Crawl Space Insulation - Process, Tips and FAQs

License #1035247

CALL NOW! San Diego: 858-246-7421 or Orange County/Los Angeles: 714-769-0228

License #1035247

CALL NOW! San Diego: 858-246-7421 or Orange County/Los Angeles: 714-769-0228

How to Insulate a Crawl Space

A crawl space without insulation is a constant source of moisture. The humidity from the ground around your home will evaporate upwards, leading to condensation on your walls and joists. Over time, the humidity will encourage mold growth.

The mold spores, humidity, and accompanying odor can ruin the air quality in your home. Your heating and cooling systems will also have to work harder in this situation. This article will cover how to insulate a crawl space ceiling and floor to prevent these issues.

How To Insulate A Crawl Space Ceiling

Crawl Space Insulation Basics

The first thing you should do when looking for how to properly insulate a crawl space is to look beyond fiberglass batts. They work in certain applications but rarely as a standalone solution. Stapling the batts underneath the first level floor as your only insulation is impractical due to the composition of the material.

Over time, the humidity in your crawl space will build up moisture in the batts, making them weak. Instead of stapling fiberglass batts to the underfloor, you need to adopt a more effective, multi-faceted approach.

Types of Crawl Spaces

The two main types of crawl spaces include:

Vented Crawl Spaces

These crawl spaces have air vents located at the top of the foundation wall. The vent positioning allows outside air to flow in and out of the space.

Sealed Crawl Spaces

A sealed crawl space doesn’t have any wall vents. Therefore, air from outside cannot enter the space. However, sealed crawl spaces still require insulation to protect against moisture from the ground and foundation walls.

The Crawl Space Insulation Process

Some people start out looking for how to insulate a crawl space ceiling or how to insulate a crawl space floor separately. However, as mentioned above, you must do both if you want the best results.

Before you begin the process, you must first gather the necessary tools and materials for the job. Some of these include:

  • A fine-toothed saw
  • A caulking gun
  • A shovel
  • A rake
  • Utility knife
  • Caulking gun
  • Insulation foam board
  • Foam insulation
  • Adhesives
  • Butyl and polyvinyl tape

The insulation process is as follows.

Step One: Check for Possible Moisture Sources

Examine the crawl space for water pooling. Stop all external moisture sources by redirecting downspouts and regrading soil to move water runoffs away from your home.

You should also check for internal sources of moisture. Using the flashlight, check the pipes within the joists for dripping. Areas directly beneath kitchens and showers require special attention. You can proceed with the insulation if no such moisture sources exist within the space.

Step Two: Seal Vents and Doors 

All doors, vents, and hatches that lead into your crawl space will undo your insulation efforts. Seal them off using durable materials such as concrete. This step is essential if you’re looking for how to insulate a vented crawl space. Check out our 10 tips for sealing air leaks for more information.

You can also cover up the space with floorboards. For small cracks and holes, use outdoor caulk in your caulking gun.

Step Three: Block Gaps in Sills and Rim Joists

Check your crawl space in daylight to find gaps in your sills and rim joists. If you can see any crack letting in light, that’s a gap you don’t want.

We recommend sealing the smaller cracks with silicone caulk and larger ones with foam insulation. Spray foam insulation can often serve multiple purposes and can be very effective.  This is an important step if you are looking for how to properly insulate a vented crawl space.

Step Four: Insulate Your Crawl Space Walls

Here’s how to insulate a crawl space with a foam board.

Using your saw, cut out some insulation foam for your walls. Be careful with the wall measurement to avoid having too many seams. Attach the foam to the wall using latex adhesive and seal all seams with polyvinyl tape.

Step Five: Insulate the Crawl Space Floor

Cover the crawl space floor area using a vapor barrier. Cut out some of the material to adequately seal up protrusions like posts and piers. Use butyl tape to hold the material in place tightly.

Once done, seal all seams between barrier sheets. To ensure adequate completion, run the vapor barrier 12 to 14 inches up the walls (after insulation) and use some tape to hold the vapor barrier material on the wall.

Step Six: Insulate the Crawl Space Ceiling

You can insulate the crawl space ceiling with fiberglass batts or insulation foam; the material is more effective in this application. Use mechanical fasteners to hold the batts in place.

Tips To Keep in Mind When Insulating Your Crawl Space

  • Always choose insulation with a minimum thermal resistance of R-9.
  • Be sure to only use waterproof tape during the project.
  • Consider adding a dehumidifier to the crawl space if living in a humid environment.

FAQs on Crawl Space Insulation

Does a Sealed Crawl Space Need Insulation?

A sealed crawl space needs insulation to protect against moisture from the ground and walls. A sealed crawl space can still become damp and encourage mold growth, especially with a dirt floor.

What Is the Best Insulation To Use in a Crawl Space?

The best insulation to use in a crawl space is water-resistant polyisocyanurate. You can find this in home improvement stores, and you can also buy directly from insulation manufacturers. You can also read more in our article about Signs that your home may be under-insulated.

How Do You Insulate a Crawl Space With a Dirt Floor?

If you’re looking for how to insulate a crawl space with a dirt floor, start with a strong vapor barrier. A thick vapor barrier on the floor keeps the moisture from the floor out of the air.

How Much Does It Cost To Insulate a Crawl Space?

You can expect to spend between $2,000 and $10,000 on your crawl space insulation. However, before searching “How much to insulate a crawl space,” you need to measure your crawl space’s dimensions.

Conclusion: Get Help From Professionals

Whether you’re looking for how to insulate a tight crawl space or just how to insulate a crawl space in general, Attic Projects Company can help.

Call Attic Projects at 858-923-4083 for a free quote on your San Diego, CA, crawl space repair and insulation installation.