Garage Wall - Block Cavity Wall - What Layers?

[danhx]

I'm building a new 20sqm garage to replace an existing prefab garage that leaks from bellow and above. I'd like to insulate it to a reasonable degree so I can heat it if I'm working on a project in the winter.

I'm thinking that I will use 25mm celotex insulation to keep the overall thickness down, but can't fathom if I need to use any ventilation or membrane layers?

(edited to clarify I will be building using block for both skins - had thought about wood for the inner skin but pillars become an issue.)

 

[noseall]

Go for something like a 50mm fully filled (dritherm) cavity.

It is simpler to build and no different in thickness as you would still need a 25mm (min) air gap when using 25mm celotex.

The first skin of blocks are your sacrificial layer and are all that should be getting wet. Also, dritherm insulation is water repellent. No need for additional membrane.

 

[danhx]

Ok another question, on two sides the garage will be butting up against some existing stone garden walls, these walls are retaining/partially retaining. Should the DPM be run on the outside face of the external most wall, or on the inside face of it to give it more protection (as I understand it will need to run up the wall 150mm above the finished ground level). The existing walls will be left, essentially buried once the garage is built. I dont want to remove them as one is a boundary wall and the other is retaining and there are trees behind it. (Can draw diagrams/take pictures if required).

Thanks,