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Hard Flooring

Using 50mm polystyrene instead of 50mm celotex for extension

We own an old Victorian cottage that was originally built in 1840 and are having an extension built. It has timber suspended flooring. Our builder has quoted for 50mm Celotex but I have seen that they are using 50mm polystyrene. I have questioned this with our builder and he has said that they are having to use polystyrene because it is lighter, and that celotex is too heavy for the old joists. I am not saying that the builder is trying to mislead us, BUT I am interested to hear other opinions/hear advice as I haven't a clue. Everything I read online describes how good celotex is. Thanks for your help.

3 Answers from MyBuilder Flooring Fitters

Best Answer

polystyrene is cheaper than celotex.
R value or 50mm polystyrene is 1.25.
R value of 50mm Celotex is 2.25.
It has to be noted that over 7-10 years Celotex will drop in R-value to match the polystyrene as polystyrene will not drop.
Wickes supply 50mmx1200mmx2400mm polystyrene @ £14-56 per sheet (2.16KG per board average density)
Wickes supply 50mmx1200mmx2400mm Celotex @ £22-78 per sheet 2.45KG per board.
Bottom line is probably your builder has gone for the cheaper option and saved himself 36% on materials cost.


Answered 2nd Jan 2014

Polystyrene is a poor substitute and I never use it. The bit about the joists is comical and he's blatantly trying to squeeze more money out of the job.


Answered 2nd Jan 2014

Kevin has hit the nail on the head with this one, sounds like your builder is trying to pull a fast one. If he has quoted you for using celotex, then that is what he should be using. Also worth mentioning that the building inspector may not pass any work done because of the u value. Check any plans you may have and see what the architect specified. If your builder is using polystyrene, he should be doubling up to get the same u value.



Answered 2nd Jan 2014

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