How to Insulate a Crawl Space (2023)

Insulation is important for keeping any home warm while controlling energy costs. One of the most important ways to keep your home warm is by insulating cinder block or concretecrawl space walls and sealing the floor. Correct crawl space insulation can prevent your crawl space from becoming a moist environment that grows and harbors mold and mildew. Controlling crawl space temperature and moisture is a dual process that works toward a common goal: a temperate lower area that will keep upper floors warm, while your home's foundation remains in sound condition.

Crawl Space Insulation Basics

The proper way for homeowners to insulate a crawl space is to insulate the walls and lay a vapor barrier on the ground.

Spray foam may be used by professionals, but most do-it-yourselfers lack the equipment or experience for working with spray foam. Instead, for do-it-yourselfers, the easiest type of insulation to use is rigid foam on the walls.

With a plastic vapor barrier on the floor, the two materials are joined with tape. It is important to seal any gaps or cracks in the walls before installing the insulation to ensure that it is effective.

Vapor barrier in crawl spaces is typically a thick plastic sheet that is used to prevent moisture from entering the crawl space and to help control humidity levels. The plastic is a 6 mil or thicker reinforced polyethylene plastic sheeting.


Stapling fiberglass batts between joists to the underside of your home's floor may help in the very short term. But moisture eventually builds in the crawl space and grows on this highly porous surface. Moisture-laden fiberglass will sag and fall. Adding fiberglass batts to open floor joists is an outdated method that is not just ineffective but regressive, as well.

With crawl space insulation, the idea is to condition the crawl space, much in the same way that you might condition other parts of your home. Rather than trying to cut off the crawl space from the conditioned upper floors, you should bring the crawl space nearer to the upper floor's temperature by leaving off the underfloor insulation, by insulating the walls and sealing the floor against outside moisture and temperatures.


  • Keeps pests out of home

  • Reduces moisture

  • Conserves energy

  • Adds dry storage space if you can access insulated space

  • Adds resale value

    (Video) Different Ways To Insulate Your Crawl Space


Rigid Foam Insulation Basics

Rigid foam insulation is a dense, stiff material made from polystyrene, polyurethane, or polyisocyanurate, and is known for its high insulation value and durability. It is the favored insulation for crawl space inside walls. Rigid foam insulation works for any type of masonry wall: concrete, block, brick, and even stone.

One of the main benefits of rigid foam insulation is its high insulation value, which means it is able to provide a high level of thermal resistance with a relatively small thickness. This makes it an efficient choice for many applications, especially in basement walls.

Rigid foam insulation is easy to install, as it can be cut to fit around electrical wiring and other obstacles. It is also resistant to moisture, pests, and mold, which makes it a durable choice for many applications.


Rigid foam insulation may be faced with silver foil, with the foil facing inward toward the crawl space. Though the rigid foam is the chief insulator, the foil adds a bit more energy savings by reflecting heat into the crawl space.

Crawl Space Ventilation

For this type of insulation system, crawl space ventilation to the exterior is sealed off. All avenues to the outside are shut off or sealed with caulk.

An airtight, insulated crawl space will make your house, as a whole, more energy-efficient by keeping your floors warmer in cool months and thus reducing your heating bills. During warm months, this process works in reverse by keeping your floors cooler and reducing the load on your air conditioner.

(Video) How to Insulate a Crawl Space with a Dirt Floor

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What You'll Need

Equipment / Tools

  • Caulking gun
  • Utility knife
  • Rake and shovel
  • Flashlight
  • Fine-toothed saw


  • Expanded polystyrene foam board
  • Construction adhesive
  • Latex adhesive for foam board
  • Silicone caulk
  • 6-mil minimum thickness clear polyethylene plastic
  • Double-sided butyl tape
  • Poly PVC tape
  • Foam insulation



  1. Prevent Moisture From Entering the Crawl Space

    Assess your crawl space and locate pooled water or any type of moisture that collects in that area. Redirect downspouts that may be forcing water alongside the foundation walls. With a shovel and rake, regrade soil banked up against the outside of the house, so that water moves away from the structure.

