Breather membrane lap on a timber frame

100 mm

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

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

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

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

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

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.

Timber frame — critical dimensions

Breather membrane lap on a timber frame

Cavity barriers at timber frame panel junctions

Clear cavity behind the breather membrane in timber frame

Lateral restraint strap spacing at floor and roof level

Racking board fixing centres

Sole plate DPC height in a timber frame wall

Timber moisture content before closing up

Wall tie spacing to a timber frame