Can I put insulated plasterboard on top of exiting plaster walls?

[user131914]

Our house has an old extension on it. It isn't very big - about 2.5 m wide and 5m across but the 5m bit is french doors. It is freezing and I suspect there is very little/no insulation (blockwork walls). It is plastered etc just like any other room in the house.

Can I put insulated plasterboard directly on top of this to add insulation? Would that in itself cause any issues? Obviously thinking about damp etc. I don't mind losing a bit of depth at the sides of the room - if it would help to make the room warmer it will be worth it.

I know you can buy insulated lining paper but Im not convinced it will make enough of a difference.

I am certainly going to try it, but will leave a gap for air circulation.

Is it thin skinned? What's it made of? What's the roof and floor construction? Plasterboard on the walls?

You can get cork based plasters. It might it be worth insulating the outside, but the floor could be an issue. Do you get sun through the doors?

We did room by room, 200 year old cottage. We did remove skirting, batten out the walls prior to plaster boards though. Have a look on you tube. We did most of the prep but left it to the professional guys to do this job. Plastering large areas is a specialist skill.

We also lifted the floor boards and insulated underneath the floor as well.

We are planning similar, but are going to insulate and render the outside so we don't lose any space inside. Would this be an option for you?

Be very careful here. Son is an architect who's specialisesin remedial work. The problem with insulation on the outside is when it degrades water ingresses, cannot evaporate so moves inward causing damage to the fabric of the house.

People don't realise that houses move and crack in a hot summer drought. Expanding again in a cold wet winter

DH is a lime plasterer so also spends a lot of time fixing damp issues! Render will be breathable with wool insulation (I think, I'm no expert).

A lime plasterer that's wonderful. And using wool, a craftsman then.

The room is north facing, block built (with cavity), concrete slab floor (not insulated, was an old garage conversion long ago) and a vaulted ceiling again without much insulation I suspect.

I have thought about losing the vaulted ceiling to enable insulation but this would make the room feel very closed in.

outside is already rendered.

Yes you can use insulated plaster board over existing plaster. You could make the vaulted ceiling slightly less vaulted as insulation would make a big difference

I think the general advice is if gypsum plaster or brickwork then fine but if you have lime plaster then this needs to breath so won’t be happy if you overboard with no air void. I have a similar idea for our Victorian terrace that has zero insulation. From my reading (as we have lime plaster) you should use roofing battens on the walls (about an inch thick) and then put your plasterboard ontop of that. This gives a void for air to circulate and to be extra sure, put a small vent or two at the top of the walls / some other way for air and moisture to escape. This at present is the method I will be using when I do mine unless I read anything to the contrary.