Installing aluminium bifold

[dormermike]

Hello

I'm considering DIY installing aluminium bifold actually 3m so trifold, and am unsure if I mount them to the outer leaf or somehow in the cavity?

Construction is cavity, breeze block outer and thermalite blocks inner, which are very soft. I have a slider door in another part of the property which sits back from the outer leaf, sort of inline with the cavity but I can't see how to do that with the new location as the cavity is open?

Thanks

 

[^woody^]

They fit the same as any door or window frame - set back from the face and project slightly past the back of the outer leaf to cover the DPC.

 

[dormermike]

They fit the same as any door or window frame - set back from the face and project slightly past the back of the outer leaf to cover the DPC.

So with this wall, it would be bolted to the outer leaf but overlap the cavity so it can be set back 20mm or so?

What's puzzling me and maybe I'm overthinking it, is that the outer wall doesn't seem deep enough.