I would believe it but I would still add a binder for anybody crawling around up there.
what size for ceiling joist
- Thread starter DIYedboy
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- Ronnie............you're a life saver!...........all I want is a simple life, I guess the joists will be at 600mm centres to allow for the velux's (will that make a difference?). There won't be anyone crawling up there unless they are gonna strip off the tiles n underfelt!
Me too.
Despite what the tables say, I don't believe that 4" joists over 4m won't sag a little as they dry out and then cycle through moist and dry phases. It's not all about the loading.
How wide is the extension? A 4x2 joist is going to cost you ~£8 per 4.8M length, versus £10 for a 6x2 (150mm) ~£11 for a 7x2 (175mm) or £13 for a 8x2 (200mm)
Why not sail a bit less close to the wind given that (presumably) you're going to want your BCO to sign this off, or I'd at least ask him to approve the span, 600mm spacing, and the binders you intend to use.
ETA - My copy of the span tables only has the 0-.25Kn column. Ronny - where do you get your calcs based on 0 Kn?
Why not sail a bit less close to the wind given that (presumably) you're going to want your BCO to sign this off, or I'd at least ask him to approve the span, 600mm spacing, and the binders you intend to use.
ETA - My copy of the span tables only has the 0-.25Kn column. Ronny - where do you get your calcs based on 0 Kn?
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Yeah, if there is a chance that somebody will end up crawling around in the void then the point load will govern the design. Whether or not the full 0.9kN needs to be taken is debatable as it seems unlikely that the full load would be applied to one joist in this situation. However, 6x2s will still work without binders - I would be tempted to use them if it's likely people will end up in the void at some point.
Tables? As if I'd use tables
All timber joists / beams will creep over time - this applies to floors, roofs, you name it. Not allowing for a point load, the deflection would be around 7mm using C24 which is well within the limit of 0.003 x span for a 4m joist.
I did a calc - you won't find anything in the tables for a case where there is no imposed load - I just took the self weight of the joist and 0.20kN/m² for plasterboard, skim, and insulation. If we are taking a point load of 0.9 (assuming there is a chance of this happening) then this load case will govern regardless of joist spacing, and as said above, 50x150s will be ample.
Binders still won't be needed!
I am going the full plans to BcO route, the architect is finalising the regs plans and his SE is doing the 'calculations'. His regs plans don't specify ceiling joist size.......unless the SE has to add that part
I think someone's "architect" needs a swift kick in his noggins. Why the hell wouldn't he size up the ceiling joists? Or if he was especially useless at least make a reference to the structural engineer's design. The plans wont get through Building Control without it anyway.
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