Crawl Space Insulation: Why It Matters and How to Do It Right

When it comes to home insulation, crawl spaces are often overlooked—but they shouldn’t be. If your home has a crawl space, insulating it properly can significantly impact your energy efficiency, comfort, and even your indoor air quality. At Kent Insulation, we believe that an informed homeowner is a better homeowner, so in this post, we’ll walk you through the essentials of crawl space insulation: what it is, why it’s important, and how to get it right.

What Is a Crawl Space?

A crawl space is a shallow, unfinished area beneath your home—typically between the ground and the first floor. Unlike basements, crawl spaces aren’t tall enough to walk in (hence the name), but they still serve an important function. They provide a buffer zone between your home and the ground and often house utility lines, pipes, and ductwork.

Because crawl spaces are exposed to the earth below, they’re highly susceptible to moisture, temperature changes, and even pests—all of which can affect your entire home if left unaddressed.

Why Crawl Space Insulation Matters

Proper crawl space insulation can:

1. Improve Energy Efficiency

Poorly insulated crawl spaces can become a major source of heat loss in winter and heat gain in summer. Insulation helps regulate the temperature, reducing the workload on your HVAC system and lowering your energy bills.

2. Control Moisture

Moisture in crawl spaces can lead to mold growth, wood rot, and even structural damage. Combined with a vapor barrier, insulation helps control humidity and prevent moisture problems.

3. Enhance Indoor Air Quality

About 40-50% of the air you breathe on your home’s first floor comes from the crawl space. If the air down there is damp and moldy, it can affect your health. Insulating and sealing the space contributes to a cleaner, healthier indoor environment.

4. Prevent Frozen Pipes

In colder climates, uninsulated crawl spaces can cause pipes to freeze and burst. Insulation helps keep temperatures more stable, reducing the risk of costly damage.

Vented vs. Unvented Crawl Spaces

Before insulating, it’s important to know what type of crawl space you have:

• Vented Crawl Spaces have exterior vents that allow outside air to circulate. These were originally designed to reduce moisture, but in many climates, they can actually worsen moisture and energy issues.

• Unvented (Sealed) Crawl Spaces are closed off from outside air and often include a vapor barrier and conditioned air. This is now considered the best practice in most modern building codes.

Most insulation experts, including those at Kent Insulation, recommend sealing and insulating crawl spaces rather than venting them. A sealed crawl space better controls temperature and moisture and can drastically improve the performance of your home’s insulation.

How to Insulate a Crawl Space Properly

Here’s a step-by-step look at the best practices for insulating a crawl space:

1. Seal Any Air Leaks

Start by sealing cracks, holes, and gaps—especially around ducts, pipes, and rim joists. This keeps unwanted outside air from entering the crawl space.

2. Install a Vapor Barrier

A vapor barrier is a heavy plastic sheet that’s laid on the floor of the crawl space to block moisture from the ground. It should cover the entire ground surface and be sealed at the edges and seams.

3. Insulate the Walls, Not the Ceiling

Instead of insulating the subfloor above the crawl space (which can leave ducts and pipes exposed), it’s usually better to insulate the walls of the crawl space. Rigid foam boards or spray foam are great options for this, as they provide excellent thermal resistance and moisture control.

4. Condition the Air (Optional)

In some cases, especially in very humid or cold climates, it might be beneficial to add a small amount of conditioned air to the crawl space to keep temperatures stable and moisture levels low.

Choosing the Right Insulation Material

Not all insulation is created equal. For crawl spaces, consider the following:

• Rigid Foam Board: Durable, moisture-resistant, and provides a high R-value per inch. Ideal for wall insulation.

• Spray Foam: Great for sealing gaps and insulating irregular surfaces. Offers both insulation and air sealing in one application.

• Fiberglass Batts: Often used but not recommended for crawl spaces unless they’re kept very dry. Fiberglass can absorb moisture and sag over time.

At Kent Insulation, we can help you select the best material for your specific climate and crawl space conditions.

When to Call a Professional

While DIY insulation might be tempting, crawl space work can be challenging—and even risky if done incorrectly. Moisture problems, poor sealing, or the wrong insulation type can cause more harm than good. That’s why it’s often best to consult a qualified professional who can assess your home’s needs and ensure a proper installation.

Kent Insulation has years of experience insulating homes across a variety of climates and structures. Whether you’re retrofitting an older home or building new, our team can help you get the job done right.

Final Thoughts

Crawl space insulation might not be the most glamorous upgrade, but it’s one of the most effective ways to improve your home’s comfort, efficiency, and longevity. By taking the time to insulate and seal your crawl space properly, you’ll enjoy lower energy bills, better air quality, and peace of mind.

Have questions or want a free assessment? Contact Kent Insulation today—we’re here to help you build a better, more comfortable home from the ground up.