  2. Look at Interior Sources of Moisture

    Water can also come from within the house. Inside the crawl space, shine a flashlight around the underside of the house and look for water dripping down. Look at pipes running through or within joists. Pay special attention to areas of prevalent moisture on the floor above: dishwashers, showers, bathtubs, and sinks.

  3. Seal All Crawl Space Doors and Vents to the Outside

    On the outside of the home, seal up any vents, doors, or hatches that open into the crawl space. Load up the caulking gun with exterior-grade caulk and insert caulk into cracks and holes.


    In some areas where radon gas is a concern, the space shouldn't be completely sealed.

  4. Seal Rim Joists and Sills

    Go inside the crawl space during the day. Turn off the flashlight briefly and examine rim joists and sill areas for outside light shining through. With the light back on, seal up these cracks with the silicone caulk. For large cracks, use low-expansion foam insulation.

  5. Insulate the Crawl Space Walls

    Cut rigid foam pieces to size with the saw and attach the pieces to the inside crawl space walls with the latex adhesive. Aim for as few seams as possible by installing large sheets of foam. Seal seams between the boards with PVC tape.

  6. Lay the Vapor Barrier on the Ground

    Lay the vapor barrier over the entire crawl space ground area. Make cut-outs for every protrusion such as piers and posts. Run the vapor barrier up against these protrusions and seal them tightly with the butyl tape. Seal seams between separate vapor barrier sheets.

    (Video) Insulation Installation - R-Value In Walls, Attic, And Crawl Space (cost of material and labor)

  7. Seal the Vapor Barrier to the Wall Insulation

    Conclude by running the vapor barrier about 12 inches up the insulated walls and taping the edges to the wall insulation.


  • Should you encapsulate the crawl space?

    Not every crawl space should be insulated or encapsulated, and a crawl space or foundation specialist can help you decide. In addition, insulation (which helps warm the rest of the house by sealing air leaks) differs from encapsulation (which handles ground moisture). If you live in a humid area or flood zone, encapsulation may not be a good idea. For example, if you see large pools of water sitting in your crawl space, closing up the space will trap the moisture, causing more problems such as mold or structural rot. If you don't live in a humid region or flood zone but see standing water, mitigate the water before encapsulating the space.

  • How much does it cost to have a crawl space insulated by professionals?

    Depending on how big—and most specifically how tall—your crawl space is, it can cost several thousand dollars for a foundation servicing company to insulate it. Encapsulation is more costly.

  • Should you put plastic over insulation in a crawl space?

    The foam board for the walls is typically considered a vapor barrier, as well. But if you prefer a more aesthetic look, you can put a vapor barrier over the foam board, as well. Don't put a vapor barrier under the foam board, however, because it can become damaged or pierced when installing the foam board over it.

When to Call a Professional

While insulating a crawl space is not complicated, it is a labor-intensive, time-consuming project if you choose to do this yourself. The project can be especially difficult due to limited access to the crawl space.

(Video) How To | Total Crawl Space Encapsulation | Step-By-Step | My DIY Center

For this reason alone, many homeowners choose to hire an insulation company or a water infiltration mitigation company to make the repairs.

(Video) How to install Ceiling Insulation in a Basement or Crawlspace & why you should. R30, R21, R19, R13.


How to Insulate a Crawl Space? ›

The best way to insulate your crawl space when vented is to install fiberglass batt insulation in the sub-floor. This way the sub-floor becomes the thermal break to help keep the cold crawl space air from transferring to the living space. Closed crawl spaces keep cold and hot air out.

How do you insulate an unheated crawl space? ›

Best Practice: Install crawl space vent covers on the outside of the vent openings of the encapsulated crawl space. Seal the rim joists with rigid foam board insulation and use foam sealant to seal the opening between the top of the crawl space wall and the sill.

What is the cheapest way to insulate a crawl space? ›

Insulate Under Floor: Fiberglass insulation batts or rolls are the most economical and easiest DIY choice for insulating between the floor joist in a crawl space. The U.S. Department of Energy recommends R-11 (3½”) insulation under floors in warm climates and an R-25 (6” to 8”) in cold climates.

