Single Brick Outhouse with Concrete Roof - Lots of questions

6 Feb 2009
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United Kingdom

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 for so many questions, I've g ot a good idea how to the basics, but I want to make sure I get it right as I don't want to do the job more than once.


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sounds to me like you have it sussed. ;)

can i suggest you ask more specific questions, but try and limit the amount. :eek:

i.e walls.




Ok, Thanks

I wanted to give a bit of detail but probably went a bit far. I'll just list my questions:

1. For walls, do I install:
Wall, vapour barrier, battons, insulation, plasteroard OR
Wall, Battons, insualtion, vapour barrier, plasteroard?

2. Does the vapour barrier need sticking to the base batton with caulking or similar?
2a. Does it need venting anywhere?

3. For the ceiling do I need to use vapour barrier?

4. If so, do I put it above or below the insulation in the ceiling and does it need to be sealed with tape to the wall vapour barrier?

5. Do I need to vent the void space above the ceiling?

6. The floor, can I use paint on DPC stuff or should I just make a smooth level on the rough stoney concrete and lay proper DPC?

7. Plasterboard. Is there a specific reason for having different thicknesses? Should I use a different thickness for walls and floor?

Thanks in advance

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take a look at this as a guide to insulation diagrams.

you can buy insulated flooring deck from kingspan that requires no vapour control layer.

i personally do not like or use 9.5mm boards unless i have to, i.e. due to thickness constraints.

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