Clear cavity behind the breather membrane in timber frame

50 mm

Clear residual width, measured from the face of the breather membrane to the back of the outer leaf

Every figure for this topic is on one page: Timber frame stud spacing, sheathing and restraint straps

A drained and ventilated cavity is needed between the breather membrane and the masonry cladding so that water crossing the outer leaf can run away rather than reach the frame.

Basis in regulation

Part C
Approved Document C
Read the source

How to check it on site

Check the cavity is clear of mortar snots at each lift and that the gap is maintained where ties and services cross.

Common failure

Mortar droppings bridging the cavity onto the membrane, wetting the sheathing behind.

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

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

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