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

Every figure for this topic is on one page: Cavity barriers and fire stopping around openings and services

The cavity behind a timber frame must be closed where it meets a compartment wall or floor, and around every opening, so fire cannot run up the void.

Basis in regulation

Part B
Approved Document B
Read the source

How to check it on site

Check at window and door reveals, eaves, and the separating wall line before the cladding closes the cavity.

Common failure

Barriers pushed out of position by insulation or omitted at the top of a panel.

Effective from 22 August 2026. Last updated 23 August 2026. This is our editorial summary of publicly available regulation, not building control approval or a warranty determination.

Related dimensions at this stage

Minimum

Breather membrane lap on a timber frame

100 mm

Horizontal laps shingled downwards; vertical laps over a stud, taped where the manufacturer requires it

Minimum

Sole plate DPC height in a timber frame wall

150 mm

Measured from finished external ground or paving level to the underside of the sole plate DPC

Maximum

Timber moisture content before closing up

20 %

Measured with a calibrated meter at several points, including sole plates and the base of studs

Maximum

Wall tie spacing to a timber frame

Max 600 mm horizontally (at stud centres) and 450 mm vertically

Ties screwed into studs, not sheathing alone; closer spacing at reveals and movement joints

Maximum

Lateral restraint strap spacing at floor and roof level

2 m

Straps at floor and ceiling level, carried over at least three joists with solid noggins

Maximum

Racking board fixing centres

150 mm at board edges, 300 mm at intermediate studs

Fixings kept at least 10 mm from the board edge; pattern to the frame designer's specification where it is tighter