Simply refixing the same boards in the same pattern, or replacing individual boards without addressing the cavity or treatment behind them, tends to produce the same cupping again over the following seasons, because nothing about the moisture imbalance has changed.
A proper repair looks at the whole system behind the visible boards — the cavity, the treatment, and the fixing pattern — not just the boards that are currently showing the problem.
What has to be opened up
Removing the affected boards, and usually a wider run either side of them, allows the cavity and wall construction behind to be properly assessed rather than guessed at.
The correct sequence of works
Each element needs correcting together, since a ventilated cavity with wrongly treated boards, or correctly treated boards with no cavity, will both still fail.
- Refix boards at correct centres, allowing genuine movement gaps rather than tight, restrictive spacing
- Treat all faces of the boards, front and back, before refitting rather than leaving the back face raw
- Form a properly ventilated and drained cavity behind the boards, with vents at top and bottom to allow air movement
- Replace any boards that have distorted beyond what can be pulled back flat, rather than reusing them
Why simply refixing the same boards fails
Pulling a cupped board flat and screwing it down harder can hide the distortion temporarily, but the moisture imbalance between the two faces hasn't changed, so the board keeps trying to cup and either pulls the fixing loose again or splits along the grain under the stress.
Interfaces with other trades
Where the cavity and any breather membrane behind it need attention, this crosses into general building fabric work, and it's worth checking the wall's overall build-up and any insulation while the cladding is off, since it's rare access to see it again without removing boards.
How you know the repair has worked
Check the refitted boards after a full season through both wet and dry weather — they should sit flat with fixings staying flush, rather than lifting again as conditions change. A properly ventilated cavity should show no trapped moisture or staining if inspected again at a later maintenance visit.
Common questions
Do all the boards need replacing, or just the cupped ones?+
Only the boards too distorted to pull back flat need full replacement — others can often be refixed correctly once treated on both faces and given proper spacing, provided the cavity is corrected at the same time.
How do I know if the cavity behind my cladding is properly ventilated?+
Look for vent openings or gaps at the top and bottom of the cladding run. If the cladding appears sealed tight to the wall with no visible venting anywhere, it's likely the cavity isn't performing as it should.
Will treating both faces of the boards really make a difference?+
Yes — an untreated back face absorbs and releases moisture at a different rate to a treated front face, and that imbalance is one of the most direct causes of cupping, so treating both faces evenly removes a major contributing factor.
Get a written quote to fix your cupping cladding
We'll refix at correct centres, treat both faces, form a proper ventilated cavity, and quote it all in writing.