Are you seeing signs of mold, leaks, or rot in your attic, and wondering if poor ventilation could be the hidden cause? Did your roofer replace your roof but skip checking your attic ventilation entirely?
At RoofSmart, we identify and fix ventilation problems on hundreds of Seattle homes every year. We always inspect the attic to make sure that we’re not missing any issues that will impact the quality of your roof.
In a rainy, damp area like Seattle, it’s crucial that your attic ventilation is working properly to avoid mold and rot.
In this article, we’ll walk you through the most common attic ventilation mistakes we see Seattle roofers make, including outdated code compliance, mismatched ventilation types, blocked airflow, and more.
You’ll learn which ventilation mistakes to watch out for, why they cause problems on your roof, and what happens to your roof when you have poor attic ventilation.
What are common ventilation problems or mistakes?
Having proper attic ventilation is a crucial part of building a roof that actually works properly. However, roofers who are inexperienced or rushing through the job can easily make mistakes that ruin your attic's ventilation.
Here are some of the most common attic ventilation problems we see during inspections:
1. They don’t check if your attic ventilation is updated: This could happen for a number of reasons. Your roofer might assume that what's there is fine, so they didn't look, and they certainly didn't do the math. It could be that they're incompetent, negligent, or just not worried about doing things to code. This probably means that they don't care if you get a warranty or if it's voided before they leave.
2. Combining closed soffit with bird blocks: As a general rule, you should not have more than one form of intake ventilation in your attic (the same goes for exhaust ventilation). Closed soffit is a type of intake ventilation that has open slats or holes where air can get in and travel into the attic.
If you have bird blocks behind that, you’re creating an obstacle for the air to get into the attic. Bird blocks are a type of intake ventilation installed under the roof line that have holes to let the air through:
Having closed soffi means that your bird block vents are closed into the roof. This setup then creates a double-screen effect that chokes off the air, even though it looks like it should work because it has double ventilation. But there's too much static pressure, so it fails.
3. No baffling or baffling that has failed: If you’re using bird blocks on your roof as your intake ventilation, then you need to make sure that the insulation in your roof isn’t blocking your roof. Baffling is used to compress your insulation so that air can easily flow inside. If you don’t have any or if it’s not working, then your roof won’t have proper airflow.
This is what properly installed baffling looks like (notice how the insulation is pushed down):
4. The framing of your house blocks ventilation: So it’s really common with an older house that the attic has been converted to a second story or third story that has knee walls or short pony walls, and the air doesn't pass above them. It just stops in that little chamber. This is a bigger problem if you have a cathedral ceiling because it means we can’t inspect the attic and find this problem. What we find is that most roofers just put it back the way that it was.
We see this issue with cathedral ceilings a lot. Here’s a picture during a recent job that shows our plan for mapping out where the air paths need to be:
5. Not having enough intake vents to meet current code: Attic ventilation requirements have been updated a lot in the last 30 to 40 years. Seattle has a lot of older homes that were built before these changes were made. As a result, lots of homes in the Seattle area do not have proper ventilation.
The reason the current code has been upgraded is that they realized the old minimums were causing things to fail. So they upgraded the bare minimums. And if you don't bring it up to current code, then it avoids the warranty, or the manufacturer may not honor it.
6. Not having the right amount (balanced) exhaust ventilation: You have to do the math to make sure that your exhaust vents are sufficient, but you don't want to overdo it so that it's unbalanced with the intake. And there are many different types of vents for exhaust.
You've got your static roof vents, various sizes, and very often, people replace the plastic ones that the builder put in with metal ones. It sounds like they're better, but they're smaller (because the plastic ones allow 50 square inches of air, but the metal ones are only 38). So they just swap out the part, and they actually reduce the ventilation. And if they didn't do the math, then they don't add enough to make up for it, and it's worse than when they started.
7. Mixing different types of exhaust ventilation: You're not supposed to mix static roof vents with power vents (like ridge vents and whirlybirds). You're supposed to have one type. If you have a power vent and then you've got other static roof vents nearby, then air takes the path of least resistance.
So, instead of drawing from the intake, it draws from the adjacent exhaust vents, which throws off the balance of your intake and exhaust system. Also, if this happens while it’s raining, it'll suck in rain.
8. Using gable vents for intake ventilation: You should only use gable vents as your form of intake ventilation if it’s your only option. If you're trying to force air to come through the intake, that is the hardest path for it to take. It has the most resistance and is the farthest distance to travel.
And so if you have an open gable vent, air will cheat in through that, and you'll have stagnant air for most of the attic. So for that reason, ventilation engineers and manufacturers of ventilation equipment recommend blocking gable vents (in most cases).
9. Choosing the cheapest ridge vent option: Choosing the cheapest ridge vent just to check the box and move on can cause problems later on. Cheaper ridge vents can plug or have problems. It’s important to do your research and talk to your roofer about your options.
Here’s a plugged vent that grew moss:
Here’s an example of a poor nailing job:
10. Bath vent doesn’t vent through the roof: It’s pretty common for bath fans to just blow into the attic, which defeats the purpose of venting it. It’s also common for the hose to be incorrect. Usually, people use a flexible dryer vent hose, or something that's uninsulated, that will condense in the winter when steam goes through it. It's common for the hose to be too long. You want it to be as short as possible and for it to grade uphill. And it's common for those to have been installed but fallen off because they use the wrong tape or the wrong fastener. We also commonly find range and sewer vents that don’t get properly vented through the roof.
11. Not using a humidistat on your power vent: The humidistat is there to help you prevent issues caused by excessive moisture. Without a humidistat, your vent can get moldy.
12. Using an oversized power vent: It's common to oversize a power vent. And so it's shaking the house, trying to find enough air, and then it burns out. It'll pull air through the ceiling fixtures because it's struggling for air.
Using an oversized power vent: It's common to oversize a power vent. And so it's shaking the house, trying to find enough air, and then it burns out. It'll pull air through the ceiling fixtures because it's struggling for air.
Why is proper attic ventilation important on my Seattle roof?
The Seattle area is famous for being humid, damp, and rainy. In this type of environment, it is crucial that your roof has great ventilation. Otherwise, moisture can build up and cause damage.
Common problems we see caused by poor attic ventilation include:
- Water damage
- Rotting wood
- Mold
- Mildew
- Structural damage to framing
These issues can develop quietly and worsen before you even realize they are happening. And the worst part? They cost thousands of dollars to fix.
How do I find a roofer who can help me fix my attic ventilation issues?
As you can see, there are countless ways to mess up your attic ventilation. And unless you’ve had your attic ventilation installed or updated recently, your home might have one or more of these problems.
But here’s the real dilemma: not every roofer in the Seattle area is qualified to help you fix your attic ventilation. In fact, a lot of them don’t even check it. So how do you know which roofers can help you with attic ventilation issues?
Read our article “Is Your Seattle Roofer Actually Good? Here’s How to Tell Before It’s Too Late” to learn how to quickly and effectively evaluate your roofer’s qualifications. Make sure that you also ask them if they’ve worked on attic ventilation before and request job photos.
It’s important to find a roofer who is knowledgeable about roofing AND has experience specifically with attic ventilation. Otherwise, you’ll be right back to square one (or worse off).
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