Celtex is not cheap, but polystyrene board is by comparison. What about making my own? Say by laying a space blanket over it...only 57p for one here...
Worth it to save £20 a board don't ya think?
What you think chaps? A good idea?
Steve
Polystyrene is only half as good as celotex. The blanket,while good, is no match for celotex.
Polystyrene is also highly flammable, and gives off toxic fumes, which is why its only really allowed underground, inside screed, or in small quantities.
There are reasons why things are done the way they are. Sometimes they are idiotic and politically inspired. But mostly in the building regs there are sound reasons for everything.
No because the insulating properties of Celotex, Kingspan etc. (polyisocyanurate foam) is considerably better for a given thickness than that of Styrofoam.
Since the U value for the complete surface (wall, floor, roof etc.) is typically regulated, one has to achieve that factor. Even looking at it on a pure energy cost saving basis, one wants to achieve as low U values as makes sense.
Given that the U value for a complete surface is affected the most by the material having the highest insulating property (usually the insulating material rather than the bricks or tiles), then this determines what the U value of that material needs to be. If one doesn't care about the thickness of the material, then the material chosen doesn't matter. However, usually one does care and so the thinner the material the better. This is why PI foam is attractive.
The foil covering is predominantly there as a vapour barrier. Although it has reflective properties, it is really the foam that makes the main contribution.
The second point is that one should not look at the cost of sheet insulating materials on a capital cost basis. The real point is the lifetime saving and payback period. For any of these, it's short, even if the application does not mandate use for regulatory reasons. Therefore the real discussion is on loss of space vs. capital cost. Even on that basis, in many applications, saved space is worth having more than the minor cost saving.
(Note to self: Check Kingspan stock, Celotex appears to be privately held)
In message , Andy Hall writes
What of Cellular glass insulation? The seems to be concern about the dense smoke given off by PIR.
Yep, like part P.
;-)
Steve
FWIW Selco (trade only) has an own-brand Kilospex knock-off that's quite a bit cheaper.
Ecotherm is also significantly cheaper...
(I paid about £14 per 8x4 sheet of 50mm - about the same as jablite in a builders merchant)
Having been through this with a cost-shaving and spec-ignoring builder, you have check carefully with the cheapo stuff whether you are getting PUR instead of PIR.
Indeed. Always worth being careful with the spec, but that does not mean there are not sacings to be had. Mine was foil faced PIR. The notable differences from branded Celotex was lack of the silk screen printed lines marking 400mm increments, and there were no fibreglass strands embedded in the boards as you get with some Celotex ones. Neither of which was a particular issue in the application.
I wasn't trying to suggest otherwise, just a note of caution because 'celotex' has sort of become become a generic term for any yellowish foam board with a foil face.
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