Raised floor, drylined walls & ceiling...and underfloor


Postby gelert » Sun Feb 22, 2009 5:36 pm

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.
gelert
Posts: 3
Joined: Sun Feb 22, 2009 4:53 pm

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Postby kbrownie » Tue Feb 24, 2009 9:52 pm

Why do you want to waste warm air behind plasterboards?
kbrownie
Posts: 1757
Joined: Mon Mar 05, 2007 9:36 pm


Postby gelert » Wed Feb 25, 2009 6:43 pm

[quote="kbrownie"]Why do you want to waste warm air behind plasterboards?[/quote]To stop damp forming behind the plasterboard due to the fact that it's a solid brick wall to the environment.

However, the way that we've planned it, if the air remains warm (albeit cooling all of the time) it will rise, eventually "blowing out" of the ceiling vents - and as it hits the warmer air of the actual room at ceiling level it will drop.
Alternatively, any cold air behind the plasterboard / above the false ceiling will drop and eventually "blow out" of the vents at ground level.

In any event, what we're trying to achieve is air circulation - this, we think, will stop damp becoming an issue.

Are we in foreign territory here...?
gelert
Posts: 3
Joined: Sun Feb 22, 2009 4:53 pm


Postby kbrownie » Thu Feb 26, 2009 4:41 pm

a little bit complex for my liking may be i'm in foreign land. Have a look at a couple of post that I have offered info on see if it will suit your application.
Hammy and doitwell
KB
kbrownie
Posts: 1757
Joined: Mon Mar 05, 2007 9:36 pm


Postby gelert » Thu Feb 26, 2009 6:47 pm

[quote="kbrownie"]a little bit complex for my liking may be i'm in foreign land. Have a look at a couple of post that I have offered info on see if it will suit your application.
Hammy and doitwell
KB[/quote]

Thanks KB.

I looked at a couple of your other posts but didn't glean any further insight to our plasterboarding situation.

However, I get the distinct impression that you and I have the 17th edition in common. I get to play with Industrial Electrics & PLCs & Robots etc during my working day, coming home to play with home-built PCs & Analogue+Digital Recording equipment at night.

Whatever - I'll try asking some of my local builder-buddies for their input in this matter. And if I get a definitive working solution from them, I'll post the results here.

Thanks for your input.

Gelert
gelert
Posts: 3
Joined: Sun Feb 22, 2009 4:53 pm


Postby kbrownie » Fri Feb 27, 2009 7:28 am

Hi gelert,
Look forward to hearing from you.
Good spot qualified sparky, mostly domestic and small/medium industrial, not really in to the electronics side.
But my past live I used to do a lot of dry-lining and plastering was family business. So needed to branch ouy a little.
KB
kbrownie
Posts: 1757
Joined: Mon Mar 05, 2007 9:36 pm


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