Most homeowners don’t give much thought to their crawl space – until it’s too late.

By the time we realize there’s a problem, moisture, pests, or wood rot have taken hold and we need to fork out thousands on foundation repairs or mold remediation.

That’s why waterproofing a crawl space should be a top priority for your home. But how do you waterproof a crawl space? Is it a simple DIY project? Or do you need to call a professional?

In this article, we answer all your questions about waterproofing a crawl space – and throw in tips and advice along the way.

We’ll begin by explaining what a crawl space is and how it can be waterproofed using vent seals, pumps, vapor barriers, and external waterproofing. Then we’ll help you identify the causes of water seepage and how you can minimize their impact on your home.   

Are you ready for a clean and moisture-free crawl space? Then let’s get started!

What is a Crawl Space?

A crawl space is a narrow gap under your house that provides a buffer between the floor and the earth below. It also provides airflow and allows access to plumbing, electrical wires, and floorboards.

crawl space
Crawl spaces are located under your house for wiring and plumbing

Unlike basements, crawl spaces are quite small and can be 1 to 1.5 m high. This gives you just enough crawl space (hence the name!) to replace a pipe, run cables, or repair a broken floorboard.

Crawl spaces are usually unfinished, but they can have vents (or windows) for airflow and an external door for access. Sometimes they are used for storage – if moisture isn’t too much of an issue – but mostly they’re left vacant. 

Why Does a Crawl Space Need to be Waterproofed?

Even though crawl spaces are designed to protect the foundations of your home, they are not impermeable. In fact, they can be prone to pest infestations, water seepage, and mold. Let’s take a look at these problems and find out why they pose a risk to your home.


Insects or vermin are attracted to moist, dark spaces – which is why they love crawl spaces. Common culprits are termites, rats, and cockroaches, but you can also find crickets, spiders, and ants. So how much damage can pests do? Well, a lot more than you think!

If you’ve got wood joists and floorboards (particularly if they’re damp), termites will gnaw at the wood and compromise the foundation of your home. Rats will chew through wiring and leave you with exposed or damaged wires, and insects like cockroaches, ants, and spiders can crawl into your home and cause infestations.

Dry rot

If there’s dirt in your crawl space, there’s a chance it may contain a fungus known as Serpula lacrymans. This is responsible for dry rot, which is one of the most destructive types of wood decay. It can darken, shrink, and weaken the wood in as little as a few months.

rotting floor boards
Dry Rot can destroy the foundations of your home

Dry rot spores can live in your house for years, waiting for conditions that will activate it – like moisture and humidity. Like wood-chomping termites, it can destroy the foundations of your home and cause structural issues, resulting in costly repairs and replacements.


Crawl spaces get notoriously moist, particularly after rain or snow. Unfortunately, there isn’t enough light or air to dry it out quickly, so you get mold growth. This can manifest as white, grey, or brown patches on your walls.

While mold may seem harmless, it can release dangerous spores into the air. Since 40 to 50 percent of indoor air comes from your crawl space (hot air rises!), you and your family will breathe in these spores without realising it (unless you have carpet or insulation under your floorboards).

Molds can be release dangerous spores

Over time, exposure to mold spores can result in chronic health issues such as asthma, eye irritation, skin rashes, and coughs. Unfortunately, most people don’t realize there’s a connection until they move house – or the mold is eliminated.

Water damage

After rain or a storm, it’s common to have water run-off under your house. This can enter through vents, gaps or cracks in external walls. You could also have a leaking pipe or poor drainage. Either way, you can wind up with stagnant pools of water in your crawl space.

If these pools of water are not removed, they can cause serious damage over time, such as weakening wood, causing rust, and triggering electrical short circuits. And let’s not forget about the smell of stagnant water wafting through your house!

How to Waterproof a Crawl Space

Now that we’ve covered why a crawl space needs to be waterproofed, below are five ways you can remedy the situation or avoid it in the first place. Your approach will depend on the condition of your crawl space, as well as the construction type and location of your home. Feel free to use one or more of these methods to ensure that your crawl space is properly waterproofed.

crawl space
Waterproofing crawl space

Pro Tip: If you’ve taken a peek at your crawl space and it’s already infested with mold or pests, it might be best to call in the experts. They’ll use special tools to assess the damage before recommending a comprehensive waterproofing plan.

Seal vents and windows

While crawl space vents are designed to provide airflow, this can actually be detrimental to your home. Vents allow humidity to build, which breeds mold, attracts pests, and weakens the foundation of your home.

To fix this, seal all vents or windows. This can be done by adding foam or fully closing the vents if they’re louvred. Sealing will prevent pests from gaining access and you won’t get the humidity that results from the warm air meeting cold air in your crawl space.

Install a pump

If you’ve got standing water that needs to be removed, you’ll need to use a sump pump. This device will pump water into the perimeter drain and syphon it away from the foundation of the house.