Should you insulate crawl space under house? ›

Crawl space insulation is just as important as wall insulation. Insulation beneath the floors of your home and along foundation walls can help improve energy efficiency and preserve your home's air quality.

What is the best way to insulate a crawl space with a dirt floor? ›

What is the best way to insulate a dirt floor crawl space? To hold back the moisture from making its way into the air in your crawl space and eventually into your home, the best way to 'insulate' is through a process called crawl space encapsulation. Insulation is just one part of the encapsulation process.

What is the best insulation for unheated crawl space? ›

Foam, not fiberglass, is the right choice

The best insulation material for crawl spaces is rigid foam insulation board. Instead of installing the foam insulation between floor joists in the crawl space, we install the foam board against the crawl space foundation walls.

Can you insulate a crawl space yourself? ›

Insulating Open Crawl Space

The best way to insulate your crawl space when vented is to install fiberglass batt insulation in the sub-floor. This way the sub-floor becomes the thermal break to help keep the cold crawl space air from transferring to the living space. Closed crawl spaces keep cold and hot air out.

Will insulating crawl space make house warmer? ›

Crawl space encapsulation along with insulation will make your home drier and warmer during the winter. While crawl space encapsulation along with a dehumidifier will make the air in your home cleaner and drier, adding an insulation vapor barrier as well will make your home warmer.

Should a crawl space be vented? ›

Building codes generally require working vents in the crawlspace to allow outside air to circulate under the floor in the summer to prevent moisture buildup that, among mildew and mold, encourages wood rot.

Is it worth insulating crawl space walls? ›

Crawl Space Insulation is Key to Energy Efficiency

The short answer is YES you should insulate your crawl space IF you want to make your home MORE energy efficient.

Is it better to insulate attic or crawlspace? ›

Most people understand the need for insulation in the attic and exterior wall spaces, but they often forget that insulation is necessary for crawls spaces as well. These wide-open spaces – many of which are ventilated – can act like heating/cooling vacuums when they aren't adequately insulated.

Is it worth insulating under the floor? ›

Insulating your ground floor is a great way to keep your property warm. Generally speaking, you only need to insulate the ground floor. If you're on an upper floor, you don't usually need to insulate your floor space.

Is spray foam good for crawl space? ›

The Building Science Corporation recommends spray foam for the crawl space no matter which installation method is used. This is because the insulation material creates an air barrier that will work to make your home more energy-efficient and comfortable.

What happens if you don t have a vapor barrier in a crawl space? ›

Oftentimes, moisture can seep through the dirt floor of your crawl space when you do not have a vapor barrier installed. Additionally, poor grading and improper vapor barrier installation can lead to rainwater leaking into your crawlspace, causing a huge standing water issue.

What material to insulate crawl space? ›

The two materials considered the best crawl space insulation are fiberglass and spray foam.

Should you insulate the ceiling in a crawl space? ›

Your approach to insulating your crawl space is going to depend on whether it's vented or not. If vented, the crawl space ceiling's floor joists should be insulated, protecting the floor above; if unvented, the crawl space walls should be insulated to keep the entire space warmer.

How do you insulate between floor joists in a crawl space? ›

Fill the ends of joist bays with rectangles cut from rigid board insulation. Use foam sealant, such as Great Stuff, to seal the joints. Use caulk or foam sealant to seal the joint between the top of the crawl space wall and the sill.

Does rigid foam insulation need to be covered in crawl space? ›

It is not necessary to apply insulation to the underside of the floor above a closed crawlspace because the rigid foam board insulation applied to the walls provides the necessary thermal protection.

Should crawl space insulation be faced or unfaced? ›

With a ventilated crawl space, unfaced insulation is the best choice. Unfaced insulation does not have the vapor barrier that faced insulation does. It's important to secure insulation and cover it with a vapor barrier in order to prevent the harmful effects of moisture and mold.

What kind of foam board for a crawl space? ›

Bora-Foam insulation is the best foam insulation board for closed crawlspaces, the most effective, and easiest to work with. It is a highly effective vapor barrier because it has 3 mil poly on each side of the board.

Should you insulate crawl space vents in the winter? ›

It is always a good idea to block the vents when the crawl space has uninsulated water supply pipes if the temperature gets below freezing. Frozen, busted pipes result in paying for plumbing repairs and possible water damage.

