Shed Refurbishment

[Christopher Key]

Hi,

I'm trying to decide on the best way to insulate and line a shed in order to make it a bit more habitable.

Having searched the Google archives, it seems that the best approach is to line with a DPM, followed by suitable insulation, and then foil backed plasterboard. Being relatively inexperience with such matters, I do however have a few questions.

1) What sort of DPM is best? Is polythene sheeting suitable, or would something breathable (builder's paper?) be required?

2) How thorough does the coverage of the DPM need to be? Do joints in the DPM need to be sealed? Is it acceptable to staple gun it into place? Should it cover the batons, or just be attached between them? How should I handle anywhere that something needs to come through the DPM, e.g. armoured cable.

3) The intention is to lay plywood to strengthen and stiffen the floor. Should a DPM be used below this too?

4) What thickness of plasterboard is best?

5) Sockets and lighting will be added. Will the DPM provide sufficient protection that flush mounting dry lining fittings can be used?

6) What the best way to run cabling past the batons? The best solution that I've come up with is to remove a section of the plasterboard wherever a cable needs to pass a baton (within the permissible cable routes), and then plaster it back in.

7) Is there anything I need to know / have forgotten to ask?

Many thanks,

Chris Key

[Christian McArdle]

Yes, the type of insulation. Use Kingspan/Celotex. You rarely have much thickness available in a shed, so you should use the best available.

Christian.

[John Rumm]

Also using that you could probably do away with both the vapour barrier, and the foil backed plasterboard (since this type of insulation is foil covered)

For a shed you may want to consider using ply in place of the plasterboard. That makes it so much simpler for mounting brackets and shelves etc - since you can just screw straight in without farting about with cavity wall fixings.

[Christopher Key]

Thanks John, Christian,

Is Kingspan / Celotex generally available from the major DIY sheds, or is it likely to be a special order job?

I assume that damp bridging across the batons isn't a problem then. Would adding a DPM outside the insulation (so that I can use flush mounting electrical fittings) be ok?

Chris Key

[usenet]

Just as a little aside, they're battens, not batons.

[Christian McArdle]

Get it from

I would use metalclad surface fittings in a shed. However, I can't see any issues using standard flush mounted fittings. Any damp protection is for increasing the life of the wood. Assuming you've blocked all the gaps, there won't be nearly enough water to trouble an electrical installation, even with no damp protection at all.

Christian.

[John Rumm]

They are well known brand names for foil covered Eurothane or PIR (PolyIsoCyanurate) foam. It is a rigid board insulation with a very high insulation performance for a minimal thickness (30mm of the stuff is better than a 9" brick wall for example).

Lots of companies make it, the above named ones are often amoung the more expensive. The big sheads may have some, builders merchants will also have it. However I would suggest you look for specialist suppliers for the best deals. It is well worth shopping around. The spread in prices I was quoted varied by over two grand!

It ought not be a problem. It will depend a bit on how the place is built in the first place and how thick the cladding and timbers are.

I built my shed/workshop with 19mm shiplap on a 3x2" frame, with internal 1/2" ply cladding. I used 2" thick polystyrene insulation (had not heard of the PIR stuff then!), and installed the electrics in the remaining inch inside of that. All in all it seems to work very well.

[Christopher Key]

Oops! Probably explains why I kept trying to spell it with two t's though.

[Christopher Key]

Sorry, you've confused me there. If the DPM is attached on the inside of the shed, then surely this will tend to keep body of the shed wetter.

[Christopher Key]

I'll shop around. What sort of ballpark figure would be considered competitive?

12mm outer, on a frame of ~32mm x 45mm. My gut instinct was that it wouldn't be that all that waterproof, and that adding a DPM now would prevent major headaches in the future.

Chris Key

[John Rumm]

For 50mm thick 8x4' sheets Jewson wanted best part of 30 each. I paid 14 in the end. 25 or 30mm which may be more suitable for your usage should be in the 6 to 10 quid range I would have thought.

It ought to be pretty water resistant as is it. Remember also that some of the water you will generate inside and want it to get out rather than the other way round. So it does not need to be completely sealed.

[Christian McArdle]

No idea. I didn't fit any damp membrane to mine at all. I'm assuming that by having it all open to the elements, it will dry out naturally to the outside.

Obviously the insulation is foil backed (which has largely been taped together), so there is vapour barrier on the inside.

Christian.

[Christian McArdle]

Seconds and co charged me 11.52+VAT per sheet (genuine Kingspan), plus

20+VAT delivery charge. This is for 40mm thick sheets suitable for a 32mm x 45mm framed shed.

Christian.

[John Cartmell]

That's a small shed! ;-) What size were the sheets?

[Christian McArdle]

Yes, it for a doll's house.

Full size 2.4m x 1.2m x 40mm.

Christian.