Consider two appliances in front of a wide window.
- Replace the 255mm double-brick wall under the window with a lintel.
- Extend by epoxy-needle the raft-overhang from 0.27m for a new wall.

So creating a "box-bay" with 1.3x0.40m internal space.
The appliances sit flush with the lintel on the inside.

Whilst it may be a curious idea under Permitted Development, the real
cost would be BR re foundations (existing raft toothpaste clay), wall
construction, insulation, micro roof & insulation etc. Such a cost
that it would be pointless compared to building a more conventional
extension.

I am certain I have seen it done, except by bolting to the wall so
nothing touched the ground. Was that how they got around past
regulations by creating essentially a "wall mounted cupboard"?