Advice on what to look for re: floor insulation

[gwebstech]

Hi all

 

Ive been given my building regs spec by my architect, and he says that 100mm kooltherm is fine for the concrete slab, (its a new build) he says a recent project used it and it got a B energy rating.

 

Ive looked at the prices and its circa £30 sq.m where i can get celotex 150mm for about £22 sq.m ! so a saving of about £600.

 

do i need to look at which has the highest R value to see which gives best heat insulation? the kooltherm R is 5.5m2k/w and the celotex is 6.8 m2w/k

 

or do i need to look at the thermal conductivity?

 

thanks

[PeterW]

Go for the Celotex and also look at Seconds & Co for floor insulation bargains. 

[Ed Davies]

10 hours ago, gwebstech said:

or do i need to look at the thermal conductivity?

 

No, the R-value (higher is better) or U-value (lower is better) is what you need to look at.

 

Conductivity (often written k or λ) is a property of the material independent of the thickness, so only makes sense for comparison if you have two sheets of the same thickness. It's useful, though, if you know how much insulation value you want and then need to work out the thickness needed to achieve it.

[A_L]

@gwebstech ,

 

for floors you cannot just invert the R value to obtain the U value, you must also have the exposed perimeter and the total areas as thermal resistance of a uniform floor varies with distance to the edge because you have to add in the thermal resistance of the soil

[gwebstech]

Thanks for the help guys