Difference Between C16 And C24 Grade Timber? | DIYnot Forums

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You are using an out of date browser. It may not display this or other websites correctly.You should upgrade or use an alternative browser. Difference between C16 and C24 grade timber?

• Thread starter john10001
• Start date 25 Mar 2013

J

john10001

Joined 15 Feb 2007 Messages 22 Reaction score 0 Location Yorkshire Country What is the difference between C16 and C24 grade timber? And what exactly are C16 and C24 to start with? Is it to do with the finish or treatment the wood is put through?  

AronSearle

Joined 18 Nov 2011 Messages 3,770 Reaction score 432 Location Buckinghamshire Country It is a structural grade, the higher the number the stronger the timber. Each c grade has structural values (the grades go from c14 to C35), these values allow the engineer to do his calcs.   P

PeakOakFrames

Joined 12 Aug 2012 Messages 19 Reaction score 1 Location Yorkshire Country C grading is only for softwood. Structural hardwoods upto a certain size are graded as D grades then above that go to THA THB grades. C and D grades are mechanically graded which is why you can get graded timber that is worse than useless, computer says yes! THA and THB are visual only grades used for large section hardwoods, often graded green.  

AronSearle

Joined 18 Nov 2011 Messages 3,770 Reaction score 432 Location Buckinghamshire Country Few corrections, not that much of this is relevant to the OP. C grades can be visually or machine graded, C16 is mostly machine graded, C24 tends to be more mixed, all machine grades have visual over-rides. Oak comes in grades TH1 TH2 THA and THB, some of these equate to D grades rather than oak being specifically graded to a D grade, these grades are all visual, very rarely are hardwood's machine graded.   R

RickyLee53

Joined 30 Jun 2012 Messages 130 Reaction score 2 Location Yorkshire Country Sorry to go slightly off topic but it might help the op, recently I changed some floor joists in my house to "upgrade them". They were 7 inch probably 100 year old joists. (no idea what timber they used back then). They were all over the place twisted etc. So we removed them all and replaced with 9 inch (to lower the ceiling slightly and remove any bounce) C16 joists. The 9 inch joists are actually worse for bounce than the old joists. What was used in the olden days? C16 8" joists are what were actually recommend for the 4m span. Would say a C24 8 inch joist be better than the 9? I thought it was just less knots etc?  

AronSearle

Joined 18 Nov 2011 Messages 3,770 Reaction score 432 Location Buckinghamshire Country 100 year old joists where likely equivalent to C24 or possibly C27.   D

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