Plastic sheeting over floor insulation

blast06

Hi,

Looking for opinions on whether to put sheets of polythene over the foiled floor insulation before i pour the screed. There seem to be different schools of thought.... one seems to be to prevent damage to the insulation foil and to prevent corrosion over time between the screed concrete and the insulation plus i guess potential cold bridges for any concrete the filters through to the sub-floor.

If i do it though it will be over the insulation, hot & cold water piping and waste water piping (which will be all dug into the insulation ... 2 x 70mm sheets) but under the underfloor piping which is over all the ground floor.

Any thoughts ?

Cheers

DOCARCH

Main reason for doing this is to stop the screed getting between and under the insulation and causing the insulation to float in the screed thus reducing the amount of screed over the UFH pipework.

If using polythene, use a very light gauge.

Alternative would be of course to ensure your insulation is very tightly fitted and taping joints with a foil tape. I have not heard of the screed being incompatible with foil-faced insulation?

blast06

Thanks.
I had a look on the insulation providers website (Kingspan 70mm (x2 for me) polyiso) and found the full technical spec for the insulation. Includes lines below:

Insulation boards should be overlaid with a polythene sheet (not less than 125 micron / 500 gauge), to prevent the wet screed penetrating the joints between the boards, and to act as a vapour control layer. Ensure the polythene sheet has 150 mm overlaps, taped at the joints, and is turned up 100 mm at the walls.

Also, from a few more searches, found below post (check from the 3rd post):

http://www.boards.ie/vbulletin/showthread.php?t=2056270048

Of course i don't know if this is overkill for what i have .... i.e.: perhaps taping the insulation boards together would be be every bit as good plus cheaper and quicker

homewardbound11

blast06 wrote: »

Thanks.
I had a look on the insulation providers website (Kingspan 70mm (x2 for me) polyiso) and found the full technical spec for the insulation. Includes lines below:



Also, from a few more searches, found below post (check from the 3rd post):

http://www.boards.ie/vbulletin/showthread.php?t=2056270048

Of course i don't know if this is overkill for what i have .... i.e.: perhaps taping the insulation boards together would be be every bit as good plus cheaper and quicker

Also when laying the polythene run it up the walls a few inches. Stops ingress into the skimmed plasterboards. Ours was a timberfrane so it was an obvious choice.

fclauson

also run insulation around your walls - not just the external ones - we have 50mm of insulation around EVERY wall - so each room is effectivly a tray of screed

One thing - and I did not get the right - put expansion joints in the middle of the screed -check with your engineer but I beleive you should have not distance more than 3m/9ft without a exp. joint

sydthebeat

fclauson wrote: »

also run insulation around your walls - not just the external ones - we have 50mm of insulation around EVERY wall - so each room is effectivly a tray of screed

One thing - and I did not get the right - put expansion joints in the middle of the screed -check with your engineer but I beleive you should have not distance more than 3m/9ft without a exp. joint

If you have 50mm of insulation around every screed pour, that should be more than sufficient to deal with any expansion.

By virtue of having a constant internal temp the expansion/contraction movements should be very minimal.

blast06

Thanks for the comments folks.
Insulation (2 x 70mm) is down (yesterday), first fix plumbing (that which has to be under the screed) tomorrow along with polythene, underfloor piping Tuesday and 1st half of Thursday and then - depending on the weather - screed on Thursday.

I am presuming i don't have to be overly particular with using double sided tape where the polythene overlaps cos the underfloor piping will keep all the polythene down and tacked to the insulation ? (Builders providers only had 2 bloody rolls of 5m double sided tape yesterday so don't want to have to head to the next town tomorrow morning for the sake of this!)

I'm not sure how to work getting the polythene to run up the walls by 10cm or so.... is this part critical given that i have quinn lite blocks on outer leaf and on the 1st row of blocks for internal walls with the rest concrete ? i.e.: i won't have plaster boards on any block walls.

Also, i certainly hadn't considered expansion joints cos have one room for example about 7m x 5m with only 2 of the walls external ones, i.e.: with the edge insulation. Must talk to guys doing the screed but should be fine given that i will have 'constant internal temp' - almost an A2 house (presuming i do as per the prelim BER report)

One lessons from the comments below .... i never put the damn edge insulation around internal walls :mad:

fclauson

sydthebeat wrote: »

If you have 50mm of insulation around every screed pour, that should be more than sufficient to deal with any expansion.

By virtue of having a constant internal temp the expansion/contraction movements should be very minimal.

sort of true - but our hall way cracked - our house is a L shaped with the corned of the L at 45 degrees -the hall is about 15 paces long and runs down the spine of the L hence is sort cranked in shape

all of the big regular shapes seems ok

Curious Geroge

Sorry for reviving an old thread but its the best one I've found. If you do the perimeter edge insulation around each room (internal and external walls), do you continue that edge on the doorway to create your tray ? ie: close off each room to allow for expansion? Also, on the second floor holicore, is perimeter edge insulation as critical on the internal walls; planning on doing the external to allow for expansion but its time consuming on smaller rooms. And lastly, do you put insulation and screed in the fireplace? thanks

fclauson

I can only answer as follows being a bungalow. What we did (I think) is made each room a separate "tray" - but be aware tiles if they cross the threshold of rooms sound "hollow" when walked on afterwards

On the fireplace I know there was a discussion about underfloor insulation and melting but I cannot remember where it ended up

galwaytt

blast06 wrote: »

Thanks.
I had a look on the insulation providers website (Kingspan 70mm (x2 for me) polyiso) and found the full technical spec for the insulation. Includes lines below:

....correct, because polyiso is hygroscopic (will absorb moisture), and when that happens it's u-value plummets. For that reason alone, used polythene to keep it from getting damp from the screed. Getting it wet may also affect it structurally (slumping).

....imho, even though it has a lesser u-value, the styrenes, either EPS or XPS are a better material. More durable, and the material is unaffected by damp from the screed, or indeed damp ingress from below either. Of the two XPS is even more rugged than EPS. Just my 0.02 as they say.

cocoa123

Is putting of polythene sheeting under the Techni-board wood flooring underlay a good idea? The concrete underfloor is dry, but just in case.