Building standards technical handbook 2020: domestic

In order to reduce the risk of fire spreading from one dwelling to another, fire separation should be provided between dwellings and between dwellings and any common spaces. Such separation should form a complete barrier to the products of combustion; smoke, heat and toxic gases. In semi-detached or terraced houses, or between flats or maisonettes, the barrier will normally be in the form of fire resisting walls and floors where appropriate.

The guidance in clause 2.2.9 (Openings and service penetrations) and clause 2.2.10 (Junctions) is common, not only to separation, but also to the relevant guidance in Standard 2.4 Cavities and Standard 2.9 Escape. To avoid duplication, these clauses are referred to throughout the Handbook and the reader is prompted to return to these common clauses whenever it is considered appropriate.

Conversions - in the case of conversions, as specified in regulation 4, the building as converted shall meet the requirements of this standard in so far as is reasonably practicable, and in no case be worse than before the conversion (regulation 12, schedule 6).

A separating wall or separating floor with at least a medium fire resistance duration should be provided between adjoining dwellings.

A separating wall or separating floor with at least a medium fire resistance duration should be provided between a dwelling and any other part of the building in common occupation. A protected zone and a common access corridor should be considered as being in common occupation. Any self-closing fire door installed in these separating walls should have at least a short fire resistance duration and in the case of a high rise domestic building, a medium fire resistance duration. For ancillary rooms and spaces, common external escape stairs or open access balconies, see the guidance to Standard 2.9.

A separating wall or separating floor with at least a medium fire resistance duration should be provided between a domestic and non-domestic building. Reference should also be made to the guidance for non-domestic buildings where appropriate.

There is a risk posed by the storage of combustible materials and other highly flammable substances in garages which are integral or attached to a dwelling.

A separating wall or separating floor with a short fire resistance duration therefore should be provided between an integral or attached garage and a dwelling in the same occupation. It is not necessary for a roof space above the garage to be separated from the dwelling where the garage ceiling will serve as a separating floor with a short fire resistance duration (see annex 2.A).

Every lift well should be enclosed by separating walls with a medium fire resistance duration. Where the lift well does not extend the full height of the building, the lift well should form a junction with a separating floor with a medium fire resistance duration. Where a lift is installed, the landing controls and lift car controls should be of a type that do not operate on heat or pressure resulting from a fire.

A platform lift constructed in accordance with the guidance in BS 6440: 1999 (see Section 4 Safety), need not be enclosed by separating walls or separating floors.

Separating Walls - in a building with no storey at a height above 18m, separating walls may be constructed from combustible products provided the appropriate fire resistance duration is maintained.

To reduce the risk of a fire starting within a combustible separating wall or a fire spreading rapidly on or within the wall construction:

Where an opening is created to allow services to pass through the wall, the opening should be constructed in accordance with the guidance in clause 2.2.9.

Separating floors - in a domestic building with no storey at a height above 18m, separating floors may be constructed from combustible products.

Where a domestic building also contains non-domestic accommodation, every part of that separating floor (other than a floor finish e.g. laminate flooring) should be constructed from products which achieve European Classification A1 or A2. This is not necessary for a floor:

Occupants in high rise domestic buildings may not evacuate the building immediately and fire-fighting and rescue operations will take longer to commence if the fire is on a floor high above the ground. Therefore in order to improve occupant and fire-fighter safety in high rise domestic buildings every:

Where an element of structure (see clause 2.3.0) provides support to a separating wall or separating floor constructed from products which achieve European Classification A1 or A2, the supporting element of structure should also achieve European Classification A1 or A2.

Where an element of structure provides support to a separating wall or separating floor which attracts a higher fire resistance duration, the supporting element of structure should have at least the same fire resistance duration.

General - Separating walls and separating floors are intended to prevent fire passing from one part of the building to another part under different occupation. Openings and service penetrations through these walls or floors can compromise their effectiveness and should be kept to a minimum. The solum and roof-space should not be forgotten. Openings and service penetrations should be carefully detailed and constructed to resist fire. This can be achieved by following the guidance below.

A self-closing fire door with the same fire resistance duration as the separating wall should be installed in accordance with the recommendations in the Code of Practice, ‘Hardware for Fire and Escape Doors’, published by the Door and Hardware Federation and the Guild of Architectural Ironmongers.

