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Crawl Space Insulation: How to Choose the Right R-Value

New house under construction with rockwool insulation material

Most homes are built with a crawl space, which is the area between the ground and the first floor. Crawl spaces can be vented or unvented, but most homes have a vented crawl space. While a vented crawl space is intended to keep the area dry and free of moisture, it can also lead to problems with drafts and energy efficiency. 

What Is R-value?

When it comes to insulating your home, one of the most important things to know is the R-value. But what is the R-value? Simply put, R-value is a measure of a material’s ability to resist heat flow. The insulating qualities improve with increasing R-value. That’s why it’s important to choose materials with a high R-value for your home’s insulation.

Why is it Important?

Choosing the right R-value can be tricky because different areas of the country require different R-values to meet energy efficiency requirements. For example, a home in Florida will have much lower insulation requirements than a home in upstate New York. 

You also need to consider your home’s location, the climate, and how well your home is insulated. More insulation is required in colder climates than in warmer ones, and older homes are generally less insulated than newer homes.

 Professional worker man installing thermal insulation rock wool in the crawl spaceDifferent Types of Insulation And Their R-values

There are many types of crawl space insulation, but only a few are commonly used. The three most common types are:

  • Fiberglass is the most common type of insulation. It comes in rolls or batts and is made of glass fibers. The R-value of fiberglass ranges from 2.2 to 2.7 per inch.
  • Cellulose is another common type of insulation. It is made from recycled paper products and has an R-value of 3.2-3.8 per inch. Cellulose is available in loose fill or batts.
  • Although spray foam insulation is the priciest, it also offers the best insulation performance. Spray foam has an R-value of 3.6 to 3.9 per inch and can be sprayed into place using a special machine.

How to calculate the R-value you need for your crawl space?

When most people think about insulating their homes, they tend to focus on the attic and exterior walls. But your crawl space is another important area to consider when it comes to energy efficiency and comfortable indoor temperatures. Here’s a quick peek at calculating the R-value you need for your crawl space insulation.

The first step is to determine the square footage of your crawl space. Once you have that number, multiply it by the recommended R-value for your climate zone. This will give you a good starting point for how much insulation you need to purchase.

Keep in mind that the type of insulation you use will also play a role in the overall R-value. For example, fiberglass batts have a lower R-value than spray foam insulation.

Why is it Important to Keep My Crawl Space Dry?

Crawl spaces are humid by nature. The soil surrounding your foundation is constantly evaporating moisture, which then works its way into your crawl space. This process can lead to mold and mildew growth and even structural damage if left unchecked.


A home is a significant investment, and protecting that investment should be a top priority. One often-overlooked area of the home is the crawl space. Many homeowners are unaware of the importance of insulating and sealing the crawl space and the risks associated with not doing so.

Because they are frequently damp and humid, crawl spaces can support the growth of mold and mildew. By taking the time to insulate your crawl space, you can avoid these problems and keep your home comfortable and efficient.