Insulation - Conflict of Opinion :(

[Ed21]

Hi All, 

Back at end of January I asked on here about what method of internal insulation to use on a bungalow
with cavity walls and got some good advice.
Turned out the joists in the room were shot so had to replace all the floor first  ? 

The consensus at the time was  50 mm fixed to the wall, battens on top of that followed by plasterboard
making a sandwich of 50+25+12.5 = 87.5mm. 

Now had a spanner thrown in the works from another local builder who said fix battens to the wall, fill voids 

and cover the lot with insulated plasterboard. This is very close to what I had planned originally with the
exception of being separate insulation/plasterboard. 
This version would be 62.5mm 
 

He also sent me a link https://www.youtube.com/watch?v=X4QWdw5vmok 

Ceiling and Floor is done, walls are prepped ready and have the materials to do both, so as this sets the
precedent, which version would you choose?

Ed

[Mr Punter]

Insulated plasterboard is quite pricey.  Are there many sockets, switches and rads?  Thicker one makes stuff a bit easier to run but not much in it.

[Ed21]

Yeah won't be buying insulated, all separates. 
As the floor had to come up, new rad and rewiring sockets anyway, that's not an issue. 
 

Suppose what's confusing me is why Xtratherm don't have a gap in the video. 

[TonyT]

The 50mm insulation on the wall first when it’s taped up will act as a better insulator as it’s completely covering the whole wall.

 

the battens fixed to the wall first , will give cold bridges.  

[tonyshouse]

Better, a lot better in air leakage terms and bridging and cost not to have them 

 

insulation fixings are good - fixing foam then mechanical fixings for me