C 24 and C 16 timbers ?

[mikric]

Ok so i know that C24 timber is obviously a better grade than the normal C16 but what is the advantage of useing C24 4"x2" as roof timbers over the normall 6"x2" spec on a mono pitch extension i am doing, this is the spec from the drawings but just wonder why? anyone else come across this before? Also C 24 is a special order from my local builders merchants And the local timber yard said they could simply go through the standard timber, pick out the good bits and regrade it from C16 to C24 and charge extra for it!!!

 

[Symptoms]

mikric - without seeing the design drawings and roof loading calculations it's difficult to pass an opinion on your situation. Ask your architect why he's specified C24.

Timber is strength graded and quality graded. Strength grading is mainly carried out on timber which is commonly known as carcassing and is used for structural frameworks (so it's selected for its strength not its looks). Quality grading takes into account the appearance of the softwood mainly used in joinery & machining. Rules regarding strength grading are contained in British and European Standards.

Scandinavian timber is graded slightly differently to Russian stuff.

It is acceptable for timber to be re-graded locally at your timber merchant, if the stock is reduced beyond permitted levels by re-sawing for example. This re-grading should only be carried out by an experienced visual strength grader so there is likely to be a charge levied for this service.