Roofing Shingles Installation

18February 2019

Common Mistakes to Avoid

While working for many years for Coquitlam Roofing Contractors,  I’ve inspected literally thousands of shingle roofs, on all types of buildings in an all manner of disrepair.  During those visits, I’ve noticed that most problems people are having related to their asphalt roofing shingles are related to just a few common installation mistakes.

Roofing Shingles Nailing Pattern

On installing asphalt shingles at Coquitlam Roofing the number one mistake people make when installing shingles is using the wrong nail pattern or not using enough nails.Diagram showing the correct nailing patter on Asphalt Shingle Roof

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 blow and leave too few nails in that shingle.  For most asphalt shingle profiles the nail needs to have at least 8 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.   The is
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 where to place them in the shingle.

Flat Roofing Shingle Problems

Shingles are designed to be installed on roofs with a pitch greater than two over twelve.  That’s nine and a half degrees and they really perform best on roofs with a 4-12 pitch or greater that’s eighteen and a half degrees.

While you can get away with installing roofing shingles down to a to twelve pitch with special precautions, I’d strongly advise you to avoid any applications below of 412.

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 sloped 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 Problems

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 has just worn out and the
rubber has split around the pipe letting water in.

Just as common though, our leaks that come from nails that are placed too
close to the corners of the flashing.  Over time these nails work themselves
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 gasket screws which also resists backing out.

There is a technique for doubling up your pipe boots to avoid problems caused by the rubber wearing out and splitting.

Incorrect Overhang Of The Shingles

So many times I’ve gone out to look at a roof, even a new installation and see 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,  roofing shingles that are left to overhang the roof more than an inch and a half,  are prone to do some serious sagging.Shingle Roof Tile Overhang Explained With Red Arrows

Well, this not only looks bad for years to come, but these shingles that are left to flop over the edge of the roof are also gonna 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 1/2 to 3/4 of an inch.  For best success use a pre-sub drip edge like this and follow your shingle manufacturers specific installation instructions.

Problems With Applying Architectural Shingles With a Racking Pattern

While applying shingles vertically is an acceptable technique for 3 Tab shingles, you should never use this method for architectural style shingles.

3 Tab Shingles

While the roofing shingles go on fine and they look normal when they’re applied this way years later they will not develop serious cracks along the seam that lead to leaks and premature failure of the roof system.  Joints should not be visible and they should be covered by a lap.  The Architectural shingles are specialized asphalt shingles and weigh 20%  more than 3 Tab Shingles or normal asphalt shingles and have a 25- year warranty if installed correctly.Diagram of how to insall Architectural Shingles


Please note that all shingles come with specific installation instructions printed on every package.  They’re there for a reason!

I hope this article was educational in helping you understand Asphalt Shingle Roofing applications.  But if you have any problems or need expert help contact us

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