Hi Jon ...
... if you tell me the size of the joists and the span I can give you
a good idea ...
However builders use the BS joist span tables for their sizing ... choosing
the smallest joist they can get away with for the span .. result you cannot
put much applied load on it

If you could arrange to spread the load over say ... 4 joists and also
arrange that the load comes off at the 1/3rd points, that will give you best
spread.
i.e. fix a counter beam to 4 joist 1/3 out and parallel to the wall ... and
the same for other wall, and support your 'bits' from the centre of these
counter beams ..... joists are at their strongest at the 1/3rd points.
(send me a mail if this is unclear)

Rick


wrote in message
oups.com...
I have a detached double garage, which was built about 6 years ago by
McAlpine.

I want to rig up a 'chain block' to do some lifting.. I am only
planning to lift a max of 200kgs and wonder if my joists will take this
kind of load.

The plan I had was to put a bar along a number of joists (Probably 4),
to spread the load a little.

Would this be safe?

Jon