I’m approaching the end of a self-built oak framed garden room / conservatory project at home. I’ll shortly be ‘knocking through’ into the main house by removing a window and old external French doors. The old external wall of the house is going to be plastered – the brickwork is too poor to be left exposed. The house is quite old (1908) and the DPC is original (and not brilliant) – I am worried about the wall becoming damp both from below and above. The building adjoins the chimney breast so cavity trays haven’t been possible.

I’ve got a number of options for the method of covering this wall (which I’m going to have done professionally) – either standard dot and dab plasterboard, dot and dab incorporating a damp control and air gap plastic sheet or a breathable lime plaster.

Can anyone offer any advise for the best solution?