Insulating 1930's semi

[essex123456]

We have a 1930 semi, the outside wall is very cold in the winter acting like a huge ice block. I have looked at it and it appears to be 9inch solid construction. in the small box room upstairs at some time its been plastered (putting it politely) in a popcorn finish that looks awful. Id like to skim over this. But could I fit insulated plasterboard with expanding foam?, as this would saving having to disturb the surface and also add some much need insulation. I have read up a lot but am still confused if this will cause problems. I have looked on a traditional building page, but they are against anything that is not built of twigs and installed by druids. I'm sure there must be a modern solution.

thanks for any help.

 

[motorbiking]

The right thing to do is take the old plaster off, back to brick and as you say add insulated plasterboard. Its actually cheaper to use standard celotex and plasterboard. Yes you use plasterboard foam to glue to the wall. No battens and fill any gaps with standard foam. It must have no gaps for warm air to flow between the celotex and the existing wall.

To make a difference you need 50mm of Celotex and it will make a massive difference. The U value will drop from around 2 to around 0.4. Possibly lower given the small air gap the foam will produce.

By the time you've taken the old plaster off and added the insulation you will lose about 3-4cm of the room.

 

[essex123456]

Thanks for the reply, I was hoping not to remove the current popcorn as I’m not 100% when it was put on and what it may contain. Hence wondering if I could go straight over top?

I’d like to do the hall as well but due to the layout, it would cut into the stairs

 

[motorbiking]

Have you tapped it? does it sound blown or hollow? If its the original "plaster" yes it will be nasty stuff. But depending on size, you will have this done with 1 extra day and yes it is messy.

You can attach the insulation on top, but you will of course lose another 2-3cm. In that case you may want to go with celotex PL4040 and mechanical fix.

 

[essex123456]

It’s like artex finish, I’m worried in might have asbestos as I don’t know when it was done.

 

[motorbiking]

you can take samples and test for £30. But if you are going over the top, you need more mechanical fixing as the foam will stick to the paint.

 

[JohnD]

An inch of rigid foam is equivalent to two inches of mineral wool, so still worth having.

 

[kp00110]

I am currently planning exact same project - what is the thickness of dot and dab to allow for once squeeze and boards pushed into final position - is 10mm OK? planning for window boards and radiators and the like

 

[motorbiking]

I used

Soudal Genius Gun Plasterboard Adhesive Foam

Soudal Plasterboard Adhesive Foam is a fast curing replacement for traditional mortar adhesives. Use it to fill cavities and for bonding plasterboard to walls. You'll find that this foam is suitable for use on all common materials such as concrete, stone, plaster and wood.The adhesive comes...

www.toolstation.com

relative expensive, but fantastic stuff. Depending on how hard you push its 5-10mm. Also need to add some mechanical fixings to 1, make the job easier, so you don't have to stand there while it goes sticky for 5 mins and 2 helps keep it on the wall in a fire.

An inch of rigid foam is equivalent to two inches of mineral wool, so still worth having.

I used 25mm the first time, to be honest I couldn't really see the difference in warmth and its a load of work, so might as well go 40-50mm and give the radiators/boiler a rest.

 

[noseall]

10 year old reg's suggested 50mm Celotex (for old solid 9" walls). Then it jumped to 75mm and now is anybody's guess since the latest June 2022 ammendments.

50mm (PIR) as a minimum is a good place to start.

 

[essex123456]

Thanks for the replies