Floating Floor on Celotex Without Concrete

[diybellydancer]

Hello All,
My first post so please be gentle!!
I am currently replacing an old single skin lean-to, with an extension. I have kept the original wall, studded it and insulated it with 85mm plasterboard backed insulation.

I am not working off plans, but am using a Building inspector, and so far, he's been happy with all my work. He also stated that because the floor is already in situ, and insulating on top of it would be impractical, due to it creating a step up, I do not need to alter the floor. This was good news until I removed the wall separating the extension and the old room, and found a 10mm height difference.

After getting into a discussion with a local builder in the pub, about different flooring methods, he stated that he had done two builds recently, where he lay 100mm celotex and dpm on top of 100mm crushed concrete (blinded), and then glued tongue and grooved chipboard on top, with no concrete slab at all, which leads to my question, does this method seem acceptable. It is certainly appealing, and I will be asking my building inspector about it, but wanted to know other opinions first.

Any opinions appreciated.

Many Thanks

DBD

 

[freddiemercurystwin]

I would quite like to see the look on your Inspectors face when you propose this!

 

[diybellydancer]

FMT, I should have had a camera, but I think his face was as you expected. Needless to say, I am now having 150mm crush, 100mm concrete, 100mm insulation and 70mm screed.

I've decided not to ask for advice in the pub any more!!

DBD

 

[freddiemercurystwin]

Fair play Jellybelly for coming back to report that! Many don't.

 

[limerockconstruction]

I've decided not to ask for advice in the pub any more!!

DBD

Its funny, everyone in the pub used to be a builder and knows best....would have been a sight to see!

 

[tony1851]

What's the problem, if the hardcore is well-compacted?
I knew a cellar-conversion company which did this when excavating for greater headroom - well-compacted h/c, dpm, kingspan and chipboard.
They compact hardcore under roads, so why not under kitchens?

 

[freddiemercurystwin]

So why do we bother with slabs at all then tony? You do know its 2013 and not 1851 don't you?

 

[tony1851]

So why do we bother with slabs at all then tony? You do know its 2013 and not 1851 don't you?

Yes, I did check the calender.

But seriously I wonder if the original purpose of the concrete slab was to keep damp down before the advent of flexible membranes, rather than to provide a load-bearing element.

I believe my original point is still valid. When you have new block paving for your driveway, they put compacted hardcore down first, then the blocks. They don't put a concrete slab down. So if that holds the weight of a vehicle, why do we need a concrete slab to support the weight of people?

 

[freddiemercurystwin]

Maybe because some movement under block paving or similar is forgiveable (ie not a problem) yet under a kitchen floor that was maybe tiled it could well be disastrous

 

[tony1851]

Fair point, though that goes to show how finnicky we are today about fitted kitchens and designer units and fancy fittings etc. It wasn't all that long ago when our floors used to be beaten earth topped with straw.

 

[freddiemercurystwin]

Truth is tony I don't know the origin of floor slabs at ground level in this country and what dictated their introduction other than guessing as above. Google has failed!

 

[themiddleagedun]

Mmmm, one to ponder on... Well compacted type 1 certainly sets very hard, and is stable. So providing the blinding is flat and level, to take the insulation and chipboard I reckon it would work... Why not?

 

[freddiemercurystwin]

Well compacted type 1 certainly sets very hard

But not as hard as concrete!

 

[tony1851]

It's not just hardness that matters, stability is just as important.

Q. Plain concrete is hard and brittle, so what stops it settling and cracking?

A. Well-compacted hardcore.

 

[freddiemercurystwin]

Local Authorities down this neck of the woods insist that ground bearing slabs rest on the inner skin, to avoid the dpm (radon protection) being compromised should the hardcore ever sink etc. Theoretically well compacted hardcore is seemingly solid as a rock, reality is that it isn't and can and does sink.