NHBC Chapter 6.2, Approved Documents A & B · 21 checks · proplot.co.uk
Timber frame erection checks — sole plate and DPC, panel plumb and line, holding-down straps, breather membrane, cavity barriers, racking boards and weather exposure.
21 checks · Reviewed by the ProPlot site team · How we write these guides
In short
The timber frame erection inspection takes place once panels are up and before the external cladding closes them in. The inspector checks the sole plate level and fixings, panel plumb and alignment, holding-down straps and restraint, racking board nailing, the breather membrane and laps, and the moisture content of the frame.
A timber frame goes up in days and is closed in within weeks, so the inspection window is short and the consequences of missing it are large. Almost everything structural — straps, restraint, racking board fixings, joist hangers — is behind a breather membrane and then a masonry outer leaf before anyone comes back.
The inspector starts at the bottom. Sole plate level, bedded and on a continuous DPC, correctly fixed down, and the frame set out square to the substructure. Then panel plumb and line, the fixing pattern between panels and to the floor decks, holding-down straps at the frequency the frame designer specified, and racking boards fixed at the correct nail spacing rather than "roughly every foot". Above that, the joist and roof connections, and then the envelope: breather membrane lapped and taped, cavity barriers and fire stopping at compartment lines, and the cavity kept at the designed width once the outer leaf starts.
Weather exposure is the item unique to this stage. Frames have a maximum tolerable exposure period before the moisture content of the timber and the condition of the boards become a problem. Record the erection date, keep the frame covered where you can, and take moisture readings before you close it in.
When it happens
As the frame is erected and before the breather membrane is covered by the outer leaf, insulation or internal linings. On multi-storey frames, at each lift.
Who inspects
Warranty provider inspector, building control, and the frame manufacturer's own erection sign-off — most suppliers require their completion check before their warranty applies.
If it fails
Structural fixings missed on a frame usually mean taking down brickwork or opening internal linings to reach them. A frame left exposed too long can require drying, replacement of swollen boards, or a moisture survey before it can be closed in.
Concealed work cannot be re-photographed later. Take these before the element is covered and file them against the plot.
A Reportable Item (RI) is a defect the inspector records against the plot. NHBC weigh each one by its Damage Potential, and the score feeds your site's Construction Quality Review. These are the ones raised most often here:
The measurable values most often argued about at the timber frame erection visit, each traced to an openly published source. Take a tape to the ones that apply before you book.
| What | Value | Type |
|---|---|---|
| Breather membrane lap on a timber frameHorizontal laps shingled downwards; vertical laps over a stud, taped where the manufacturer requires itCheck laps before the outer leaf rises past them — they are unverifiable afterwards. | 100 mm | Minimum |
| Cavity barriers at timber frame panel junctionsBarriers tight to both faces of the cavity, fixed and continuousCheck at window and door reveals, eaves, and the separating wall line before the cladding closes the cavity. | At every compartment junction and opening edge | Maximum |
| Clear cavity behind the breather membrane in timber frameClear residual width, measured from the face of the breather membrane to the back of the outer leafCheck the cavity is clear of mortar snots at each lift and that the gap is maintained where ties and services cross. | 50 mm | Minimum |
| Lateral restraint strap spacing at floor and roof levelStraps at floor and ceiling level, carried over at least three joists with solid nogginsConfirm straps are fixed down the full leg and that noggins are tight, not just nailed on the face. | 2 m | Maximum |
| Racking board fixing centresFixings kept at least 10 mm from the board edge; pattern to the frame designer's specification where it is tighterSpot-check a panel per house against the designer's nailing schedule before the membrane covers it. | 150 mm at board edges, 300 mm at intermediate studs | Maximum |
| Sole plate DPC height in a timber frame wallMeasured from finished external ground or paving level to the underside of the sole plate DPCCheck before the frame is loaded — once panels are up the DPC line cannot be adjusted. Photograph each elevation against a levelled datum. | 150 mm | Minimum |
| Timber moisture content before closing upMeasured with a calibrated meter at several points, including sole plates and the base of studsTake readings low down on the frame where water collects, and record them with the pre-plaster photographs. | 20 % | Maximum |
| Wall tie spacing to a timber frameTies screwed into studs, not sheathing alone; closer spacing at reveals and movement jointsCount ties per square metre on a sample bay and confirm each one lands in a stud, sloping outwards with the drip clear. | Max 600 mm horizontally (at stud centres) and 450 mm vertically | Maximum |
0 of 21 ticked — saved on this device
Check sole plate is level, fully bedded and set out square to the substructure (NHBC 6.2)
