flashing. Many times the flashing is just worn out and the rubber has split around the pipe, letting water in. Just as common, though, are leaks that come from nails that are placed too close to the corners of the flashing. Over time, these nails work themself loose and allow water to flow under the edge of the boot and leak into the hole created by the nail. You can avoid this by placing your nails further away from the edge of the boot and, better yet, use one of these gasketed screws, which also resist backing out.
Watch the section in the main video that covers pipe flashings to learn about my technique for doubling up your pipe boots to avoid problems caused by the rubber wearing out and splitting.
Incorrect Overhand of Shingles
Another common mistake that I see involves an incorrect overhang of the shingles. So many times I’ve gone out look at a roof, even a new installation, and seen the shingles hanging way too far off the edge of the roof. While they might have looked okay at the time that they were applied, shingles that are left to overhang the roof more than an inch and a half are prone to do some serious sagging. While this not only looks bad for years to come, these shingles that are left to flop over the edge of the roof are going to crack over time and open up those areas of the roof to leaks and rotting of the fascia and soffit.
While manufacturers and shingles differ somewhat, most shingles are designed to hang over the roof only half to three-quarters of an inch. For best success, use a piece of drip edge, like this, and follow your shingle manufacturer’s specific installation instructions.
Applying Architectural Shingles with a Racking Pattern
The last common mistake that I see all the time involves applying architectural shingles with the racking pattern. While applying shingles vertically like that is an acceptable technique for three tab shingles, you should never use this method for architectural style shingles. While the shingles go on fine and they look normal when they’re applied this way, years later they will develop serious cracks along the seam that lead to leaks and premature failure of the roof system.
In the section of the video on installing shingles, I give you a technique that will work well with both three tab and architectural shingles. I’d also note that all shingles come with specific installation instructions printed on every package. They’re there for a reason.
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