Sagging roof

For years the roof of my house has been wavy, due apparently to the builder using a puny 1/4" plywood decking, but now in one section the roof is definitely sagging.
I don't want to simply prop up the sagging roof against the attic floor, for fear that this will only transfer that sagging force to my garage ceiling.
How do you fix a sagging roof in a case like this? Can I run a 2x6 lengthwise along the underside of the roof and attach it to the rafters?
If I need to call someone to take a look at it, am I better off calling a roofing company or a structural engineer?
Thanks.
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How old is the house, what type of roof and how many layers are on it if its shingle. Call an architect or engineer for help.
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- Brian Anderson -

- Nehmo - The decking is too thin. Tear off the roofing material and re-deck over the old decking. If the roof isn't ready to be replaced, wait.
- Brian Anderson -

- Nehmo - You mean additional rafters in between to existing rafters? Won't work. The roofing fasteners are protruding below the decking and the rafter has to be flush.
- Brian Anderson -

- Nehmo - A roofer can handle a tear-off and a re-decking. There's no good way to shore up sagging too-thin decking.
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* Nehmo Sergheyev *
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As Nehmo says, if it is the decking that is sagging wait for a re roof, strip, and re deck (roofer). You could also add cross blocking (bridging) between the rafters to raise the decking, but it would be quite a chore to force the warp back out of the existing decking.
If it is a cut roof and the rafters are sagging , you will need a different solution. The rafters can be beefed up with a purlin and braced appropriately. This could be handled by a good carpenter / contractor. Is there a chance that the attic floor you mentioned is carrying such a load that it is pulling down on the rafters? A structural engineer could be added to the equation if it would make you more comfortable. ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Keep the whole world singing. . . . DanG

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Brian:
BA> For years the roof of my house has been wavy, due apparently BA> to the builder using a puny 1/4" plywood decking, but now in BA> one section the roof is definitely sagging. BA> BA> I don't want to simply prop up the sagging roof against the BA> attic floor, for fear that this will only transfer that BA> sagging force to my garage ceiling. BA> BA> How do you fix a sagging roof in a case like this? Can I run BA> a 2x6 lengthwise along the underside of the roof and attach it BA> to the rafters? BA> BA> If I need to call someone to take a look at it, am I better BA> off calling a roofing company or a structural engineer?
I would go with a roofing company, making sure they tear off the old " plywood and replace with whatever is appropriate. (What is appropriate??) The complete tear-off is going to cost you a little more but I would think would be more stable and secure. (If the old " stuff is left you have to nail through that thickness, plus may be damaged.)
The thing I would do is have the chief roofer (supervisor) inspect your roof framework for water damage, termite damage, etc., that could be another cause of the sag.
- barry.martinATthesafebbs.zeppole.com
* Over the hill? I don't recall ever getting to the top!
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