Loft joist loading capacity

Anybody out there who knows about joinery? I want to turn my loft into a storage space, nothing fancy, just storage, but I am afraid about the sagging of the ceilling. The question is: can I get away without strengthening of the structure with the following layout: - Joist 2" X 4" (50 X 110 mm) centre to centre 15" (380 mm) floor span max 12 ft 6" (3.5 mts) There are also some timber across and on top of the joists coming from the out walls to the inside ones. I just want to put some chipboard boards and used as storage. Thanks in advance
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Oscarelo wrote:

4X2 timbers are plenty strong enough for light to moderate storage (no play rooms or other habitable rooms though, although I have seen loft rooms DIY'ed in this way on 4X2's without any sagging)...just make sure you lay the chipboard so that it joins on a joist or you will create a trap-end.
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Thanks Phil Very helpful and thanks a lot for your advice , but could you tell aproximately if the loading in that set up, is it bigger than 25kg/m2, which I read would be if the centre to centre where 600mm( mine are 380mm) and also there are 3 bedrooms and a bathroom underneath, all with proper walls coming from the ground/ foundations?

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Oscarelo wrote:

4x2 15" 12ft is at the bottom end of load bearing capacity, and is ok for light storage, and you could even make a room of it if you didnt mind a bouncy floor and plaster cracking.
I dont see that what room is underneath has any bearing on it, unless you mean there is an additional wall supporting halfway laong the 12', giving a 6' span. That would be one small house though.
NT
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Oscarelo wrote:

It depends on quite a few factors...
How long is the span of the joists? - it's OK them being 380mm apart, but if they stretch from the front to the back of the house then they won't take much extra weight. Are the timbers c16 or c24? - if they are not C anything then they are ungraded and this may take it down a bit more. (it would be stamped on the side in ink, C16 or C24)
There are tables around, but they go in kN/m2 (kilo newtons) and they are bizzare to say the least, apart from being exceedingly rare, there is a copy I have found (you normally have to pay 17 believe it or not) and it's here: (Acrobat req)
http://bauing.f2.fhtw-berlin.de/lehre/professoren/damm/conrem/Timberdesingtables.pdf
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