Hi all,
I'm new here so please treat me gently...!
I've read quite a bit on the web about dry lining - but much doesn't apply to our situation, so I've come here for some advice.
We have a rectangular single storey extension on our house with a flat felt roof onto a poured-in-situ concrete ceiling. It has 3 external sides of 9" single thickness brick walls and one side internal of cavity wall. The floor is concrete but does have a dampcourse.
It houses our backdoor as well as two other internal doors to other rooms.
Therefore, in order to make best use of this room, we have floor-tiled the small area by the back door, and have raised the floor level of the majority of the room using 5" x 2" pre-treated joists and 22mm P5 boards. This new floor height marries-up with the existing floor levels of the two other internal doorways that access this room.
We know that the 9" exterior walls suffer from a little rain penetration but we are prepared if necessary to paint some clear rain proofing "render" onto the exterior brickwork (e.g. Wickes Water Seal). The felt roof is brand new and has massively cured the previous damp problem.
We have allowed full airflow under the raised floor by means of 42mm holes through all of the joists and end members - and there is a 25mm gap between the P5 boards and the internal faces of the exterior walls to allow air to rise / fall. There is foil-backed 2-3mm expanded polystyrene sheet between the P5 boards and the top of the joists, with the foil facing uppermost.
We plan to put 25mm deep battens onto the internal faces of the exterior walls and then fit vapour-barrier 1/2" plasterboard onto them. No insulating materials between the wall and the backside of the plasterboard.
We plan to fit 50mm deep battens onto the underside of the concrete ceiling and ditto fit vapour-barrier 1/2" plasterboard onto them. And again, no insulation between the concrete roof and the plasterboard.
We plan that there will be unimpeded air flow from vents at the end of the raised floor by the floor-tiled backdoor area, passing underneath the raised floor, up behind the wall battened plasterboard, and through the ceiling battens...ultimately moving through some vents in the false ceiling.
We also plan to fit a radiator to one of the exterior walls, with the central heating pipework looping through all of the raised floor joists before connecting to the radiator.
So...are we barking mad... :lol: ...or will this idea of having a draught of warm air from pseudo underfloor heating moving up behind the plasterboard walls and over the plasterboard ceiling actually work...?
And are there any pitfalls that we haven't thought of...? e.g. cold bridging, condensate pooling in the ceiling etc...?
All advice gratefully accepted.
