Shingle Rows & Exposures
There is a right and wrong way to install shingles. They should be in even rows and placed based on manufacturer guidelines. Additionally, it is critical to the life of the shingle that the correct number of inches of the shingle are exposed. As we can see in the picture above, improper shingle rows and exposures lead to uneven, zigzaged shingles, and the issues with these are beyond just cosmetic.
Here are some points to consider to develop a better understanding of laying shingles properly:
- Shingles staggered correctly.
- Straight Shingle Rows.
- Dimensional/Architectural shingles Vs. Three tab shingles.
- Correct Shingle Exposure.
How To: Install GAF Timberline Shingles: Proper technique for creating shingle rows.
Shingles Staggered Correctly:
One of the most important factors of a shingle install is ensuring shingles are installed with the proper stagger pattern to minimize seepage at shingle transitions. The stagger of the shingle is the offset pattern that the individual shingles are applied in; This stagger pattern prevents water from getting down between the shingles. If shingles are staggered less than 4 inches apart it can allow water to get below them and move towards the butt edge joint or nail heads and cause leaks. Keep in mind, the lower the pitch of the roof, the more likely the water is to pool and cause leaks. What do you do when the roof leaks from improper stagger? Unfortunately you have to tear the whole thing off and start again. Since improper stagger voids the warranty on a roof this can be a very expensive mistake.
Straight Shingle Rows:
Wavy Shingle Row
Creating straight shingle rows starts with a chalk line, which is made from string covered in chalk. Lifting the string up and allowing it to snap back into place creates the chalk line to use as a guide for laying shingle rows.
While many modern synthetic underlayments have printed grid lines to help keep rows straight and exposures satisfactory, we do still keep the practice of using chalk lines at set intervals to maintain proper exposure in straight lines to make a consistent look.
Proper Chalk Line Technique
When it comes to the importance of straight shingle rows there is the obvious reason – aesthetics. But more important than just the look of the roof is the consequence of shingle rows that are not straight. Shingles are typically supposed to have an approximate 5.5” exposure, but if a row is uneven it might have a shorter or longer exposure. The longer exposures can leave the shingle susceptible to wind blowing up under it and ripping the shingle off. Even the shorter rows are not without their risks. The adhesive line of the shingles are meant to line up in a specific spot on the next shingle row. If these spots are not lined up correctly a proper seal will not always form, again leaving the shingles susceptible to weather concerns such as high rains and wind blown shingles.
Dimensional/Architectural Shingles vs. Three Tab Shingles:
Dimensional shingles are thicker and widely accepted as more durable than three tab shingles. But the differences don’t stop there. The method used to install the two types of shingles are different as well. Dimensional shingles are installed in a stair step method while three tab shingles are installed by racking them. Racking shingles is when they are installed straight up the roof. It is important that dimensional shingles are NOT installed in a racking method as this will result in a leaking roof. See the below pictures for examples of this:
For more information on racking shingles please see the GAF Technical Bulletin:
Correct Shingle Exposures:Most shingle manufacturers will recommend a five and half to six inch exposure on three tab or dimensional shingles. The exposure is defined as the area of the shingle that is within view or “exposed” verses the part of the shingle that is overlapped or hidden by shingles next to it or above it.
When there is too much exposure there are two primary risks:
- The nails (if nailed in the proper nail line on the underlapped shingle) will be visible and exposed to rainwater, which can expose them to leaks.
- If the nails are raised to be covered by the overlapped shingle then this indicates what is called high nailing which leads to lower wind resistance and can cause dimensional shingles to delaminate due to weight.
Too little exposure has its risks, as well. The primary risk being that the adhesive strip on the shingle will not fall in the correct spot and will result in the shingle being more susceptible to wind blowing the shingles off.
Common Issues with Improper Shingle Nailing
Your Roof and Insurance:
If damage occurs as a result of improper exposures or nail placement insurance companies will generally cover that damage. However, there is a risk that in some cases insurance companies will not cover these damages as technically they do reserve the right to refuse payment on improperly installed roofing, making it even more critical to make sure the job is done right the first time.