Using foil insulation on a stud wall to prevent damp penetration.

[Frazer G]

I have been working to "cure" damp in a house with random stone walls. The recommendation by a damp "consultant", who's suggestion was supported by local building control, has been to construct a stud wall withing the house leaving an air gap so there is no physical contact with the external wall.. The damp is thought to be a degree of rising damp with the added effect of condensation on the cold stone. 

 

The stud wall has been built (2 x 4" timbers floor to ceiling) and the spacings between the stud will be filled by 25mm PIR (I might use 30mm where space allows) which will be set back slightly within the stud frame to leave a gap between the internal surface of the PIR and the subsequent plasterboard . All the gaps etc will be taped or foam filled.  My plasterer recommended that I also use a layer of aluminium foil insulation (the type with an internal bubble gap) before I fit the plaster board. I have researched the options which seem to condense into two types, one is around 4mm thick and the other about 1mm. 

My concern is if I use 4mm (the best for insulation) will the plasterboard squeeze the bubbles to ensure that the plasterboard does not "float" but is tight and rigid to the stud work. I would be using normal drywall screws. Given there is minimal price difference I want the solution which will not give me a problem later.

[ETC]

That won’t cure anything. Just hides the problem.

[saveasteading]

Polythene on the outside of the stud would be normal. Then another inside. The bubbles will barely help so use polythene sheet from a builders merchant. 

Better to use polystyrene backed plasterboard than bubblewrap.

 

Be aware that you may still have dampness through the floor.

[Frazer G]

ETC that is exactly the objective with a major BUT if the rising damp is endemic in a random stone built wall about 18" thick short of total demolition it is impossible to stop, french drain (been there), external cladding (been there as well) so the key is to let the damp do what it will do anyway but protect the inner occupants from it's effect. Air circulation in the generated cavity will prevent unpleasant smells, mould etc. The key is to make the barrier as effective as possible hence my question as I have not used this material previously.

 

Saveasteading  I am trusting that the PIR which is foiled on both sides tightly packed between the studs and foam sealed will in effect be the inner layer of prevention as you suggest. The second barrier which will leave an air gap between the inner surface of the PIR and the PB will allow for the secondary air circulation. The only issue I have is the uncertainty if the PB fixed to the studs (effectively they are acting as battens) will be if the fixing will squash the foil at the fixing points (it obviously will not squash the portion between the studs) so that the PB is solid to the touch. I would prefer the 4mm thickness from a thermal perspective (either will give the same moisture resistance) but I am concerned the thickness will not squash sufficiently to give a "hard fix" to the PB.

 

In regard to the floor it is suspended wood so there is no direct contact with the ground.

[saveasteading]

OK it is  compromise of a job, but I wouldn't use bubble wrap. It will barely help insulation and your concern  about it crushing unevenly is valid.

[Mike]

22 hours ago, Frazer G said:

Air circulation in the generated cavity will prevent unpleasant smells, mould etc.

I hope you have adequate air vents through the external walls to allow a cross-flow of air to and from the outside behind your studs? If not, you'll make the wall wetter and risk condensation on the back of the studwork, causing bigger problems in the future.

 

On 12/01/2025 at 16:53, Frazer G said:

My plasterer recommended that I also use a layer of aluminium foil insulation (the type with an internal bubble gap) before I fit the plaster board.

Don't use bubble wrap - you risk trapping moisture behind it. If you need anything then it would be a moisture-permiable VCL, but may be better with nothing - you'd need a WUFI analysis to help make that decision.

 

 

BTW If this is the same wall mentioned in your previous thread, this is unlikely to be the best solution.

 

Edited Monday at 15:57 by Mike