PAS 63100 battery fire placement

PAS 63100:2024 gives the fire-safety requirements for small domestic battery energy storage systems within its scope. Its starting point is straightforward: where practicable, put the batteries outdoors. If an indoor location is necessary, the design must deal with fire separation, ventilation, detection, access and escape.

The rule applies to the storage batteries, not automatically to every inverter or control component. A designer still has to assess the complete system, the manufacturer’s instructions, BS 7671 and the building’s fire strategy.

Locations the specification excludes

PAS 63100 says batteries must not be installed in:

• rooms intended for sleeping;
• unprotected escape routes, including landings, stairs and corridors;
• the corridors, shafts, stairs or lobbies of protected escape routes;
• firefighting lobbies, shafts or stairs;
• cupboards, enclosures or spaces opening into a sleeping room;
• an outdoor position within 1m of an escape route, door, window or ventilation port;
• voids, roof spaces or lofts;
• a position within 2m of stored flammable material, a fuel tank or a fuel cylinder; or
• a cellar or basement with no access to the outside.

The list should be applied to the actual layout. A hallway cupboard is not made acceptable merely by adding a door, and a room labelled as a study may still be intended for sleeping. The designer needs to identify the real escape route and adjacent openings before choosing a position.

What an indoor location needs

Where outdoor installation is not practicable, PAS 63100 permits an indoor location only if it is not one of the excluded locations and the relevant fire-separation and ventilation provisions are met.

The indoor battery location must have fresh-air ventilation to outdoors. The external edge of that ventilation opening must be at least 1m from the edges of doors, windows and ventilation ports serving other locations. The ventilation must not compromise the fire resistance of the enclosure or compartment.

The specification requires the battery location to be separated from the excluded indoor locations by walls, ceilings and floors providing at least REI 30 to the BS EN 13501 series, or 30 minutes under the relevant BS 476 series tests. Service penetrations need suitable fire stopping so the compartment is not defeated by cables or ducts.

For an infrequently visited battery location, such as a store cupboard, PAS 63100 requires a smoke alarm or multi-sensor fire alarm in that space, interlinked with the dwelling’s fire-alarm system and conforming to BS 5839-6. Its note describes at least Grade D2, Category LD2 as appropriate for premises containing a battery system. The fire-alarm design still has to suit the dwelling and the position of the battery.

Garages and outbuildings are not all treated alike

PAS 63100 says an outdoor location can include an outbuilding not intended for habitation when it is detached, or when a main wall separates it with at least REI 120 fire performance. That definition should not be confused with the separate capacity rule for an attached garage or outbuilding.

For total stored energy, the specification allows up to 80kWh where batteries are outdoors, in a detached garage or outbuilding, or in an attached garage or outbuilding with at least REI 60 separation. The limit is 40kWh in other cases.

These ratings apply to defined construction, not simply to a layer of plasterboard. The design identifies the wall, floor, ceiling, doors and service penetrations that form the separation and records how their performance was established.

Capacity and enclosure limits

PAS 63100 limits the energy stored inside one battery enclosure to 20kWh. That is separate from the 80kWh or 40kWh total for the dwelling location.

Adding modules can therefore affect both the enclosure limit and the total allowed for the location. A later expansion should be treated as a design change, with the original fire and electrical assessment revisited rather than assuming spare physical space means spare permitted capacity.

Outdoor mounting still needs a fire assessment

An outdoor position is preferred, but it is not free of constraints. In addition to the 1m and 2m distances above:

• the enclosure and equipment must be suitable for the weather and external influences;
• fixing the system must not compromise the fire performance of the external wall;
• penetrations must be fire stopped and wall cavities protected; and
• equipment exposed to vehicle impact or other mechanical damage needs suitable protection.

The manufacturer’s temperature, clearance and ingress-protection limits also apply. A position can satisfy a PAS distance and still be unsuitable for the product.

Position during the 2026 wiring-regulations transition

BS 7671:2018+A4:2026 introduced Chapter 57 for stationary secondary batteries. Its Regulation 570.6.7.203 says batteries in dwellings are to be installed in accordance with PAS 63100.

As at 22 July 2026, installers could work to Amendment 4 or to the preceding Amendment 3, which remained valid until 15 October 2026. The chosen edition should be stated in the design and certification. A July 2026 reference to PAS 63100 on its own does not establish that Amendment 4 was used.

PAS 63100 and BS 7671 are standards, not legislation in their own right. They can nevertheless be required by a contract or certification scheme and are important evidence of accepted safety practice.

Existing batteries need assessment, not slogans

An older loft or indoor battery is not made automatically unlawful by the publication of a later standard. Equally, its age does not establish that it is safe. The owner should check:

• which standard and manufacturer’s instructions the installer used;
• the electrical and MCS certificates, if applicable;
• fire detection, ventilation and escape-route effects;
• structural support, temperature and access for maintenance;
• any insurer or lender conditions; and
• whether later alteration or expansion changes the applicable design.

If the location is a concern, use a competent battery-storage designer or electrician to assess the actual installation. Do not move, isolate or dismantle a battery without the manufacturer’s procedure.

Related entries

• PAS 63100 domestic battery fire specification
• BS 7671 IET Wiring Regulations
• IET EESS code of practice
• MIS 3012 battery storage standard
• BS 9991 residential fire safety
• Battery location and ventilation
• Thermal runaway containment