# Sistering Roof Rafters



## Bondo (Dec 8, 2007)

> 1) will sistering a 2/4 to the side and not the full length provide the required stability
> 2) are 3/8" bolts to wide for a 2x4 or even a good choice?


Ayuh,.... I would probably sister 2, 2x4s, 1 on each side of the failin' wood, as long as possible to get into place,.....

After I jacked things into place(straight), I'd probably run in 3/8" lag bolts, clean through all 3 pieces of wood, to end up with a bolt every 12"/ 18" of the length,...


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## de-nagorg (Feb 23, 2014)

After jacking to realign the roof decking, I too would use as long as I can 2X4 to sister both sides, and lag from alternate sides to hold it all together.

Alternate sides 1 from left, 2 from right, 3 from left, etc until the final, every foot.


ED


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## kwikfishron (Mar 11, 2010)

I'd use a 2x6 on one side myself.


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## Fix'n it (Mar 12, 2012)

i did a sister just like that. jacked it up, nailed in a good old board. when i removed the jack, it went right back where it was before. but, i do know that at least it is stronger.


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## de-nagorg (Feb 23, 2014)

Fix'n it said:


> i did a sister just like that. jacked it up, nailed in a good old board. when i removed the jack, it went right back where it was before. but, i do know that at least it is stronger.


Not to be mean, but you used A board and NAILS.

You needed at least 2 boards, and BOLTS WITH METAL BRACING.

Your nails probably pulled out a bit, and let it return to where it wanted to be, not stay where you wanted it.


ED


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## SevenHillsCC (Nov 28, 2016)

Looks like a long span for a single 2x4. I'd try to upsize to a 2x6 or at least use two 2x4s, just use a continuous piece and find a way to attach the new lumber to the bearing points on top and bottom if you can. If the existing lumber is solid & not rotten, I'd put one on each side and nail both into the existing rafter, otherwise I'd nail two together like a small beam and sister it into the existing rafters. I would think 16d nails would be fine to fasten it, just use two nails every 12-16". You'll need to get the rafters straight before attempting to put the new lumber in. Use a jack to raise the parts that have sagged, maybe nail in a temporary brace mid-span to keep it straight, then insert new lumber.


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## motolz (Nov 27, 2016)

All, thanks for the great advice! Seems I am on the right track here, just need to lengthen my sister boards and do both sides. I plan to stick with the 3/8" carriage bolts with large washers. May still do a kneel wall for additional support across all. Again, your advice was much appreciated!


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## Fix'n it (Mar 12, 2012)

de-nagorg said:


> Not to be mean, but you used A board and NAILS.
> 
> You needed at least 2 boards, and BOLTS WITH METAL BRACING.
> 
> ...


not mean at all. actually i was waiting for just such a reply.

i have 2x4 rafters also = WTH were they thinking ! :vs_mad:
the board i used was a very solid old growth piece removed from elsewhere in this F'ed up old house. 
i jacked up till straight, no small feat. 
i used my framing nailer with ring shank nails.
board about 12' long.
i put in a lot of nails, 20 perhaps.

i then lowered the jack. the whhole thing went back to sagging like it was, taking the sistered board with it, like it was nothing.
the 2 boards DID NOT pull away, separate, whatever, at all = like is was made that way new.


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## de-nagorg (Feb 23, 2014)

Fix'n it said:


> not mean at all. actually i was waiting for just such a reply.
> 
> i have 2x4 rafters also = WTH were they thinking ! :vs_mad:
> the board i used was a very solid old growth piece removed from elsewhere in this F'ed up old house.
> ...


At that point I would have jacked it back up to straight, and added a 2" X 10' piece of angle iron. lag bolted into the assembly with bolts every foot .

Then let it down again, saying HOW DO YOU LIKE THEM APPLES WISEGUY" 

I doubt that it would have re-bowed. 


ED


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## Fix'n it (Mar 12, 2012)

yeahh ED. but i wasn't trying to fix the bow. there was a knot, just wanted to keep it from getting worse . but i didn't think it would bow back as much as it did. i really learned something that day.


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## JustinK (Oct 4, 2009)

A new 2x4 will sag also. That old 2x4 is stronger than new lumber and now it is a curved board and it wants to stay that way. A new 2x4 will be fighting 2x4 and roof load. looks like you have room for 2x6 i would use that. 2x8 would be even better. Use construction adhesive and structural screws like ledgerlok every 16 inches. Carriage bolts will work too but alot more work and cost. Good luck


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