What Happens to Asphalt Shingles on a Roof with No Ventilation?

Have you been told your asphalt shingle roof just "wore out," even though it's only 10 or 15 years old? Are you worried that replacing the shingles alone won't solve the real problem and that you'll end up dealing with the same leaks, mold, or rot all over again?

At RoofSmart, I've inspected hundreds of roofs throughout the Seattle area where the shingles weren't actually the root of the problem. In this case, a local church had shingles that were failing years before they should have because the roof had virtually no ventilation, and ongoing condensation was quietly rotting the structure beneath them. By identifying the underlying issues instead of simply replacing the shingles, I was able to design a roofing system that addressed both premature shingle failure and the moisture causing it.

In this case study, you'll see how poor ventilation and condensation can dramatically shorten the life of an asphalt shingle roof, why replacing shingles alone isn't enough, and how installing a properly designed vented roof deck helped protect this roof for the long term.

How long do shingles last on a roof with no ventilation in Seattle?

Having proper attic ventilation is an important part of keeping your shingles in good condition for as long as possible. So, if your attic has poor airflow, your shingles can fail prematurely (typically around 15 years or less).

An attic with poor airflow usually gets extremely hot, especially in the summer. This roasts your shingles from the inside, causing them to dry out and crack. It also leads to heavy granule loss. This can happen as early as 10 years after getting the shingles installed.

For example, we recently replaced the roof on a local church that had no ventilation. The shingles had been installed only 10 years before, but they were already dry and starting to crack, warp, and come apart.

In addition, the owner noticed sections that clearly had moisture damage. It was initially thought to be a leak, but when I did my inspection, I realized that it was actually condensation.

The roof had no ventilation and not enough insulation, which caused condensation to form. As a result, there was a lot of rotting wood all over the roof.

There were two sections on this roof with shingles: the main chapel area and the gymnasium area. The gymnasium roof was also failing prematurely (cracking shingles), so we decided to add it to the project to make sure that the customer had the same warranty protection on both sections.

How Poor Ventilation and Condensation Damage Asphalt Shingles

How do you get rid of condensation and ventilation issues in the attic?

This church has vaulted ceilings, which don’t typically leave a lot of space in the attic for ventilation. So, to fix this problem, we can do something called a vented deck, which is where we add foam insulation to the roof and then use wood runners to elevate the roof deck.  

That way, air has room to flow underneath the shingles. And the foam insulation keeps the roof at the right temperature to prevent condensation from forming.

Here are the steps that the roofing crew took to replace the roof and add a vented deck.

• Tear-off: Some sections had asphalt shingles nailed directly into the foam insulation. In other spots, there was a second layer of shingles under the first. Once all of this came off, the crew could replace any boards that were rotting to make sure that the roof decking was all solid and in good shape.
• Vented deck: The next step was to add a new vented deck system on both sections of the roof. Over the gymnasium roof, we used drip edge vents, and on the other section, we used vented fascia as intake vents. The crew installed furring strips vertically along the roof to create an elevated surface for the vented deck. Then they installed plywood over top of that.

After that, the next two layers installed were ice and water shield and then the shingles.

• Structural Repairs:
• Car Decking: Our crew also replaced 3x6 car decking that was damaged by moisture intrusion on the ceiling. This required custom sourcing.
• Rotted Beam: There was a very rotten beam in a corner of the roof that needed to be completely replaced.

Why did the customer choose RoofSmart for this roof replacement project?

At RoofSmart, we understand that we’re more expensive than other roofing companies out there. However, we also do high-quality work and pay close attention to detail so that we can properly fix all of your roofing issues.

Understandably, our high prices can make customers hesitant at first, but once they see that we also offer top-quality work that addresses issues other roofers don’t, they choose to work with us.

For example, that’s what happened with this customer. Our proposal was higher than the others that this customer got, but we were also doing more work. No one else was going to a vented deck, which is the only way to fix the condensation and ventilation problem.

Also, a vented deck was required to maintain the CertainTeed shingle warranty (it gets voided if the roof does not have proper ventilation). The customer was upset that the roof didn’t have proper ventilation and voided the warranty the first time, so it was a priority for him to make sure that he would be able to maintain it this time around.

As I always do, I made sure to clearly explain to the customer why our prices were higher than others and the added value that he would get if he chose us. He decided to go with us at RoofSmart because he could see that we had the expertise to fix all of the roof’s problems.

In the end, he was very happy with his decision and is relieved that there are no more condensation problems causing the roof to rot.

Why do cathedral ceilings usually have condensation problems in Seattle?

As this case study demonstrates, asphalt shingles weren't the reason this church's roof failed after only 10 years. The real issue was that the roof assembly had excessive heat and moisture. Without adequate ventilation and condensation control, the shingles deteriorated from the inside out while hidden moisture quietly rotted the roof structure beneath them.

This is a common problem on buildings with vaulted or cathedral ceilings. Because there's little or no attic space, these roofs don't have the airflow that conventional attics rely on, making them especially vulnerable to trapped moisture, mold, and premature roof failure if they aren't designed correctly.

Read our article "Is Your Cathedral Ceiling Trapping Moisture and Ruining Your Roof?" to learn why cathedral ceilings create unique ventilation challenges, the warning signs of hidden moisture problems, and the roofing systems that can help protect your roof for decades instead of just a few years.