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Single Brick Outhouse with Concrete Roof - Lots of Questions

Postby ko_racer » Fri Feb 06, 2009 3:41 pm


I've got a single brick outhouse (4mx4m roughly) which is attached to the house on one wall. (built with the house around 1950)

I'm looking to stop the damp and make this a much warmer area to be in.
The Walls are single brick all round with one brick above the ground then DPC.
The floor is concrete but doesn't seem to have a dpc.

What I plan to do it the following:

Insulate the floor & Fit Underfloor heating
Batten the external facing walls, insualate and plasterboard them.
Dob & Dab Platerboard for internal walls.
I also want to add a false ceiling and insulate above that. It's currently 3m high and I was planning to drop it to the height of a plasterboard sheet (roughly 2.4m)

I've a few (well quite a lot) questions about actually doing this.

With the floor what's the best way to add a DPC and insulate?
Do I put a thinset over the rough stone finish concrete to make smooth, then lay the dpc and tie in with the curent dpc in the walls. Then lay insulation such as kingspan followed by heated flooring, flexible tile adhesive and then tiles?

For the walls, what the best way to do this to stop any condensation problems?
I assume for internal wall and ones attached to the house I can just dob and dab the plasterboard on without issues.
But for the external walls do I batten the walls, use kinsgpan in the gaps, then use vapour barrier, followed by plasterboard or do I put up the vapour barrier first them batten the walls, insulate and plasteboard?

For the ceiling I want to make sure that there is no damp/condensation problems as it's a concrete roof and in the winter at the moment it build up lots of condensation as we've got the tumble drier and washer in there.

To lower the ceiling I was planning on using substantial cross supports to make a framework and then plasterboard over that.
With the ceiling, do I need to use a vapour barrier? If I do does is need to go above the insulation or below between the plasterboard and insualtion?
As I'll need to keep the void accessible for wiring etc, I was planning to make a loft hatch and seal it in. Is this a good Idea or should I fully close it up and seal it.

From what I've read I will also need to have some venting in the void space above. Is this correct? Do it need to be much? Do I need ventilation behind the external wall insualtion as well if this is the case?

Sorry there are lots of questions, I have a reasonable idea of what I need to do I think, but I want to make sure I get everything right as I only want to do it the once.


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Simply Build It

Postby stoneyboy » Sat Feb 07, 2009 9:18 am

If you are not going to have problems with condensation you will need to form an insulated box inside the outhouse with a ventilated gap on all sides including the floor.
Do not use dot and dab even on the house wall - this was probably an external wall in the past and will be damp near to exposed sides.
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