Hi,
Would I be right to think that celotex, kingspan, and xtratherm are all pretty much the same and 50mm of one is as good as 50mm of another, or is one better than the other?
Daft question #2: if attaching to an exterior wall to add insulation, should the foil side face the exterior wall or the inside of the room?
TIA
Fred wibbled on Friday 16 July 2010 10:48
If the base substance is the same, then basically, yes. There might possibly be variations in foam density for different applications.
The only other thing to check is if the product has the required fire retardent (ie non spreading/self extinguishing) properties for the application.
I though they were usually foil faced on both sides? My BallyTherm board is.
Perhaps they are. I've never bought any before but am about to place my first order. If so, that would stop me worrying about which way round was the right way! BTW are the ebay sellers the best for price and service? They all seem to offer free nationwide delivery and I am pretty sure they are all just agents fro builder's merchants.
Polyisocyanurate has the highest R value pf 7.2" initialy, it is rated here at R6.7 or so as it looses some R value as it cures, its the product that is foil faced here in the US. Polystyrene is about R5"-5.5", and the white foamboard R 4-4.5" With the added value of a foil radiant barrier Polyisocyanurate is the best beal. Liqued foams are the same, they vary depending on type from R4 - R 7 per inch
FWIW it's worth getting an insulation contractor to quote as well (if you can find a proper one that can with jobs that don't consist of just rolling out loft roll).
We found one that would supply & fit for less than it would have cost us to buy in the insulation ourselves (even at ebay prices). Which was a bit counterintuitive - something to do with bulk buying discounts I would imagine.
Mostly - they are usually PIR foam based boards and hence will have similar insulation values. What differs is what is used to cover them. Some like celotex also have reinforcement fibre strands that run through the board ever few inches (not that it does much for you).
The finish is often a foil vapour barrier on at least one side and often both, although other options include cork and bituminous layers (for sound deadening), and timber coated on one side (roof decks), plasterboard (dry lining) etc.
If you download the data sheets from the celotex or kingspan sites they specify ways to do it. (IIRC they include an adhesive layer as well). However I expect that the commonly available double sided foil boards would perform adequately in this application.
Vapour barrier should be on the warm side to stop 'dew' forming as water vapour permeates through it - so in england on the inside, in the tropics if its for keeping cool then on the outside.
Insulate & Weatherize (Taunton's Build Like a Pro) [Paperback] Bruce Harley
So these threads are supposed to strengthen the board but do nothing to affect the u-vales? I was hoping to buy celotex but I was told the local depot stocked xtratherm instaed. I'd never heard of that. If it is the same thing, then I'll stop worrying then. Thanks.
Basically - they also make it harder to cut since they can snag saws etc. I can't see they add much practical strength in a typical application.
Loads of people make PIR foam boards... (ecotherm, ruberoid, and plenty of others) they all do much the same thing.
In SI units, polyisocyanurate (PIR) has a conductivity value (k-value) of 0.023W/mK. Divide the thickness by the k-value to get the R-value, so 50mm thickness gives an R-value of 2.17m^2K/W.
American R-values are effectively resistivity values, as they are expressed as Rnn per inch, which is a) a little misleading and b) not entirely accurate, as some materials have different resistances as they get thicker.
Thanks everyone. After all that they delivered Celotex. Now to cut it; what's best: a fine toothed saw or a knife? I was thinking a snap off knife extended to the depth of the board but is that safe? the instructions say not to extend the blade very far.
Snap off knife perfectly ok, but I found a tenon saw best of all - saw, saw, saw down the line, thump it to free last bits, then once it flaps over - use the blade on the remaining foil layer.
snipped-for-privacy@gglz.com wibbled on Wednesday 21 July 2010 22:28
I used a wavey breadknife (not serrated). Serrated cuts really well, but makes a lot of dust. Wavey knife was harder through the foil, but made for less mess.
Some people like saws - that'll drop a lot of dust and crumbs (not too good to be breathing a lot of those in - not toxic, but it is classed as a mechanical respiratory irritant, so basic dust mask advisable). The good news is that the dust/crumbs are clean and not sticky and a domestic hoover sorts them out wonderfully without knackering itself.
I use either a snap off blade knife with extended blade, or a general purpose jack saw. The latter is better for fiddly bits and cutouts. The former makes no dust.
Thanks everyone for your help again.
I hadn't discovered celotex when I insulated my loft some years ago, so I bought those rolls of insulation. I did see some "spaceboard", which I think is celotex without the foil, and it said that one sheet was equivalent to so many millimetres of rolled insulation but I can't remember how many. Does anyone know the equivalence?
IIRC the recommendation is to use 270mm of roll insulation (what is the proper name for it- rockwool?); how much celotex would that be equivalent to?
I would like to board the loft to make storage space and if I replaced the rolls for celotex, that would give me more head room but it seems a shame to replace all those rolls. Is there a second hand market on ebay for them I wonder! One advantage of the rolls is that by having two layers perpendicular, they cover the joists. If I cut celotex into the gaps between the joists, is the heat loss through the joists significant? Is it still best to cover them?
Thanks again.
BCO told me that Celotex was equivalent to roughly twice the thickness of normal insulation. I.e. 150mm Celotex = 300mm roll insulation etc.
We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "John Whitworth" saying something like:
The numbers will tell for sure, but I have a recollection of 100mm fibreglass = 50mm aeroboard = 25mm Kingspan. However, and it's a big however - the insulation values claimed for Kingspan, Celotex, et al, only apply if the fit is perfect. Air leaks around the sides reduce its effectiveness considerably, which probably takes it into line with your BCO's estimate.
Some numbers at the end of this:
No need to replace all of it... leave 100nn between the joists (assuming they are 100mm deep!), and stick say 80mm of PIR foam on top followed by your floor boards. That will give you the equal of 270mm of quilt.
Using the PIR over the top of the joists is the best way. No titting about cutting it to shape then!
So in cross section:
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Just to clarify, there has been lots of discussion elsewhere about various methods of constructing raised floorboard support. Are you saying simply perch them on to of the PIR foam?
Chris
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