How to Insulate a Crawl Space 

Insulating a crawl space

Being narrow, small, and hidden below your house, a crawl space is hardly on the list of your top priorities. Right?

Well, it should be, and here’s why:

A crawl space lets draughts of cold air in during the winter, which makes your house feel colder than it should. This doesn’t only mean you’ll face temperature regulation issues, but it also means you’ll face higher energy bills.

It doesn’t end here, too. During the summer, the difference in temperature between inside and outside air causes a sharp rise in humidity in your crawl space, which can lead to issues with moisture and condensation.

If you don’t want to deal with any of this, the answer is easy: insulate your crawl space.Here, we’ll tell you how to insulate a crawl space, how to choose the proper materials, and when to call a professional to handle it.

What Type of Crawl Space Do You Have?

First, knowing the type of crawl space you have helps you choose the right material for insulating it, along with the best practice for insulation.

There aren’t many types of crawl spaces, so this shouldn’t be hard to navigate. Your crawl space is either ventilated or unventilated. 

While this seems easy enough, it could make all the difference in your insulation strategy.

Ventilated Crawl Space

Ventilated crawl spaces are more challenging to insulate than their counterparts because you have to insulate the ceiling, which is typically the largest area of the crawl space. They’re also more expensive to insulate for the same reason.

For these crawl spaces, the best practice is to insulate under the subfloor, which lies underneath your house and above your crawl space. 

Most people use fibreglass to insulate vented crawl spaces because it has a tendency to absorb moisture. However, we prefer rigid foam insulation because it’s highly resistant to mould and water damage. Though fibreglass is a cost-efficient option, it can sag and fall out of place after a while because of its absorbing tendencies.

Unventilated Crawl Space

In areas with low flood risks, unventilated crawl spaces are preferred because they don’t cause immense heat loss in the winter like vented spaces do. Additionally, these crawl spaces are more affordable to insulate because you only have to insulate the walls without the ceiling.

Not only that, but unventilated crawl spaces are also safer during hot, humid conditions because they don’t circulate the humid air inside, so they’re less likely to cause a sharp rise in humidity.

The good thing about insulating unventilated crawl spaces is that you don’t have to separately insulate the pipes and ducts—you’ll be insulating the walls altogether.

Most people use fibreglass or foam to insulate these spaces, and it’s recommended to install a vapour barrier to keep moisture from moving to another place.

How to Tell If Your Crawl Space Needs Insulation

Since a crawl space is out of your sight most of the time, you won’t be able to tell whether it needs insulation unless you give it a once-over. Checking it for yourself can either urge you to start insulating quickly or decide to wait for a while — depending on the current state of your crawl space.

Here’s how to tell if your crawl space needs insulation immediately or if it can wait for some time:

Water Damage and Pest Infestations

The best way to tell if your crawl space needs insulation is to wear the oldest clothes in your wardrobe and get under there. 

Not the best way to spend your morning; we’ll give you that, but it’s necessary for the wellbeing of your house.

Using a flashlight, inspect the walls closely for signs of water damage. The most common sign is discolouration — it’ll come in the form of yellow, brown, or green stains on the crawl space’s walls. You may also notice peeling or bubbling paint. Other signs include a musty odour, which could indicate mould growth in the crawl space.

Aside from water damage, you’ll also want to look for signs of a pest infestation. If the humidity is too high in your crawl space, it can invite unwanted pests and insects inside. 

If you see any of these signs, you’ll have to start your insulation plans earlier than you intended.

Cold Feet

The good news about this part is that you don’t have to get inside the crawl space. This time, you’ll look for signs inside the comfort of your own home. 

Pay close attention to the temperature of your house’s floor. If it’s too cold under your feet, it possibly means your crawl space needs to be insulated. The same goes if the floor’s temperature changes from one room to another.

Additionally, if the floor is creaking a lot, and it has nothing to do with a loose board, it may mean the wood is contracting and expanding constantly due to temperature differences in the subfloor.

An Overworked Heating System

The lack of proper insulation in your crawl space can lead your heating system to be overworked. With drastic temperature changes and a substantial difference between the outside and inside temperatures, it’ll be harder to keep your home warm in the colder months.

Though this doesn’t necessarily mean your heating system will suffer, it does mean you’ll get higher energy bills. In the long run, you’ll also have to pay higher maintenance costs.

So, if your energy bills are getting higher, it’s time to check your crawl space for insulation.

How to Insulate Your Crawl Space: 5 Pre-Installation Steps

Before jumping head first into insulating your crawl space, it’d be wise to prepare first. You’re already working in a narrow, tight space, so it’s not an entirely foolproof process. You’ll want to be as prepared as you can to lower the chances of something going wrong.

