Hi,
Could anybody who has access to the regs for unsupported timber span sizes, give me an idea as to what size timbers I need for a floor? It will be 3300mm between supports, spaced at 400mm, and will be used for a shed / workshop (no particularly heavy equipment, just desk / chair / electronics workbench etc).
Floor on top will be 18mm bitumenised OSB, with insulation between the joists.
If I increase the spacing to 600mm, does that make much of a difference?
Thanks for the help
Gary
My unsupported span is 4.00 metres and old fashioned 7 x 2 inch joists were used. This is a loft area and not walked on. To convert the area into a living room the joists should be 9 x 2 inch or the new metric equivalent.
Have a look here, there's a lot of info inthis site....
Minimum seems to be 50 x 170 C16 grade @ 400 or 450 c/c. At 600 c/c span is given at 3290, but this may be a little too bouncy.
50 x 200 will be OK @ 600 c/c.dg
Thanks very much - just what I needed.
errm, 50x170 - that's 7x2 isn't it? ;-)
Sorry I don't speak imperial, but grandpa says its 7x2. :-)
dg
The "old" way to do it, and in imperial, is half the span ( in feet plus an inch, so for instance a 12' span would be half 12 = 6, plus 1 = 7, so 7 x joists. That would be at 16" centres. I know there are all sorts of regs/charts/tables etc but this is useful rule of thumb
-- Nick H
In Impeial peak, the rule of thumb is that, for a 2 inch thickness, at
16inch centers, the size (in inches) is the span (in feet) divided by 2 plus 1. e.g for a 12 foot span, 12/2 =6 +1, so a 7x2 joist is needed. I stress that this is a rule of thumb. Malcolm175mm x 50mm is 7 inches by 2 inches ... BUT.. you may find you've been sold 165mm x 47mm instead when you come to actually measure it. Also I used C16 but found that three out of the fourteen that I'd bought did warp badly in the 165mm. direction. If I was doing it again I would use Redwood. It just feels a lot stronger than the C16. Also I was exposing the underside of the joist by setting the 12mm. plasterboad back by about 35mm. to give a slightly old fashioned look to the ceiling.
Chris.
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