# Workshop floor - how much weight can it take?



## acxlll (6 Oct 2020)

I'm setting up a workshop in a timber framed building. It's about 6x12m large.
The foundation is concrete posts in 3x3m grid spacing, tied together with 150x200 composite timber beams.
On top of that are 50x200 floor joists, at 500mm spacing. Finally comes 21mm plywood for the floor. 
Joists and beams are actual dimensions, not planed down 45x195 etc.

Now I'm wondering how much and how heavy machines can I safely put into this space?
I believe I want at least 3-4 bigger machines - tablesaw around 400-500kg, planer, thicknesser 400-600kg each (go for combo to minimize weight?) and a large bandsaw at around 400kg. 
Is this realistic at all?
Perhaps it would be good to put the saw and the P/T directly over the middle posts to minimize any possible deflection?
Any thoughts?


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## Sheptonphil (6 Oct 2020)

I had a 350kg lathe on my 8x2 suspended floor in my last workshop. It really wasn’t good. There was always a little deflection as soon as anything heavy or out of balance was put on the lathe, it never felt solid. In the end I cut a hole in the floor, poured a one tonne concrete pad, replaced the floorboards directly on top the concrete pad. Worked superb after that, solid with no vibration or deflection.


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## acxlll (7 Oct 2020)

Doesn't sound good...
What was the span and spacing on your joists?

Still, I hope placing directly over concrete posts might help.


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## sometimewoodworker (7 Oct 2020)

acxlll said:


> I'm setting up a workshop in a timber framed building. It's about 6x12m large.
> The foundation is concrete posts in 3x3m grid spacing, tied together with 150x200 composite timber beams.
> On top of that are 50x200 floor joists, at 500mm spacing. Finally comes 21mm plywood for the floor.
> Joists and beams are actual dimensions, not planed down 45x195 etc.
> ...


You should really ask a structural engineer, however it looks significantly under engineered for the point loads you are planning. If it’s already built you could add a torsion box floor or large torsion box bases for the machines. Alternatively assuming it’s yours not rented, take the plywood up and double up all the frames.

With the workshop I built it’s engineered to allow cars to park on the floor so there’s no deflection with any point load.


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## PAC1 (7 Oct 2020)

You need a structural engineer as it all ultimately depends upon the ground bearing strength of your ground and the permissible load on your concrete posts. As to joist centres I would usually aim to get them to work for the plywood flooring width or length and balance size with span and spacing to get the optimal size, but again a job for the structural engineer.


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## acxlll (7 Oct 2020)

I found some calculators that show this floor to support 400kg/m2 with a safety factor of 2.
With a point load of 400kg giving 6mm deflection.
Also information about heavy aquariums and safes seem to point out that this sort of typical floor can take up to 400-450kg objects if placed near the wall (not in the middle of span)
So maybe all is not lost?
I definitely should be looking at 300-400kg machines max though.


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## Ttrees (7 Oct 2020)

Is cement and rubble that expensive over timber,
Or does the sand and DPM make it considerably more expensive?


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## acxlll (7 Oct 2020)

The issue is the finished floor level is about 70cm above ground


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## Cabinetman (7 Oct 2020)

My floor is pretty similar 16 inch spacing and the joists weren’t nearly as heavy as yours, I used 2.4 x 600 tongue and groove 18 mil OSB roof panels which I gave 2/3 coats of floor varnish, still looks good, I sometimes need to move the TS and PT a bit never had a problem, that was nearly 10 years ago and I use big heavy cast-iron equipment on it (Sedgwick 315 TS) I didn’t do any calculations but it works fine. I’m sure yours will be too


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## Cabinetman (7 Oct 2020)

I would rather be higher off the ground than have a concrete floor, most unpleasant to work on, and if you ever drop your plane it’s had it.


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## RobinBHM (7 Oct 2020)

acxlll said:


> I found some calculators that show this floor to support 400kg/m2 with a safety factor of 2.
> With a point load of 400kg giving 6mm deflection.
> Also information about heavy aquariums and safes seem to point out that this sort of typical floor can take up to 400-450kg objects if placed near the wall (not in the middle of span)
> So maybe all is not lost?
> I definitely should be looking at 300-400kg machines max though.


I reckon you will be fine.

Any machine will be supported on more than one joist.

If your machines are close to the edge or centre, the load capacity will be much greater.

It's a bit more complicated by the nature of your beams and joists, but my guess is the beams have a pretty big load capacity anyway


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## Cabinetman (7 Oct 2020)

If you use sheets of ply you will need to put noggins in inbetween the joists where the sheets meet. 
I used the T and G OSB for this reason and also because I like the look of it when it’s varnished.


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## Oddbod70 (7 Oct 2020)

That's a big workshop. Lucky you 

You wont go through the floor, that's for sure, but 500mm is quite a big spacing. Too big really

I think you'll notice a little bit of bounce but its unlikely to make too much difference with those machines. The ply will almost certainly distort over time, which will be a pain. If you can I'd add additional joists to halve the spacing. That'll bring you close to the "standard" joist spacing.

A big lathe is where any bounce will really show up. So if you have one of those in the plans you will definitely need to beef it up - at least where it sits.

I must admit I'm a fan of the 4" of rebar'd concrete brigade for a workshop base! Cover it with insulation and ply if you want, but when necessary you can always put concrete pads through the floor covering to bolt stuff down to.


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## spb (7 Oct 2020)

Going by MikeG's thread on building a workshop with suspended floor, you've got a few things to think about:

- 200x50 should be OK to span up to 4m, so your 3m spans are OK there
- 22mm flooring should span max 400mm, which is less than your 500
- Floor joists should be doubled under heavy machinery.

Now, your plywood is stronger than the chipboard he suggests, so I wouldn't be overly concerned about that - the Sagulator says that 21mm ply over 500mm will deflect less than 22mm chipboard over 400mm. However, I'd still be doubling up the joists where you want the machinery to go.


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## acxlll (7 Oct 2020)

Here's a sort of test by fire. I just received and unloaded 3.2 m3 of tongue and groove cladding for the walls and ceiling. stacked in the workshop on 3 battens 1 m apart. It should be about 1400 kg total, so 400kg+ on each batten. 
Checking with a long straightedge there is no sag. I guess the beam and concrete post below it can take the weight. So i reckon putting things along the middle beam should be ok.


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## Bm101 (7 Oct 2020)

Think you guys might be overthinking this...


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