I wish to extend a floor 1.8m to an existing wall. I'm confined to
using 4 x 2 joists which I'm assuming would be a bit light if used at
standard spacing so what spacing would I need to use, or what are the
alternatives ? The critical dimension is the 4 inches Standard grade
flooring chipboard will be placed on it.
Paul Mc Cann
He is assuming that it is a ground floor, so you can just lie the thin
joists on sleeper walls, which are masonry walls with lots of holes in for
ventilation/damp resistance built for the express purpose of supporting
joists that would be too shallow. If it isn't a ground floor, then it won't
Thats what I thought he menat but my mind was running along the lines of
the actual problem which is not at ground floor level.
I'm actually trying to extend a steel framed mezzanine floor which
already uses 4x2s across the steel horizontal beams.
A prevous poster kindly pointed me towards load calculation tables and a
quick google (which I suppose I hould have done first) threw up a few
more such tables. They all suggest that 4x2 will span 1.8m @ 400mm
centres but it looks awfully light to me when viewed in situ.
I think I'll just space the 4x2s a little closer, I have plenty off them
=================I've just replaced a downstairs suspended floor (house is about 60 years
old). The joists are 4" x 2" at 16" centres (virtually the same as your
proposed metric figures). The sleeper wall is 6 feet from the outer wall
so the joist span is also 6' . Since this was apparently the standard 60
years ago and there has been no failure in my joists I would think that your
dimensions / lengths are perfectly acceptable. I would suggest that you use
galvanised 'joist hangers' on the outer wall and overlap the inner ends of
your new joists with the old. Use either coach bolts or coach screws to
secure the overlaps.
If your new extended floor is intended to take unusually heavy weights then
it may be necessary to use heavier joists but for domestic use your proposed
sizes should be perfectly safe.
A sleeper wall is built under the floor, usually with some spaces in
the bond to allow air through. You then put a DPC on the top and a
wall plate (i.e. piece of timber) on top of that. Finally, the floor
joists run perpendicular and on top of the plate.
However, when you say that you are confined to 100x50mm joists does it
mean that you are short on height?
To email, substitute .nospam with .gl
Mailly ventilation, to keep a cross-flow going via the air-bricks
through the underfloor void. The wall plate is a piece of 4x3 or
even 4x2 laid on top of the sleeper wall on a DPC of slate, felt
or whatever, that the floor joists bear on.
Ooops! The highest dwarf wall in existance, perhaps?!
Can't you put in a new piece of steel to match existing supporting
If you've 4x2 over an RSJ (or whatever) could you use (say)
8x2 notched at one end to fix over the steelwork and give
a surface under to finish?
A photo is worth many words...
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.