What plasterboard & vapour barrier for bathroom walls & ceilin

[Andy135]

Hi PW'ers - need some advice on the below.

 

I have a downstairs bathroom that is consistently cold and suffers from condensation on the walls and ceiling which is causing mould and general mustiness.

 

I plan to strip out the bathroom and replace the suite (bath, loo, sink, shower tray and surround) - at the same time I need to replace the ceiling, which is sagging, and insulate the walls somehow in order to keep the room warmer and to prevent the condensation forming on the cold walls. The house is single skin brick built and the bathroom has one external wall, which is what's making the room cold I think.

 

So my current plan is as follows:

 

1. Replace ceiling with moisture-resistant plasterboard.

2. Renew/upgrade extractor fan

3. Remove existing wall plaster back to bare brick on the external wall and the two internal side walls.

4. Install batten framework on walls to provide insulating air gap.

5a. Install poly vapour barrier then moisture-resistant board on walls

or

5b. Install foil-laminated plasterboard onto batten framework instead of using a poly vapour barrier. Which option is most appropriate for a bathroom?

6. Shower cubicle to be clad in Aquaboard.

 

If using a poly barrier, does it need to be installed down to the base of the wall under the floorboards? And would I also need to poly barrier the ceiling too?

 

Finally, I plan to replace the window with a double-glazed unit (currently single-glazed) - when would be the best time to do this - before or after the walls have been finished?

 

As you can see there's lots to do - any advice on the order of events and on which plaster board/insulation options would be really helpful.

[sitsinhedges]

Knock the plaster back to the brick. Get tyvek breathable roofing underfelt and fix that to the wall with 25mm roofing lath screwed vertically to the wall, fill between the lath with 25mm celotex or kingspan board, cover over all of that with a polythene membrane, board and skim. Drop the polythene low enough so if any moisture runs down it can exit below the floor if possible. Maybe look at insulating between your floor joists too.

 

Foil backed plasterboard that I've used has been just silver coloured paper, not foil and would have no particular moisture resistance that I'm aware of.

[al4x]

use the plasterboard that has kingspan or equivalent stuck to it and you could just stick it to the wall, then just reboard the ceiling normally. Your issues are mainly a lack of ventilation added to the cold wall so the addition of a decent sized rad and an adequate fan should sort most of the problems on their own. Insulating that wall just goes one step further

[sitsinhedges]

use the plasterboard that has kingspan or equivalent stuck to it and you could just stick it to the wall, then just reboard the ceiling normally. Your issues are mainly a lack of ventilation added to the cold wall so the addition of a decent sized rad and an adequate fan should sort most of the problems on their own. Insulating that wall just goes one step further

 

You wont stick it to a damp wall with plasterboard adhesive.

[al4x]

is the wall damp though or being a shower room is it all condensation made worse by the single skin un insulated wall

[Andy135]

Thanks for your help al4x and sitsinhedges.

 

Wall isn't damp i.e. no rising damp or anything like that, but is usually moist to the touch for a while after the shower/bath has been used and with beads of condensation forming on external wall (but not so much on the interior side walls). Mould grows in corners of room suggest condensation and poor air circulation Also, the ceramic toilet cistern is mounted to the external wall (gets cold) and this literally drips with condensation - all pointing to condensation not damp.

 

So my gut feel is that it's condensation that's causing the problem, so insulating the cold walls/window and improving the circulation should cure it.

 

After doing some further research an insulated plaster board with integrated vapour barrier (Kingspan or the cheaper Gyproc Thermaline Plus) mechanically fixed to bare brick walls seems like the way to go.

 

Couple of questions on this...

 

A. How do you vapour seal the gaps between the boards? Metallic tape, then jointing tape & skim? Or some form of mastic between the boards as you fix them to the battens?

B. Can the insulated boards support ceramic tiles ok - for bath and sink splashbacks?

Edited May 14, 2013 by Andy135

[sitsinhedges]

A small gap between the boards gives the plaster a key and makes for a better job, less likely to crack.

Fixing battens and infilling with insulation gives you some scope for fitting sanitaryware to if you work out where the fixings will go before hand.

If a board is fixed to the wall properly tiling wont be an issue

[al4x]

Thanks for your help al4x and sitsinhedges.

