How to Insulate a Crawl Space

a crawl space with insulation and water barriers
  • 5-50 hours
  • Beginner
  • 300-2,000

Crawl space insulation and moisture barriers can improve your home's energy efficiency and help prevent water damage. It can also be a step on the path toward finishing your basement, and help prevent hazards like mold from floating up through your floors. To keep your home dry, comfortable, and safe, check out this piece for tips on how to insulate a crawl space.

Why Do I Need to Insulate My Crawl Space?

Without insulation in the crawl space area, you will experience very low efficiency in heating and cooling your home: heat rises and cold sinks. If you haven’t insulated your ground floor, your heat will be pushed higher by cold air seeping through the floor, and your cool air will sink beneath the home into the crawl space.

Energy Efficiency

In studies done by the Environmental Protection Agency, approximately 15% of all homes have a crawl space to insulate. Fully insulating and properly encapsulating these spaces can save you between 15 and 20% on your heating and cooling costs. When you’re not losing heat through your flooring, you spend far less on keeping your home cool in the summer and warm in the winter.

Moisture Protection

When your crawl space isn’t fully sealed against moisture, it becomes a prime place for mold, mildew, and rot to set your home's foundation. Depending on the size of your home, professional mold and mildew removal can cost $400-4000.

The cost of this service isn’t a tiny expense and can deplete your budget for home repairs in a hurry. Further, mold can cause several health concerns, mainly respiratory disorders and severe allergies. The EPA has stated that mold contributes significantly to instances of hospitalizations related to indoor air quality.

Added Home Value

Homeowners are always looking for new ways to add value to their homes in the case of resale. While crawl space encapsulation is becoming standard on much higher-end home builds, the market is shifting to demand upgraded sealing and insulation.

Insulated crawl spaces add value by creating a safer and more comfortable space to live in, and by reducing the potential for hazards and waste. An adequately insulated space may even reduce your homeowner's insurance and energy costs.

Reducing the likelihood of rot and mildew will also interest buyers with the long term in mind because it means the home will be healthier for their loved ones and prevent foundation settlement. Creating a clean and dry crawl space will create a better area for utility maintenance and upkeep on the bones of your home.

Insulating and sealing your home’s crawl space is especially important in regions with excessive rainfall, heavy snow, and high humidity. If the wood footings in your crawl space have more than 20% moisture, there is nearly a 100% chance there is already rot and decay.

Can I DIY My Crawl Space Insulation?

The skills required for installing, upgrading, or replacing crawl space insulation aren’t complex, and they can save a lot of money over the professional installation. The worst part of installing insulation is the cramped spaces and the creepy crawlies that frequent dark, cool areas.

The average cost to professionally insulate and encapsulate your crawl space ranges from $1,500-15,000, with a national average of $5,000. Suppose you're handy with essential tools and comfortable spending a day in the company of your furry and many-legged neighbors. In that case, you will find this project a massive benefit to your budget and the enjoyment your family gets from the space.

How to Insulate a Crawl Space

crawlspace with insulation

1. Assemble Safety Gear

Insulation materials can be incredibly irritating to the eyes and lungs. Before starting your project, ensure you’re using proper gear to protect you and those helping you. Wearing safety glasses and a painting or dust mask will prevent many insulation-related injuries.

The additional kit you should have on your checklist before you start includes heavy work gloves to protect your hands, a hat to keep fiberglass out of your face and hair, and loose-fitting clothing with long sleeves to keep the fiberglass shards off your skin as much as possible.

2. Assess Existing Insulation

If you're not starting from scratch, put on your safety gear and check out the existing insulation. If it isn’t moldy or tattered, you can add a new layer between the joists and the old insulation. If your insulation is damaged beyond recovery, you’ll need to remove it before moving forward on the project.

The top causes of damage to crawl space insulation are rodents, bugs, and moisture damage. When assessing your insulation for damages, you’ll want to do your best to fix the problem before you put the work into the replacement.

If you have pests, call in an exterminator. If you have moisture, mold, or mildew, you will need to repair whatever is causing the water damage and dry the space before you begin the project.

3. Measure Your Space and Get Your Materials

Using a measuring tape, measure the length and width of the space you’re insulating. Multiply the length by the width to get the total area you’re covering. If math isn’t your strong suit, you can get the measurements and plug them into an insulation calculator.

Cut your insulation rolls to the length you need to fill between the floor joists. You’ll want these rolls to fit snug, without wiggle room, and with no gaps in the ends or sides. Ensure you have all of your supplies before descending into your crawl space.

