Insulation for brick double garage - I'm confused

[LeeElms]

I'm confused between the various types of insulation available, as to which is most cost effective. I plan to use it behind plasterboard on 3x2 CLS timber framework filling in between the double thickness piers. I also plan to insulate above the plasterboard ceiling.

So, hoping for simple advice as to how to provide a reasonable amount of insulation for a reasonable cost.

My confusion is due to the range of insulation products available, and because when I tried to understand the various U values and prices, it appeared that Celotex, which I had assumed was a relatively expensive option, was cheaper than Rockwool (for the same insulation value). Another consideration (just to complicate things) is which option is better for sound insulation -- although, in respect of both the heat and sound insulation I realise that what I do with the garage door is a signficant factor.

 

[RobinBHM]

if your walls are reasonably flat, you could simply fit a continuous layer of celetex PIR sheet insulation all the way round. Fix in place with 2 x 1 or 3 x 1 laid flat and plasterboard over.
you will then have no gaps or thermal bridging at studs, so you will get the most bang for your buck! I would think 50mm would give you a good amount of insulation.

Try the kingspan site for a u value calculator to compare

Im not sure about acoustic insulation, Id be tempted to do a double layer of plasterboard, or 1 layer of 18mm osb and 1 layer of plasterboard.

Rockwool can be used for sound insulation, but the batts for that are much higher density so probably not much good for heat.

 

[Blister]

I used a 4"x 2" batten frame work with celetex panels between the uprights , then covered with 8 x 4 sheets of OSB board , painted a light cream colour , using OSB gives good fixings for plug sockets / switches / shelfs etc

 

[MMUK]

If you use the CLS end on and use 50mm Celotex, by the time it's boarded you should have plenty of depth for dry lining socket boxes. 50mm Celotex is roughly equivlaent to 150mm poystyrene or 225mm fibreglass. As a guide, I pay £14.50 +VAT for an 8'x4' sheet of 50mm Celotex from Magnet.