Plastic between insulation and underfloor

rebellad

The underfloor heating company I am getting to install my system have said that they require me to put plastic on top of my insulation before the put down the ufh pipes is this normal?? Also is is alright to staple the plastic to the insulation if I need to put the plastic down??

RKQ

Spoke to a Technical rep last week. 500 guage plastic is recommended to prevent a "cold bridge".

They recommend two 60mm foil layers, each layer stepped on the previous. The plastic stops wet conc pushing between the sheets causing a cold bridge between the slab and the hardcore. (this is where there is no insulation and cold can travel across this bridge).

Plastic also prevents the cement reacting with the foil but this did not concern the rep.
Pinning pipes thru plastic will be fine.

rebellad

Thanks RKQ, had spoke to a few people that put down underfloor and they didn't have to do it at all.

rahman

put down 2 layers of insulation in a criss cross pattern and this will prevent any concrete seping into hardcore

yop

You have to tape the joints with a good strong tape, cannot think of the exact name of the tape but I got rolls of it in the plumbers suppliers, really strong stuff. I taped each joint twice and also along by the wall where the vertical and horizontal insulations meet.

anon1

Several ufh companies recommend the plastic in their procedures manuals. The plastic will aslo prevent foot traffic from damaging the insulation. I'd recommend you do it. don't second guess the professsionals

BadCharlie

Had to do this in my own home. Took a good while to do it but was worth it. As other poster said you need to tape all the joints. Also plastic to run up the walls, well i did and i used silicon to stick it to the walls as i found the tape did not work. Worked out fine in the end but took a good bit of time.

muffler

BadCharlie wrote: »

Had to do this in my own home. Took a good while to do it but was worth it. As other poster said you need to tape all the joints. Also plastic to run up the walls, well i did and i used silicon to stick it to the walls as i found the tape did not work. Worked out fine in the end but took a good bit of time.

And well worth the time to ensure a good job. Well done.

sinnerboy

Floor to wall junction , behind skirting is a weak spot in terms of air tightness

Polythene is usually called for to stop the screed from reacting with the foil facing of the insulation layer . But if you also take the trouble to extend it up and bond it ( tape / silicone ) behind the skirting board - this is worth the effort .

Another aspect of this junction - in the case of a dry lined wall - thermal continuity . Regs will call for a min 25mm of edge insulation between floor slab or screed and the wall . Now if you are using a composite plasterboard ( say plasterboard with 50mm bonded to it ) - then an experienced contractor will "lift" the board min 10mm off the floor to stop the drying out screed from spoiling the plasterboard and decoration . This gap is an unwanted break in the continuity of the insulation , which must later be filled ( but rarely is )

SO - use 80mm edge insulation between screed and wall - so that the plasterboard is the "offered up" tight to this edge insulation . A 15mm strip of the edge insulation will be visible after the wall boards have gone up - which will be eventually concealed by the skirting board . Together with the polythene wrap up behind the skirting the detail now is air tight and thermally continuous .

sunnysoutheast

...or you could just tile up to the edge and put your skirting on top.

That's some detailing! What's the best way of fitting skirting? I think our guy ended up using hammer-in Hilti fixings. He said it may have been better incorporating a batten around the bottom of the wall to fix it to. You could put your polythene behind this too.

SSE

sinnerboy

sunnysoutheast wrote: »

...or you could just tile up to the edge and put your skirting on top.
SSE

this does not achieve the same result in terms of quality of detail -

• issue of gap between floor and plasterboard is not addressed
• floor surface and skirting bottom edge always results an an air gap - tiliing or no tiling

Fixing skirting s - or rads , shelves , wall units etc - plan carefully in advance hardwood blocks as required - cut away insulation around them tightly . Keep the blocks as mean and small and as few in number as possible - no continuous bands for skirtings .

Hassly ? yes . Demands close supervision on site ? yes . Worth it ? - YES

.

sunnysoutheast

I just meant you could put tiles down first and then fix the skirting after. You'd still have the polythene running up the wall providing the seal, you'd just have the tiles butted up to it. Personally I prefer the "skirting on top" look but each to their own.

Doing the individual blocks for skirting would surely drive anyone round the bend, we had to fix our (oak) every 10 inches I think.

SSE

sinnerboy

Thermal imaging photography typically shows up floor / wall / skriting junctions as "heat sinks" i.e. weak points thermally

So close attention to detail here is required and is worth it .

( 10 inch fixings spacings - SSE your skirtings will remain in place long after you and me are pushing up daisies )

sandt

will be insulating floors myself shortly & came across this thread.

im going for standard rads throughout, gonna put 80mm kingspan tf70 in the floor with 25mm on edge on external walls. is this ok?
do i need 500 guage polythene on top of my insulation before i pour my screed or is it just for UFH?

also (prob a stupid question but....) is it best to have floors insulated before the plumbers lays pipes or better to cut sheets around them when they are laid??

thanks.....

RKQ

Sandt there is another recent thread explaining this in detail.

http://www.boards.ie/vbulletin/showthread.php?t=2055424831

A slip sheet of plastic is used to prevent wet concrete reacting with the foil on high density insulation board. It is becoming more common in use. It has nothing to do with UFH.

1. Basically floor insulation requirement depends on the application date / grant date of your planning permission. (120mm + is becoming standard to comply with current Regs)
2. The standard floor construction is hardcore, sand blinding, Radon, insulation with pipes on top. Then pour 150mm thick conc. slab on top. See Homebond manual.