Info on insulation boards for loft

[Ghostrecon]

I need to sort out the insulation in the loft at the moment it only has

90mm thick. Unfortunately we need to use the loft for storage so its part boarded with 18mm chipboard over the insulation - some fixed with many scraps of board to spread the load. I know that the standard answer is to lay joist across the existing ones and then insulate between these with boards on top but these joist would need 150mm to get a decent amount of insulation up there. This is likely to be expensive....

What would be the best alternative? are there any that would give a similar thermal insulation value but still allow the storage. Loft area is about

54m^2 (6.6 x 8.2) with coldwater tank and central haeting header tank

I will b doing this myself so labour is cheap lol

Thanks for any help

[Another John]

My answer to a similar question a few months was that I have used 50mm thick Celotex *on top of* the boarding. Dead easy, but quite expensive [for my own make-do'n'mend mentality].

I don't honestly know what the thermal value is compared to 6"-9" of conventional fleece, but I do know that Celotex is very efficient, is lovely to work with, and provides a smooth, firm "floor".

Of course, it will not take *a lot* of walking about, but it's definitely sturdy enough to take me[1] walking about on it in soft shoes now and again, to shift boxes in and out. And of course the stuff just sits there: it doesn't compress the Celotex, which is very strong for a spread load.

hth John

[1] Admittedly: 10.6 stone, 67kg.

[NT]

If you've got a lot of free scrap chipboard, you could also use a chip/ polystyrene/chip sandwich

NT

[george [dicegeorge]]

celotex/kingspan is thinner than rockwool for a fixed amount of insulation but more expensive.

Rockwoll/glass fibre/y-stuff is subsidised by energy companies so available very cheap on special offers every so often.

[g]

[george [dicegeorge]]

PS kingspan seconds are a bit damaged but a lot cheaper than perfect sheets.

[g]

[Ret.]

I recently did a similar job. My house was built in the mid 70's and hence has a very shallow roof-pitch with a lot of cross bracing in the roof supports. My existing insulation just reached the top of the joists and I had boarding down the centre of the loft to provide a platform for storage.

I obtained the requisite number of insulation rolls via a discount offer from Npower (although I'm not an Npower customer). The rolls plus a safety kit of gloves and goggles and face mask cost around £32.

I bought some chipboard loft boarding from B&Q and created a raised platform over the top of the new insulation. I did this by fixing some lengths of wooden floorboards (that I already had) across the inverted 'V's of the roof supports. I then placed the chipboard panels over the top of these cross pieces and screwed them into position.

The raised platform is now far superior to the rather Heath Robinson mishmash of boards and planks that formed the platform before.

[John Rumm]

Fill all the existing space with cheap quilted insulation, and then lay a PIR foam board insulation on top of the existing floor joists. Lay the flooring directly on top of the insulation. No need for extra joists etc (they would only add cold bridges through the insulation anyway). For storage purposes the flooring on top only needs to protect the top layer of the foam - so thin ply or even hardboard would probably do.

PIR foam boards are getting on for twice the effectiveness of fibreglass quilt.

[Ghostrecon]

sounds like a good plan - looking at second & Co they have Kooltherm boards

- anybody know if they would be suitable ??

[John Rumm]

being a problem for your application. The foam is quite dense and so will easily take weight on top - especially if spread by the flooring.

[<me9]

That's more or less what I did, and it has proved effective over the last couple of winters. I used kingspan seconds from Ebay, but placed them under existing T&G chipboard flooring which was already in place in the loft. The bigest problen was clearing the junk from above the existing flooring to allow it to slide along to put the kingspan underneath.

[Chris J Dixon]

The centre area of my loft was already boarded with a mixture of materials that had accumulated over the years.

I then covered this with two layers of Knauf space board insulation,(1200 mm x 500 mm x 50 mm) with the joints staggered.

As I needed to hold everything down, and the insulation will dent from point loads such as bony knees and storage box feet, I covered it with hardboard (full sheets cut across into 500 mm strips {plus off cuts} at B&Q) and screwed it all down to the boarding using M6 x 120 mm woodscrews which were on offer at CPC.

I was very pleased that the installation went exactly as planned. I did drill pilot holes, but the screws would probably have self-drilled.

The only slight problem, which became apparent after a few weeks, is that (despite the fact that the hardboard spent some of the autumn stored in the caravan, until I could get the job done) the sheets have expanded slightly and bowed a little.

Chris

[Ghostrecon]

Thanks for that - so out of my 54m2 loft I can get about 18m2 storage with

100mm rockwool with 62mm pir board on top which I reckon is the equivalent of 231mm of rockwool and then do the rest to 270mm depth of rockwool - um total cost of insulation delivered about £180 does that sound reasonable?

[John Rumm]

Sounds ok. You will get a bit of extra insulation from the boarding and any "stuff" you store on it as well.

If you work on say a nominal temperature difference of 10 degrees averaged over the cold months, and assume the u value of the exiting 90 mm of quilt is 0.44[1] that means you currently loose heat at a rate of

54 * 10 * 0.44 = 237W.

Adding 62mm of PIR would give a total u value of 1/( 1/0.44 + 1/0.40 ) = 0.2 for that section. The 270mm of quilt works out about 0.14.

So the new heat loss would be 10 * (54 - 18) * 0.14 + 10 * 18 * 0.2 =

100W or thereabouts. So reducing the rate by 137W or about 3kWh a day. That ought to pay back in under two years. [1] Figures from

[Andrew Gabriel]

One warning - you don't want a moisture barrier on top of breathable insulation, as it will form a condensation surface which will eventually wet the insulation and any timbers in it. Make sure there's a ventilated gap between the top of the fibreglass and any solid boarding. Another possibility might be using floorboards with gaps between them, but make sure the stored items don't seal the gaps.