wrote:

Thanks for the info so far. I have no intention of not doing it right,
I just what to know what part of right I have to do. Being more
specific, the current span of garage roof is 6.6m, on 4x2 timber (sorry
to mix units but thta is what size they are.). The joists are at 36cm
(14in) centres. I doubt that these are large enough to be a floor so

That span is way to long really. (I take it there is some additional
support for the 4x2"s since at that length I am supprised they can hold
themselves up!)

options are, bigger joists, (if so what size ), or an RSJ at mid span
(There are brick pillars on the garage wall at mid points thos that is
a clear option).

Yes, cutting the span down is the way to go.

How wide is the garrage?

It may be that you could use a sizeable wood beam or a flitch beam (i.e.
slightly easier to work and handle) across it rather than needing a RSJ.

If an RSJ is the best option by reducing span to
around 3.5m will the 4x2 serve or do I still need new joists.

You still need new joists, but can get away with relatively small ones -
6x2" on 400mm c/c or better would be fine at that length and only a
floor to carry.

How are you for head room? One thing that springs to mind is that it
would probably be easier to put the cross beam in over the existing 4x2"
joists to save supporting, cutting, and re hanging them. Obviously that
could take the finished floor level up too high to meet those of the
existing first floor. You may be able to solve this if you could place a
a partition wall along the cross beam, then you can hang the new floor
joists below it on long hangers.

--
Cheers,

John.

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