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Does a Crawl Space Really Need Insulation?

Does a Crawl Space Really Need Insulation?

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Most new houses don’t have crawl spaces. Instead, they have basements or cement slabs. However, about 15% of America’s houses still have them. That’s almost 27 million houses.

So, does crawl space need insulation? After all, it’s a part of the house. Right?

Yes, crawl spaces need insulation, especially in big houses. In fact, it’s crucial to insulate your house’s crawl space for many reasons. The most important of which is saving energy.

Keep reading to know more about crawl space insulation, why it’s important, and what type of insulation is best for your crawl space.

Why Insulate a Crawl Space?

Insulating crawl spaces is mandatory according to international residential building codes. However, before 1990 building codes didn’t mandate insulation for crawl spaces.

One of the most important reasons you need to insulate your house’s crawl space is energy efficiency. The cooled or heated air inside your house can easily escape through the floors.

Therefore, insulating your crawl space, whether it’s vented or encapsulated, will help reduce the energy bills, as well as increase the air quality inside your house.

A crawl space forms a perfect environment for mold and pests to grow because it’s usually damp. That’s why it’s best to keep it moist-free, dry, and tightly sealed.

What Type of Insulation to Use for Crawl Space?

The type of insulation for your house’s crawl space depends on many factors. Two of these factors are the climate zone and the type of crawl space.

Choosing to keep your crawl space vented or encapsulated would affect the type of insulation that’s best for the area.

Preparing the Crawl Space

Before insulating your crawl space, you first need to prepare the area. Preparing the crawl space includes mitigating radon, blocking the moisture, and sealing the floor.

You need to install a radon ventilation pump to mitigate the dangerous radon gas seeping through the soil and into your house.

Similarly, to mitigate moisture, make sure that the gutter drainage pipes don’t come in contact with the house’s foundation.

Additionally, covering the entire floor with a plastic barrier that goes up the wall at least 6 inches helps with moisture control.

Vented Crawl Spaces

If your crawl space is open or vented, then you need to insulate the subfloor because those vents allow the outside air and temperature into the crawl space.

Installing fiberglass batts between the floor joists is the best solution for insulating your house’s subfloor. Additionally, you can see fiberglass insulation in most old houses’ walls and attics.

Make sure to seal any gapping around wiring or plumbing fixtures with spray foam or caulk.

Encapsulated Crawl Spaces

If your crawl space is sealed, then insulating the walls and foundation would be better and more cost-efficient. Consequently, you won’t need to insulate ducts and pipes individually.

The best choice for insulating the walls is installing foam boards.

What is R-value for Insulation?

R stands for resistance. The R-value is a number that indicates how well the material can resist heat. The higher the R-value of the material, the better the insulation is.

The R-value doesn’t apply accurately to the loose or blown-in insulating material. It’s more accurate for insulating materials like fiberglass or mineral wool.

That’s because the R-value depends on the thickness and density of the insulating material, which varies when it comes to loose insulation.

For example, fiberglass has an R-value of 3.7 per inch. That means that a 5-inch thick fiberglass batt has an R-value of 18.5.

Moisture and aging also can affect the R-value of the insulating material. So, don’t expect your insulation to work optimally if it’s not compatible with your house’s moisture level.

What R-value Insulation Do I Need for a Crawl Space?

The minimum recommended R-value for a crawl space is R-13. Consequently, the more cold the area you live in is, the more R-value you’ll need for insulation.

So, if you’re living in climate zone 1, R-13 insulation is just okay. For zone 2 and 3, the R-value recommended can go up to R-19 and R-25, respectively.

Similarly, the minimum recommended R-value for insulating your crawl space in zone 4, 5, 6, and 7 is up to R-30.

What Is Fiberglass Insulation?

Fiberglass is a plastic-based material that’s reinforced with glass fibers for additional strength and insulation capacity.

Pros of Fiberglass Insulation

  • Fiberglass insulation is inexpensive compared with other materials.
  • Fiberglass insulation is easy to install. So, it doesn’t require a professional to do it.
  • Fiberglass comes in batts or rolls that are suited for standard joist spacing.

