crawl space moisture barrier

Crawl Space 101: What They Are and Why They Require a Crawl Space Moisture Barrier

Roughly 250,000 crawl spaces are built per year in the United States.[1]

Crawl spaces are great. They make it easier to fix pipes underneath the foundation. And there’s no need to excavate the foundation when that happens.

Nonetheless, crawl spaces without moisture barriers can cause more bad than good. Without a crawl space moisture barrier, these leaks we’re speaking about can cause water damage, which eventually attracts mold.

With that being said, here is everything you need to know when it comes to crawl spaces, including why having a crawl space moisture barrier is beneficial to your home.

Think of this as your Crawl Space 101 class.

First, what is a crawl space?

A crawl space is a space located between your foundation and the ground. It’s just high enough so a person can “crawl” under, hence its name.

The main reason crawl spaces are great is, as we mentioned, they make wiring and plumbing repairs accessible.

The benefits

Other than making wiring and plumbing repairs a lot easier, these spaces tend to be cheaper than basements.

While they may be more expensive than slab foundations, crawl spaces aren’t as sensitive to cold temperatures.

During cold winters, slab foundations suffer wear and tear from the frozen-thaw cycles.

And in warmer regions, the topsoil is unstable, making a slab foundation near impossible—unless, of course, you want your house to fall over or dramatically slant.

Because of this instability, a couple of feet of topsoil would need to be dug out, so why not add a crawl space?

Also, an elevated house just looks nicer.

And…your house won’t suffer damage from flash flooding should you reside in a flood zone.[2]

Not everything is great, though…

When homes were being built in the early 20th century, waterproofing crawl spaces (or basements for that matter) weren’t a pressing issue.

Because of this, owners of these vintage homes are facing water infiltration problems today. Owners, like this one, aren’t too thrilled.

Waterproofing still didn’t seem to be a big issue during the 1950s either.

During the 1950s, crawl spaces were built over dirt floors[3] and weren’t inspected too often. They also didn’t have moisture barriers over the dirt floors.

There were a lot of great things in the 1950s (home microwaves and transistor radios being two of them), as with the 1920s. Crawl spaces just weren’t one of them.

While we aren’t in the 1950s anymore, owners who own homes built during that time face some of the same problems as those who own vintage homes—water infiltration, water damage, and mold infestation.

Not to mention, some homes today are still built without moisture barriers in the crawl spaces.


So what is a crawl space moisture barrier?

This moisture barrier is a thick plastic liner that blocks the moisture from the ground.—It traps a much as twice the moisture, reducing the likelihood of mold growth and the amount of water damage.

(In case you’re worried about wear and tear, the thickness of the plastic can withstand a lot of impacts.)

The role of moisture

We need moisture.

It forms clouds, which expel rain.[4]

It makes us cool during a run (but it can also make us hot because an excessive amount of moisture leads to humidity).

However, moisture attracts mold.

To be more specific, it’s the moisture from the soil below the crawl space that spurs on mold growth.

You can read more in our article, What You Need to Know About Mold: From Mold Inspection to Mold Prevention, about the many ways mold negatively contributes to our health.

Put it this way, at best, mold is highly allergenic; at worst, it causes illnesses. And, if it’s black mold that’s been there for years, in some cases it causes death.

While it’s great that crawl spaces make it easier to fix repairs, without a crawl space moisture barrier, it doesn’t do much good when leaks happen, as there’s now mold (and maybe even water damage and possible floor buckling).

Read these articles, Part 1 and Part 2: The Low-Down About Water Damage, Including Why Water Damage Restoration is Necessary, which discuss how to identify it.

Even if there isn’t a leak, a lot of times (especially if French drains aren’t installed), water runoff goes under the foundations. When water meets more water (moisture is water vapor), you have mold paradise.

And on top of that, you may get insects and bugs because, like with mold, they thrive off of moisture.

So, without a crawl space moisture barrier, not only do you risk water damage and a mold infestation, but an insect problem as well.

Benefits of a moisture barrier

On top of cutting out the moisture level, which reduces mold growth and insect infestations, this barrier will also make the air in your house cleaner.

Not only that, but your wooden floors will last longer because the crawl space moisture barrier reduces the moisture levels. (A high level of moisture ruins flooring.)

What to do so mold doesn’t grow in your crawl space

Install French drains so that the runoff water is directed to those drains than under your house.

This will lower the mold levels.

On top of this, inspect your crawl space periodically, checking for any leaks in your pipes. Doing this will minimize the chances of water damage and mold.

Always call a professional

When it comes to crawl space moisture barriers, call a professional. They have years of experience and know what they’re doing.

In fact, why not contact us? We’d be happy to provide you a quote and answer any comments or concerns you have about your crawl space.

Was this Crawl Space 101 class helpful? Have any questions about crawl space moisture barriers (or just crawl spaces in general)? Let us know by commenting in the comment section below or on social media.


Image Credit: Crawl Space via Midwest Basement Tech


[1] ASHI Reporter: Closing the Crawl

[2] FEMA: Crawlspace

[3] Angie’s List: Is Your Crawl Space Built to Today’s Standards?

[4] UCAR: Clouds And How They Form

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