Extension through brick to existing timbers

[Greg Toal]

Hi everyone. I'm planning a 2 storey rear extension, timber framed, to my 2 storey (plus basement) house. The house is internally timber framed with rendered exterior brick and fyfestone up to ground floor level (split "stone" of 3 shades). The plot slopes to the rear,so it will be a basement level extension into garden with the extension's upper floor at the house's ground floor level. There is access beneath the whole house, of varying height.

My question is about supporting the new 1st floor joists. As I understand, a ledger bolted the outer skin of rendered brick is not well enough supported and the new frame needs tied into the old without compressing the external wall. Can the outer skin be removed and then a new ledger/rim joist be attached past the air cavity to the existing rim joist? Should new joists be cut through onto internal supporting wall?

I can't quite get my head round the design.

I've attached pics showing basement foundation wall and timber frame.