Solidifying / Stiffening New Timber Floor

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18 Sep 2018
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I'm a long time lurker and occasional poster. Hope this question isn't too off topic...

We're currently in the process of finishing off a lean to extension on the back of the house that will have a floating timber floor and I was hoping to get some opinions on the best way to solidify / stiffen it - currently the joists are in place but nothing else.

The joists are 47 x 200, the max span is 3.6 meters and they are about 150mm above a solid concrete 'oversite' base. The floor will be 22mm chipboard.

What's the best way to make sure that the floor is as solid as possible? I think the builder's current plan is for the joists to be tied together with a noggin and then some timber legs sat on the concrete below.

Are there alternative approaches? Will we get much more stability from additional noggins/legs? Is there a specific optimal way of doing it (particularly thinking of the legs).

There'll be a kitchen island which won't be excessively heavy but could definitely do with a bit of extra support.

Picture attached to give an idea (excuse the mess :D ) and a section of the plan for context.

Thanks in advance.


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It is compulsory that there be blocking or other similar stiffening (strutting, timber or steel straps) at half-span (at least.....more often in wider floors). This will stiffen up the floor enormously, as will the chipboard (obviously this will be glued at the T&Gs). There is absolutely no need to contemplate any further work to stiffen this floor. It doesn't need a prop down to the oversite below. If there is a point load such as an island unit (I doubt this needs any extra support.......) then double up the joists under it.

BTW, it isn't a "floating floor". It is a suspended floor.

Incidentally, this isn't something that a builder should be making decisions on. Whoever designed your extension should have designed the floor, and Building Control will want to see calcs for it if they have any doubts.
Thanks Mike. Was hoping you would chip in! The planning for this was a little haphazard as it was a late change - the spec for the joists did come from the SE.

That helps enormously, cheers.
Sounds crude but it works - slip some blocks under the joists down the middle, or more under the stove etc. Leave plenty of space for air circulation Concrete blocks or bricks with bits of slate or tile to make up the difference. Top with plastic by way of DPM.
My whole basement floor was done like that (100+ years ago) - quite small joists supported every 3ft or so on bricks sitting on a compacted hard core sub floor.

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