C16 Or C24 Timber ? - Green Building Forum

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Green Building Bible, Fourth Edition

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1. • CommentAuthormarsaday
   • CommentTimeAug 5th 2010
   I only need to use C16 joists for my new floor, but thought the cost difference of using C24 is pretty small. Are there any benefits of using C24 timber ?
2. • CommentAuthorjon
   • CommentTimeAug 5th 2010 edited
   The grading selection is different: C24 is estimated by the graders to have a higher strength than the C16. That's all. (edit though sometimes the timber is a different species allowing the higher grade)
3. • CommentAuthorMatt Bridgestock
   • CommentTimeAug 5th 2010 edited
   C24 timber is almost exclusively imported. If you specify C16 FCS with chain of custody, you are likely to get homegrown timber. If you got direct to a sawmill such as BSW, they will do you C16 Scottish timber. Personally I object to the over engineering of timber kits which means that the majority of our structural timber is imported, meaning the industry is only set up for imported material. I have done a couple of projects now which prove that Scottish C16 timber are suitable for mainstream UK housing industry. The Forestry Commission have a lot more information here: http://www.forestry.gov.uk/forestry/INFD-6B2JFBRegardsMatt
4. • CommentAuthorfostertom
   • CommentTimeAug 5th 2010
   I'm reminded to have a good read through this great resource - thanks. Quite right about C16 vs C24 - the latter to be avoided by design except when nothing less will do (much like use of concrete).C16 is definitely lower 'quality' if by that you mean it has a quirky life requiring chippies to use it with some skill and sympathy, rather than (in imported e.g. CLS form) an inert commodity that can be knocked together fast and brainlessly.CLS is so hugely reduced from basic size, rounded corners and all, that you have to ask about material wastage and even embodied electricity in the machining. I hate the stuff - might as well be made from recycled drinks cartons.C16 may be a bit banana shaped but can be regularised (put thro a rough planer) at little extra cost, to give two straight parallel edges. This is often done at the merchant just before delivery, so all the accumulated bending to that date is taken out. I specify regularised C16 for most things, unregularised for short bits/that matter less - and highest-strength quality stuff perhaps even better than C24 only where essential.All untreated, but borate sprayed in situ after assembly, where dry/internal. Semi-durable untreated e.g. doug fir where exposed/external. No pressure impregnation except for slating battens, and occasionally where in ground contact or similar.
5. • CommentAuthormarsaday
   • CommentTimeAug 5th 2010
   What i get from what you have posted is that the C16 could be a bit twisted. I would prefer to work with a more finished product if possible and C24 caters for this ?Really all i want is for the top of the joist to be straight and level. Will C16 give me problems here ? I dont mind if it bends a bit to the left or right.
6. • CommentAuthorfostertom
   • CommentTimeAug 5th 2010

   Posted By: marsadayall i want is for the top of the joist to be straight and level. Will C16 give me problems here ? I dont mind if it bends a bit to the left or right.

   That's exactly what regularisation achieves - the 'working' edges are skimmed, the 'sides' left as-is. Regularised are the sizes that used to be given for joists in BR AD Part A (removed from current edition, sadly) - 'regularised from BS4471 basic sawn sizes', so 150 and below it's 50x147 (3 deduction); 175 and above it's 50x170 (5 deduction).
7. • CommentAuthorMatt Bridgestock
   • CommentTimeAug 5th 2010
   At the risk of getting this deleted (its not advertising)Here is a link to BSW's spec sheet with sizing etcIt is treated, but I only post this for information on dried regularised timber.http://www.bsw.co.uk/products/construction.htmlCheersMatt

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