Insulation on ground floor for underfloor heating

JD6910

Planning on installing underfloor heating and trying to decide on insulation for underneath it. Can i use silver EPS floor insulation - say 200MM or should i use 150MM PIR.

The PIR is massive money and i wonder will the 200MM silver EPS do the same or damn close a job?????? Also i am getting a very good price on the 200MM EPS. Broad figures of €2000 for EPS Versus €5000 for the 150MM PIR.

I wonder is there any reason not to use the 200MM EPS floor insulation with is being supplied by a reputabale supplier.

sydthebeat

you need to engage someone to "crunch the numbers"

JD6910

the 200MM EPS gives a u-value of 0.12 and the 150MM PIR gives a u-value of 0.13.

but is the PIR a better product than the EPS???

sydthebeat

define 'better' ?

is your engineer happy to pour a screed on 200mm of EPS?

JD6910

better - as in is the PIR a longer lasting product??

need to speak with my engineer about pouring concrete on 200MM but was wondering does anyone have any opinions on it??

sydthebeat

longetivity:- both products should have IAB / BBA certification which will satisfy testing to the "lifetime of the building"

It is accepted now that the foil face on the PIR should be protected by a light gauge DPM prior to concrete screed pour.
PIR and PU have been known to break down when wet. EPS doesnt have this problem.

Also, PU + PIR are blown with pentane gas which can "off gas" during its life time to be replaced with air. This would result in a small increase in its thermal conductivity and thus reduces its insulative properties slightly. Its hard to get any hard and fast facts on this.
EPS is air blown and thus doesnt "off gas".
Both products are oil based.
PIR has slightly better compressive strength than EPS.

manufan16

I recently completed this part of my build, I originally intended on 2 x 100mm sheets of PIR but for a materials price difference of €800 and a uvalue difference of 0.02 I went with 100mm EPS on bottom then 100mm PIR overlapped on top this was followed by 500gauge plastic UFH pipes then screed.

paddym3

what does pir and eps stand for. just for lay people going purchasing insulation in future. i pricing my house and just looking for 150mm ridgid insulatio double foiled. maybe shpuld be asking for 150 pir or eps if knew the differences

sydthebeat

Paddy,

PIR is polyisocyranuate. PU is polyurethane.
Both of these are the yellow foam with the foil facing, probably commonly known as kingspan insulation.... although there are more than one manufacturer.

EPS is polystyrene, more commonly known as styrofoam. This is a different product to the above. theres no foil facing.

JD6910

I did some number crunching last night.

In my particluar case the 200MM EPS gives a u-value of 0.12 and the 150MM PIR gives a u-value of 0.12 AND there is a price difference of approx €1200 for my floor. The 200MM EPS is cheaper. if i put in the 200MM EPS i will have to install a 3 inch soap to allow the screed to be poured but even with that i am saving €1000.

is this a "saving" i wonder or do i bite the bullet and get the PIR from the "recognised" Brands??

sas

JD6910 wrote: »

I did some number crunching last night.

In my particluar case the 200MM EPS gives a u-value of 0.12 and the 150MM PIR gives a u-value of 0.12 AND there is a price difference of approx €1200 for my floor. The 200MM EPS is cheaper. if i put in the 200MM EPS i will have to install a 3 inch soap to allow the screed to be poured but even with that i am saving €1000.

is this a "saving" i wonder or do i bite the bullet and get the PIR from the "recognised" Brands??

Those u-values look somewhat off. What thermal conductivity are you using for the build up, specifically the EPS?

Example, 200mm of Silver EPS (TC 0.031) by itself (not include screeds etc) has a u-value of 0.155 by my math.

What thermal conductivity are you using for the PIR while we're here.

sydthebeat

JD6910 wrote: »

I did some number crunching last night.

In my particluar case the 200MM EPS gives a u-value of 0.12 and the 150MM PIR gives a u-value of 0.12 AND there is a price difference of approx €1200 for my floor. The 200MM EPS is cheaper. if i put in the 200MM EPS i will have to install a 3 inch soap to allow the screed to be poured but even with that i am saving €1000.

is this a "saving" i wonder or do i bite the bullet and get the PIR from the "recognised" Brands??

the u value of a floor depends on its 'area' to 'perimeter' ratio.

BryanF

Op don't forget about using some form of low thermal conductivity blocks at the perimeter to keep the insulation line continuous

IMO Get a ber assessor or better passive house certified arch to help you out

JD6910

the area is 183M squared and i have 80M of perimeter. thermal resistance of eps is 0.03.

apparently the u-value is therefore 0.12 using 200MM of EPS.

any thoughts guys????????

BryanF

JD6910 wrote: »

..........apparently the u-value is...
any thoughts guys????????

elaborate? please

JD6910

the u-value cals are being given to me from the supplier. the document shows the details caluations using the neceesary software.

paddym3

thanks for the abrevation list. i am starting digging my site this week and am using 150 pir insulation. qas going to use two layers of differentthickness i.e 100 and 50mm but think one layer of 150 is enough. putting expanding foam between joints nad heavy guage plastic over to stop the cement burning the foil