Skip to Content

Can You Put A Junction Box In A Crawl Space

All electrical outlets and switch boxes should be compliant with your local housing regulations. While different regions have different requirements, the basic regulations are the same throughout the country. The placement of junction boxes is strictly governed as shoddy workmanship during installation could result in sparks, fires, or even explosions.

A crawl space is located right beneath the floor and can be a great out-of-the-way space to house a junction box. Before installing a junction box, check that the crawl space is compliant with your local area codes. Regulations must be complied with if you use the space for any electrical equipment.

A junction box can be placed in a crawl space, but specific regulations define the type of junction box and the space required around it for easy access and safe maintenance. The junction box must be adequately protected from moisture due to the humid environment of a crawl space.

Do Building Codes Prohibit Junction Boxes in Crawl Spaces

The placing of a junction box in a crawl space is not expressly prohibited. According to Chapter 34 of the International Residential Code, the regulations give clear instructions on how and where a junction or electrical box can be placed.

Different regulations do, however, apply to different areas of the country. Before installing a junction box in a crawl space, you should research the local codes applicable to your location. Local codes take preference over the IRC, so always keep up to date with local codes.

The fact that electrical equipment such as junction boxes are not prohibited from being installed in crawl spaces means that dehumidification of crawl spaces is very important.

If your region is prone to seasonal flooding, check the local codes to see the requirements and safety codes for installing any electrical outlets in your crawl space before you start.

Related article: Can You Put a Subpanel in a Crawl Space

Requirements of Junction Boxes in the Crawl Space

The biggest consideration should be how much space is available. The space size determines the size of the junction box that you can install and where to put it. You should at least have open space to work in as you need easy access to the junction box for repairs and maintenance.

Accessibility to the Junction Box

IRC code 3405.1 states that the working area should be clear and unobstructed and should comply with the local codes regarding the height and depth of the space.

Practically, your crawl space should be big enough for your to comfortably work in while you are using tools without having to destroy your home or the space. The recommendation is a space of at least 40″ (1 m) on all sides to provide an adequate working area.

Typically, batt and loose-fill insulation do not count as obstructions, so you can install these over the junction boxes.

The Best Location For A Junction Box

According to the IRC code E3405.2, when electrical equipment is installed in a space with limited access like a crawl space, the following should apply:

  • The accessible opening should be no smaller than 22″ by 30″ (559 mm by 762 mm).
  • The width of the working area should be at least equal to the width of the equipment housing enclosure or not less than 30″ (762 mm), whichever is the greater of the two.
  • The doors of the enclosure or the hinged panels should open to at least 90 degrees.
  • The area where the junction box is installed should not be used for storage purposes.

The physical placement of the junction box should require some common sense—never place it on the floor or onto loose soil, especially if the space is prone to damp or flooding. 

Always use a junction box to fit the space. Find a suitable location away from dripping water and any water entry points. The ceiling of the crawl space is generally a good location.

Metal or Plastic Junction Box in Crawl Space

Junction boxes are designed for surface mounting only, so they should be strong enough to withstand the conditions and hazards of the environment where they are installed.

Junction boxes offer protection and durability to the wires housed within. Most boxes are made from either metal or plastics (polymer) and are available in various sizes, mounting styles, and sealing configurations.

  • Metals conduct heat and electricity more efficiently than other materials.
    • Stainless steel is often used in damp environments because of its strength and resistance to corrosion.
    • Aluminum is less expensive and lightweight but is an excellent conductive metal.
  • Plastic or polymers have varying properties.
    • ABS is a rigid, complex thermoplastic polymer but can crack under stress.
    • Fiberglass is strong and durable and can withstand extreme temperatures.  
    • Polycarbonate is solid but cannot withstand chemical corrosion.

The best materials for a junction box in a crawl space will depend on the location of the box. A crawl space will be damp and could cause the box to rust. Always choose a waterproof box that has been treated for rust and corrosion.

Even though your junction box is waterproof, it still needs to be installed correctly to protect the wiring according to the local safety codes in your area.

Junction Box Covers

Every junction box needs a cover. A junction box with a lost or missing cover is not considered safe. Firstly, and most importantly, the cover protects against accidental human contact.

Secondly, junction box covers can prevent the spread of electrical fires. Heat created by the electrical flow can cause electrical fires. The more wires that are joined together, the more heat is produced. Too much heat build-up at the splices could cause a fire to break out. If you have chosen to install your furnace in your crawl space, this can add to the risk.

A junction box cover will contain sparks and small fires that may start due to the heat build-up. Junction covers may be hot to the touch depending on the box’s materials, so always approach with caution.

Benefits of Putting a Junction Box in the Crawl Space

Placing a junction box in a crawl space does have many advantages when installed correctly:

  • A crawl space is an inconspicuous area, generally out of the way of everyday foot traffic in the home.
  • As long as you have easy access to the crawl space, repairs and maintenance are hassle-free.
  • Cost-effective and convenient, a crawl space is generally already built under your home, so you do not have to go through any costly re-modeling to create a space.
  • As with all electrical fittings, a junction box can look out of place when installed on a wall in your home. A crawl space installation ensures that it is out of sight while still doing its intended job.

Drawbacks of Putting a Junction Box in the Crawl Space

Although installing a junction box in a crawl space is a good idea, there are a few things that could go wrong:

  • The junction box is out of sight in the crawl space, so it could take a while to notice if a fire starts or if the box or wiring is damaged in any way by rodents.
  • The size of the junction box is limited because of the size of the crawl space.
  • Water could damage the junction box.

Best Junction Boxes for Use in a Crawl Space

All junction boxes have to comply with NEMA and IP ratings. Junction boxes are rated in amps, typically 5, 20, or 30 amps, with 3,4,5, or 6 terminals. The size of the junction box required depends upon the application.

The best junction box for use in a crawl space should comply with all the IRC, NEMA, IP, and local regulations.

Related article: Can You Put a Water Heater in a Crawl Space


Amazon and the Amazon logo are trademarks of, Inc, or its affiliates.