Kingspan for loft flooring?

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Several questions asked in Lofts section but virtually no answers.

I would like to "floor" my loft with Kingspan probably 100 mm thick or twice 50 mm.

Firstly how problematic would it be to occasionally walk on it to access things I have stored on it?

My joist spacing is a little closer than normal so shorter span. That I don't think will be a problem.

Is any particular make/brand better than others for walking on?

Are "seconds" available at a worthwhile saving? If so from where?

Tony
 
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you can do that, but you need to put ply or chipboard or other material on top of the foam if you are going to walk on it.

Knauf used to sell foam slabs for that purpose and their instruction leaflet may still be available.

Between the joists, use mineral wool which is cheaper and, not being rigid, is easier to pack between the timbers without gaps.

I now only use wool treated with Ecose, which prevents it shedding irritant dust and fibres. It is made by Knauf but also sold as own-brands. Look for the word Ecose on the wrapper. It is brown, not yellow.
 
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100mm PIR/PUR (plus p/board and chipboard) is only going to give a U of about 0.23 which is not much better than 175mm of rockwool. That's pretty poor - you will be losing over double the heat through your loft than you would be if you insulated to best practice (which would be about 400mm+ mineral wool or 200mm+ PIR/PUR).

It's a bit of a pain to cut for the joists - very messy. If you're going to do it, foam the gaps, because gaps down to the p/board dramatically hamper the insulatory effect.
 
100mm PIR/PUR

no, he is going to put a deck of foam slabs on top of the joists, with board on top. Nobody with any sense would leave the gap between the joists unfilled, so it will be plaster+100mm mineral wool+100mm foam+chipboard

Will be much better than 175mm wool.

If the joists are deeper than 100mm there could be more wool.

You mention 400mm wool. Are in in Sweden, or is your wool free so there is no cost:benefit calculation to be done?

Do you think that 100mm foam loses twice the heat of 200mm foam?
Extra thickness only cuts the reduced amount, so benefits decline with every layer.
 
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Apologies, I thought because he asked about the joist spacing he was intending to put it in there.

Regarding cost/benefit, it depends on the benefits you are trying to optimise for. If it's financial saving, given the lifetime of mineral wool of say 20 years plus 400mm will pay back. It also depends on your heating fuel and so on of course. The economics make this much more complicated.

If it's carbon saving you have to consider the embodied energy - from memory this flips at about 700mm so no problem there.

Plus there's the comfort and environmental benefits.

100mm foam has twice the heat loss of 200mm assuming perfect fitting conditions, yes. 400mm foam has half the heat loss of 200mm and so on.
 
100mm foam has twice the heat loss of 200mm assuming perfect fitting conditions, yes. 400mm foam has half the heat loss of 200mm and so on.

No it doesn't.

For a simplified example, suppose your uninsulated ceiling loses 3kW.

Suppose one layer of material X reduces it by 50%, saving you 1500W.

The heat loss is now 3kW x 0.5 = 1500W

Another identical layer of X will not save you another 1500W.

It will save you 50% of the new heat loss, which is 1500W.

So your second layer will save you 1500W x 0.5 = 750W

The heat loss is now 375W

A third layer of X will save you 375W x 0.5 = 188W

The third layer is not an economic proposition, unless it is free.

The first layer has the best cost:benefit, and subsequent layers get worse and worse.
 
Ask in the Electrics forum too. ban-all-sheds has done this I believe.

I rockwooled between the 3" original joists, crossed with 4" new joists then 90mm celotex between those.
 
No it doesn't.
[...]

Didn't you prove my point?

First layer, heat loss was 1500W.

Add a layer, heat loss became 750W. 1500/750 is 2. Hence, half.

Add a third layer, (this is twice as thick again) again it halves to 375W.

Double the insulation, halve the heat loss. I assume you don't disagree with that? It's fundamental physics.

I don't disagree that adding insulation gives diminishing returns, but that doesn't mean it's a bad idea to add more.

