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
would it work? I suppose the main issue would be if the space blanket
will stay reflective. I have one between the flysheet and inner lining on
my tent and its still reflective 3 years on.
Worth it to save £20 a board don't ya think?
What you think chaps? A good idea?
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
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
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)
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.