Cons of Fiberglass Insulation

  • Although fiberglass insulation doesn’t absorb moisture, it holds it. Unfortunately, that can eventually cause it to sag away and droop. Not to mention causing your floors to dampen.
  • Fiberglass, when moist, can cause mold growth. Additionally, damp floors attract insects like termites.
  • Fiberglass insulation forms a suitable environment for rodents to nest in.

Can You Use Spray Foam Insulation in a Crawl Space?

Yes, spray foam insulation is commonly used to insulate the subfloors of crawl spaces.

Spray foam insulation is made by combining two components to form a sprayable foam. Once you spray it over surfaces, it expands and fills every gap. Eventually, it hardens to a solid state.

Pros of Spray Foam Insulation

Just as any other insulating material, spray foam has some advantages. Here are the pros of using spray foam for insulating your crawl space:

  • Spray foam insulation gets to the smallest gaps and cracks, blocking any leaks from the outside. Therefore, it helps maintain a warm floor in cold weather.
  • Spray foam insulation has a long life extending to over 80 years because it adheres so well to the surface.
  • Spray foam insulation has a higher R-value than fiberglass, which makes it perfect for colder zones.
  • Since spray foam hardens after drying, it doesn’t offer a comfortable nesting place for rodents and pests.
  • Spray foam insulation repels moisture, preventing mold growth and moisture from damaging the wood floors.
  • Spray foam insulation completely seals your crawl space, which enhances the air quality inside your house.

Cons of Spray Foam Insulation

Having so many qualities doesn’t make spray foam insulation flaw-free. Here are some of the drawbacks of using spray foam for insulating your crawl space:

  • Spray foam insulation isn’t cheap. When compared with fiberglass, spray foam insulation is much more expensive.
  • Spray foam insulation is there forever. It’s permanent. So, if you need to remove it for any reason, it’s not going to be easy.
  • If sprayed over moist or moldy wood, spray foam can trap both moisture and mold inside, which is not good in the long run.

Should You Use Faced or Unfaced Insulation in a Crawl Space?

Insulating batts come in two varieties, faced and unfaced. Faced insulation means that the insulating material has a face on one side, which is made of paper, plastic, vinyl, or foil.

It’s recommended to use faced insulation in your crawl space subfloor because that layer acts as a moisture barrier.

Additionally, when insulating the walls of your crawl space, you should use faced insulation only if you’re living in a climate zone that requires a moisture barrier.

The only case you shouldn’t use faced insulation is when you’re adding a layer to the currently existing insulation to increase the R-value.

Which Way Should Insulation Face in a Crawl Space?

Generally, you should lay the faced side of the insulation closest to the living space. It means that when insulating your crawl space, you should lie the insulation faced side up.

However, in some cases, like living in an area with really hot summers and mild winters, it’s the other way around.

That’s because the faced side should always face the warmer area to prevent heat and moisture from seeping through.

That’s why you should consider the climate when insulating your crawl space.

What Is Blown-in Insulation?

Blown-in insulation, also known as loose-fill insulation, is any insulating material that is loose and has a high R-value.

Various materials are used for blown-in insulation, like loose fiberglass, styrofoam pellets, or, most commonly, cellulose.

Blown-in cellulose insulation is made from a mix of recycled paper, wood, and cardboard. It gets treated to be flame and mold-resistant.

That insulation material is fluffed and blown using specialized, really expensive machines, which you can rent.

Can You Use Blown-in Insulation in a Crawl Space?

Blown-in insulation is perfect for insulating the attic and walls of the house. However, when it comes to crawl spaces, it’s not recommended to use that kind of insulation.

Blown-in insulation absorbs moisture easily, even when a vapor barrier is installed. Additionally, it’s much heavier than fiberglass, which makes it prone to sagging.

Final Thoughts

Does crawl space need insulation? There’s no doubt that it does. The question is what type of insulation to use for it.

It all depends on the area you’re living in. Does it get really hot in the summer? Does it freeze in the winter? It also depends on whether the crawl space is vented or unvented.

Some types of insulation are easy to install. However, if you can’t do it yourself, hiring a professional is always a good idea.


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