Got a 1920’s house which is single skin on the upstairs and one room (north east corner) is freezing. Its a double brick thick wall but with no real cavity to speak of. Damp has been an issue at some stage and wall vents have been installed. These appear to have exacerbated the problem with damp by creating really cold spots where condensation has formed.

I’ve replaced the floor, sealed around joists, insulated between joists with loft insulation and picked up 25mm celotex plaster boards. However I’m now wondering if this is enough?

The opposite corner room has been dry lined with plaster board on batons and dpm and that room is noticeably warmer in the winter.

Questions are, do I sacrifice more of the room and add in another 400mm of celotex say?
And can the boards just be dotted and dabbed or do they need batons and dpm again?
Finally, can I do away with the retrofitted wall vents as they seem to cause more problems than they solve?

Oh and before you ask, we only bought the place in December.

We mounted the 50mm celotex directly to the wall and battened the boards and added fireboard dry lining to the 50x25mm battens.

Just use pre backed board on dabs. The reduction of cold bridging (causing damp) onto warm interior walls will be reduced immediately. 400mm cellotex seems overkill 😉

Sorry, extra 40mm of celotex I meant! So the plasterboard with 25mm celotex on should be enough you reckon? And dabs are fine?

Oh, do I put a top and bottom continuous seal on the rear also?

The issue with dot and dab insulation boards is the dabs can create a bridge for moisture so you have to apply tanking slurry the wall first. This is why we went for the separate boards and insulation. this also has the added advantage of an air space between the two.

More is better. Its a job you only want to do once. If you’ve insulated the floor, you might not be getting too much heat from downstairs. I went 50mm in rooms that were approx 10x10ft.

Pretty sure you’re meant to fix it to batons, but not an expert. Really important to pay attention to vapour barrier integrity.

Good luck, mine is like a different house. The old cold bedrooms, which used to be the coldest rooms in the house are now the warmest 🙂

No I’d go for the thicker boards. And dot and dab isn’t an issue for bridging damp unless the walls are wringing wet. The air space created by the dabs also help.

I had to insulate the floor as it was freezing, the cold that came through it was ridiculous so I was losing everything from below in any case. Point taken about the vapor barrier though

I’ve done 50-100mm Celotex/Kingspan held to the wall with battens, then screw plasterboard to battens. Before you plasterboard go round all the foil edges with tape, and use expanding foam in every little gap. 100mm of insulation to underdraw ceilings too and you can make a room toasty. Disadvantage is the fixings can be cold bridges, but I’ve not found it much of an issue(never tried to measure it either, but can’t feel a difference).

My preference is to avoid dot and dab, as if a gap appears on the outer skin through movement or pointing breakdown, drafts will soon find a way through to give cold spots, if the insulation is clamped hard to the outer wall it’s less likely. I’ve also had mice runs behind dot and dab before.

With separate insulation and plaster, wiring and services are easier to deal without digging big chunks out and making cold spots. I think regs say you should have some mechanical fixings for fire safety, even if you dot and dab. I think there is a combo foam/glue that would make the job a bit easier if your walls are suitable.

We’re in the process of putting insulated plasterboard up in each room of our 1930’s house as we gut and decorate each room.

Most of the rooms have been done with Gyproc Thermaline 50mm boards (9.5mm boards with 40.5mm of foam on the back plus have a moisture barrier built in) dotted and dabbed with a couple of mechanical fixings through each. The pointing on the walls has been tidied up where required and the edges sealed with foam to minimise drafts.

They’ve made a massive difference to the temperature in the rooms we’ve done, but it massively shows up any drafts through floorboards and round windows. The next job I have to sort is a draft coming through the bay window in my lads room that I wouldn’t have noticed before.

Make sure that you put something into your window reveals as well. I didn’t engage my brain and used uninsulated board in the windows of one bedroom and get a tiny bit of mildew in winter. 👿 😳

edit – your damp could just have been bad condensation. It was for us in both bedrooms, the walls were so wet I thought the roof was leaking at first when we moved in!

The specifications are all in the regulations. Start here:

Energy Saving Trust

I think you may have to inform building control.

I’ve used Marmox board because it’s a thinner board for the same ‘R’ value as an insulated plaster board.This is more expensive than plaster board, but you lose less of the room.

Hth
Marko

I think you may have to inform building control.

😆 I give in!

So many British houses were built at at time when coal was cheap and most families had a young maid or relative who could run around with buckets of coal all day. This kept the house reasonably warm and very well ventilated as so much air was sucked up all those chimneys. With the vogue for blocking everything up, condensation has become a big problem.

We also had a room in an extension that was freezing. Having the unheated garage below it didn’t help. We put battens and Kingspan on the walls topped with plasterboard backed with polystyrene foam, as well as thick Kingspan in the ceiling and it’s just amazing how the room has been transformed; it’s now the warmest, cosiest and quietest room in the house. I wish we had done all the other exterior walls when we moved in and gutted the house. Too late now.

The only downside of the plasterboard backed with polystyrene foam is that it compresses so when you push on it, the fixing screws can pop out.

Next house we buy will get the full treatment, all over, before we even move in.