Insulating a wall

chookmom

Hi, My home has a cavity wall but was deemed not suitable for CWI as the cavity has too much rubble inside.
2 of our rooms are particularly cold as they are on the end of the house and have outside walls on 3 sides and windows on 2. One is the living room and manageable, the other is a large bedroom.
I am trying to interest my husband in building an internal insulating layer across the back wall of this room (no windows, chimney runs up the outside of it). He thinks there is enough wire in the sockets to bring them forward a bit.
Is this a bad idea? Will it cause damp? If ok, what thickness of Kingspan type insulation would be appropriate.
Thank you

FreeBear

There are several ways of insulating a wall internally. In no particular order -

• Build a studwork frame and use mineral wool batts or PIR foam boards (Celotex/Kingspan). Then cover with plasterboard. Cheap, but not that quick to do.
• Use a thermal wall board - Either polystyrene or PIR bonded to a layer of plasterboard so you just have one sheet to handle. Quick, but expensive.
• Warm battens - Cover the wall with 50mm PIR foam boards, fix 50x25mm battens at regular intervals (typically 400-600mm), and then fill the spaces with 25mm thick PIR boards. Plasterboard is then fixed to the battens. Fairly cheap, but not the fastest method.
• Studwork and fill the space with sprayed Polyurethane foam and then plasterboarded over. Be aware that there may be health issues from the fumes as the foam cures.

PIR foam will give much better performance than the equivalent thickness of mineral wool - 75mm should be more than enough to meet current guidelines on a cavity wall. If you use mineral wool, 100mm or more would be needed. The other advantage of using PIR foam boards is that they include a damp proof membrane unlike the stud methods.

When I get to the point of installing wall insulation, I'll be going the warm batten method - Materials will be lighter (per sheet), and I should be able to manage to do it without a helping hand.

SailorSam

How did you find out about the rubble ?
Hasn't that caused you any damp problems ?

chookmom

Thank you Freebear for your comprehensive reply that has been very useful.

Sailorsam, we applied to British Gas for free CWI, they came and did a survey, drilled a few holes low down in the walls outside and said not suitable. The rubble is not causing problems. We have no damp at all.

patman99

It is possible to get the ubble out from the cavity if you don't mind a bit of work.

You need to remove 4 bricks - 2 from the DPC + 2 above, reach in and scoop out the rubble before replacing the bricks, moving along the wall and repeating. A good brickie should be able to undertake this for a small amount of cash.

Your cavaties will then be free of rubble and might well then be suitable for CWI.

FreeBear

chookmom wrote: »

Thank you Freebear for your comprehensive reply that has been very useful.

Just to add - Regardless of which method you use, the experts recommend stripping off any plaster & screed back to bare brick. Then give the wall a thin skim of cement screed to level & smooth the surface.

Depending on how thick your plaster is, this could shave half an inch or more off the total thickness of insulation & plasterboard. On my walls, the plaster is over one inch thick in places, and the less floorspace I lose, the better.

Davesnave

If the end wall of the house is in an exposed place and you live in a high rainfall area, I'd go with the interior insulation rather than risk clearing the cavity and filling.

chookmom

We have now insulted the wall using the warm batten method and it has made a significant difference. Thank you for pointing s in the right direction

FreeBear

How thick was the insulation layer in the end ?