4. Remove Damaged Insulation

Removing the previous insulation should be done in long strips and rolled up to dispose of (in most places, you're not supposed to put this stuff out in bins, so call your local trash authority to check). You’ll want to work at an even and steady pace, avoiding shredding the insulation as much as possible.

Fiberglass particles like to dig into soft skin and sensitive spaces; if your roll the previous layer into manageable sections, you’ll have less debris to cling to you. Your local waste authority will have information on the best way to dispose of or recycle your building materials.

5. Install and Secure the New Rolls

Using a staple gun (if you’ve chosen faced insulation), tack each roll into the joist spaces, overlapping the facing. If you’ve decided on unfaced insulation, have your wire hangers on hand to secure the pieces as you work along the floor.

Focus on one joist row at a time, securing the insulation every 18-24 inches. Use the wire hangers to add extra security by stapling them over the insulation and directly into the wood of the joists. If your home is more extensive, this task can seem daunting, but taking the project one row at a time breaks it into manageable chunks.

6. Install a Vapor Barrier

moisture barrier with stapler

Even if you’ve decided to go with faced insulation for your project, adding a moisture barrier in the form of plastic sheeting will keep the moisture, pests, and rodents out of the insulation materials, prolonging their life and reducing the frequency of replacement.

This vapor barrier will also protect your family from airborne pollen and spores from fungus, mold, and mildew that might otherwise seep up through the flooring.

Similarly, install your vapor barrier as the faced insulation. Roll out the plastic sheeting and attach it to the joists with a stapler. Leave an overhang of 8-12 inches on the sides of the structure, and overlap the rows of barriers by about eight inches for extra moisture protection.

Use a utility knife to cut excess, and don’t forget to tape together oddly shaped corners and around foundation footings. Another great feature of a securely attached vapor barrier is the reduction of scents from wildlife seeking shelter under your home.

Face vs. Unfaced insulation

Now that we’ve determined that the insulation in your crawl space has a significant impact on your enjoyment of your home and is worth the worry, it’s time to decide what kinds of insulation there are and which is the best for your situation.

There are two common types of insulation used for crawl spaces in the DIY range: faced and unfaced insulation rolls are available for the DIYer and the typical contractor. Some professional contractors also offer spray-in foam insulation inflexible or rigid foam options for higher prices.

unfaced insulation roll

Unfaced Insulation Rolls

Unfaced insulation is created from fiberglass packed into stud width rolls or bricks. It is considered inflammable and is often favored for walls within a home because of its ability to stop or slow a flame’s progress through a burning building. However, it is harder to install as it has nothing to tack staples to hold it in place before installing wires or a plastic sheeting vapor barrier.

Unfaced insulation can be layered onto unfaced insulation for added protection and can be layered with faced insulation if needed. Per foot, the cost of unfaced insulation is lower than that of faced insulation.

Faced Insulation Rolls

These rolls of fiberglass fluff are backed by a permanently attached vapor barrier made from moisture-resistant kraft paper. This makes the rolls more durable and easier to maneuver and secure. The paper facing removed the inflammable label from this form of insulation, but it is still flame resistant.

If you’re going to go with faced insulation for your crawl space, it’s essential that the paper facing is on the exterior for warm climates and the interior for cool temperatures.

The most important thing to remember when layering this form of insulation is that you’ll encourage water damage if you sandwich the paper barrier between layers of the foam wool. The cost per foot for rolls of faced insulation is slightly higher, reflecting the convenience and additional materials.

Sealing or Encapsulating Your Crawl Space

Installing the insulation and vapor barrier is all you need for most crawl spaces. However, you can get extra security against dampness and large creatures taking up residence by sealing or encapsulating your space. This process includes lining the crawl space's floor, walls, and joists in a heavy plastic layer.

Professional encapsulation can cost $2,000-$5,000 or more, depending on the contractor. You can do this task independently, but cutting corners or using inferior products can lead to a shortened lifespan or a faster breakdown of your seal.

What R-Value Should Your Crawl Space Insulation Be?

R-value is the insulation's thermal quality. The higher the value, the more efficiently the insulation will prevent heat bleed from inside to outside.

For insulation under floors, the US Department of Energy suggests using at least R-9. In more moderate climates, you can get away with just insulating in between the joists, but for areas that freeze in the winter, you might want to consider sealing the entire area for maximum heating efficiency.

Faced insulation is easy to install, keeps moisture from seeping into the joists and subfloor, and holds temperature fluctuations at bay. Unfaced insulation is less expensive but more complex to install, with extra steps and better flame mitigation.

Do It Yourself Insulation

Now that you know about insulating crawl spaces, you might want to consider further improving your home's energy efficiency by adding insulation to your attic or garage or finding and fixing leaks in your current insulation.