Is 5" enough to install an oak plank floor ?

[masochists-r-us]

On the basis we have rejected the reclaimed York stone flags we had planned to install ( they looked like paving slabs), we decided to go for a suspended oak floor. However, our builder says the 5 inches depth we have is not enough to install one so recommends a new concrete screed with engineered boards on top (!!!!). Beacause the floor level has already been lowered by approx 6-8 " many years ago, we're not keen to risk undermining the foundations of our 17th C stone farmhouse by removing yet more.
Is there a way of achieving what we want with the 5" depth we have available ?

 

[Penners]

What's the base above which you have 5" of space? Is it just earth?

 

[masochists-r-us]

Yes Penners. Earth.

 

[FamilyWiggs]

Better than Wind. Or Fire.

 

[Penners]

Well, the following are entirely my own deranged, amateur ramblings, but I don't see why you couldn't install a floating floor in a 125mm gap.

Assuming your floorboards are around 21mm thick, that leaves you 104mm to play with. So you could use 50mm x 100mm joists. These aren't stout enough to span the full room width without unacceptable flexing, but if you were to dig a series of founding holes, perhaps 500mm x 500mm x 300mm (or more) deep and at 1 metre centres, you could concrete in a line of short vertical supports of 50 x 100 timber, projecting 100mm above the soil. Placed accurately in line, these could then be screwed to the side of each joist, in order to support and stiffen it.

Obviously it would be advisable to use Tanalised timber for all of these components. And I would bash a number of randomly placed nails into the vertical supports, below the surface of the concrete, to help ensure that they are held fast by the concrete. I would also insulate under the floating floor, leaving an air gap above the earth.

Finally, make sure that the cavity under the floating floor is well ventilated by air bricks in the walls.

OK, this idea is lot more work than simply pouring a concrete floor, but it depends how much you want your floating timber floor!

 

[middi]

Penners idea is a good one, provided you have more thas adequate ( say, one per 2.5 metre) external air bricks to promote good circulation of air, preferably on two opposing sides of the proposed floor. Instead of using timber for the short posts that go into the ground, you could use just single brick piers sunk into the exisisting floor on a small foundation ( this depending on the type of subsoil you have), capped by small damp membrane and 100x50 joists resting directly on this with stabilsing " noggins" between the joist face. You would have to insulate with ( say 50mm thick) Celotex or similar rigid insulation boards sealed between the floor joists. This ( done correctly ) would give you 25@mm(75mm between joists) air circulation space , below a 50mm insulation, this below a dpm above the joists and 25mm oak floor above.

Middi

 

[Penners]

MRU - I expect you know that Middi is an expert in period property restoration..

His suggestion is a substantial improvement on mine.

But either way, you can tell your builder that a floating floor IS definitely possible!