Hi, I have a 500 year old house that needs complete renovation. I need
to put in 2 new floors. The floor plan measures 6m x 6m (approx 20ft x
20ft). the old joists are really small. What size of joists would I
need to span this distance without using support posts? The house is
in croatia so I dont think I will have access to I-beams. I could buy
100mm x 200mm or 140mm x 200mm fir. Would these be strong enough ?
In the U.S, the standard joist lumber is 2" (~50mm) wide, with depths
up to 12" (300mm) I don't think either of the sizes you mention
are adequate to span 20' in one leap. My tables call for
2x12s (50mm X 300mm) spaced 16" apart if the span is just UNDER
20', or 12" apart if the span is up to 21'.
20' is a long ways for simple floor-joists, you can probably
save a fair amount of money if you find some way to run
a beam or load-bearing wall down the middle.
with a 500 yr old house where is it located??? not in the US, if so then
it was built when Columbus came to the americas? why not use some old
ship timbers they should be able to support the floors of the old stone
castles....what was there for the first 500 yrs????
use the same thing that was there....
even if it only last for a hundred yrs or so then it will serve the
i can't even imagine what a 500 year old house needs for repairs...
other than demolition and re-build.
I'd also think that if its still standing, its got quite a bit of
masonery construction, which is obviously heavier than std.
Hold onto your hat. My book shows for floor joists that you need
2x12s on 16" centers. 2x8s on 16 centers would be good for only 13
feet so 100m x 200m (about 4 x 8) would have twice the strength
(actually 3 times when you consider the finished sizes in the U.S.)
but don't know how this affects the length. It's just a guess but
140mm x 200mm on 12" centers would probably be acceptable by U.S.
standards. Note that the table assumes 10 pounds per sq ft dead load
and 40 pounds per sq ft live load. If you know the load will be less
than that you could adjust. It may be that the standard loads in
Croatia are less.
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