Maximum joist length?

Someone has asked me to help put in an upper floor in a farm outbuilding. The room dimensions are 7 metres by 5 metres constructed with a single thickness of breeze blocks. He is planning having 7 metre long joists and fixing down traditional tongue and groove floorboards on top.

Is this feasible? 7 metres sounds like a very long span unsupported, assuming that you can even get 7 metre long joists? I would have thought that at least one cross beam would be needed for such a span.

I'm happy to lay floorboards and do the associated DIY but I'm no structural engineer!

Suggestions?

Reply to
David in Normandy
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Engineered joists will do it (just).

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for example.

Reply to
dennis

Our 2nd floor (22mm chip on top, plasterboard underneath) is supported by 7 x 2 joists at normal spacing and it is, erm, "bouncy". These joists are only 4.5m long...

Gut feeling is that 7m is going to need some seriously chunky bits of timber, 8 x 4, 8 x 6? they won't come cheap in 7m lengths.

Why doesn't he use the 5m dimension for the joists?

Reply to
Dave Liquorice

Table A of the Building Regs suggests a 9 x 3 will only span about 5.5m, so probably no.

Reply to
The Medway Handyman

Is there some earth-shattering reason for not laying the joists in the

5m direction?
Reply to
dom

Eet ees ze French way, m'sieur. ;-)

Seriously, the costs to buy the larger number of 5 metre joists will be a lot lower than for the 7 metre ones, the cheapest way may end up being a steel joist in the centre of the long dimension, supported by two

450mm square piers in the wall, and 3.5 metre joists, which will be about half the size of five metre ones, which, in turn, would be about half the size of seven metre ones, if he can get them. Unless he's got a load of seven metre long steel joists laying round in the farmyard somewhere.
Reply to
John Williamson

8 x 2 (250*50mm) would be to code for 4m span, 400mm spacing - I think, for domestic floor loads.

Depth is what counts. Strength is proportional to square of the depth, Stiffness is cube of the depth.

Reply to
dom

In article , David in Normandy writes

Might be a job for engineered joists but even then 5m sounds better than

7m which I suspect could get a bit expensive and bouncy.

This came up on a quick search (engineered joist span):

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data here on spans and rigidity:
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plenty of options at about 5m diminishing towards 7m.

Not local to you of course but I'm sure there will be outfits in France too.

Reply to
fred

If using joints, then run them the 5m direction...

even then its making life difficult. A 7m steel down the centre and 3.5m joists either side sounds much better.

Reply to
John Rumm

I am building a lean to in the UK Length 27' x death 8' x height 8' with a slope for the roof upto 10' I am considering using 2" x 4" for all the Framing with 16" between each uprights. Again for the rafters I was thinking of using the same wood 2" x 4" at 9' lengths to allow for some overhang. Does anyone have any concerns or suggestions

Reply to
carlhitchmough6

Perhaps more uprights than you need? With a bigger support at the lower end, say a 6x2, you might get away with uprights at say 48 inches (although I would be inclined to use 4x4 uprights).

What roof material? Is this in an exposed or windy area? What about snow load?

You'll need some diagonal bracing for the outer "wall", I think; A suitable roofing material would provide diagonal bracing for the roof plane.

Reply to
newshound

really depends on the weight of the roof covering. Will it be tiled with artificial slate or marley concrete tiles or something lightweight like epdm ? . You might have to go up to 6x2 for the rafters.

The manufacturers of whatever hard roofing you choose should have tables on their website showing the amount of overlap neeed for your 12? degree pitch. There are limited tile choices for a pitch that low, eg

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Reply to
Andrew

though there are ways round those limits to some extent.

Reply to
tabbypurr

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