Repairing old slate roof

Hello, Photos showing this at http://www.flickr.com/photos/89810542@N02/ Please could I ask for advice from anyone who has experience of repairing old slate roofs? Two adjacent rafters on the same side of the roof have slipped down where they rest against the ridge pole, and are now partly below the ridge pole. If they go another inch or so they will be below the ridge pole so will have no support at the top.
I can't see why they have moved so I assume they have simply bent a little between the ridge pole and the top purlin. The ridge pole appears to be still straight, and the corresponding rafters on the other side of the roof are ok.
Is it better to leave the slates and timbers where they are, and try to reinforce the timbers from the inside, and if so any suggestions on how to do the repair?
Alternatively, should I remove some ridge tiles and slates, and try to add new sections of rafter from the outside?
Or some other method? Any practical hints gratefully received. It's a barn with stone walls, roof span 9.3m (30ft). Three purlins on each side. Rafters 50mm x 50mm. Quite old, but I don't know how old. Cheers, James
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On 04/08/13 16:19, James wrote:

I'd definitely be inclined to get some props under that and jack up the joists and somehow (joist hangars? ) reattach those rafters to the ridge and leave the slates in place
I'd also look carefully at the outer end of the rafters - they make have slipped down because whatver should stop them moveing sideways, isn't.
More than that and I thnk you are in for a lot of expense.
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On Sun, 4 Aug 2013 16:19:02 +0100, James wrote:
That's a roof that hasn't had any attention for a while... Nice big hole as well, I guess that being totaly waterproof is not a requirement for this barn.

I suspect that those rafters are not contigious bits of timber from the wall plate to ridge but seperate lengths with the joins on top of each purlin. It wouldn't take much movement on the top of a purlin for the rafter to slip down the ridge.
Think I'd get a sturdy scaffold tower, acro prop up the sagging rafters as a unit, then put galvanised angle plates under each one to stop them slipping down and similarly fix the bottom end of the rafters to the purlin.
If you start playing with taking slates off etc I think you'll end up with a every growing and expensive topsy job...
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Cheers
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Thanks for those comments. The ridge is (estimated) just over 6 metres above a wooden floor, with another 2 metres to ground level. Don't know whether I'll be able to jack hard enough from a diy scaffold tower.
If not I can try clamping the rafters in their present position. In either case perhaps a couple of extra short rafters from the top purlin to the ridge would help to reinforce it as well as hangars or angle plates.
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Thanks for those comments. The ridge is (estimated) just over 6 metres above a wooden floor, with another 2 metres to ground level. Don't know whether I'll be able to jack hard enough from a diy scaffold tower.
If not I can try clamping the rafters in their present position. In either case perhaps a couple of extra short rafters from the top purlin to the ridge would help to reinforce it as well as hangars or angle plates.
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On Sunday, August 4, 2013 4:19:02 PM UTC+1, James wrote:
Please could I ask for advice from anyone who has experience of repairing o ld slate roofs? Two adjacent rafters on the same side of the roof have slip ped down where they rest against the ridge pole, and are now partly below t he ridge pole. If they go another inch or so they will be below the ridge p ole so will have no support at the top. I can't see why they have moved so I assume they have simply bent a little between the ridge pole and the top purlin. The ridge pole appears to be still straight, and the corresponding rafters on the other side of the roof are ok. Is it better to leave the sla tes and timbers where they are, and try to reinforce the timbers from the i nside, and if so any suggestions on how to do the repair? Alternatively, sh ould I remove some ridge tiles and slates, and try to add new sections of r after from the outside? Or some other method? Any practical hints gratefull y received. It's a barn with stone walls, roof span 9.3m (30ft). Three purl ins on each side. Rafters 50mm x 50mm. Quite old, but I don't know how old. Cheers, James
Very much doubt if you will be able to lift the rafters level because of th e weight of slate used. The only way I know of is to get a length of 4"x2" 100mm x 50mm and place across under the rafters either side under the top e dge and you may be able to lift the dropped rafters. Screw one end to a goo d rafter and prise up to try to get a fixing in one of the other secure raf ters. Then screw the drop rafters to the 4"x2"
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... Kipper at sea wrote:

It has been raining steadily for some time today and there is no leak. Also, the plaster and timber are fairly well intact, if old and displaced. So it's tempting to apply only a little force to try to move them back into place, then fix them in the way Kipper at sea suggests.
This might perhaps be U or L shaped brackets fitted to the ridge pole from underneath, held by wood screws into the side of the ridge pole (have to be diagonal, there's no space to get a screwdriver straight in from the side). Fixed to these, some kind of hanger/jacking screw to lift a metal or wood strap under each dropped rafter, and leave in place as high as it will lift without too much force.
Please does anyone have a suggestion on how to make this? If there is a standard hanger that's available that would be easier.
ps apologies for the duplicate post - my newsreader showed an error on first sending
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