Insulating new workshop

[robgraham]

Timber framed workshop, 5m by 3m, framing is 3 x 2 studs with weatherboarding. What should I use for insulation - I'm planning to line the walls with OSB board, with a polythene membrane under it. The insulation level does not need to be high as I've lived for years quite happily in the old one which has some thin poystyrene slabs stuck to the walls.

Thanks for suggestions

Rob

[Andy Dingley]

Rockwool roll between the studs and damn the cold bridging at the studs (only a workshop). You've enough depth there to be useful and it's cheaper than yellow foam slabs.

Watch out for water ingress though, as damp rockwool is unpleasant. If it's leaky outside, consider the yellow PIR foam anyway (although even that's no guarantee against a sustained leaky roof). Alternatively go for double water barriers both inside and out. This is tricky though, as the outer barrier needs to be 4 or 5 times more breathable than the inside one, either by choosing different membrane materials, or by provided a ventilated airgap under the outside membrane.

OSB is a better choice on the inside than plasterboard, as you won't knock holes in it. Won't be so fire resistant though, which might be an issue for you.

[Phil L]

It's cheaper because it's not been treated with a water repellant.

To the OP: - if it were mine, I would use the fibreglass batts used in new build projects - they meet all the standards required for new homes and they are, as I've already said, water repellant - that is to say, they won't soak up any water like normal loft insulation type fibreglass (or rockwool) will

[John Rumm]

A job I have just been doing in mine. I went for the foil faced PIR foam slabs (50mm) this time. A place near us does seconds at about £10 each which works out about the same price as polystyrene.

[robgraham]

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And where, John, is "near you" ? So that I can take advantage of your source.

I was thinking along the lines of polystyrene as I've got 40mm slabs in my present workshop - I'm sure the PIR is better but does ordinary polystyrene have any disadvantages ?

Rob

[John Rumm]

APCO Wholesale in Benfleet Essex - just off the A13 between Saddlers Farm roundabout and the bottom of Bread and Cheese hill.

PIR is about twice as effective IIRC. Ordinary poly is ok, although you ideally want a fire retardant treated one - Jabfloor or Jablite would probably be fine.

[robgraham]

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Thanks John - bit far from Edinburgh then !!

Not sure that in a wooden shed, and behind OSB board, fire retardancy is going to make much difference.

Rob

[John Rumm]

Erm, yup! Don't think they do mail order!

Probably not... having said that, most products designed for building with will probably be treated anyway.

[Andy Dingley]

All over the place - it seems relatively common to find "seconds outlets" for insulation boards. I'm nowhere near John (or Edinburgh), but we've a local one too.

On the whole, I think Phil L might be right and the glasswool batts being about the right compromise between loose rolls and rigid foam.

[John Rumm]

I bought some of those recently for a different project, and I have a feeling they worked out more expensive than my source of PIR. So shop around whatever you get.