Improving the insulation properties of timber frame + brick skin wall.

[Andrew2004]

Our external walls have 90cm internal stud frame infilled with rockwool, 18mm sterling board, a 40mm gap and a brick skin. It doesn't meet thermal regs for an internal garage to room conversion.
Our architect specified removing the inner plasterboard, putting in foam boards then adding 42mm kingspan over that.
Question: I think there may be not enough advantage to just replace existing rockwool with kinspan insulation boards, especially as good fitting of such boards needs a lot of work. Is it just as good to leave the rockwool and plaster board and clap some 75mm or thicker kingspan on top of that?

 

[endecotp]

I presume you mean 90mm rockwool not 90cm.

(a) 90mm rockwool between wooden studs at 600mm centres (?) plus 75mm kingspan:

0.038 / 0.09 = 0.42 (rockwool)
0.12 / 0.09 = 1.33 (studs)
Say 10% of area is studs.
0.42 x 0.90 + 1.33 x 0.10 = 0.51 (studs and rockwool)
0.022 / 0.075 = 0.29 (kingspan)
1/0.51 + 1/0.29 = 1/ 0.185 (total)


(b) 90mm kingspan between wooden stids at 600mm centres (?) plus 42mm kingspan:

0.022 / 0.09 = 0.24 (kingspan)
0.12 / 0.09 = 1.33 (studs)
Say 10% of area is studs.
0.24 x 0.90 + 1.33 x 0.10 = 0.35 (studs and kingspan)
0.022 / 0.042 = 0.52 (kingspan)
1/0.35 + 1/0.52 = 1/ 0.209 (total)

So method (a) is about 13% better than method (b)

* Check these calculations before you rely on them *

 

[Andrew2004]

Wow, thanks a lot. so helpful.
Actually option a) includes 12mm skimmed pbd which I would leave and cover with the 75mm+12mm kingspan/pbd. so probably even better than 13%, and it saves a whole load of time and materials.

 

[Andrew2004]

And thanks whoever moved my question to the right forum.
Its about 8 years since I had a DIY question and DIYnot is as brilliant as it was then.

 

[endecotp]

Actually option a) includes 12mm skimmed pbd which I would leave and cover with the 75mm+12mm kingspan/pbd. so probably even better than 13%

Still 13%, to the nesrest %.

 

[Andrew2004]

Cheers