What would you do?? Insulation....

[Batesyboy]

The scenario is this -

A small timber framed bungalow, with an external "chicken wire" pebble dash render over wooden weatherboarding. All of the old lath and plaster walls and ceilings have been removed exposing the 10cm cavities. A full central heating system will be installed and with a view to retaining that heat but what would you choose to use to insulate the walls and why? New plasterboard walls and a skim will then be placed in. Your views and opinions would be most welcome - many thanks

 

[freddiemercurystwin]

100mm of Celotex or Kingspan between the studs any gaps sealed with expanding foam, add a 25mm continuous layer on the inside then plasterboard and skim.

 

[AronSearle]

100mm of Celotex or Kingspan between the studs any gaps sealed with expanding foam, add a 25mm continuous layer on the inside then plasterboard and skim.

If this is an old timber frame (and I assume so if it has lath and plaster rather than plasterboard), with-----Studs, softwood boarding, and render direct to the board (with no cavity) this "could" be very bad.

A lot of older timber frames have cladding direct to the frame, but no real insulation. Small amounts of moisture will penetrate through the cladding material, but the frame is protected in a twofold manner. Firstly the lack of insulation means a lot of heat is lost through the wall, and this drives the moisture back out, keeping the frame dry, and secondly some of the moisture is able to evaporate in the cavity, rather than pool.

I have seen some instances where filling the cavity, eliminates these two actions, causing decay in the frame, however in sheltered locations you may "get away" with it.


The least invasive option, is to fill the cavity with rigid foam up to 80-90mm thick (you can put in some timber battens to maintain the cavity), leaving the 10-20mm gap directly behind the softwood boarding attached to the studs. the heat loss effect is obviously lost, but at least moisture that penetrates the render is not directly trapped between the two surfaces, and this helps to somewhat dissipate it.


Obviously if you do have a cavity, then yea, full fill it.