Housing - Renovation: Bathroom - Solid wall insulation - Damp

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- CommentAuthortvrulesme
- CommentTimeApr 18th 2022 edited
In the process of renovating an 18th Century Listed Building and attempting to go traditional and breathable where possible.

A later extension built in the 1920s is of solid wall construction and has no DPC. We are putting a bathroom (shower, WC and sink) into this extension and I'm concerned about damp as an existing stud wall was completely rotten at the bottom. We've sorted the ground levels outside which were high and the entire floor will be breathable Limecrete with limestone pavers.

As a listed building I am not able to insulate externally but would like to insulate the internal walls and wondering if someone could recommend what to use?

Wood fibre for the bathroom seems to be out given the moisture content of the bathroom so should I just ignore breathability just for the bathroom, get the best extractor fan I can and effectively tank the bathroom with tile backer boards or is there another way?

If I put tile backer boards on a treated timber frame what insulation could I use behind? Breathable would be pointless because it could not escape through the tile backer boards.
- CommentAuthortvrulesme
- CommentTimeApr 18th 2022
Picture showing the wall which was very damp at the bottom. The timber frame attached to this wall was completely rotten.

As the wall is very uneven I will need to get something to smooth it out. Treated timber battens with tile backed boards attached, galvanised studs or something else?
- CommentAuthortony
- CommentTimeApr 18th 2022
No battens for me, wood or metal, I would foam on 80mm composite sheets then mechanically fix them with insulation fixings,
- CommentAuthordjh
- CommentTimeApr 18th 2022
What's the conservation officer's view of the 1920s extension? Does it add to the older building or detract from it? They might allow you more flexibility with it than with the older part.

If it is solid wall with no DPC and was built in the 1920s then it sounds to me more like it was intended as an unheated storeroom or something rather than part of the living accomodation
- CommentAuthortvrulesme
- CommentTimeApr 18th 2022
Posted By: djhWhat's the conservation officer's view of the 1920s extension? Does it add to the older building or detract from it? They might allow you more flexibility with it than with the older part.

If it is solid wall with no DPC and was built in the 1920s then it sounds to me more like it was intended as an unheated storeroom or something rather than part of the living accomodation

Yes I think that's what it was used for. A detached garage was added in 1994 so I think this was basically the dumping ground prior to that. Not really keen on attempting to knock it down and rebuild as everything I touch reveals another 6 things which need to be done. It's stood since the 1920s so will last many more years. Just need to sort the damp.
- CommentAuthortvrulesme
- CommentTimeApr 18th 2022
Posted By: tonyNo battens for me, wood or metal, I would foam on 80mm composite sheets then mechanically fix them with insulation fixings,

Thanks Tony. Struggling to find what you mean by composite sheets. Any chance you could post a product name?
- CommentAuthorNick Parsons
- CommentTimeApr 18th 2022
Composite: Probably insulation/plasterboard laminates. Celotex PL4000 (PIR), for example, or Kingspan K118 (phenolic foam). I prefer separate ins and pl'bd so that you can tape the VCL tight before applying the plasterboards. A composite sheet has a VCL between pl'bd and insulation, but where's the VCL on the board joints?
- CommentAuthortvrulesme
- CommentTimeApr 18th 2022
Posted By: Nick ParsonsComposite: Probably insulation/plasterboard laminates. Celotex PL4000 (PIR), for example, or Kingspan K118 (phenolic foam). I prefer separate ins and pl'bd so that you can tape the VCL tight before applying the plasterboards. A composite sheet has a VCL between pl'bd and insulation, but where's the VCL on the board joints?

Ahh got you. I know that as insulated plasterboard.....

So I think if we're going down the non breathable route I'd rather go for cement board and tile throughout. The plaster I ripped out was wet as hell which wasn't the best advert for me. So leaning towards regular foil backed insulation with the joints taped and cement board on top. Or maybe something like this fixed directly to the walls?

https://www.wetrooms-online.com/products/wedi-tile-backer-insulated-building-board-600mm-width?gclid=CjwKCAjw9e6SBhB2EiwA5myr9vLTh0vjUVp5SteGNa85S0W0KVC0yeQDiDx0g9sPiUfx5KYVWC8C5BoCnpYQAvD_BwE

One issue it won't solve is my wonkey wall seen in picture so I don't think I'm going to be able to get away from using some kind of timber or other support
- CommentAuthorkristeva
- CommentTimeApr 18th 2022
Posted By: tvrulesme

Wood fibre for the bathroom seems to be out given the moisture content of the bathroom so should I just ignore breathability just for the bathroom, get the best extractor fan I can and effectively tank the bathroom with tile backer boards or is there another way?

I seem to remember there was chap in a previous thread who raised the question of using wood fibre board in his bathroom, I think he ended up phoning Steico who told him it was fine. I'm assuming he was aiming for a breathable system.

A good extractor fan is a must in any bathroom of course, and it would be good to be sure the high ground was the cause of the damp.
- CommentAuthortvrulesme
- CommentTimeApr 18th 2022
Posted By: kristevaI seem to remember there was chap in a previous thread who raised the question of using wood fibre board in his bathroom, I think he ended up phoning Steico who told him it was fine. I'm assuming he was aiming for a breathable system.

Thank you, I'm using a lot of Steico elsewhere. Will give them a call. To be honest if this one small part of the house is the only bit which is non breathable I can live with that. I can't really get my head around wood fibre being ok in a humid environment. It's only the glue itself which is impermeable.

Posted By: kristevaA good extractor fan is a must in any bathroom of course, and it would be good to be sure the high ground was the cause of the damp.