Here’s how to prepare for insulating your crawl space:

  1. Review the building codes in your area before attempting to insulate your crawl space. In some areas, there’s a minimum R-value you have to fulfil for insulation. Some areas also dictate that the insulation must be fire-resistant.
  2. Choose the right material for the insulation. Fibreglass is the most cost-efficient option, but it’s a short-term choice because it sags after a while due to moisture. Rigid foam or spray foam would be the better option for most houses. You can also use fibreglass and cover it with rigid foam.
  3. If you have old insulation in your crawl space, you’ll have to remove it before attempting to install new insulation. If you leave it, you’ll be basically inviting mould and mildew to stay.
  4. Crawl spaces are no strangers to moisture and dampness, so chances are, your crawl space has some water spots that need dealing with. Before installing the insulation, use dehumidifiers or fans to dry out the entire crawl space. If there’s standing water because of rain or something else, it might be a good idea to use a sump pump.
  5. Lastly, make sure to measure every piece of insulation material and cut it accurately to make sure it fits. You’ll likely need different lengths because of pipes, dirt, etc. Measuring the pieces before starting helps you minimise faults.

How to Insulate Your Crawl Space in 5 Steps

Now that you’ve finished your preparations and cut your material, it’s time to start getting your hands dirty (literally and figuratively). Here are detailed steps for insulating your crawl space using foam insulation:

Step 1: Redirect Moisture

Even after you’ve dried your crawl space of any water spots or standing water, you need to make sure no water pools around while you’re installing the insulation. That’s why you should direct all downspouts away, or else you’ll end up with water on the foundation walls.

You can also use one of the oldest tricks in the book and use a shovel to move the soil against the exterior of your house away. That way, any water coming from the downspouts will move away without pooling against your foundation walls.

Step 2: Seal All Air Leaks

The first step in insulating your crawl space is to seal all air leaks inside and around it. Air leaks can alter the temperature inside your house, and they can cause water leaks if there’s plenty of rain. So, you’ll want to start with those.

To seal the air leaks, fill your caulking gun with exterior-grade caulk, then start piping the caulk into all the holes that could let air in. You can also use spray foam insulation if you want.

It’s worth noting that you should use a sealant for any water leaks first before using caulk or spray foam.

Step 3: Seal All Joists and Sills 

If there are visible cracks in your floor joists or sills, you’ll want to seal those using silicone caulk. Although tiny and mostly unnoticeable, these cracks can let moisture and air in if left for long enough.

It might be hard to locate these cracks with the dim lighting of crawl spaces, so you may want to try something else. During the day, go into the crawl space without a source of light and check for cracks letting through outside light. This should let you know the areas that need to be sealed.

Step 4: Install the Insulation Material

Now that you’re done with the sealing, it’s time for the real deal. Put on your mask, goggles, and protective clothing, and start attaching the cut pieces to the walls of your crawl space. You can use a latex adhesive for the job.

For insulating such a narrow area, it’s better to use larger pieces of foam to get as few seams as possible. If you already cut the pieces small, you can always seal these seams using PVC tape.

While installing the insulation, keep in mind that it should fit snugly between the joists without loose areas. You should also make sure to secure it around the common obstructions in crawl spaces, like electrical wiring and pipes.

Step 5: Install the Vapour Barrier

Some people prefer to install the vapour barrier before the insulation, but we recommend keeping it for last to be able to seal it to the wall insulation. We also recommend using polyethylene plastic sheeting because it allows for overlap and is generally pretty resilient.

The first thing you should do is lay the barrier over the crawl space’s ground, then start marking the areas with posts, piers, and other protrusions. After making your marks, cut out these areas, making sure to do it accurately so you don’t get unnecessary holes. After you’re done, seal them using butyl tape.

If you’re using multiple sheets for the vapour barrier instead of a single one, make sure to seal the seams as well.

Lastly, run the plastic barrier up the walls — around 10–12 inches — and tape the edges.

When to Call a Professional

Let’s face it; dealing with a crawl space isn’t something anyone likes to do. 

Between literal crawling, high humidity, and plenty of dust, it’s likely your least favourite area to deal with around the house. Not to mention, the idea of spending long hours on your knees in a place commonly known for hosting spiders doesn’t seem like a good idea.

Aside from that, insulating a crawl space isn’t a walk in the park. It’s not a complicated process, but it’s time-consuming and pretty challenging due to the limited space. If you’re not a DIYer, the insulation project may get out of control.

In this case, it doesn’t hurt to hire a professional to do the job for you. It may cost you more, but it’ll buy you peace of mind. And to make things easier for you, we can help you find the best contractors in your area with the click of a button.

Final Thoughts

If you don’t worry much about your crawl space, it might be time to start doing so. If there’s water damage, pest infestations, or leaks in your crawl space, it’ll affect your quality of living, the cleanliness of your house, and your energy bill.

It’s time to get proactive and insulate your crawl space before it starts causing you a headache.

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