Commercial, Mixed-Use and Strata Roof Maintenance in Vancouver, B.C.

9+ Possible Causes Of Wavy Shingles: Why Do Roof Shingles Look Wavy?

9+ Possible Causes Of Wavy Shingles: Why Do Roof Shingles Look Wavy?

Wavy roof shingles are a common problem with shingled roofs all over the world. It could happen to newly installed as well as old roofs. If you are experiencing this phenomenon, you might want to know why this happens.

Shingles turn wavy for a couple of reasons. It could be due to poor installations, defective shingles, improper ventilation, molds, multi-layered roofing, uneven decking and a few other technical reasons.

In this article, we discuss 10 of them and suitable solutions to fix this problem.

Should Your Roof Shingles Always Lay Flat? Are Wavy Shingles Common Occurrence? 

Contrary to common belief, roof shingles do not lay flat immediately after installation. Newly installed shingles may look a bit bumpy in the beginning. They eventually settle down, within a few days, due to the heat.

However, if the shingles continue to look bumpy/wavy, after a couple of days. Then you may have an issue.

10 Causes Of Wavy Shingles. 

Below are some common causes of wavy roof shingles. If your shingles have become wavy, it may be due to one of the reasons mentioned in the list below. Or maybe due to a combination of them.

Plywood Is Leaky.

Beneath the shingles, there is a layer of underlayment, and below that is a layer of plywood decking. This plywood is the last line of defence between the inside of your home and the outside elements.

Sometimes water penetrates through the cracks and gaps between the shingle and the underlayment. And reaches this plywood decking. Or there could be trapped moisture in the plywood decking, that did not escape prior to the installation of the underlayment and shingles. Leaving the plywood moist underneath.

Once the plywood gets wet, it begins to rot. Swelling the shingles above. This ultimately causes wavy roof shingles.

Plywood Is Not Thick Enough.

Professional roofers suggest a 1/2″ plywood, below the shingles. However, uninformed homeowners or the once on a budget use 3/8″ thickness plywood. Instead of the suggested option.

This plywood is thinner compared to the other one. Which means it won’t be able to hold much weight over the roof. Foot traffic, rainwater, snow, debris, etc. add weight to the roof. If the plywood is thin, it sags easily. Resulting in several roofing issues. A wavy roof is also one of them.

Attic May Be Sweating Due to Improper Ventilation. 

Your attic may seem like big dark storage space, of little importance. However, the attic is one of the most crucial parts of the home.

Homeowners often neglect attic ventilation, until there are visible repercussions. If your attic lacks natural ventilation, make sure there is mechanical ventilation up there.

As the seasons change the attic has to face extreme heat, rain and ice damage. Especially, in summer when the temperatures are high, the heat gets trapped in the attic due to the lack of free-flowing air. This heat is hard on the roofing materials. Causing the shingles to curve and appear wavy.

Attic May Have Mold, Compromising Plywood Integrity.

Poor ventilation may stagnate the air in the attic. Trapping moisture and giving rise to a pungent odour. Unfortunately, this is a perfect environment for a mold colony to grow.

If there is mold in your attic, which is unattended for a long time. It will eventually spread to the roof and infest the plywood decking. This will wet the plywood and compromise it in the process.

As mentioned above, moist and rotting plywood causes waves in the shingles.

A Truss May Need to Be Reinforced Below. (Causes of Wavy Shingles)

The truss or rafters form the backbone of the roofing system. They give shape and structure to the roof.

If one or several of these rafters are compromised. The roofing layers above may sag, causing the shingles to buckle and curve giving the roof a wavy look.

Reinforcing the truss may be necessary in such a case.

Generally, each rafter is placed 16″ apart from one another to offer better support to the layers above and to avoid sagging. This increases the lifespan of the roof.

Shingles Haven’t Been Sealed Yet. (Causes of Wavy Shingles)

As mentioned above, shingles are not meant to look flat from the get-go. They settled down eventually.

However, sometimes even after weeks, the shingles remain uneven and wavy. This could be due to a lack of sealant between the layers.

In such a situation it’s best to reinstall the wavy patch of shingles.

Multilayer Roofs. (Causes of Wavy Shingles)

New shingles must always be laid after removing the previous ones. Old roofing materials be it shingles, underlayment or plywood decking, deteriorate over the years.

If new shingles are laid over the old ones. They may swell instead of lying flat, due to the poor condition of the roofing layers below. This could cause future roofing problems, like condensation in the attic, leaks, mold, etc.

Laying new shingles is not just about attaching new shingles to your roof. Before the process even begins, it’s a must to remove the old ones and check the roofing layers below for damage. And then proceed to lay the new shingles.

This entire process is as good as replacing the whole roof if you have roofing damage in layers below the old shingles.

Defective Shingles. (Causes of Wavy Shingles)

It’s no news that a lot of shingles are required to cover a roof. When shingles are bought in a bulk, a few of them may be defective. That is broken, cracked, curled, improper in size, etc.

If such shingles are used over the roof, they are more susceptible to the elements. Resulting in various roofing issues. One of which could be a wavy roof.

Shingle Expansion. (Causes of Wavy Shingles)

The majority of roofing materials expand due to the warm climate. Shingles are no exception to this.

During installation, many times shingles are placed very close to one another. This leaves no space for the shingles to settle on the roof after expansion.

Eventually, when the shingles expand, they crowd over the roof, giving rise to uneven waves.  

Poor Installation/ Poor Craftsmanship. (Causes of Wavy Shingles)

Roofing is an amalgam of selecting the right material and installing it properly. Even if you successfully pick the best material for your roof. Failing to install it correctly, may ruin your efforts.

If shingles are incorrectly installed, i.e. if they are crowded, not nailed properly, not sealed, etc. They may over time become wavy, crack, or worst blow away with strong wind.

This all is a reflection of poor craftsmanship. So, make sure to hire a reliable and experienced roofer, to tend to your roofing needs.


Hopefully, this article has given you an insight into the causes of wavy shingles. Feel free to reach out to us by commenting below. And if you are looking for a professional and reliable roofer, contact us anytime!

Leak-Stop is a one-stop destination to meet your roofing-related requirements. We offer roof repair, replacement, maintenance and inspection services all over GVRD (Greater Vancouver Regional District).

We offer a free inspection to first-time clients. Connect with us TODAY at 1 866 777 0084 for immediate assistance!

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