How does crawl space stay warm in winter? ›

The recipe for having warm floors over a crawlspace is not a huge secret. Install a vapor barrier over the crawlspace floor, block and air seal the foundation vents, and insulate the foundation walls.

Is it better to seal or unsealed crawl space? ›

The closed-versus-vented question

Closed or “encapsulated” crawlspaces are now preferred to open, or vented, crawlspaces. Closed crawlspaces are consistently better at controlling moisture that enters via the damp earth or from warm humid air that would otherwise infiltrate from the outdoors.

Should I keep my crawl space vents open or closed? ›

Most people prefer to close vents in the winter so that the pipes in the crawl space don't freeze. If you have a dirt floor crawl space and keep your vents open throughout the year, the floor will become a never-ending source of moisture.

Should crawl space be sealed or vented? ›

Because much of the air you breathe in your home comes directly from your crawl space, most contractors today agree that the crawl space should be treated as part of your living area—in other words, it should be sealed, insulated and kept free of moisture.

How do you insulate an old house without tearing down walls? ›

How to Insulate Walls in an Old House
  1. Apply a house wrap/vapor barrier to exterior walls.
  2. Attach 1-inch foam board insulation.
  3. Install siding over the insulation.
  4. Replace old windows with energy-efficient units.
  5. Caulk window trim and use weatherstripping to reduce air leaks.

Where is the most important place to insulate a house? ›

Arguably the most important space in the home to insulate is the attic. This is primarily because heat naturally rises, which means that the attic will hold a lot of the heat generated in the home. During the winter, having that heat escape through the attic will push up energy bills.

Should I insulate between 1st and 2nd floors? ›

The best way to prevent unwanted heat loss and gain is to use insulation throughout the home, including between floors. Mid floor insulation can reduce heat loss and gain between the different levels of your home, creating climate zones.

Which is the best underfloor insulation? ›

Here's a list of the five best underfloor insulations to keep your home warm.
  • Rigid Expanded Polystyrene Panels. The Rigid Expanded Polystyrene Panels or EPS panels are quite famous in the insulation industry. ...
  • Foam Board. ...
  • Polyester Rolls. ...
  • Fiberglass Batt. ...
  • Zig-Zag Foil Sheets.
Nov 22, 2022

What is the cheapest way to insulate a floor? ›

Fiberglass batt and foam board insulation are the two most popular types of insulation for floors for DIYers because of their ease of installation compared to other materials. Both fiberglass batt and foam board typically run cheaper than spray foam.

Does floor insulation need a vapor barrier? ›

After the insulation is in place you will want to add a vapor retarder, sometimes called a vapor barrier, if you need one. Not every wall does. A vapor retarder is a material used to prevent water vapor from diffusing into the wall, ceiling or floor during the cold winter.

What is the R value of a crawl space? ›

Where you live matters
ZoneR-value recommendations for crawl spaces
2R13 to R19
3R19 to R25h
4R25 to R30
5 to 8R25 to R30
1 more row
Nov 8, 2021

How many inches of spray foam do I need for a crawl space? ›

Be sure to cover all seams to air seal and coat the band joist with 1-2 inches of crawl space spray insulation foam. Closed cell crawl space foam insulation also creates a moisture barrier and helps prevent condensation.

Should I spray foam between floor joists? ›

It does not have to be sprayed between joists like fiberglass batting, because it completely blocks air flow at the outside perimeter. Spray foam can also be used to seal off crawl space vents for encapsulation. To insulate crawl space walls, we recommend a blanket insulation product like radiant armor.

Is spray foam or rigid foam better for crawl space? ›

Spray foam insulation is the best insulation for crawl spaces. It provides a tight, air-sealed barrier in crawl spaces to prevent air and moisture from entering your living area.

Can I put new vapor barrier over old in crawl space? ›

Our best practices are that the old vapor barrier is left in place and the new one is placed over it. The old barrier even if it does not cover the entire crawl space serves to provide some additional moisture blocking and also help protect your new vapor barrier from any rocks or debris on your crawl space floor.

