Do you have bird block vents along your roof and assume your attic is getting enough airflow simply because the vents are there? What if those vents look completely normal from outside, but they’re actually blocked, allowing moisture to build up in your attic and cause damage before you realize anything is wrong?
At RoofSmart, we’ve inspected hundreds of Seattle-area attics where the attic intake ventilation wasn’t providing the ventilation the homeowner expected. The problem is that many of the most common failures happen behind the vent where you can’t see them, and they can develop years after the ventilation system was originally installed.
In this article, I’ll explain how bird block vents work and the most common reasons they stop providing adequate airflow, and what you can do to catch hidden ventilation problems before they contribute to moisture damage in your attic.
Bird block vents are a type of vent installed along the outer edge of your roof that are used as intake vents to supply air to your attic. They have small openings for air to come in, with a layer of mesh installed behind the openings to keep out birds and other pests.
These are a popular intake vent option because they are fairly cheap and easy to install while still being effective. A lot of homes in Seattle have bird blocks.
Although bird blocks are commonly used in the Seattle area and work well on most houses, it is still possible to experience issues that prevent the bird blocks from letting air into your attic.
Here are some examples of common issues that cause bird blocks to fail:
Having issues with your bird block vents, whether it’s due to poor installation or some kind of blockage, means that your attic ventilation is not working properly. In the Seattle area, this is a huge concern because it means that the moisture getting into your attic isn’t drying out.
Moisture building up in your attic typically leads to mold and rotting wood, which are expensive to deal with and can cause significant damage to your roof if left untouched for too long.
So, if you have bird blocks, it’s important to make sure that they are clear of debris and working properly.
| Bird Block Problem | What Causes It | How It Affects Attic Ventilation | What to Do |
|---|---|---|---|
| Insulation blockage | Wind washing moves loose insulation toward the bird blocks | Partially or completely blocks intake airflow | Inspect behind the bird blocks and move insulation away from the openings |
| Collapsed cardboard baffles | Humidity or wind-driven rain gets the cardboard wet and causes it to collapse | Creates an air dam between the bird blocks and attic | Replace failed baffles and restore a clear ventilation path |
| Paint overspray | Soffits are painted without protecting the bird block screens | Paint clogs the mesh and reduces airflow | Protect vents during painting; severely clogged vents may need replacement |
| Dust buildup | Bird block mesh acts like a filter and gradually collects airborne dust | Increasingly restricts intake airflow | Inspect bird blocks periodically; this article recommends checking roughly every 5 to 10 years for dust |
| Too few bird blocks | Ventilation was undersized during installation or requirements have changed | Attic doesn't receive enough intake ventilation | Calculate the ventilation requirements for the attic and determine whether additional intake is needed |
| Air dam from new soffits | New soffit ventilation is added while the original bird blocks remain in place | Creates a trapped chamber that prevents air from reaching the attic | Have the intake assembly evaluated and remove the obstruction between the new vent and attic |
| Blocked insect screen | Paint, dust, or other material accumulates on the required screen | Reduces the vent's effective open area | Keep the screen clear and replace the vent if it can't be adequately cleaned |
| Poor ventilation design | Bird blocks are used without considering the complete intake-and-exhaust system | Intake may be inadequate even if individual vents appear open | Have the complete attic ventilation system evaluated |
| Hidden blockage | Problems develop behind the vent where they aren't visible from outside | Homeowners may assume ventilation is working when it isn't | Inspect the attic side of the vents, not just the exterior |
| Long-term inadequate airflow | Any of the above problems can reduce intake over an extended period | Moisture may remain in the attic, contributing to mold and wood rot | Correct the ventilation problem before moisture damage becomes more extensive |
Bird blocks may or may not be the right fit for your home depending on the layout and style of your roof. It’s best to consult with a roofing contractor who is knowledgeable about attic ventilation (and most actually are not!) to help you figure out which attic intake vent is best for you.
Every intake vent is going to have some kind of insect screen because it's required by code. So they're all going to be susceptible to clogging or getting blocked to one degree or another.
If you’re worried about dust, make sure that you check it every 5 to 10 years. It shouldn’t clog faster than that, unless you live on a dirt road. You can also check to see if your baffles are still in good condition and that the insulation or baffles haven’t moved to block the bird blocks.
If you have someone painting near your bird blocks, make sure they’re careful to not paint them. If they do get painted and are too clogged, you’ll have to replace them.
Bird block vents can be an effective and affordable way to bring fresh air into your attic, but simply having them installed doesn’t guarantee that they’re working properly. Insulation, collapsed baffles, paint overspray, dust, undersizing, and poorly designed soffit upgrades can all restrict airflow without creating an obvious problem you can see from outside your home.
If your attic isn’t receiving enough intake air, moisture may not dry out properly, increasing the risk of mold and wood rot over time. Checking the attic side of your bird blocks periodically can help you catch these problems before they contribute to more expensive damage.
Bird blocks also aren’t the only way to provide intake ventilation. Your roof design, existing ventilation system, and the amount of airflow your attic needs can all influence which type of intake vent makes the most sense for your home.
Read our article “Comparing Types of Attic Intake Ventilation: Which Is Best for My Seattle Home?” to see how bird blocks compare with other intake ventilation methods and what you should consider when deciding which option is right for your Seattle-area home.