Sag in ridge board

[chriz1]

so I'm about to embark on my roof retile this week. 

I have a sag in the ridge, from the attic I have ridge baord and my understanding is that I havea ridge baord which doesn't provide any structural support and just a baord for the rafters to nail to. 

When looking along my ridge board inside I can see it has sagged at the join probably only by half an inch (2 seprate boards join in middle. But also the board looks like it has sag in itself.

Can I jack this up when all tiles are removed and Add some vertical suports along its length to improve the ridge level ? 

The doesnt appear to be any sign of rafter movement or cracks to suggest anything more serious.

 

[Big Jimbo]

Jack it up, but put any new supports down onto an internal wall, rather that a ceiling joist. if you are going to re-tile you might as well get rid of the sag.

[PeterW]

Worth checking the ridge hasn’t moved because the rafters have moved. Can sometimes happen and is worth putting collar ties in on alternate rafter pairs to stop spread in the future. 

[chriz1]

Cheers guys, is it also worth 'sistering'  the 2 ridgeboards where they meet ? And can this be a simple 4x2 bolted and sandwiched to rid baord join? 

 

[tonyshouse]

No, when you say retile, was it tiles before or slates? 
 

the ridge will have gone in straight and roof settled a tad, purlins look good, I would add a single bolted collar on top of the purlin above the prop/hanger if it was my roof and live with the sag. It is possible to straighten the sag by disconnecting rafters at the ridge while coverings are off and introducing perfect size shim packers to realign it, not for me though, too much hassle for too little gain. 

[chriz1]

House was built in 70s and these are the original redland tiles. So getting replaced with marley. 

Will have a go at jacking it up when everything is off and see how it goes.