Absolutely. I'm going to oversize the fan given the damp history. I quite like the sound of the Vent-Axia PureAir Sense with it's continuous use feature.

I've got some time before I'll be ready for the walls so will monitor the damp now the levels outside have been lowered. Gutters looked in good condition so I can't really see what else would be the cause. Nothing else came up on my very extensive survey
- CommentAuthorjms452
- CommentTimeApr 18th 2022
Slightly different to you but we had a solid walled bathroom with horrendous damp.
Plan was to fix it via external wall and mvhr.

mvhr was fitted a year before the external wall and solved the whole thing (i.e. ventilation fully resolved it)

John
- CommentAuthortvrulesme
- CommentTimeApr 18th 2022
Posted By: jms452Slightly different to you but we had a solid walled bathroom with horrendous damp.
Plan was to fix it via external wall and mvhr.

mvhr was fitted a year before the external wall and solved the whole thing (i.e. ventilation fully resolved it)

John

Nice, which MVHR did you go for? Decentralised or whole house?
- CommentAuthorkristeva
- CommentTimeApr 18th 2022
Posted By: tvrulesme
Posted By: kristevaI seem to remember there was chap in a previous thread who raised the question of using wood fibre board in his bathroom, I think he ended up phoning Steico who told him it was fine. I'm assuming he was aiming for a breathable system.

Thank you, I'm using a lot of Steico elsewhere. Will give them a call. To be honest if this one small part of the house is the only bit which is non breathable I can live with that. I can't really get my head around wood fibre being ok in a humid environment. It's only the glue itself which is impermeable.

Posted By: kristevaA good extractor fan is a must in any bathroom of course, and it would be good to be sure the high ground was the cause of the damp.

Absolutely. I'm going to oversize the fan given the damp history. I quite like the sound of the Vent-Axia PureAir Sense with it's continuous use feature.

I've got some time before I'll be ready for the walls so will monitor the damp now the levels outside have been lowered. Gutters looked in good condition so I can't really see what else would be the cause. Nothing else came up on my very extensive survey

I would say it certainly is the high ground if that's what was discovered externally. I'm of the opinion rising damp is pretty rare, my house was condemned with 'rising damp' before i bought it but the reality was quite different.
- CommentAuthorJeff B
- CommentTimeApr 18th 2022 edited
Posted By: tvrulesme
Posted By: Nick ParsonsComposite: Probably insulation/plasterboard laminates. Celotex PL4000 (PIR), for example, or Kingspan K118 (phenolic foam). I prefer separate ins and pl'bd so that you can tape the VCL tight before applying the plasterboards. A composite sheet has a VCL between pl'bd and insulation, but where's the VCL on the board joints?

Ahh got you. I know that as insulated plasterboard.....

So I think if we're going down the non breathable route I'd rather go for cement board and tile throughout. The plaster I ripped out was wet as hell which wasn't the best advert for me. So leaning towards regular foil backed insulation with the joints taped and cement board on top. Or maybe something like this fixed directly to the walls?

https://www.wetrooms-online.com/products/wedi-tile-backer-insulated-building-board-600mm-width?gclid=CjwKCAjw9e6SBhB2EiwA5myr9vLTh0vjUVp5SteGNa85S0W0KVC0yeQDiDx0g9sPiUfx5KYVWC8C5BoCnpYQAvD_BwE

One issue it won't solve is my wonkey wall seen in picture so I don't think I'm going to be able to get away from using some kind of timber or other support
I had a similar problem when lining what was effectively a rough stone cellar wall. I did not use battens but instead used expanding foam adhesive (Megastik) to attach the PIR insulation sheets to the wall which compensated for the large variations from the vertical. Once set the bond was incredibly strong. We then made up a timber framework flush to the PIR, screwed it to the floor and ceiling to anchor it, and attached plywood sheets to that. Although we could have attached plasterboard to the frame we did not, as it was a storage area in a food bank and the plasterboard would have been damaged if the heavy trays of tinned goods were pushed against it.

A tip when using the foam adhesive - allow it to expand for a few minutes before attached the PIR boards otherwise the expanding foam will push the boards away from the wall!
- CommentAuthorJonti
- CommentTimeApr 19th 2022
As djh has asked, I would get the CO's take on the extension and whether it compliments or detracts from the original building. If the CO is not so fussed then you may be able to externally insulate and add exterior cladding that is tidy and makes the addition obvious.

Regardless of the above does the listed status prevent you installing a damp proofing?
- CommentAuthortvrulesme
- CommentTimeApr 19th 2022
Posted By: JontiAs djh has asked, I would get the CO's take on the extension and whether it compliments or detracts from the original building. If the CO is not so fussed then you may be able to externally insulate and add exterior cladding that is tidy and makes the addition obvious.

Regardless of the above does the listed status prevent you installing a damp proofing?

Good shout but unfortunately the exterior of this wall is directly butted up against the pavement so any further depth would not be within the property boundaries so internal is my only option.

The listed status does not prevent damp proofing. The problem here is that remediation work has been done so poorly that it's actually made the damp worse.
- CommentAuthorjms452
- CommentTimeApr 19th 2022
Posted By: tvrulesme
Posted By: jms452Slightly different to you but we had a solid walled bathroom with horrendous damp.
Plan was to fix it via external wall and mvhr.

mvhr was fitted a year before the external wall and solved the whole thing (i.e. ventilation fully resolved it)

John

Nice, which MVHR did you go for? Decentralised or whole house?

Whole house but I'd imagine that decentralised would also work.

This suggests that out problem was due to condensation on inside of the (cold) solid wall which may be different to yours but the effect was striking!

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