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.