Foundation vents are a fairly innocuous fixture in most homes; however, they do serve a fairly critical purpose in the home’s long-term integrity. Also known as crawl-space vents, foundation vents are fixtures that allow airflow through the low but open space in the foundation of a house.


The airflow assists in the removal of moisture that can cause wet rot that potentially attracts termites (especially in wooden foundations) and ultimately costly damage to a home. 

During the winter, however, foundation vents have the potential to allow chilly air into the house. For this reason, you may need to cover your home’s foundation vents in order to keep your house nice and warm during the winter months. 

Thankfully, the process is quite easy to do, and in this guide we will show you all of the tools and steps you need to follow to cover your home’s foundation vents without any external help.

Covering Foundation Vents

When covering foundation vents, the first thing you need to do is to identify what type of foundation vent your home is equipped with. Generally speaking there are three different types of foundation vents: manual vents, automatic vents, and powered vents.

The reason why the distinction is important is that automatic vents and powered vents already have built in mechanisms of their own to open and close as needed. For this reason, installing foundation vent covers may end up being counterproductive in some cases.

Regardless, the process of installing the actual vent cover is more or less the same for all 3 types of vents, which goes as follows:

  1. Measure your foundation vents and buy the correct size vent cover. Since foundation vents are built in standard sizes, it should be pretty trivial to find the cover that fits your vents correctly.
  2. Align and mount the cover onto the vent opening on the exterior side. 
  3. Attach and secure the vent cover onto the foundation vent. Depending on the type of cover you have, the mounting mechanism either requires screws and hex nuts or is simply a force-fit that locks into place. 

And that’s all there is to it!

Types of Foundation Vent Covers

Besides the size, foundation vent covers can also vary on a number of different attributes, such as the material, additional features, and the mounting mechanism that we touched on earlier. For the purposes of this article, though, we will only be focusing on two types: a screen vent cover and a full vent cover.

The full vent cover is as you would expect from the name—a plastic or metal plate that slots into the foundation vent and completely blocks off all (or at least a significant amount of) air and water ingress. 

When mounting full vent covers, homeowners have the option to line the edges with silicone caulk for a more robust seal. The full vent covers could also be attached with foam blocks to provide more insulation. 

A screen vent cover is essentially a metal or plastic frame with a wire lattice pattern in the middle. Instead of blocking out airflow, however, the screen vent is meant to block out leaves, insects, and rodents from entering into the crawl space through the vent. 

These screen vents are, therefore, typically used in conjunction with a full vent cover as an additional deterrent. 

Should You Keep Foundation Vents Covered?

The information that we’ve discussed so far now leads us into the greater question of whether or not homeowners should be keeping their foundation vents covered all year round. 

The fact of the matter is that there really isn’t a single best answer for all homes, as the best solution would depend on a variety of factors about the house itself. 

As we mentioned at the beginning of this article, keeping the foundation vents closed will prevent cold drafts from entering the house through the floor. However, this also increases the humidity inside the crawl space that is the perfect catalyst for mold, mildew, termites, and wood rot. 

Opening the foundation vents every so often can rectify this problem, allowing critical air to flow into the crawl space to regulate its internal humidity. But the effectiveness of such a solution  might not be enough if, for instance, the home is built in a particularly humid region in the first place.

To explain why this is, let us first understand how air in a crawl space actually works. Generally speaking, air wafts up from the crawl space into the first floor above, which itself is drawn from the air going through the foundation vents. 

Now, what most people aren’t actually aware of is that, despite the vents supposedly serving to reduce the humidity of the air in the crawlspace, there is still a lot of humid air that is brought up into the house because of the natural moisture that is found in the ground just a couple of feet below the surface. 

It is this same moisture that causes the same problems that opening the foundation vents is supposed to fix in the first place.

If your home has this problem, installing automatic or powered foundation vents may not be enough to solve the problem. Instead, one of the most effective ways to go about this is to actually modify the interior of the foundation’s crawl space. 

This measure is usually done by installing a liner made of a plastic called polyethylene, which is placed along the entire surface of the crawl space floor. Compared to similar plastic liners (such as those used on weather-resistant barriers), crawl space liners are much thicker to make them strong enough for crawling onto during later maintenance.

In addition, the thicker liner also makes it practically impossible for insects to crawl up into the upper floor from the crawl space. Further protection is added with the installation of an anti-microbial liner.

To complete the treatment, a specialized humidity control system is installed in the crawl space that is connected to the home’s HVAC. 

Editorial Contributors
Matt Greenfield

Matt Greenfield

Matt Greenfield is an experienced writer specializing in home improvement topics. He has a passion for educating and empowering homeowners to make informed decisions about their properties. Matt's writing focuses on a range of topics, including windows, flooring, HVAC, and construction materials. With a background in construction and home renovation, Matt is well-versed in the latest trends and techniques in the industry. His articles offer practical advice and expert insights that help readers tackle their home improvement projects with confidence. Whether you're a DIY enthusiast or a seasoned professional, Matt's writing is sure to provide valuable guidance and inspiration.

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