Where to put a home battery in the house: garage, loft, utility room

The British standard for home batteries, PAS 63100, prefers them outdoors where practicable, and sets conditions for indoor spaces. A garage can work with extra protection, a utility room can work if it meets the conditions, and a loft is not recommended.

What the standard is

BSI published PAS 63100:2024, covering protection against fire of battery energy storage systems in dwellings, on 20 March 2024, as BSI's catalogue entry shows. It is a published specification, not an Act of Parliament, but installers and insurers may refer to it. We have not checked how each insurer uses it.

It has exclusions, such as dwellings over 200 m² and second-life batteries. If your home falls outside its scope, your installer should explain which rules they are following instead.

Outdoors first

According to BSI's summary of the specification, batteries should be installed outdoors where practicable. An outbuilding not used for habitation can count as outdoors if it is detached or separated by a wall with at least REI 120 fire performance. Outdoor spots within 1 m of escape routes, doors, windows or ventilation ports are to be avoided.

A wall-mounted unit outside is one answer, if the product is rated for it and the wall and surroundings suit. Check the manufacturer's datasheet for the temperature range and ingress protection rating of any unit placed outside.

Indoors: garage, utility room, loft

If outdoors is not practicable, the summary says indoor spaces need fire-resisting separation (at least REI 30) from habitable and escape areas, and ventilation to the outside. Rooms where people sleep, and cupboards opening into them, are to be avoided, as are non-protected escape routes such as landings, stairs and corridors.

Garage. Batteries in attached or detached garages, or next to indoor car parking, need protection against mechanical impact of at least IK10, per the summary. That means a unit in a garage is not simply screwed to the wall: ask what protection is included.

Utility room. The standard names conditions rather than rooms. A utility room can work if it has separation and ventilation, and is not on an escape route. A cupboard that is rarely visited needs a smoke or multi-sensor detector linked to the home's fire alarm.

Loft. Voids, roof spaces and lofts are on the avoid list. Cellars or basements without access to the outside are too, and so is anywhere within 2 m of stored flammable materials or fuel tanks.

Practical points beyond the standard

The standard limits each enclosure to 20 kWh and total stored energy in a dwelling to 40 kWh, rising to 80 kWh outdoors or in a detached garage or outbuilding. Most homes are far below this, but it matters if you plan large storage later, like the sizes in our 10 kWh and 20 kWh pages.

A 2020 review of domestic battery safety commissioned by government, published by OPSS, listed siting away from living areas, separation from combustible materials, detection, ventilation and qualified installation among recommended practices. Also think about cable runs, access for service, and whether you want the unit near the inverter. A battery used for whole home backup needs to sit close to the consumer unit.

Common questions

Related guides

Keep reading, or check your own numbers:

• Whole home battery backup: how does it work?
• 10 kWh home batteries
• Home batteries
• How much does a home battery cost in the UK?