Crawl Space Insulation: The Definitive Guide

There are currently over 27 million homes in the United States with crawl spaces. Crawl spaces are unique structures placed under the house but over the ground to provide the owners with living areas on level ground, untouched by moisture and other elements.

They provide enough and more space as a buffer between the ground and the house and provide access to plumbing, electrical wirings, heating systems, and cooling systems without excavating beneath the house.

The question remains that even when you have insulated all over your house, if the crawl space is left, the house is still exposed to the elements from the ground and can cause problems such as moisture content seeping into the home.

It is also possible that even after continuously working your heating systems in your insulated home, if your feet are still cold, then it might be due to the lack of insulation in the crawl space of your home.

Crawl Space Insulation

Generally, considering just the energy efficiency of one’s home, it is recommended and a worthy investment in insulating the crawl space.

However, before you go rushing off to pick insulation, many factors, such as the size and accessibility of your crawl space, must be studied carefully to make an informed decision.

In this article, we will look into the various aspects of insulation for crawl space under the house and explore some of the best methods to do so.

Should you insulate the crawl space under the house?

Should you insulate the crawl space under the house

Crawl space under the house is a general-purpose place whose utility is defined by the user. It is like a basement of sorts and is often considered a viable alternative to basements.

It can be used for storage purposes, if maintained well, and can house the heating and cooling systems of one’s home since all the vents can be accessed through the bottom of the building without hassle. It can also house the plumbing, electrical wiring etc., without excavating into the ground.

Insulating your crawl space is more of a personal choice than a general one. One must weigh in all the pros and cons of the utility of the crawl space and weigh it against the merits and demerits of an insulated crawl space, and see which is better.

Insulated crawl space regulates the temperature and provides ambiance without the need for the operation of heating/cooling devices. However, you may have to give up the space, and it can’t be used for storage purposes anymore.

Suppose you’ve insulated your entire home with premium solutions and still the cooling and heating systems struggle to maintain an ambient temperature in your home. In that case, the chances are that the crawl space sees a lot of energy leakage and causes your energy bills to skyrocket. If you don’t use your crawl space for storage purposes, you can consider the space for insulation.

Should you insulate a vented crawl space?

Should you insulate a vented crawl space

Now, the question arises where there is a vented crawl space. Should I insulate my already vented crawl space?

The crawl space with sufficient ventilation is ideal for insulation purposes, as it helps remove moisture content and makes the installation of the insulation under the subfloor and between the joists of the floor all the easier. However, the insulation must be protected using a vapor barrier to secure it from the formation of mold and mildews.

It is also recommended that a vapor barrier of polyurethane be installed over the dirt floor to protect the insulation from the elements further. Any DIYer homeowner can typically do crawl space insulations without experience, but it is recommended to approach a professional for better efficiency and good finishing. They are well suited to handle or dispose of the existing insulation and disinfect the place so that microorganism doesn’t tamper with the new insulation.

What kind of insulation do you use in a crawl space?

What kind of insulation do you use in a crawl space

Now that you have made up your mind about insulating the crawl space under your house let’s discuss the material of insulation one should choose.

The primary concern for any insulation solution is the efficiency of insulation. Nevertheless, it is only one factor to consider. The expectations and priorities of each homeowner for an insulation project might be different. Some might opt for a greener solution, whereas some might opt for the best performance. Also, the installation cost is another driving factor that determines the insulation material.

Let’s look at some of the best insulation solutions suited for crawl spaces available in the market currently.

Foam Board

Foam Board

Rigid foam insulation or foam board insulation is one of the best choices for crawl space insulation. This is because the foam board insulations available in the market are mostly waterproof. Rigid foam insulation comes in different varieties depending on the manufacturer and the material used to make it. The most commonly used materials are extruded polystyrene, polyisocyanurate, expanded polystyrene, etc.

Rigid foam insulation offers one of the best R-values per inch. Generally, the R-value of rigid foam boards varies from 1-15 and mostly depends on the material used, the thickness of the board, and the number of layers used. Rigid foam boards are well suited for enclosed, tight spaces, and thus, it is a perfect candidate for insulating crawl spaces.

Spray Foam

Spray Foam

Crawl spaces in your home might not be big enough to enter, and it can get quite difficult to reach corners or too deep into the center of the house. In such cases, spray foam provides a viable alternative for conventional insulation solutions. Spray foam consists of isocyanate and resin and expands after being sprayed to take shape and fill the space. Spray foam can expand upto 60 times the volume of the starting volume.

Along with being a good insulator, it also creates air-tight seals. It hence allows you to maintain more stable temperatures inside your home without having to overwork the heating/cooling devices in your home. There are two varieties of spray foam; open-cell and closed-cell.

