Energy Storage Systems: 2023 NFPA Code

January 4, 2024 | Reading Time: 6 minutes

As of 2020, National Fire Prevention Association (NFPA) 855 code requires very strict rules on installation locations of energy storage systems (ESS). This article outlines the rules for single-family and two-family dwellings.

Where can the batteries be installed?

  • Outside on exterior walls or on the ground
  • In an attached garage separate from the dwelling unit
  • In a detached garage or structure
  • In a finished and enclosed utility closet

Who do these rules apply to?

The rules in this article apply to single-family and two-family property. If your property has more than two dwelling units, then you must follow all rules of your state’s enforced NFPA 855 code.

Read More: NFPA Code for Commercial Buildings

What are enclosed utility closets made of?

The walls and ceiling of the utility closet must be finished. If the walls and ceiling are already finished with a protective material then they can be left as is. If the walls and ceiling are unfinished, then they must be made of 5/8-inch, Type X gypsum. This is a 60-minute fire-rated sheetrock that acts as a flame insulator and increases a household’s escape time should a battery catch fire. The enclosure must also be equipped with a smoke or heat detector interconnected with the home.

Isaksen Solar’s Additional Recommendations:

  • Although code does not specify, we highly recommend a 20-minute fire-rated door to seal the room.
  • Mudding and taping the seams of the gypsum is highly encouraged to secure the fire-resistive drywall.
  • We recommend installing the drywall if noncombustible walls are not already implemented to maximize fire-resistance.

How big does my utility closet have to be?

On average, a utility closet with three batteries will be 4 ft x 4 ft. The size of your utility closet will depend on the model and number of batteries installed. Keep in mind, they will be set up on the ground or mounted to the wall. Most batteries require eight inches of clearance in the front, on the sides, and above the batteries.

Isaksen Solar’s Insider Knowledge: Implementing at least twelve inches of clearance whenever possible allows for ample space should the batteries need maintenance.

How many batteries can I get?

Depending on the energy capacity of your batteries and the location you’re storing them in, you can determine the number of batteries you can get. The NFPA limits the amount of energy that can be stored in each location.

  • Outside Wall Mounted – 80 kWh
  • Outside Ground Mounted – 80 kWh
  • Attached or Detached Garage or Structure – 80 kWh
  • Utility Closet – 40 kWh

How are unfinished utility closets brought up to code?

Unfinished utility closets are equipped with 5/8 inch Type X gypsum, designed to contain fire for 60 minutes. A heat detector or alarm, interconnected to smoke alarms, is also installed to ensure timely notification of a fire.

When do utility closets need to be installed?

Utility closets must be installed when you’re adding batteries to a basement or living space.

Once the system is added, the electrical inspector, building inspector, and fire department must approve the structure before the system can be turned on.

Who installs my utility closet?

You can choose to build your utility closet yourself or you can use your battery installer.

How much do new utility closets cost?

Utility closet costs will vary depending on the initial state of the enclosure, size, location, and materials used. The price usually ranges from $2,500 to $6,000.