How to Install Crawl Space Insulation: A Handy Guide

Crawl spaces are often forgotten about when it comes to home improvements, but doing so could cost you in more ways than one. Insulating your crawl space is well worth your time and effort, but how exactly can you do it?

In this handy guide to DIY crawl space insulation, we cover two possible ways to do it- and why it should be at the top of your to-do list.

Why Should I Insulate a Crawl Space?

First things first, why is it important to add insulation to crawl spaces below your property? Here is the answer.

• Floors often feel colder if the space below is uninsulated.
• It is harder to keep the downstairs areas of your home feeling warm and cozy without it.
• Your heating systems will have to work overtime and are unlikely to be able to run efficiently with cool air coming in through the crawl spaces.
• Moisture can also get into your floorboards easier if there is none, which can lead to dampness and mold.
• An insulated crawl space can save money on energy bills.

How to Insulate Your Crawl Space: Two Possible Methods

There is more than one effective way to add insulation to your crawl space:

• On the walls
• On the ceiling joists

Both have pros and cons but are doable. Here is a simple explanation for each method.

Insulating the Walls

This method is arguably the easiest of the two and requires the fewest tools and materials. However, it may not give you as much protection from cold air coming through the floorboards.

What Do You Need?

• Measuring tape
• Rigid foam board insulation
• Utility knife
• Waterproof glue or waterproof adhesive spray
• Waterproof tape

The Method

• Step One: Measure the height of your crawl space walls between the ground and the top. Bear in mind that they may not all be even, so take a few measurements in different places and work from the tallest height.
• Step Two: Measure the length of the walls from corner to corner, making sure you pull the tape tightly and get right into the corner for the most accurate measurement.
• Step Three: Buy enough rigid foam board to cover the entire area you just measured. It is important to choose one that is at least two inches thick and has an R-value (efficacy by climate) of 7.7 or higher. You can find it in most home improvement stores, and you don’t need to buy a vapor barrier because it already comes built in.
• Step Four: Use a utility knife to cut the foam board to shape. Be precise- it needs to fit your walls exactly, or the insulation won’t be effective. Make sure you cut in a single motion rather than a sawing action.
• Step Five: Coat the back of the foam board with waterproof glue and attach it to the wall. Press firmly to ensure a strong hold, and place the pieces as closely together as possible to avoid gaps.
• Step Six: Seal the joints with waterproof tape. Make sure it extends the entire length of the board. Otherwise, moisture can get in and ruin it. It needs to overlap the foam boards by at least one or two inches on each side.

Insulating the Ceiling Joists

Applying insulation to the ceiling of your crawl space gives you the best energy efficiency and heat control, but there is a bit more work involved to do it properly.

What Do You Need?

• Measuring tape
• Fiberglass insulation batts
• Protective gloves, goggles, and mask
• Utility knife
• Wire supports
• Wire cutters

The Method

• Step One: Find the total area of the crawl space ceiling by mearing its length and depth from corner to corner. Be precise- you need to cover every inch to have it properly insulated. You also need to measure the distance between the ceiling or floor joists to determine the size of panels you require.
• Step Two: Buy fiberglass insulation batts rated R-11 or R-25 (11 for most climates and 25 if you live somewhere that experiences sub-zero temperatures). You may be able to find ones that fit your joists, but if you can’t, buy a bigger size and cut them down.
• Step Three: Put on your protective gear- including a dust mask that covers your nose and mouth, safety gloves, and goggles. It is also best to wear long sleeves and full-length pants to avoid contact with your skin as much skin as possible.
• Step Four: Lay the fiberglass batts with the vapor barrier side up and cut them to fit your ceiling perfectly between the joists. Again, it is important to be precise and cut in slow, smooth motions using a sharp utility knife.
• Step Five: Push the insulation between the ceiling joists, keeping it as flat as possible but not compressing it. Remember to cut spaces for any plumbing or wiring.
• Step Six: Place wire supports horizontally between the joists to hold the pieces in place. These should be roughly 12 to 18 inches apart and stick directly into the wood of the joists. You may need to cut them a little, which is easy enough to do- just make sure they are long enough to firmly support the insulation.

A Few Other Considerations

Remember, insulation only works if you are precise and make sure every bit of exposed wall or ceiling is covered. It must be firmly secured but not compressed, and any gaps should be sealed.

You should never try to insulate a crawl space that has standing water or excess moisture. The risk is too high in terms of mold and rot damage spreading.

Final Thoughts

It is worth taking the time to insulate your crawl spaces, and these two methods are worth considering. There are other options using spray foam insulation, vent sealing, and other techniques, but these are a little more cost-effective and straightforward.

Of these methods, the first (choosing to insulate the walls) is cleaner and easier but not quite as effective. It is probably enough if you live in a mostly mild to warm climate. But to be sure, please consult with a trustworthy insulation contractor.

However, those who live in places prone to harsh winters and low temperatures are better off going for the second option. Working with fiberglass is a little trickier, but the method will make a bigger difference to the cold air and moisture getting into your home.

Either way, it does make a difference. You can test new features of your DIY skills and feel the difference the next time the temperature drops.

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