Should You Seal Your Crawlspace Vents? Here's the Truth

The Truth About Open Crawlspace Vents

If you've ever looked at your crawlspace vents and wondered whether they should be open or closed — you're asking the right question. And you're definitely not the only one.

A customer asked us that exact question recently. There was a little hesitation in their voice. Like maybe sealing them up felt like the wrong move. Like something bad might happen if the air couldn't get in.

That hesitation makes complete sense. Here's why.

What Crawlspace Vents Were Actually Designed to Do

Crawlspace vents were designed to let air pass through on specific kinds of days. We're talking low humidity, decent wind, mild temperatures. The kind of day where outside air is actually drier than the air sitting under your home.

On those days, open vents do what they're supposed to do. The air moves through. Moisture levels drop. Everything works the way it was intended.

The problem is those days are rare.

Here in Central Illinois, that kind of weather shows up maybe six times a year. The rest of the year — we're dealing with heat, cold, and humidity that has no business getting into your crawlspace. But if those vents are open, it's getting in anyway.

What Actually Happens When Vents Stay Open

When humid outside air enters a cool crawlspace, it doesn't just pass through. It settles. It hits your floor joists, your pipes, your insulation — and it leaves moisture behind.

That moisture is where problems start.

Mold finds it. Wood rot finds it. Pests find it. And slowly, the air quality in your living space starts to reflect what's happening in the crawlspace below it — because air moves up. Whatever is down there eventually makes its way into your home.

Open vents don't prevent this. In most conditions, they're the reason it happens.

So What Does Sealing Them Actually Do?

When your crawlspace is properly encapsulated and the vents are sealed, you're creating a controlled environment. No outside air getting in. No humidity settling on surfaces it shouldn't touch. No condensation building up where you can't see it.

The crawlspace stops being a liability and starts being a non-issue.

Your floors feel more stable. Your home holds temperature better. The air you're breathing upstairs isn't being filtered through whatever was growing down below. And you're not setting yourself up for a repair bill down the road because moisture quietly did its work for years before anyone noticed.

The Question Is a Good One

When that customer asked us if they should really seal up their vents, they weren't being difficult. They were being careful. They wanted to understand what they were agreeing to before they agreed to it.

That's exactly the right instinct.

The answer just happens to be different than what most people expect. Sealing your crawlspace vents — when it's done as part of a proper encapsulation — isn't risky. It's the point. It's what makes everything else work.

Building science caught up to this a while ago. We just don't always get the memo as homeowners because nobody sits us down and explains it.

Not Sure What's Going On in Your Crawlspace?

If you've got vents and you're not sure whether they're helping or hurting, that's worth finding out. My Guys serves homeowners across Central Illinois and we're happy to take a look and give you a straight answer.

No pressure. No scary sales pitch. Just an honest conversation about what's actually happening under your home — and what, if anything, needs to be done about it.

Reach out to My Guys today and let's take a look together.