Extending Rafter Guidelines

[Engibeer801]

Im a PE in mechanical, and I have a friend who asked me to look at some shoddy work done by a contractor. A central beam was replaced in his building due to water damage, and when the contractor took the beam out, they saw that maybe 10-11 of the 2x10 rafters (which span 18ft) had rotted out where they rested on the beam. The contractor simply took new 2x10s that were 9ft long, and nailed them onto the existing rafters to extend new wood over the new central beam. Im sure this can't be sufficient, and I have suggested that full length replacements be installed, but he is very hesitant because says there is a lot of duct work, air lines, and electrical that will have to be dealt with, and he is already over budget and battling with other problems caused by the same contractor.

Analyzing spliced rafters isn't something I am very familiar with. I really want to help him out with a cheap solution, so I am wondering if there is there a guideline or some literature on bolting patterns that would help me come up with a proper solution? It would seem like I really just need to focus on the shear force as we are talking about the ends of the members, but I want to be certain about the length and bolt pattern of the splice.

Can anyone point me in the right direction?

 

[SWComposites]

please add a sketch. or a photo.
flat roof or angled?
did they add one sistered 2/10 to each cut off rafter? or add one on each side (two)?
how many nails/bolts did they use? and pattern?
is this being done under a building permit? going to be inspected?
might need a local structural engineer to look at it in person.

 

[Engibeer801]

Only 1 2x10 was added per rotted rafter. Here is a quick drawing to give you a better idea. I agree, I've told him that if they don't run full length, someone needs to do some engineering details on the attachment.

 

[XR250]

It probably can be made to work with nails. Can you provide a sketch?

 

[Engibeer801]

sketch added.

 

[Eng16080]

This would come down to whether or not the connections between the new and existing 2x10s can resist the applied shear and moments, which I'll assume is most critical at the location where the existing rafter transitions from being in good condition to rotten. Besides that, you would also want to ensure an adequate connection between the new 2x10 piece and the new beam. A sketch would be helpful as already mentioned.

 

[Engibeer801]

This would come down to whether or not the connections between the new and existing 2x10s can resist the applied shear and moments, which I'll assume is most critical at the location where the existing rafter transitions from being in good condition to rotten. Besides that, you would also want to ensure an adequate connection between the new 2x10 piece and the new beam. A sketch would be helpful as already mentioned.

as far as the transition of good wood to rotten, the good wood starts within 6-10" of the center beam.

 

[SWComposites]

this needs a local engineer to run an analysis. not a normal roof. this valley is hopefully drained on the ends? is it prone to ponding? snow load?

 

[Engibeer801]

this needs a local engineer to run an analysis. not a normal roof. this valley is hopefully drained on the ends? is it prone to ponding? snow load?

roof has been replaced, roof also slopes 4 degrees in the other direction. No major pooling that I have seen, roof loads around here are 15/30.

Is the consensus that this work that has been done seems highly suspect / marginally suspect/ etc? I can tell him to have someone else come and look, but Im the one sticking my nose in his business saying that it really doesn't look right. I don't want to waste his time

 

[Eng16080]

Is the 30 psf load really a live load or a snow load instead?

Often with projects like this where there's been some shoddy work done by a contractor, you'll find more and more issues the closer you look. I'm not saying that's necessarily the case here, but you might get dragged into a mess that you didn't expect.

It's not really your question, but based on the info. in the sketch, I'm not so sure the existing rafters meet code. If I'm correct, then that complicates things a bit more.

 

[Engibeer801]

snow load, my mistake. I'll pass the message on that he needs to hire someone else, and it probably is a can of worms. Something didn't seem right about the sisters to me and I was hoping to get a definitive answer, but clearly there are a lot of variables. Thanks for the help