Floating Floors

[shelli]

Dear Fonts of all wisdom

First of All - Hello again everyone. It has been along time since I last posted.

We are finally getting somewhere near being able to -- wait for it -- actually live in our house!!!

Quick question for all you building experts.

Can anyone tell me the industry standard, building regs compliant way to make a ground level floating floor? We have two builders each giving us different versions of the latest definitive way to do it. If we don't take a stand soon it could be fisticuffs!

Please Help - I would hate to see grown men, shirts off on the lawn, in the early spring sunshine.........mmmm actually might not be too bad.
Oops sorry,drifted off there - ahem, anyway - yes please help if poss

Thanks in advance Shelli

 

[Andrew Bodenham]

Hello again, Shelli,

Good to hear that things are moving along for you.

By 'floating floor' do you mean a suspended structural floor, or a wood overlay on an existing solid or timber floor. There's a big difference!

Might help if you briefly outline the two bits of advice you have received from your builders, so that we can discuss their relative merits.

 

[shelli]

Hi Andrew ,

Sorry yes I was a bit vague, here is more detail.

We have to create a floor for our lounge from bare earth.

The lounge of the house used to be a barn. The room always smelled musty so,in advance of plastering walls and laying the engineered oak boards onto the existing chipboard floor (we've run out of cash and just want to get in !!) we thought we'd lift floor and check underneath. We found that the floor joists were just sitting on bare earth, no ventilation to outside anywhere and evidence of dry rot in wood. So it's all come out.

we have taken out large stones, removed rats nests, levelled earth and are laying fine sand over.

we need to lay membrane, concrete, insulation, wayroc/ply then the oak boards - the dispute among the boys is about the order in which to lay concrete and insulation - one school of thought is (bizarrely?) to lay the membrane then insulation then concrete , the other is to lay membrane then concrete then insulation -my common sense says second method must be right - but it is our trusted builder who says the 1st one is the way.

Any ideas ?

 

[Lime]

Can you give the measurement between what is the cleaned sand level that you have now and the intended level on which you will lay the floor boards?
i.e. what space do you have to play with between the sand and the bottom of the boards?

 

[Andrew Bodenham]

OK, we're getting a better picture now of what is involved.

It is common practice to lay concrete on top of insulation where an underfloor heating system is being incorporated - in effect the concrete acts a whole room storage heater / radiator, and the insulation below stops the heating system from having to heat up the rest of the planet too. So maybe that's what your builder is thinking of. Ask him to explain his reasoning.

If you're not putting in UFH I can think of no reason for putting the concrete over the insualtion. You will need to consider how your ply subfloor is fixed down to the concrete through the insulation. I'd suggest fixing at about 400mm centres with masonry screws (e.g. Mulit-Monti from Screwfix) which can be put into holes drilled in the (cured) concrete without the need for plugs. So you can lay the insulation and ply, then work across the floor fixing the ply down. I suppose you could use chipboard as a cheaper subfloor, but I personally hate the stuff. If you use ply it's worth routing a groove along the edges and fitting a spline in the joint - effectively creating tongue and groove boarding. I'm assuming you'll be using a rigid polyurethane insulation like Kingspan.

Your oak floor can then be laid over the ply. I'd be tempted to glue it down, or to put it on an acoustic underlay to stop it 'slapping' as you walk on it.

You mention plastering. Make sure that all the plastering work is finished and dried out before you lay the final flooring, otherwise you'll be asking for trouble with moisture related movement.

If your oak flooring is full thickness (22mm) rather than an overlay you might get away with laying it directly onto the insulation layer as a true floating floor.

Quite a few variables in this job - others may well have deeper insights into potential snags.

 

[ljn]

I had a similar job done in a similar condition. The ground under my rotten joists was London clay with lots of gravel.
The builders layed a waterproof membrane, then concrete, then Kingspan insulation. On top of that they poured a level screed with battons at 40 cm intervals. They screwed 18 mm green (that's colour, not enviromentally friendly) tongue & groove chipboard to the battons. I then layed oak parquet, glued down and pinned with headless pins to the ply chipboard.
No damp, no squeeking/flapping. All seemed fine. Looked and felt beautiful.

This may have caused increase of damp in the walls later on, but not while I was there.

I now have a new house with the same rot and lack of vents. I am looking into doin the limecrete floor as many have recommended on this forum, but the one month curing time... ouch!

As it would be breathable, I suppose wood wouldn't be advisable, so I'm thinking of flag stones with underfloor heating.

I like the feel of a solid floor rather than the hollow sounding, bouncy suspended timber floor.

 

[chuckey]

One problem with the second method is that with the foam as the top layer, is that its surface will get damaged very easily and will have depressions in it where people have walked.
I used a third method:- My house has no foundations and a lot of loose blocks so I laid 6" of concrete directly onto onto the compacted soil, in the vain hope it would act as a raft and hold the bottom of the walls where they should be. I then blinded this with sand then DPC, then 18mm P5 chipboard (green flooring stuff). This according to the foam manufacturers web site is enough for a floor. There is a small gap around the edge of the chipboard (badly fitted?) hidden by the skirting boards. The only use for concrete above the foam is to distribute any weight which the chipboard will do, or to provide a thermal mass for underfloor heating systems.
The succes of this scheme is that the foam must be laid absolutley flat, a depression will be bridged over with chipboard, which will then spring when walked on.
Frank

 

[jimjam]

Shelli, I understand from your postings that you are looking for an effective and economic solution to create a floating floor. Firstly insulation over concrete (you have no UFH and therefore are not looking to create a heat sink). 2nd, 22mm t&g chipboard flooring, (yes ply would be better, but more expensive) no need to fix boards we are creating a floating floor. I personally would glue wood flooring. You could also make a cost saving in the type of insulation you use and the thickness, 100mm Jablite as opposed to 75mm ridgid insulation but may need to consult building control regarding u-valves.

