Insulating 9" wall.

[Andrew Gabriel]

Looking at a built-in wardrobe, which backs onto a 9" north facing wall. Currently, the door is always left open because otherwise the wardrobe gets cold, with the door and to some extent the clothes doubtless forming an insulation layer comparable to that of the 9" brickwork, so the wardrobe would sit at a temperature way below the rest of the house, and would be liable to condensation. I say "would" as that hasn't happened yet as we keep the door open, the the clothes spaced away from the back wall.

Thinking of insulating options. Can't afford anything more than about

2" lost at the back, so I'm thinking of getting some of the 50mm celotex/kingspan plasterboard and dot and dabbing that on. My concern is what happens behind the board. There will inevitably be an air space of about 1/2", and this is going to get moisture in it because 9" walls always breath some moisture. Also, if there's any possibility of air from the house getting behind there, it's going to be a super-cold spot which will guarantee condensation.

So my thought is to provide some vents through the wall to trickle vent the 1/2" space behind the board to the outside, and to try to seal the insulation board to the wall using not just dots of bonding, but a continous sausage of plaster board bonding around the outer edge to prevent any house air getting behind the boards.

Anyone done anything similar, i.e. dot-n-dabbing insulated plasterboard?

[jim]

indeed I have - on solid 12" brick walls a few years ago. I actually remember looking up on manufacturer's websites and getting tech. details for it (british gypsum "blue book"??):.....

so- yes to the "continuous" perimiter of adhesive, plus usual dabs in middle (some of my boards had memorable amounts on to also true up a wonky wall).

also pay attention to board junctions (if you will have any) I had taper edge boards so could tape and fill to seal.

I did as spec said and added a couple of frame fixers through each board say 6ft high - in case worst happens and fire burns the insualtion off they (hopefully) will hold the boards up whilst we scurry out... in your wardrobe I suppose itmay be overkill but easy to do before plastering.

mine went up abt 5 years ago in lounge and dining rooms, - no probs since with damp, condensation or ought to speak of really and a lot warmer! Suspect that once equilibrium is achieved in the small spaces behind the boards, damp is less likely to "move" across from either side to the other?

NB the boards I got were sold to me as "closed cell" insulation - IIRC polystyrene (for e.g.) is open cell so damp will migrate across/ through it. The boards I got had 25mm pink insulation sheets stuck to them. Easy to dot and dab I roughed em up a bit with a plasterboard saw to give the adhesive an extra "key"

cheers jim

[John Rumm]

Hmm, uncanny that - played a very similar game here. We have the mother of all cupboards in our hall - 3 - 4' wide (varies) and about 12' deep. It was in effect made by chopping a slice off a room so as to provide a route for a staircase when the loft space was converted some time in the past.

On arrival last year it was the ideal place to lob all sorts of "stuff" that one could not work out where to place elsewhere. Several months later, investigation into the damp smell revealed a very damp back to the cupboard. The skirting and floor was soaking, and the wall seemed wet. There was no obvious source of moisture though. Had a strip of floor up at the back and found the brickwork (9" solid with render over) was soaking - droplets sitting on the surface, and a small 4x2" joist between sleeper walls that was tucked up right against the wall was rotten as well.

It seemed that part of this was a general problem that although there is a substantial underfloor void (about 4') ventilation was very poor. An extra 9 airbricks have solved that - you can now feel airflow under there. The other problem was exactly as you describe - cold wall, warm air, not much air circulation, plus stuff tucked up close to the wall making it worse, and to top it all its the place with all the coat hooks so damp coats get stuffed in there as well.

So for a quick fix, I cut some 2" foiled PIR foam to size[1] and glued it to the wall with expanding foam. I then filled any gaps around the edge with foam as well.

That fixed the condensation on the wall. Having given it a few months to work, I had a floorboard up again a couple of weeks back, and the wall is now much drier, no visible moisture, and the underside of the floor boards are also dry (they were literally dripping before). So at some point when a suitable round tuit is located, I will foam some plasterboard on top, caulk round the edges and paint it cupboard colour.

[1] I had just ordered a van load to do my workshop with, so had sheets sat there ready!