In article , John
writes
"fred" wrote in message ...
In article , Christian
McArdle writes
What size joist should I go for?, one book I read says I can use
100x50mm
(4x2) but I`m not sure.

A 47mm x 97mm joist on 400mm spacings with SC3 timber and 0.25-0.5
kN/m2
allows a span of 1.92m, making it just compliant with building
regulations.
If you had wanted a bath installed, you would double up the joists
supporting it.

If your intended flooring weighs more than 0.5kN/m2, you'll need 122mm (5
inch) joists.

A sleeper wall or thicker joists would improve rigidity, if required. If
you
install one, ensure ventilation is adequete. In fact, you must ensure
ventilation is adequete anyway. Ensure you install good insulation and
airbricks. Take the time to install underfloor heating for a new floor.

Christian.


Is there an existing floor?
--
Yes, about 2ft below the proposed (new) floor. Its concrete (no damp).

John

Ah, now I see why you're suspending it ;-), that was my only query.

Sleeper wall sounds OTT, but if 4" is the min for joists then I'd be inclined
to use 5" to limit flex.
--
fred