- Plan ItBack
- Design ItBack
- Build ItBack
- Homes
- ProductsBack
- CostsBack
- Self Build Cost Calculator
Estimate your project costs instantly with Build It's interactive self-build cost calculator
Calculate Now - Costs & Finance
- Contracts & Warranties
- Build It Estimating Service
Get an accurate, detailed cost breakdown of your project
Submit plans
- EventsBack
Q&As
How should I deal with damp in a cavity wall?
I own a new build property that is around three years old. The rear of the house is a single storey (extension-like, but original) kitchen/ diner with a low pitch roof (13 degrees). The external single storey wall facing into the garden is mainly made up of glazed bifold doors, with around 70cm of wall each side. There has been water ingress into the wall section in two areas, most likely since it was constructed, and the interior plasterboard is stained. This was caused by incorrect rooflights being installed for the pitch of the roof, which have now have now been replaced. The wall insulation is likely wet too, but I don't know what the internal construction is or if there is any membrane. Is it likely I will need to employ a cavity wall dry pressure system to get the wall dry again? The area does get some sunlight in the mornings, but not much as I'm in south Manchester. If a dry pressure system is needed should the internal plaster board be removed first?
One Answer
Hi Paul,
Thanks so much for getting in touch with your question. It’s a shame that this has caused so much disruption and unfortunately it happens too often due to poor installation, or the roof being too low pitch for the rooflight that has been fitted. In terms of the water damage, this usually requires a fair amount of time to dry out. When homes are flooded, often the plaster is removed to allow the walls to dry out and this would appear to be a similar situation – albeit you will have damage at the top of the roof potentially running down through the whole wall. Depending on how long the leak has been there and how extensive the water ingress has been, this may be a course of action you have to take.
I would start with a damp meter and probe the plaster to see if this is showing excessive moisture. The only way to penetrate the layers behind will be to remove sections of plaster to access the block or brick behind this. If you do find excessive moisture then I would suggest the entire plaster removal in the damp areas.
Externally the wall will dry out eventually and that leaves the insulation. It is possible to drill a hole into the cavity and use an endoscopic camera to see if this area is also damp. If you think it is, you may need to produce a more sizable hole using a core drill to pull some of the upper section of insulation out and assess how damp this is. If it is a PIR type insulation, then this will also eventually dry out but if it is a mineral wool type its effectiveness will be hampered by the damp and it will be more difficult to remove. It may well be that you will need to leave the plaster off for some time to enable this layer to dry out, as it would be very difficult to try and replace this. As this is a new build, you may find that you have warranty for the property that may cover any rectification works that need to be done. Therefore, I suggest you get in touch with them first to see how they want to deal with the remediation rather than you starting a process that they may not cover.
Best of luck,
Opinder Liddar (Architect, Build It expert)