 

Wall isn't damp i.e. no rising damp or anything like that, but is usually moist to the touch for a while after the shower/bath has been used and with beads of condensation forming on external wall (but not so much on the interior side walls). Mould grows in corners of room suggest condensation and poor air circulation Also, the ceramic toilet cistern is mounted to the external wall (gets cold) and this literally drips with condensation - all pointing to condensation not damp.

 

So my gut feel is that it's condensation that's causing the problem, so insulating the cold walls/window and improving the circulation should cure it.

 

After doing some further research an insulated plaster board with integrated vapour barrier (Kingspan or the cheaper Gyproc Thermaline Plus) mechanically fixed to bare brick walls seems like the way to go.

 

Couple of questions on this...

 

A. How do you vapour seal the gaps between the boards? Metallic tape, then jointing tape & skim? Or some form of mastic between the boards as you fix them to the battens?

B. Can the insulated boards support ceramic tiles ok - for bath and sink splashbacks?

What we did in my last house was lined the boards up on the wall and fixed battens on top of them with screws through the insulation into the wall so you had a continuous sheet of insulation across the wall, joints were taped with The metallic type tape you can get then plaster boards were fixed to the battens. All perfectly strong enough for tiles, if you are bothered just reduce the spacing of the battens Edited May 15, 2013 by al4x

[Andy135]

What we did in my last house was lined the boards up on the wall and fixed battens on top of them with screws through the insulation into the wall so you had a continuous sheet of insulation across the wall, joints were taped with The metallic type tape you can get then plaster boards were fixed to the battens. All perfectly strong enough for tiles, if you are bothered just reduce the spacing of the battens

 

Thanks - I'm thinking of using the insulated plasterboard i.e. with insulation stuck to the back of the plasterboard itself - so how then if the insulation is to the back of the plasterboard, do I seal up the gaps to prevent vapour/moisture from coming through?

[al4x]

you don't is the simple answer there is no way to do so but with foil boards you will get next to none through so its not really an issue, have a look here for more details, there is similar on the celotex site but you have to register to get the details

 

http://www.kingspaninsulation.co.uk/getattachment/39da3ae9-8f6c-4b8e-9220-7ae813d51603/Kooltherm-K18-Insulated-Plasterboard.aspx

[sitsinhedges]

Thanks - I'm thinking of using the insulated plasterboard i.e. with insulation stuck to the back of the plasterboard itself - so how then if the insulation is to the back of the plasterboard, do I seal up the gaps to prevent vapour/moisture from coming through?

 

You fit a damp proof membrane first as per post 2

[al4x]

and then put lots of screw holes through it..............

[Andy135]

you don't is the simple answer there is no way to do so but with foil boards you will get next to none through so its not really an issue, have a look here for more details, there is similar on the celotex site but you have to register to get the details

 

http://www.kingspaninsulation.co.uk/getattachment/39da3ae9-8f6c-4b8e-9220-7ae813d51603/Kooltherm-K18-Insulated-Plasterboard.aspx

 

Makes sense, and in fact it's way more cost effective to use your suggestions of separate insulation then plasterboard. Also means I can use board which is moisture-resistant. The Kingspan/Gyproc insulated plasterboards don't seem to be recommended for bathrooms anyway...

 

Thanks again.

[sitsinhedges]

and then put lots of screw holes through it..............

 

 

That's the way it's done, without issues.

[tignme]

Read the kingspan advice,it says insulation/vapour barrier/plasterboard all in one, we use this product daily at the moment the only difference is we use gysum metal lath with top n bottom tracks plus anchors. very simple to do.just make sure u use 400mm centres. the advantage using metal lath is obvious plus you create a small airflow cavity.

[tignme]

Read the kingspan advice,it says insulation/vapour barrier/plasterboard all in one, we use this product daily at the moment the only difference is we use gysum metal lath with top n bottom tracks plus anchors. very simple to do.just make sure u use 400mm centres. the advantage using metal lath is obvious plus you create a small airflow cavity.

Ive just finished all exterior walls in a bedroom,showerroom n a kitchen using 1oo mm board.The heating is never on at moment.

[bucksshooter]

as the man said use a 9mm plaster board with 5o mm of celetex already stuck to the back then buy a bag of browning and dab the board to the exposed brickwork