Does new C16 grade wood need preservative treatment?

Builders have overhauled part of my roof and its ready for me to start lining it.
It never occurred to me to ask the builders whether it was prudent/necessary to treat the new spars and purlins with a wood preservative before sealing everything up. The wood is all stamped "C16". Do i need to?
thanks Tony
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On Thu, 27 Nov 2003 09:57:09 +0000, Tony wrote:

C16 is the structural grading of the timber. It should also have been pressure treated but might not have been.
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