Thread: Floor joists distance apart

Generally speaking - 450mm apart is industry standard for yellow tongue flooring (19mm). Due to it being a workspace and quite small, I'd space them a max of 450 (it will only be 2 extra over the 6m) but evenly space them

I'd agree with 450 as a max, I don't feel 600 would be adequate, but the question comes to mind - are you putting in one or more big, heavy machines that are the sort that end up on mobile bases (i.e. 200Kg+ machines)?

If so, I'm no engineer, but even with 25mm T&G (I think that's a great upgrade to 19mm), I would wonder if 300mm, or something in between this and 450mm (even if it's non-standard) might be a better idea?

Maybe someone here with more knowledge than I have will be able to advise, but you gotta think that every one of those machines is 2-3 people standing, or moving, in one spot.

Give me the weight of machines and I will give you your answer.

There are several factors that will come into play, in regard to joist spacings. Machinery is only one consideration it would also need extend to stored items such as timber / steel, cabinet, work benches, flooring as everything has a weight and you will be amazed how quick it will add up. So everything needs to be considered. Additionally, what sizes are your bearers and posts and their distance apart.

For me 600 is to far apart 450 is usual however a lot of factors need to be looked into. I'm like you I would not want any spring in the floor and I would err on side of more is better . I'm sure rebuild will sort you out.

Originally Posted by Specialized29er

70mm x 210mm, 70 year old reclaimed hardwood joists.

Is using the 70mm x 210mm hardwood the best way of using them?

Personally, I would prefer to use them on other projects and buy/source lesser quality timber for the floor.

I'm no expert. Even though you have 25mm ply flooring I think you should still have joists every 450 or less. It not just the weight but also how much force is concentrated on a specific foot and how far that foot happens to be from a joist. And that item might sit in that location for years. It might not matter so much for a storage shed but it's always desirable to have a flat floor in a workshop.
As the previous posted said, perhaps you can reduce costs by using something cheaper for joists and having more of them. Then use those nice hardwood beams for something else?


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Originally Posted by DaveVman

It not just the weight but also how much force is concentrated on a specific foot and how far that foot happens to be from a joist. And that item might sit in that location for years.

Yes, it's not the joist strength in this case - just the ply strength.

Originally Posted by cava

Is using the 70mm x 210mm hardwood the best way of using them?

I'm with George, but with a twist. If you cut the joists down the middle to 70x100 you will still have joists that are way above spec (70mm wide is huge, and they are old hardwood jobbies). That way you can put them every 300mm if you want and probably have the capability of driving cars over it! You'll also have some beams left over (using 70x205 at 450 centres will use more timber.)

Whatever you do, think about what you want for now and then allow plenty extra because you just never know....

Buying in a bit late, but hopefully still a useful post.

The heavy loads (machines/timber, etc; ) you will undoubtably have are of concern in so far as the overall strength is concerned and we'd need to know what those loads are to give a detailed answer, but heavy loads won't make the floor springy. These loads will have a dampening effect on the immediate area they are in. Springiness is, obviously, the flooring bouncing up and down as you move over it

Long spans on the floor joists would spring in the traffic areas, not in the machinery areas.

BUT the heavy loads will cause increased deflection (sagging) and may well be of concern. And remember that timber creeps over time so, even with well seasoned timber, the deflection 1-2 years from now will be around 2 times what it initially is.

The 70x205 boards do seem like over kill (again without knowing the actual loads concerned) but if you do decide to cut them don't turn them in to 70x100 .

Any rectangular beam's strength of proportional to its width, but also proportional to the cube of its height. So if you cut a 205x70 into 205 x35 you get 2 beams of half the strength in bending. Cutting it into 100x70 you get 2 beams that are 1/8th the strength of the original.

Thanks guys for all the suggestion and 450 apart works well. No need to work our machinery weights because where the heavy toys sit I'd layed 8'' full concrete blocks first ( reclaimed from my dads old piggery) and then layed the ply directly over the top.

As for using the twenty 5mt lengths of reclaimed hardwood beams (piggery) and 20 sheets of the 25mm tongued ply and 15 sheets of 12mm ply these were purchased via a Grays Online auction when a hardware store was closing down and all purchased for 550 dollars. I'm using the sheets of the 12mm ply for the internal walls and hope to have the build done after installing installation in the ceiling during our 6 winter months.
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