Do I need joists strengthening for loft flooring?

[biosh]

I'm looking to floor the central area of my loft for for light storage. I would also want a loft ladder installed and possibly increase the size of the current 65cm hatch.
The area to be floored measures ~450 x 400 cm in the centre of the loft extending from the semi's dividing wall to the current access hatch.
The total loft area is 60cm x 800cm (=48 m2)
This is essentially 200cm on each side of a central wall below, dividing the bedrooms below. ??possibly loadbearing.
Joists are currently 1 x 4 inches at about 16 to 18 inch intervals. Would these need strengthening?
Is there a document that spells out these regs in a way I DIYer would understand? Or should I get someone in to look at it to give me a definitive answer? If so who??
Always grateful for your advice -
Thanks
Steve

[stoneyboy]

biosh,
Your joists are a bit light to take flooring and storage - seek advice from a local surveyor.
end

[biosh]

[quote="stoneyboy"]biosh,
Your joists are a bit light to take flooring and storage - seek advice from a local surveyor.
end[/quote]

Thanks - I was right to be concerned then!

[stoneyboy]

biosh,
A surveyor will probably suggest major works, you could try an architectural technician or builder.
end