Green Building Forum - 100mm Concrete Slab on 300mm Thick EPS Floor Insulation - Good or Bad?

100mm Concrete Slab on 300mm Thick EPS Floor Insulation - Good or Bad?

Mike George — Thu, 10 Apr 2008 15:02:23 +0100

Sounds good, maybe we could have another ranking of supporters of air flight and other CO2 producing activities as well - a sort of Code for Sustainable Homeowners - just so we can see who is consistent in their views.

100mm Concrete Slab on 300mm Thick EPS Floor Insulation - Good or Bad?

bot de paille — Thu, 10 Apr 2008 20:49:35 +0100

What about using flagstones on a bed compacted sand on the layer of hardcore, with the UFH pipes buried in the sand?

Any ideas how to incoprporate insulation into this? if 50mm slabs were laid under the sandwould the settlement be too uneven? or would it work?

100mm Concrete Slab on 300mm Thick EPS Floor Insulation - Good or Bad?

TimGlos — Wed, 04 Nov 2020 20:37:54 +0000

Just resurrecting this thread from quite a while ago as looking to do the same!

Does anyone have any suggestions about using a flowing screed or self compacting concrete for the slab?
Build up would be the same - 150mm hardcore/300mm EPS/Screed or conc with UFH.

I've calculated deflection/compression for the EPS but am struggling to find any information on what the different types of screed can accept in this regard. Does anyone have any knowledge they can pass on?

Tia

100mm Concrete Slab on 300mm Thick EPS Floor Insulation - Good or Bad?

bhommels — Wed, 04 Nov 2020 22:09:44 +0000

Don't know about what screed can accept, but this is my two pence:

I used 200mm EPS underneath, and then 80mm PIR on top.
Most insulation specifications list the compression strength at 10% deformation, but it is not so easy to get information on long-term maximum compression strength. For EPS the difference between 10% def and long term is larger than for PIR, BTW. With the screed and PIR on top the EPS will be very evenly loaded is how my thinking went, so its lower strength is not a problem. Most EPS is well strong enough for domestic application.

Also, the UFH guys liked PIR as they could use their stapler to hold the pipes down. The pipes were covered with 80mm screed.

Don't forget about perimeter insulation. I used 50mm PIR strips all around.

Most screeds are now fiber reinforced and the strength is quite impressive. The builder really regretted leaving the excess screed mix for too long as he had to work it with a pneumatic hammer to break it up and take it away.

100mm Concrete Slab on 300mm Thick EPS Floor Insulation - Good or Bad?

GreenPaddy — Wed, 04 Nov 2020 22:34:44 +0000

Tim, 125mm of C35 concrete, with A193 mesh on 50mm supports. Cable tie ufh pipes to the mesh. Save yourself a few grand deleting the screed.
Presumably you have a structural engineer to sign off all the load bearing items like foundations, floor, walls, roof?

100mm Concrete Slab on 300mm Thick EPS Floor Insulation - Good or Bad?

tony — Thu, 05 Nov 2020 09:02:44 +0000

I like insulation underneath, vapour/dpm on top of insulation, concrete on top of that , sheet insulation is virtually incompressible under a floor

I like a142 grid, nice to tie pipes to if needed, can do without screed, I always did 100mm with screed.

100mm Concrete Slab on 300mm Thick EPS Floor Insulation - Good or Bad?

djh — Thu, 05 Nov 2020 11:33:45 +0000

Posted By: TimGlosDoes anyone have any suggestions about using a flowing screed or self compacting concrete for the slab?
Build up would be the same - 150mm hardcore/300mm EPS/Screed or conc with UFH.

I've calculated deflection/compression for the EPS but am struggling to find any information on what the different types of screed can accept in this regard. Does anyone have any knowledge they can pass on?

You need a reinforced concrete slab under the screed, if you have a screed. It's not an either/or situation. Since you apparently didn't realize this, it makes it even more important to go find an engineer to design it. You need to do that legally anyway.

I suspect you need to plan on stepping back for a while and take some more time to learn about the various possibilities and the reasons that people choose them in different situations. Sorry if that comes across as a downer but I think that you will be happier at the end of the day. Perhaps you'd like to start your own thread and tell us a bit about your project?

100mm Concrete Slab on 300mm Thick EPS Floor Insulation - Good or Bad?

TimGlos — Thu, 05 Nov 2020 18:57:31 +0000

Thanks to those for the constructive comments but a shame others jump to conclusions so quickly.

100mm Concrete Slab on 300mm Thick EPS Floor Insulation - Good or Bad?

muddy — Fri, 06 Nov 2020 21:20:04 +0000

Posted By: GreenPaddyTim, 125mm of C35 concrete, with A193 mesh on 50mm supports. Cable tie ufh pipes to the mesh. Save yourself a few grand deleting the screed.

I was going to use self compacting concrete for such a floor in my barn conversion until the technical lady at the concrete co advised against it because there was not enough concrete above the mesh. She was suggesting a screed. So I am looking again at a more standÃ rd concrete mix but with 10mm aggregate, fibre and wet enough to flow. The floor is 16.6 X 4.7 m so although it has mesh there was going to be a risk with self compacting concrete and contraction cracks. It is not structural..
I want a good level finish, of course. I have a power float to play with. But the self compacting concrete appeared to offer advantages of ease of placement for a good finish.

100mm Concrete Slab on 300mm Thick EPS Floor Insulation - Good or Bad?

djh — Sat, 07 Nov 2020 10:55:51 +0000

I would have thought that a floor slab is one of the easiest pours to compact, so where the advantage of self-compacting concrete would be least?

100mm Concrete Slab on 300mm Thick EPS Floor Insulation - Good or Bad?

muddy — Sat, 07 Nov 2020 21:39:16 +0000

Having read about other self builders experiences, I think that is an easy assumption!