Best way to fix a sagging roof

Hi all,
I have a late 60's BV house with concrete roof tiles. The underpurlins are supported with a combination of struts and scissors.
My problem is that the roof has sagged wherever it is supported by the scissors (up to 40mm in some places) and it is visible from the ground. I think the sag has been caused by shrinkage of the scissor timbers allowing the apex bolts to loosen.
I intend to replaced the roof tiles later this year and I want to fix the sagging before I do.
I have 2 questions...
1) Is it possible to straighten 40yr old hardwood rafters that have sagged by gradually jacking & packing or are they set like that for life?
2) Is attaching new rafters directly to the old ones and securing new battens & roof to them a viable option? Or is there a better way to fix this?
Thanks
bludger


Read the full thread at RenovateForum.com...