Loft boarding - again I know

8 Oct 2012
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United Kingdom
Hi guys,

I know this topic is probably done to death but having looked around this morning and watched a few youtube videos I am still a little unsure of whether what I would like to do is ok as explained below.

Due to the location of the truss members, my intention would be to insulate and board the centre area of my loft space for storage (using Kingpan/Celotex thermo board insulation between joists and chipboard direct to joists) and insulate the outer area with the existing mineral wool to 270mm.

My plan for the centre area would be as follows:

The bit I am confused about is whether this would be fine as there is plenty of mention of mineral wool between the joists followed by thermo board on joists then chipboard on top etc but I couldnt see whether simply having thermo board alone is ok? Then there was mention of cold bridging and I was unsure whether this would be an issue with my plan. The area below the thermoboard would not be a bathroom as this would be under the existing mineral wool insulation and appears fine.

I intended to leave 30mm gap for ventilation, should this be above or below the thermo board of split both above and below or can I get away with 120mm thermo board to increase the insulation?

I did look at extending height of joists to take 270 mineral wool but price worked out similar once I had bought the timber.

I appreciate your input.

Thank you
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There is no advantage in leaving that 30mm gap. Just fill the whole depth with the K'span.
A cheaper option might be to use knauf insulation loft roll270 then put 200mm cuttings of 2x2 cuttings on the ceiling ties then 2x2 on top of the cuttings then your chipboard. There is also pastic feet for packing up the flooring, but not sure how good they are. Or do as tony suggests and fill the full depth with something like kingspan and then your chipboard
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Thanks for the reply.

I have considered increasing the height of the floor but this doesnt seam hugely different from a cost point of view.

The legs look like they work out at about a £1 each and 12 are needed for each square metre. This soon adds up.

Timber isnt cheap either unfortunately.
No a problem. Wood can be expensive especially if you go to B&Q I would go to a trade place they do serve to the public. I would be looking at approximately £20 /m2 doing with glass wool 2x2 and 22mm chipboard. And for doing with something like ecotherm and 22mm chipboard I would be looking at approximately £26/m2

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