NHBC 6.2Confirm continuous DPC is installed beneath the sole plate and lapped with the floor DPM (AD C)
AD CVerify sole plate fixings match the frame designer's specification for type and spacing (AD A)
AD ACheck panels are plumb, in line and within the manufacturer's erection tolerances (NHBC 6.2)
NHBC 6.2Verify holding-down straps and panel-to-panel fixings are complete at specified centres (AD A)
AD AConfirm racking board type, orientation and nail spacing match the frame design (AD A)
AD ACheck joist hangers, headbinders and floor deck fixings are correct and fully nailed (NHBC 6.4)
NHBC 6.4Verify no structural members have been cut or notched for services without approval (AD A)
AD AConfirm temporary bracing remains until the frame is permanently stabilised (BS 5268-3)
BS 5268-3Check breather membrane is correctly lapped, taped and continuous with no tears (BS 5250)
BS 5250Verify the cavity between frame and outer leaf is the designed width and clear of droppings (NHBC 6.2)
NHBC 6.2Confirm wall ties are the correct type for timber frame, fixed to studs not sheathing only (NHBC 6.2)
NHBC 6.2Check cavity trays and DPCs at openings are dressed to shed water outwards (NHBC 6.1)
NHBC 6.1Verify window and door openings are lined, sealed and weathered per the supplier detail (NHBC 6.7)
NHBC 6.7Confirm cavity barriers are installed at compartment lines, openings and around the perimeter (AD B)
AD BCheck separating wall construction matches Robust Details for fire and sound (AD E)
AD EVerify fire stopping at floor-to-wall junctions is installed as the frame is erected (AD B)
AD BRecord the erection date and monitor exposure against the manufacturer's maximum period (NHBC 6.2)
NHBC 6.2Take moisture content readings before closing in and record them on the plot file (NHBC 6.2)
NHBC 6.2Confirm the frame supplier's erection completion certificate is issued and filed (NHBC 6.2)
NHBC 6.2Photograph straps, racking fixings and membrane laps before the outer leaf is built (BREL)
BRELA timber frame is at its most vulnerable between erection and getting weathertight. Everything you do in that window decides the shrinkage and cracking snags later. No inspector will fail the visit on these — they are the difference between a plot that passes and a plot that hands over clean.
Sheet and drain any open floor deck at the end of each day
Standing water on a deck soaks into the panel bottoms and the shrinkage cracks appear in the plaster six months after handover.
When: Every day until the roof is on.
Store panels off the ground and covered before erection
Panels stacked on wet ground wick moisture up and go out of shape before they are even lifted.
When: On delivery.
Protect breather membrane edges and repair every tear
An unlapped or torn membrane is a wind-driven rain path that will not show up until the first storm from the wrong direction.
When: As each elevation is closed.
Record moisture content readings before boarding
A documented reading protects you when shrinkage cracking is blamed on the frame.
When: Before any internal lining goes on.
Protect the sole plate and DPC junction from trades and plant
Damage here is a damp bridge straight into the timber and it is buried by the first course of brick.
When: Before the outer leaf starts.
Keep fixing and strapping schedules with the plot record
Restraint straps get queried at every stage. Photographs with the plot number in shot settle it in seconds.
When: As installed.
8 inspection points that apply at the timber frame erection stage, each written in our own words from openly published guidance, with how to check it on site and what counts as acceptable. Use the checklist above on the day and this register when you need to settle a detail.
Wall ties fixed to sheathing only
Ties must land on a stud. Fixed to OSB alone they have no meaningful pull-out capacity, and it is a routine timber frame RI.
High — no meaningful pull-out capacity, and structural.
Racking board nails over-driven
A nail gun set too high punches through the board face and the fixing loses its shear value. Set the gun and spot-check the pattern.
Medium to high — reduces shear value across a whole panel.
Breather membrane torn during brickwork
Scaffold and trowel damage behind the outer leaf goes unseen. Inspect and patch the membrane as each lift goes up.
Medium — but needs patching before the outer leaf goes up.
Frame left exposed over a wet winter
Exceeding the supplier's exposure period invalidates their warranty and can require a moisture survey. Sequence the outer leaf to follow the frame closely.
High — can require a moisture survey or panel replacement.
ProPlot's audit tool includes these timber frame erection checks as interactive helpers — tick items off, attach GPS-stamped photos, and share the report with your inspector in one tap. Free while in beta.
The key stage inspection sequence on a typical UK housing plot.
Excavation & foundations
21 checks →
Drainage
20 checks →
Basement / lower ground
28 checks →
Ground Floor & Slab
19 checks →
Superstructure
22 checks →
Roof
22 checks →
Windows and External Doors
24 checks →
Insulation & Airtightness
23 checks →
First Fix
28 checks →
Fire Stopping
22 checks →
Pre-Plaster
21 checks →
Second Fix
31 checks →
External Works & Pre-Handover
23 checks →
Pre-handover
22 checks →
General Quality
20 checks →
Snag lists with GPS photo evidence
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