In some instances a self-closing fire door with a short fire resistance duration may be installed. For example in a separating wall between a dwelling and a common space (see clause 2.2.2).

A self-closing fire door should not be fitted in a separating wall between 2 dwellings in different occupation.

A lockable door to a cupboard or service duct with a floor area not more than 3m2 need not be self-closing.

Hold open devices- Self-closing fire doors can be fitted with hold open devices as specified in BS 5839: Part 3: 1988 provided the door is not an emergency door, a protected door serving the only escape stair in the building (or the only escape stair serving part of the building) or a protected door serving a fire-fighting shaft.

It is important that hold open devices deactivate on operation of the fire alarm therefore some buildings will need automatic fire detection to be installed. Electrically operated hold open devices should therefore deactivate on operation of:

An example of a Category L5 fire alarm system could be a system installed in the common corridor of flats incorporating only 2 smoke detectors, one installed on each side of the door and positioned not less than 500mm and not more than 3m from the door.

Additional guidance on the siting and coverage of fire detectors is contained in BS 5839: Part 1: 2017, and for actuation of door release mechanism, see BS 7273: Part 4: 2015.

A chimney or flue-pipe should be constructed so that, in the event of a fire, the fire resistance duration of the separating wall or separating floor is maintained.

A service opening (other than a ventilating duct) which penetrates a separating wall or separating floor should be fire stopped providing at least the appropriate fire resistance duration for the wall or floor. This may be provided by:

Fire stopping of the following services passing through a separating wall or separating floor need not be provided for:

Where a pipe connects to another pipe which attracts a more demanding fire resistance duration, and is within 1m from the separating wall or separating floor, the pipe should be fire stopped to the more demanding guidance.

Ventilation systems - the potential for ventilation systems to allow the spread of fire and smoke should be considered. A mechanical ventilation system may contribute to the spread of fire and smoke unless it is designed to shut down automatically or operate in a fire-mode if fire is detected. Ventilation ductwork passing through a separating wall or separating floor should be provided with either:

Ventilation ductwork should be designed and installed in accordance with BS 5588: Part 9: 1999. Section 6 of BS 5588: Part 9: 1999 (excluding the third paragraph to clause 6.3.3.2.2) provides guidance on design and construction including fire resisting enclosures, fire resisting ductwork and the use and activation of fire dampers.

Fire-stopping - may be necessary to close an imperfection of fit or design tolerance between construction elements and components, service openings and ventilation ducts. Proprietary fire-stopping products, including intumescent products, should be tested to demonstrate their ability to maintain the appropriate fire resistance duration under the conditions appropriate to their end use.

Where minimal differential movement is anticipated, either in normal use or during fire exposure, proprietary fire-stopping products may be used. The following materials are also considered appropriate: cement mortar; gypsum based plaster; cement or gypsum based vermiculite/perlite mixes; mineral fibre; crushed rock and blast furnace slag or ceramic based products (with or without resin binders).

Where greater differential movement is anticipated, either in normal use or during fire exposure, proprietary fire-stopping products should be used.

To prevent displacement, products used for fire-stopping should be reinforced with, or supported by, products which achieve European Classification A1 or A2 where the unsupported span is more than 100mm and where non-rigid products are used. However this is not necessary where it has been shown by test that the products are satisfactory within their field of application.

General - the basic principle is that junctions between separating walls and separating floors and other parts of the building should be designed and constructed in such a way to prevent a fire in one part of the building flanking the separating wall or separating floor and entering another part of the building under different occupation, including any solum space or roof space. Therefore, the building elements, materials or components should not be built into, or carried through or across the ends of, or over the top of a separating wall in such a way as to impair the fire resistance between the relevant parts of the building.

Where a separating wall or floor or protected route of escape abuts a structure containing a cavity, a fire barrier should be installed in the cavity so as to extend the line, and maintain the fire resistance, of the wall or floor. However, this is not necessary where the cavity is formed by two leaves of masonry or concrete at least 75mm thick and the external wall is provided with cavity barriers around all openings and at the top of the wall-head.

Junctions with walls - where a separating wall or separating floor forms a junction with an external wall, another separating wall, or a wall or screen used to protect routes of escape (see clause 2.0.6), the junction should maintain the fire resistance of the separating wall or separating floor.

Junctions with roofs - where a separating wall forms a junction with a roof, the junction should maintain the fire resistance duration of the separating wall in accordance with the following: