Gaffar wrote:

Joist spans are about 6.5 feet each with 0.5 foot overlap between the 2
approx 12 feet in total

In which case, much less to worry about. I just did some calcs in
Superbeam. Assuming a floor made from joists of this size configured as
a load sharing system (i.e. flooring over the joists). When subjected to
a nominal uniform floor load of 0.8kN/m you are only getting deflections
of about 12mm in the centre of the span. Whilst this would not meet
building regs for a genuine floor, for a storage space with less loading
you are unlikly to get ceiling damaging deflection.

With regards storage nothing extraordinary, 5-6 boxes of spare tiles,
old books, baby pushchair
bath, etc

Put the heavy stuff toward the edges or over the walls and you should be
fine.

up and thankfully no visible cracks in the ceiling yet. The only sags
i can see seem to be a red herring as it is under an area of the loft
that I have not been in (probably the result of not overboarding
securely enough)

You will get a certain amount of sag just due to "creep" (i.e. the
tendancy for the joists to deform a little over time under load).

--
Cheers,

John.

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