Hope this helps.

 

[Matt Green]

...and evidence of dry rot in wood.

I bet there wasn't.

 

[biffvernon]

If you're not putting in UFH I can think of no reason for putting the concrete over the insualtion.

It's nothing to do with UFH and all to do with thermal mass. The concrete acts as a thermal store, slowing the rate of cooling of the room above. This often makes the house pleasanter to live in. If you are going to have a concrete floor it is much better to have it above the insulation. In the long run you will use less heating fuel.

Of course concrete is evil stuff and it would be much better to think of one of the various alternatives. Why not leave it out and use the space for twice as much insulation?

 

[biffvernon]

I would hate to see grown men, shirts off on the lawn, in the early spring sunshine.........mmmm actually might not be too bad.

Looks like your lawn could get quite crowded

 

[Lime]

What you can and can't do is totally dependent on the space available, hence my question several posts above.

It may be sensible to have the insulation sandwiched between two layers of cement (or similar) but it depends on the room available.
Cement layers of any sort requires a certain thickness (even with modern hair) to have strength so space available will dictate what you can and can't do.

I don't like the idea of the boards being glued particularly if using modern glue.
It may be convenient and quick but will pose a real problem if for any reason a board needs to be raised as well as making the oak boards unable to be reused again.

Also thought needs to be given for water movement (from hot to cold) or spillage through the wood and around the insulation if it is directly under the wood.

The concrete (or whatever) will act as some form of heat sink but I'm not sure that is needed under two layers of wood.
It is not a particular advantage to make a room slow to heat up just because it may retain some heat when the heating is switched off it will just use more fuel.

 

[Gervase]

Concrete slab above two-inch Jablite or similar insulation on top of DPM is the bog-standard, accepted way of putting in a floor in a barn conversion round here. As has been said, the slab acts as a large thermal store. You generally line the walls with the same insulation, too, so that the slab is completely isolated. The screed goes over the top of that (and over a UFH matrix if desired). Insulation on top of the slab is, er, a bit DIY.
Ideally, though I'd put in a limecrete floor with no DPM! Total curing time may be a month, but you can put down boards and walk over it after a week.

 

[biffvernon]

Spot on,Gervase.

It is not a particular advantage to make a room slow to heat up just because it may retain some heat when the heating is switched off it will just use more fuel.

It's not quite so simple. Imagine two identical well insulated rooms, save that one has a large thermal store. It could be a concrete floor of a large fish-tank. When you switch on the heating the air (that's the bit you notice) heats up in both rooms at about the same rate. When you switch the heating off as you leave the room, the one without the thermal store slowly loses all its heat through the walls. But the other room initially only loses some of its heat that way, the rest being absorbed into the thermal store, only to be released again as the room cools. If you come home and switch the heating on again you will notice that the room with the thermal store has not yet quite cooled down so you won't have to burn quite so much fuel to get the temperature where you want it.

In a hot climate a house with big thermal stores evens out the day and night temperatures reducing the desire for day time air conditioning and night time heating.

 

[Lime]

Oh! But it is that simple.

Where does the heat that gets stored in the thermal store come from?
.........From the heating system.
And if the occupants vacate the room and switch off the heating the heat dissipates providing no further comfort for anyone.
It is just wasted.

Comparing the thermal lag of buildings in hot countries is hardly applicable here except in extreme heat.

 

[chuckey]

This thermal store thing, is fallacious unless you can top up your thermal store for free, i.e. solar energy or cheap - GSHP. The big thermal store fallacy is the " mediteraneum church" syndrome. Here you have very thick walls conducting a significant part of the solar heat into the ground. At night you have ground/wall heat being released. If your walls are thick enough you are living in a cave, so unless you can introduce your solar energy into it, it will remain at 10 deg C all year round.
Frank

 

[biffvernon]

And if the occupants vacate the room and switch off the heating the heat dissipates providing no further comfort for anyone.
It is just wasted.

That's ok for, say, an office that is occupied for seven hours and then not wanted for the next seventeen. You may as well let it cool right down and then start heating again shortly before work the next day. But with a home it is more useful to keep a more even temperature.

 

[shelli]

Dear All

Sorry for delay in getting back - had to abandon computer over weekend as OH had birthday.

thanks so much guys for all your help on this

Andrew - thanks for advice re fixing floor.

Lime - we have 7 inches depth.

Gervase and Biff - thanks - thats what we really needed - someone to say "you do it like this" - perfect - and the builder will be pleased as it looks like his method is the best.

anything to keep the heat in works for me.

I'd love to show you all around as (apart from nightmare lounge )it's looking pretty good elsewhere
can anyone point me to the post from last year about how to get pics onto your post?

Shelli

 

[biffvernon]

When you reply to this, click on the 'upload attachment' button below left of the writing area. Then click 'Browse' and find the your picture file on your own computer. Click 'Add the file' and you're about there.

 

[Nemesis]

I wonder what evidence of dry rot there was?