What is the plastic sheeting in a crawl space? ›

A vapor barrier is a plastic liner that covers the dirt “floor” of your crawl space. Its purpose is to block vapors and moisture in the soil from getting into your crawl space. This is important for two reasons: The air in your crawl space gets into your home.

How often should you replace the vapor barrier in a crawl space? ›

When properly installed, a vapor barrier should last twenty years or more.

Is it OK not to insulate crawl space? ›

International residential building code requires a crawl space to be insulated. If the crawl space is open or vented, it needs to be insulated. If the crawl space is encapsulated, it needs to be insulated.

How do you encapsulate a crawl space in a cold climate? ›

Seal the Crawl Space

Start by encapsulating the crawl space area. This entails covering the dirt floor and walls with a thick 20-mil plastic vapor barrier. The polyethylene material goes over obstacles and beams then sealed at the seams with a special tape. Gaps that exist along rim joists are carefully sealed.

How do I add heat to my crawl space? ›

HOW TO CREATE A HEATED CRAWL SPACE? You'll need to properly close off the venting to the outside, insulate your foundation walls, to seal all air leaks, and supply some heat to the crawl space. A heating duct and cold-air return will balance out the air exchange to and from the crawl space.

Should I use spray foam insulation in my crawl space? ›

The Building Science Corporation recommends spray foam for the crawl space no matter which installation method is used. This is because the insulation material creates an air barrier that will work to make your home more energy-efficient and comfortable.

Is it worth insulating the crawl space? ›

According to the Environmental Protection Agency (EPA), insulating a crawl space can save you an average of 15% on your energy costs. Insulating the crawlspace also insulates your home from extreme weather conditions like heat waves or cold snaps.

Is it better to insulate attic or crawl space? ›

The answer is, you should do both. The average home needs to be insulated high, middle, and low. All three areas are important. This means you need to have attic insulation, wall insulation, and basement or crawlspace insulation to produce the greatest level of comfort and energy.

Should I insulate crawl space walls or ceiling? ›

If vented, the crawl space ceiling's floor joists should be insulated, protecting the floor above; if unvented, the crawl space walls should be insulated to keep the entire space warmer.

Why not to encapsulate crawl space? ›

Are there any negatives to crawl space encapsulation? The only downside is that it can be costly since it's a major home renovation. It costs about $5,500 to encapsulate the crawl space of an average American home, but it can go as high as $15,000. Home upkeep costs could also go up due to additional maintenance.

When should you not encapsulate a crawl space? ›

Bulk water problems. The first sign that you shouldn't encapsulate a crawl space is standing water, as in the photo below. If bulk water is coming into the crawl space, covering it up with plastic is may be worse than doing nothing. That water is probably going to find ways to get on top of the plastic.

Should the vents on a crawl space be covered in the winter? ›

Closing crawl space vents in the winter is a good idea, especially if you have plumbing or air ducts in the crawl space. Unfortunately, just closing or covering crawl space vents for the winter isn't the cure-all for cold floors, frozen pipes, and pests.

Why is my crawl space colder than my house? ›

Air circulation means the crawl space will always be considerably colder than the rest of the house. So you will still need to run your air conditioner and heater — but not for long if the crawl space is encapsulated and conditioned.

When should you not use spray foam insulation? ›

DON'T use expanding foam around outlets and recessed can lights. In the quest for a draft-free home, it's natural to want to add some insulation around electrical outlets, but expanding foam might not be the best type of insulation there.

Can I spray closed foam under the floor in a crawl space? ›

Spray foam is more expensive than fiberglass, so it may not be an economical choice for your entire home. But we strongly recommend you replace any fiberglass insulation in your crawl space with spray foam. Spray foam insulation is a mixture of chemicals that are applied to a surface.


1. Best Insulation Methods for Crawl Spaces Based on Research Study
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2. Insulating Crawl Spaces
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3. How To Partially Encapsulate a Crawlspace | Lowe’s Pro How-To
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4. How to Install Insulation Yourself! | DIY Insulation Tutorial
(Home RenoVision DIY)
5. Crawl Space Insulation
(Basement Systems, Inc.)
6. Should You Insulate Your Crawl Space? - Jim Dutton
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