Quality.

    Fire stopping and compartmentation — critical dimensions

    Cavity barriers, compartment lines and service penetrations. These are the details most often found short on site and the hardest to correct once boarded.

    Minimum

    Carbon monoxide alarm position

    Ceiling mounted at least 300 mm from any wall and 1–3 m horizontally from the appliance, or wall mounted above the height of any door or window and at least 150 mm from the ceiling

    Room containing a fixed combustion appliance

    Minimum

    Cavity barriers around openings in a cavity wall

    Continuous around the full perimeter of the opening

    Includes windows, doors, and any duct or vent passing through the cavity

    Maximum

    Cavity barriers at timber frame panel junctions

    At every compartment junction and opening edge

    Barriers tight to both faces of the cavity, fixed and continuous

    Maximum

    Cavity subdivision in a roof void

    20 m

    Maximum distance between cavity barriers in a concealed roof space

    Minimum

    Clear opening of an escape window

    0.33 m² clear openable area, at least 450 mm in both height and width, with the bottom of the opening 800–1100 mm above floor level

    First floor and loft rooms served by an escape window

    Minimum

    Constructional hearth thickness and extent

    125 mm thick, at least 840 × 840 mm on plan, extending 500 mm in front of the appliance and 150 mm each side

    Solid fuel appliance on a constructional hearth

    Minimum

    Doors onto a protected stairway in a three-storey house

    Fire doors to every habitable room opening onto the stair

    Applies where any floor level is more than 4.5 m above ground level

    Minimum

    Fire barrier at the party wall and roof junction

    Continuous to the underside of the roof covering

    Gaps at truss positions and at the tile battens closed with a fire-resisting material

    Minimum

    Fire resistance of a compartment floor between flats

    60 minutes

    Includes the ceiling line, service voids and any penetrations through it

    Minimum

    Fire resistance of a wall separating dwellings

    60 minutes

    Applies to the wall and to its junctions with floors, roofs and external walls

    Minimum

    Fire stopping at a service penetration

    Reinstate the full fire resistance of the element

    Sealed with a system tested for that substrate, aperture size and service type

    Maximum

    Maximum pipe diameter through a compartment wall or floor

    40 mm

    Nominal internal diameter for a non-fire-rated pipe; larger pipes need a tested sleeve, collar or non-combustible material

    Maximum

    Maximum unbroken cavity before a barrier is needed

    20 m

    Concealed cavity in a wall or roof of a dwelling

    Minimum

    Minimum masonry thickness around a flue

    100 mm around the flue; 200 mm between flues serving different dwellings

    Masonry chimneys built with a suitable liner.

    Minimum

    Separation between a flue and combustible material

    200 mm from the flue face, or 40 mm from the outer face of the masonry

    Masonry chimneys and fireplace recesses serving combustion appliances.

    Maximum

    Smoke alarm siting distances

    Within 7.5 m of the door to every habitable room, within 3 m of every bedroom door, and at least 300 mm from any wall or light fitting

    Ceiling-mounted mains-powered alarms on circulation routes

    All critical dimensions · All topics

    These entries are our own editorial summaries of publicly available regulation. They are not building control approval, a warranty determination, or a substitute for the full source document.

    We use cookies to keep you logged in and improve ProPlot. Privacy Policy