You should always be driven by your goals for the performance of your house. And I want a high performance house.
 
seconds quality kingspan is available, try secondsandco.co.uk but be aware:

They do pallet loads of boards that are priced based on a guy with a clipboard scratching his arse and saying "ooh, that looks like a big one, 200 quid" so if youre looking in the pallets section do work out if youre getting a bargain cos some of the stuff is more than first class kingspan

be aware that some seconds stuff is seconds because it's bent or the edges didn't expand properly so it's not always a uniform size. If I were you I would also nip onto CFS's website and get some 2 part expanding foam. mix it in small quantities and paint the board edges with it as you put it together. aso mix it in disposable drinks cups because it'll wreck every container you leave even the smallest residue in (I've got loads of blocks of kingspan around site all shaped like 2 litre pop bottles ;) ). It expands a lot more and pushes its way into gaps a lot better than the canned stuff, but if you go for cans, probably the cheapest source I've found so far is a co called platinum supplies on ebay.. in the region fo £2.50 a can (plus vat) for the gunnable stuff. get a gun if youre going to be doing a lot

planetinsulation does reasonable discounts on orders over £2000 of first class kingspan, I think

in terms of what is good to walk on, most of my stuff has come from seconds, I've had recticel, kingspan, st gobain, silcart, silatherm, econotherm and loads of noname stuff. it's been coated in everything from tarry sand, paper, to fibreglass. would I walk on it without an overboard? sure, but I wouldn't stamp my feet. 9mm osb should be fine, even 5mm hardboard would probably do. the only one I'd hesitate with actually, is celotex, possibly also kingspan. the celotex is much less rigid than the other foams, and cracks/powders up. same for the particular kind of kingspan I had but it was only 25mm sheets. it was pink, and smelled like horse ****, which is odd because usually PUR/PIR smells like fish guts. It also powdered when stepped on
 
Just back to the original question......
I have found Recticel quite a bit cheaper than Kingspan, but thats maybe a local thing.
Foil backed, it can be walked on from time to time without problems.......I don't do it with my heels on though :eek:
John :)
 
Agile you need to have some boarding over your ceiling ties and then you will be fine to walk on the
insulation with soft shoes if you are going up there regularly.
 
Apologies, I thought because he asked about the joist spacing he was intending to put it in there.

I mentioned spacing to indicate that it would be more supported than on standard spacing.

It seems that a simple solution would be for me to leave walk ways between the stored things and either have permanent boards there or moveable boards which I place before walking on it.

Noted that Kingspan and Celotex may be more prone to problems but those two brands are the most popular for sale !

Thanks for your help.

Tony
 
100mm PIR/PUR (plus p/board and chipboard) is only going to give a U of about 0.23 which is not much better than 175mm of rockwool. That's pretty poor - you will be losing over double the heat through your loft than you would be if you insulated to best practice (which would be about 400mm+ mineral wool or 200mm+ PIR/PUR).

It's a bit of a pain to cut for the joists - very messy. If you're going to do it, foam the gaps, because gaps down to the p/board dramatically hamper the insulatory effect.

A few months ago I posted a question on this site asking whether the 50mm Quinntherm boards my builder put in my new side and rear extension cavity walls, were better than 100mm rock wool and I think most people said yes. Are we saying some different here on this thread?
 
Define "better"!?

In pure conductivity terms, 50mm Quinntherm will perform slightly worse than 100mm mineral wool. But that's not all you have to consider. Also ease of installation (insulation is very sensitive to quality of installation). How it reacts if it gets wet (I hope not but neither would be much good). I'd be interested to see the thread.
 
Define "better"!?

In pure conductivity terms, 50mm Quinntherm will perform slightly worse than 100mm mineral wool. But that's not all you have to consider. Also ease of installation (insulation is very sensitive to quality of installation). How it reacts if it gets wet (I hope not but neither would be much good). I'd be interested to see the thread.

Not quite what I thought I remembered but no negative opinions - //www.diynot.com/diy/threads/insulation-in-cavity-wall-during-build.439998/
 

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