Green Building Forum - Ground floor slab/insulation.

Ground floor slab/insulation.

AndrewJwaters — Tue, 09 Oct 2007 20:40:08 +0100

My agreed spec for the make up of the ground floor slab [ To a barn conversion] is as follows:-
Mot type 1
Dpm
100mm conc
50mm cellotex
Wet UFH
50-75mm screed
Floor tiles

My question is :-
Any advantage in increasing the 50mm cellotex to 100mm thick?
Thanks.

Ground floor slab/insulation.

tony — Tue, 09 Oct 2007 23:51:38 +0100

No! But there may be a good case for not having it at all under most of the floor. Just arround the edges.

If it were mine I would put it under the concrete.

What kind of use will the barn have? Full time occupancy or intermittent?

What is the thermal resistance of the whole floor -- soil MOT stuff, concrete , screed , tiles? Do you need any insulation?

Ground floor slab/insulation.

nigel — Wed, 10 Oct 2007 10:37:51 +0100

The thickness of insulation you need depends a lot on the ratio of floor area to perimeter.

Personally I would go with 100mm esp if you are using UFH as you will never add it back later.

This link should help http://www.insulateonline.com/index1.htm?floorsintro.htm~main

I would agree that it would be better to have the thermal mass on the warm side of the insulation.

Ground floor slab/insulation.

Terry — Wed, 10 Oct 2007 18:32:40 +0100

Just wondering what the reason is for having the concrete layer?
If you are going to insulate, ignoring Tony's comment for the moment on what is really required, why not replace the concrete and celotex with 150 eps?

Ground floor slab/insulation.

tony — Wed, 10 Oct 2007 22:11:46 +0100

That would be cheaper if it was necessary but you should still have a structural floor somewhere.

Ground floor slab/insulation.

Johan — Thu, 11 Oct 2007 09:33:31 +0100

300mm of foamed glass or LWA nder the con/limecrete slab will do the trick.

Ground floor slab/insulation.

Bluemoon — Thu, 11 Oct 2007 15:09:36 +0100

How about fluffy concrete, sort of similar to Celcon Solar wall blocks?

Ground floor slab/insulation.

AndrewJwaters — Thu, 11 Oct 2007 19:45:26 +0100

Thanks for all your help, i have decided that Tony has the solution, which has been confirmed by 'Kingspan' tech dept.
50mm Kingspan/Cellotex with an increase around the perimeter [greatest heat loss] - 100mm.
Thanks again.

Ground floor slab/insulation.

James Norton — Fri, 12 Oct 2007 11:04:48 +0100

I thought Celotex / Kingspan couldn't go under a slab, or am I misunderstanding the thread?

J

Ground floor slab/insulation.

Mike George — Fri, 12 Oct 2007 23:46:10 +0100

James, I have seen PUR used both above and below the concrete slab, though I prefer below.

Ground floor slab/insulation.

James Norton — Sun, 14 Oct 2007 10:01:55 +0100

I was thinking rather what Celotex / Kingspan and their BBA certs preferred...

J

Ground floor slab/insulation.

Mike George — Sun, 14 Oct 2007 17:09:53 +0100

It does not matter, either is acceptable, provided you follow their details [Detail sheet 2, figs 1&3]
http://www.bbacerts.co.uk/certs/31/3197i2_web.pdf

Ground floor slab/insulation.

tony — Sun, 14 Oct 2007 17:27:22 +0100

Couple of points 1) I can never see why there is need for both vapour control on warm side and dpm on the cold side. All I have ever done is thick polythene on top as combined dpm/vapour control.

2) concrete and screed both react with aluminium so any spills seeps etc will naff the foil layer.

Ground floor slab/insulation.

Mike George — Sun, 14 Oct 2007 18:05:25 +0100

I agree with 1, but I follow their spec as I am not sure that PUR is totally impermiable. I have heard that it is not and the BBA spec seems to back this up.

Re point 2 are you sure it is Aluminium?

Ground floor slab/insulation.

tony — Sun, 14 Oct 2007 20:52:03 +0100

Not sure that it is ali but it sure looses its shine on contact with cement.

Ground floor slab/insulation.

Mike George — Sun, 14 Oct 2007 21:00:21 +0100

Yes it does, perhaps that is why they recomend a barrier? I think it is something shiny, but not Aluminium - no proof however

Ground floor slab/insulation.

James Norton — Mon, 15 Oct 2007 21:40:32 +0100

Posted By: Mike GeorgeIt does not matter, either is acceptable, provided you follow their details [Detail sheet 2, figs 1&3]

Mike,

...well you learn something new every day, to be honest the last time I asked them it was on a commercial project w/ 5kn/m2 live floor load, perhaps it was that that scared them off.

So under slab to provide more thermal mass (I assume) but EPS or PU...?

J

Ground floor slab/insulation.

James Norton — Mon, 15 Oct 2007 21:41:12 +0100

Doh , should've used html mode.

Ground floor slab/insulation.

Mike George — Mon, 15 Oct 2007 22:23:54 +0100

A matter of choice dependent [for me] on the need for building up height to finish floor level.You need less PUR but EPS is nicer to use. Details here: http://www.bbacerts.co.uk/certs/17/1796i6_web.pdf

Ground floor slab/insulation.

bayouboy — Tue, 16 Oct 2007 08:43:16 +0100

The main thing to remember with underfloor heating is that the temperature difference between inside and outside is much greater than with indoor air temperature. Secondly, you are dealing with liquids and solids, so heat transfer is greater than air-solid-air ( as in a wall. Although the earth below the slab is more or less constant in temperature in the centre, and is not very cold, the heating pipes will be between 40C and 60C depending on the systems, rather than 20C. Your heat will flow continuously into the ground without good levels of insulation. I would go towards Johan's 300mm of foamed glass.

Ground floor slab/insulation.

Bluemoon — Tue, 16 Oct 2007 15:52:20 +0100

I am at the start of removing the screed in my ground floor bathroom. Base is about 100mm thick, there is a thick polythene film then the screed about 80mm thick. The room is 3M square. one outside wall with window. As I am laying ceramic tiles on the new screed, I want to install an electric heating mat to take the chill off the floor. I realise I won't meet the latest standards for insulation, but will about 20mm of board make any real difference? I have installed pipes for a rad, and can fit one one if needed. There is also a 800watt towel rail in the system.

Ground floor slab/insulation.

tony — Tue, 16 Oct 2007 16:39:06 +0100

How about running some pipes in the screed -- a big loop in parallel with the rad and an adjusting valve near the rad? or just extend the radiator pipes under the floor for a bit.