How to Know if Your Crawl Space Is Up to Code

Stacy Sare Cohen
Written by Stacy Sare Cohen
Updated November 15, 2021
House with crawlspace
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A crawl space is more than an escape tunnel in a spine-tingling, suspense-filled horror flick. It’s an essential part of your home built to protect you and your family from what lies on the ground below—which can also send shivers up your spine—and it must be kept up to code. 

We’ve rounded up the standard crawl space requirements to keep your home dry, safe, sanitary, and legal.

Does My Crawl Space Need a Vent?

According to a National Association of Home Builders survey, 14% of newly built single-family homes in the U.S. contain crawl spaces. Originally, crawl spaces all had vents, but after building commissions learned they became a breeding ground for mold, rodent nesting, and rotted wood building materials, the laws changed. 

Today, building codes allow for both vented and unvented crawl spaces, as long as they comply with code requirements.

International Residential Code (IRC) Requirements

The IRC designed a set of residential code requirements to ensure the construction of buildings are sanitary and safe for people who live inside. While the IRC doesn’t mandate local governments to uphold the codes, cities and counties use them as a model to develop their own construction codes. 

Read on to learn crawl space requirements homeowners and foundation contractors need to follow.

1. Unvented Crawl Space Requirements

When crawl spaces don't house a vent, the contractor needs to place a Class 1 vapor retarder, insulation material, and the right size dehumidifier for the space. Dehumidifiers come in a variety of sizes based on square footage and humidity levels. Below, you’ll find new dehumidifier sizes necessary for ventless crawl spaces (older models are around 30-pints larger).

300-Square-Foot Crawl Spaces:

  • 20-pint dehumidifier for mildly and moderately damp spaces with 50%–70% humidity levels

  • 25-pint dehumidifier for highly damp spaces with 70%–80% humidity levels

  • 25- to 30-pint dehumidifier for wet spaces with 80%–100% humidity levels

500-Square-Foot Crawl Spaces:

  • 25- to 30-pint dehumidifier for mildly and moderately damp spaces with 50%–60% humidity levels

  • 30-pint dehumidifier for highly damp spaces with 70%–80% humidity levels

  • 35- to 40-pint dehumidifier for wet spaces with 80%–100% humidity levels

800-Square-Foot Crawl Spaces:

  • 25- to 30-pint dehumidifier for mildly to moderately damp spaces with 50%–70% humidity levels

  • 30-pint dehumidifier for highly damp spaces with 70%–80% humidity levels

  • 35-to 40-pint dehumidifiers for wet spaces with 80%–100% humidity levels

1,200-Square-Foot Crawl Spaces:

  • 50- to 55-pint dehumidifier for mildly to moderately damp spaces with 50%–70% humidity levels

  • 55-pint dehumidifier for highly damp spaces with 70%–80% humidity level

  • 60-pint dehumidifier for wet spaces with 80%–100% humidity levels

If your crawl space area measures larger than 1,200 square feet, just do the math! Consider hiring a pro to encapsulate (or seal) the space. Encapsulation costs an average of $5,000, depending on the size of your crawl space and the materials used.

2. Vented Crawl Space Building Codes

Building codes require crawl spaces to maintain outdoor ventilation between the ground and floor joists. If your crawl space is vented, you’ll need to install vents on all the walls. 

The size of vents must be 1 foot for every 500 square feet or 1 foot for every 1,500 square feet when they house Class 1 vapor barriers that contain a 6-mil thick sheet of polyethylene.

3. Access Door Requirements

Crawl spaces require access doors that are easy to get to in case of an emergency or the need for repairs. According to the IRC, the size of access doors for crawl spaces must measure 18-by-24 inches.

4. Drain or Sump Pump

Crawl space floors need drains or sump pumps in the crawl space. They must be separate from foundation perimeter drains and gutters, and drain away from foundations. 

5. Height and Width Requirements

The IRC now requires all crawl space entrances to measure a minimum of 16 inches high and 24 inches wide.

6. Insulation

When using a Class 1 vapor retarder, you’ll need to install thermal insulation on the walls. Foam insulation boards placed in crawl spaces and attics must contain a thermal barrier, which safeguards crawl spaces from igniting a fire. Never use insulation materials that are porous on the ground since they absorb water.

Who Should I Hire to Ensure My Crawl Space Is Up to Building Codes?

If you’re buying, selling, or building a home, the right pro to hire for the job is a foundation contractor near you. These contractors will get down and dirty and crawl under your house to check things out. If you’re hiring a local home inspector they can take a quick look, but when there’s any doubt, they’ll recommend you call a foundation contractor.

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