Spray foam insulation is a versatile solution and can fill in hard-to-reach places in your crawl space, and it is water-resistant and makes for a great insulating seal. Spray foam typically offers an R-value of 3.8 per inch.

Cellulose (Batt/Loose-fill)

Cellulose (Batt or Loose-fill)

Cellulose is available in batts and loose-fill form and can be used according to your crawl space requirements. It is a mixture of paper and other renewable materials and eco-friendly insulation material. An advantage cellulose insulations have over fiberglass is that paper-based cellulose is waterproof, whereas fiberglass is not, making it more suited for crawl space insulation.

Loose-fill cellulose is exceptionally suited for hard-to-reach places and can be installed with the help of machinery for maximum packing efficiency. It can also be used to cover spaces or cracks crevices inside walls. Cellulose insulation is also available in wet-spray foam and acts similarly to open-cell spray foam. It can go a long way in preventing moisture content-related problems.

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How do you insulate a crawl space under a house?

Let us look at how to insulate a crawl space.

Prevention of Moisture

The first thing to keep in mind while insulating crawl spaces is to remove all sources of moisture, both internal and external. This includes leaks in the plumbing to possible cracks on the wall, which will allow moisture to enter. Redirect all possible sources of water away from the structure. Also, check for leaks and moisture content anywhere in the house.

Sealing off exits and vents

This is important. We don’t want the installed insulation exposed to the elements. Make sure that the rim joists and sills are well sealed. A way to do this is by examining light passing through the rim joists and sill areas in the morning. Seal up all cracks using caulk or foam insulation.


You can use the insulation of your choice, may it be rigid foam panels, fiberglass, spray foam, etc. and attach it to the inside of the crawl space walls using adhesives. When it comes to batts or rolls, make sure to use as little seam as possible to have higher insulation efficiency.

Vapor barrier

For the last step, we have to make sure that the vapor barrier is placed over the entire ground area and the crawl space. Take accurate measurements for cutting out pieces to fit in protrusions. Once you are done, seal the entire barrier with butyl tape.

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

To answer the question, the best way to insulate a crawl space with a dirt floor is by insulating the entire dirt floor with a vapor barrier to prevent the moisture content from reaching the insulation and the subfloor of the house. If you want your crawl space vented, you can opt for fiberglass insulation with a spray foam mixture if you need air sealing.

The dirt on the ground can act as a retardant in the efficiency of fiberglass insulation over time, as it accelerates the sagging and shifting process of fiberglass. However, sealing off all sills and rim joists will grant you a higher insulation efficiency as it prevents the entry of external moisture and temperature.

Things to Consider When Insulating Your Crawl Space

When you’re planning to insulate your crawl space, many factors to consider. These factors can help you determine whether insulating your crawl space is a worthwhile investment. They include:

Vented or Unvented

There are two types of crawl spaces; vented and unvented. The crawl spaces are often left unfinished in some cases, while some crawl spaces feature ventilation built into the wall foundation. Vented crawl spaces can carry moist air in and out and cause temperature leakage to and from your home. Insulating vented crawl spaces can provide you with a stable temperature.

Crawl Space Size

The crawl space size of your home matters as it is directly related to the amount of dissipation of energy. Larger crawl spaces can cause much more energy leakage and be considered for insulation. The smaller crawl spaces that you can barely wiggle into aren’t likely to contribute much to energy leakage.


Crawl spaces can be uneven, which can lead to insulation problems. If movement through the crawl space is restricted, installation can get tricky and even impossible at times.


Water content present in the crawl space due to external sources and leakage in the internal plumbing can contribute to inefficiency in temperature control. Ensure to seal up all leaks and insulate the rim joists and sills to prevent moisture and water content entry.

Vapor Barrier

A vapor barrier is required in dirt floor crawl spaces to create a layer of damp-proof insulation to prevent moisture content from seeping through. The vapor barrier should be laid in the crawl space ground floor to prevent the moisture content from reaching the floor of the house.

Seal Vents

Sealing vents can help restrict the entry and exit of moist air and, with it, the growth of molds and mildews. Moist air passing in and out of crawl spaces can facilitate heat transfer and result in temperature variations inside the home. This can be prevented by sealing vents using spray foam or rigid foam boards.

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Final Thoughts

In this article, we have discussed how to insulate a crawl space, the factors to consider while insulating a crawl space, and familiarized ourselves with some of the best insulation options for insulating crawl space. We have presented all the facts and comparisons comprehensively so that the reader can make an informed decision regarding insulating their crawl space.

Keep in mind that insulating a crawl space is a personal decision, and it depends on various factors discussed above. Insulated crawl spaces will provide better temperature regulation and make your home more comfortable and cozy.

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