Some pumps can sense if water is in the space or not, so they work automatically. You can even get pumps that have a battery backup in case you have a power outage.

A sump pump can be used on isolated occasions (such as flooding) or it can be an ongoing measure against water intrusion in your crawl space. In general, it’s best to use it in conjunction with other waterproofing strategies, such as vapor barriers or encapsulation.

Install a vapor barrier

If you want a fast and effective way to stop moisture from getting into your crawl space, install a vapor barrier.  To do this, measure the space and purchase some polyethylene sheets from your home improvement center. Make sure they’re at least 6 mm thick and puncture-proof.

man installing vapor barrier
Vapor Barriers are made to stop moisture

Place the sheets on the ground, walls, and around the wood joists. Tape overlapping sheets and secure or anchor edges, making sure there are no gaps.

Pro tip: Vapor barries don’t last forever. They can deteriorate over time and need to be replaced every 5–10 years.

Invest in crawl space encapsulation

If you live in a flood-prone area or on a sloping block, you may need to invest in encapsulation. This is a more expensive barrier method that seals off your entire crawl space, including the ceiling.

Encapsulation users thicker and more resilient polyethylene plastic, usually 10 mm thick. It’s taped together and sealed to create an airtight lock against subfloor moisture. This cover is often paired with a dehumidifier, which helps control moisture levels. This deters insects and improves the air quality in your home.

Crawl space encapsulation is a big job, which means that many homeowners enlist a contractor to do it for them. However, if you’ve got strong DIY skills, you can easily save money by purchasing the materials and completing the job yourself over a weekend. Keep in mind, however, that you may need a second pair of hands to help out!

Waterproof the exterior

This is probably the most expensive option, which is why it’s best done during the construction phase of your home. However, you can still install a moisture barrier if your crawl space is too small or you prefer an alternative to interior waterproofing.

A word of warning: exterior waterproofing is labor-intensive and best done by a professional. That’s because it involves excavating outside the foundation walls, applying a high-tech moisture barrier, and installing a drainage system to keep water away from your crawl space.

Once it’s done, though, it’s a highly effective, one-off solution, and it means that you don’t have to fuss around with pumps and dehumidifiers or keep replacing vapor barriers. Having said that, you still need to check your crawl space for seepages from other sources, like pipes or air conditioning units.  

Pro Tip: Exterior waterproofing can disrupt landscaping or other garden features, so factor this into your costs when considering this option.


What’s the Best Way to Dry Out a Crawl Space?

It all depends on how wet the space is. If you have large puddles or flooding, it’s best to use a sump pump to remove the excess water. If you’ve already pumped out the water and the surface is still damp, you can use a dehumidifier. This will lower humidity, add heat, and move the air around.

It can take time for a crawl space to dry out completely. It really depends on the size, weather conditions, and level of moisture, but on average it can take up to 10 hours.

If you don’t have a humidifier, you can hire or borrow one. However, it’s worth investing in a high-quality humidifier as part of your ongoing waterproofing plan.

Pro Tip: Avoid using a fan to dry out your crawl space. Fans draw air from outside, which can raise humidity levels and keep the space moist! 

Can I Use Waterproofing Paint in my Crawl Space?

Waterproofing paint can be effective in kitchens and bathrooms, but it’s not advisable in a crawl space. Firstly, walls in these spaces can be rough and unfinished, which means that paint doesn’t fully adhere to the surface. Secondly, it can deteriorate quickly and require reapplication. Thirdly, you’ll have to spend hours on your knees or back breathing in the paint fumes!

How Do I Keep Water Out of My Crawl Space?

Water intrusion is unavoidable in freak events like floods or snowstorms. But if you follow the steps above, you can successfully minimise or avoid water damage altogether. But there are other measures you can take to keep water out of your crawl space.

Make sure your home has good drainage. Get an expert to assess your home and implement strategies for improved water flow. While this may involve the installation of new drainage systems, it’ll save you time, money, and heartache further down the track.

Check for leaking pipes, broken gutters or faulty air conditioning units. You’d be surprised how many people are unaware of cracked gutters or appliance leakages until it’s too late. Get these repaired as soon as possible to prevent water from pooling in your crawl space – or elsewhere in your home.

Final Thoughts

Waterproofing a crawl space should be an essential part of your home maintenance routine.

By sealing off vents, using sump pumps, installing vapor barriers or investing in full-encapsulation, you can avoid costly foundational damage and improve the air quality of your home.

While many of these strategies can be implemented over a weekend (with a few provisions from your home improvement center), others like mold remediation, encapsulation, and exterior waterproofing should be tackled by a professional. This will ensure that the job is done safely and correctly.

We hope this article has provided some useful strategies and tips to keep your crawl space clean and dry. For more household maintenance tips, check out the articles below. Have a great day!