Insulating an old concrete floor slab

cyclonebri1

Without wittering on we are well into a refurb of an expolicehouse circa 1945. It's become a money pit so this last bit needs to be done as cost effectively as possible.

Nice flat. dry but very cold slab base, I want to insulate this. We can easily accomodate and extra 50 or even 75mm in floor height as this was a later add on and is loer than the main house, no issue with door etc due to steps. Floor area in total about 10 x 6 mtrs.

So I propose to lay 25mm or even 50mm polystyrene insulation direcdtly on the base then 18mm flooring or probably roofing grade moistur resisting chip board as the new floor surface. I will also apply 25mm of insulation to all floor/wall breaks. I intend to glue the tongue and grooved chipboard to itself rather than fix it down in any way.

Anyviews, thoughts on the subject? Underfloor heating is out due to cost I'm afraid.

27col

When I converted a garage into a bed-sit I did mostly what you are suggesting. I coated the concrete with Synthapruf to seal the floor against any damp. Then laid 50mm insulation slabs. Then covered these with polythene sheeting. Then the chipboard floor panels were laid on top. They were glued together along the T & G. The floor rapidly became so heavy that there was no need to fix it down. I did not use moisture resistant board, but I wish that I had. You seem to have thought of everything. I was going to fix it down to battens, but the BC officer said to glue it and he was quite right.

cyclonebri1

27col wrote: »

When I converted a garage into a bed-sit I did mostly what you are suggesting. I coated the concrete with Synthapruf to seal the floor against any damp. Then laid 50mm insulation slabs. Then covered these with polythene sheeting. Then the chipboard floor panels were laid on top. They were glued together along the T & G. The floor rapidly became so heavy that there was no need to fix it down. I did not use moisture resistant board, but I wish that I had. You seem to have thought of everything. I was going to fix it down to battens, but the BC officer said to glue it and he was quite right.

Lovely, that's the reply I was hoping for, I thought that once assembled and wedged in place with edge insulation it would be cound, thanks again:T

ormus

make sure you leave some sort of expansion gap all the way round the final flooring.
i assume you are using skirting boards?

beaker141

Are there any higher spec sheets such as Kingspan that you could use instead of polystyrene to give better insulation?

cyclonebri1

Ok fellas, yes I understand the need for expansion/movement allowance on the final flooring. Luckily the skirting will be the last fit so ok there.

In regard to the last post, I was just about to research if the standrd 50mm poly as suppied by say Wickes, would be good enough in terms of load bearing rating???? Any views. Kinspan or similar is likely to be much more expensive I think???

All advice appreciated, :T

fiddiwebb

Kingspan or similar is likely to be much more expensive I think???

You could try using Kingspan seconds, noticed a few sales on eBay for seconds, also Kingspan would give you better insulation than polystyrene.

Kiran

Have you thought about spray insulation?

It has the added advantage of filling all gaps however small and due to its construction it also doubles up as a vapour barrier. The link below has technical info and also sells kits for DIY installation

http://www.spray-insulation.co.uk/

HTH

cyclonebri1

Kiran wrote: »

Have you thought about spray insulation?

It has the added advantage of filling all gaps however small and due to its construction it also doubles up as a vapour barrier. The link below has technical info and also sells kits for DIY installation

http://www.spray-insulation.co.uk/

HTH

Unless i'm very much mistaken spray insulation would not be applicable for such a use.

Kiran

Why do you say that? The cured product is basically the same as a sheet material. The only difference would be to the air tightness which would be increased with the expanding foam and the fact that due to the expanding nature it can be substitued or additional vapour barrier.

cyclonebri1

Kiran wrote: »

Why do you say that? The cured product is basically the same as a sheet material. The only difference would be to the air tightness which would be increased with the expanding foam and the fact that due to the expanding nature it can be substitued or additional vapour barrier.

Because we are talking about a floor, not walls and ceiling as in the link???