On Sunday, 14 July 2019 12:29:31 UTC+1, Bert Coules wrote:
I'm thinking of building a rear-garden patio raised to the level of the
interior floors, the idea being to be able to walk though the patio doors
with no step down. The height above the existing ground level would be
almost exactly 24 inches.

Decking on legs is presumably a practical possibility but I rather like the
idea of a solid construction with a paved or stone top surface. Since this
would, I assume, have to be built onto the external wall of the house, it
would breach the damp proof course. A boundary wall of brick or blocks
could be built with a matching DPC, but what is the usual arrangement for
the solid infill? An overall membrane that covers the entire area? Or
something else? I would have to trunk out the present airbricks, but there
seem to be materials specially designed for that.

Alternatively, could a solid patio be free-standing, separated from the
building by a small but definite air-gap?

Many thanks for any thoughts.

The pressure treated wood is **** these days.
They have done away with the copper and arsenic so it rots PDQ
You can put in a vertical DPC also make sure the surface of your patio slopes away from the house to drain rainwater away.