Interior wall insulation

[tomredsky]

Hello,

[Short version]
Can I put insulated plasterboard on one or two walls only on a room or must it be fitted to all the walls?

We moved into a 1900(ish) terrace house. It has solid 9inch walls. We started "refurbishing" the front room which has a north facing wall and two party walls. On one wall there's a (non-functioning) chimney breast and alcoves. The alcoves will be fitted with built-in cupboards so I don't see any point in boarding that wall out. The wall opposite the chimney sits between the front-room and the entrance hallway. To my mind, these two internal walls are less of a concern and because we do not want to lose 100mm+ of space, I'd be happy to go with hardwall and multi-finish for these two walls.

We've ordered new bay windows for the north-facing wall. I think the addition of insulated plasterboard would be a real benefit but I'm a bit fearful.
Any thoughts?
Thanks,
Dermot

 

[accelerator]

Fearful of what exactly?

 

[StephenStephen]

One thought - if the built in cupboards are on external walls, they will provide an ideal environment for damp and mould (unless you insulate the wall behind them)

 

[noseall]

Hello,

[Short version]
Can I put insulated plasterboard on one or two walls only on a room or must it be fitted to all the walls?

We moved into a 1900(ish) terrace house. It has solid 9inch walls. We started "refurbishing" the front room which has a north facing wall and two party walls. On one wall there's a (non-functioning) chimney breast and alcoves. The alcoves will be fitted with built-in cupboards so I don't see any point in boarding that wall out. The wall opposite the chimney sits between the front-room and the entrance hallway. To my mind, these two internal walls are less of a concern and because we do not want to lose 100mm+ of space, I'd be happy to go with hardwall and multi-finish for these two walls.

We've ordered new bay windows for the north-facing wall. I think the addition of insulated plasterboard would be a real benefit but I'm a bit fearful.
Any thoughts?
Thanks,
Dermot

Add insulation to all outside walls.

 

[tomredsky]

Fearful of what exactly?

That it will be ineffective or create damp/mould on the edges where it butt's up to the uninsulated walls.

 

[robinbanks]

Buy or hire a thermal imaging camera and make careful note, when your heating is running and the house is the temperature you like it to be, which are the coldest walls

As noseall says, you should really prioritise insulating external walls, but also you may have internal walls that are solid and directly connected to external walls so they bridge across the insulation layer from the room to the cold outer wall

Ultimately insulation of the cold surfaces will help reduce your heating bill but you have to be quite critically aware of where the insulation layer has something passing through it. For example you can insulate the wall, but if you cut a large hole in the ceiling and stuck your head up into the void you'd see your thin ceiling plasterboard/plaster-lath and the floor joists and a void that goes all the way to the cold outer wall; this is a heat escape path because the plasterboard of the ceiling offers little insulation and the void is cooled by the external wall and possibly l draughts around the joist ends (depending how good the masonry is)

If you're committed to doing a complete job you really need to be looking at making the house have as continuous a layer of insulation as possible, and that can be made external on the walls, joining with the loft or roof insulation at the eaves. If you're doing it internally you're going to have a lot more places that the insulation layer has something passing through; this is the compromise you have with older properties, that you can design out of a new one when you build (but eliminating all thermal bridges retrosoecctively is so massively disruptive you wouldn't bother)

All in, any efforts you make will help, and everything you can do to keep moist room air away from cold walls will also help, but do decide how hardcore you're going to go, whether you're going to be removing a foot of ceiling plasterboard around room edges or blowing the voids full of insulation, lifting floorboards etc.. and avoid having areas where cold world air from draughts can bypass your insulation as it then means the insulation will do little to nothing at all

 

[tomredsky]

Thanks for the helpful reply.

I hope to replace the ceiling too. As you've say, it's probably lathe and plaster, I suspect there's a sheet of plasterboard laid over it.
When we get to do the room above, I'll fill the voids between the joists with Knauf or similar. I hope to do something similar to the suspended floor of this front-room but I need to replace the lead water main running under the joists first.

As I said, the other two walls are party walls. These walls don't face the outside but they will butt-up to the front, outside wall. It's really about space saving because the room is about 4m wide so we want to keep as much width as possible.

I'll start hunting about for a thermal imaging camera too.

 

[accelerator]

You only need to add insulation to the external wall, the internal ones should be ok.

 

[tomredsky]

The other question I have is what brand and type of thermal board to use?
I want the boards dot-and-daded to the wall to save space. As this is a solid wall, do I need to choice a specific kind of board? I was considering a 37mm Kingspan K118 but mostly because there name keeps coming up in my searches and youtube videos.

 

[Deluks]

I hope to replace the ceiling too.

If it's l&p and boarded over, there's not much point in replacing it unless it's in bad shape.