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Old 07-14-2012, 03:55 AM   #1
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Bowed Rafter Supports


I searched for existing threads on this, but couldn't find any - also went through a number of pages of threads, likewise no joy. So if I missed where this was already addressed, please forgive me...

While replacing our A/C system last week, our A/C guy pointed out a framing issue and I noticed another one as well.

First issue:
In the first photo, you can see a ridge support going up from a doubled 2x12 - the support has a knot near the top, and it's bowing at the knot. Photos 2 & 3 show detail of the top & bottom connections. At the bottom, the support covers part of both 2x12s, as well as the plywood sandwiched between them (see "original" in the drawing). Is it feasible and acceptable to sister another 2/4 (possibly bowed the opposite direction) to the bowed original, and then attach another 2/4 perpendicular somewhat like a strongback (see illustration)? I know the sistered piece will not contact the bottom of the ridge, but it will go next to it and could be nailed/screwed into the side. In any case, it's main function would be to counter the bow of the original support, and the strongback piece would also be directly under the ridge. Is this acceptable, or would I be better off to just put a better 2/4 just past the problem member?


2nd issue:
The remaining photos show a similar problem where the junction of the hip ridges is supported. This is a T-ed pair of 2/4s, and cross of the T has a knot which is causing it to bow away from the "upright". The bottom attaches to what I believe is a wall plate (buried under insulation) - you can see from the very last pic that there is precious little room at the top for either additional lumber or temporary support. Due to the weight on this and the lack of room, I'm thinking I should probably call in a pro on this. Would you agree?

Thanks in advance for your insight!
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Old 07-14-2012, 08:44 AM   #2
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Bowed Rafter Supports


you could probably put a 2x4 on either side of the bowed 2x4 and cut them something like 8 inches longer so as to run the 2 new ones up onto the roof ridge board to lock them in. the new 2xs would stick out past the edges of the double 2x at the bottom a little bit where they sit but that will not matter. even better is to do the same idea as mentioned above but replace the bowed 2x with a new one and triple it up so it is strong. the bow that is there now could either be from weight from the ridge or the 2x4 is just bowed, hard to say for sure but if that were a critical weight load spot then they would not have installed just one 2x vertical like that.

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Old 07-15-2012, 03:37 AM   #3
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Bowed Rafter Supports


Thanks, Hand Drive!

"if that were a critical weight load spot then they would not have installed just one 2x vertical like that'
I don't know about that - they pretty much went with the minimums on everything (and less on somethings, like attic ventilation & A/C"

BTW, the first and last actual photos in the original post actually go with issue #2 - for some reason, the photo sequencing is incorrect in the OP.

Any one have thoughts on what to do re. issue #2? The photos are bottom & top (zoomed out), then top & bottom (closer detail). Again, this is where all four hip ridges meet and the junction is supported by a long 2x4 T, and the "cross bar" of the T is bowing due to a knot. The bottom seems to be on a wall plate - to the left (in the last pic) and under the plywood to the right are 2x6 joists (13' long, which I believe is max span?) on 24" centers. If thinking about temporary support, there are 2 or 3 more joists in parallel to either side, then 2x6 joists coming in perpendicular on either side. As you can (hopefully) see from the closer-in pic (1049), there isn't much room at the top due to the cross ties. I would personally not feel comfortable (at my experience/skill level) trying to build a temporary support to relieve load while replacing the bowed member, but what about nailing in another "cross bar" on the opposite end, essentially creating an I-beam? Would that be enough, or do I need to call in a pro?

Thanks again!
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Last edited by texasprd; 07-15-2012 at 03:39 AM. Reason: Photo sequencing changed again after upload
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Old 07-15-2012, 11:31 AM   #4
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Bowed Rafter Supports


I'm having a difficult time seeing what exactly the knot-bow issue is up in the ridge/intersect pic. Is there any way to get up in there with the camera to get more detail of the bow and how everything connects. Thanks
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Old 07-15-2012, 11:53 PM   #5
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Bowed Rafter Supports


There's a lot connecting up there in a small space. I hope these pics will help = hopefully, they are big enough.

I put in letter codes to make it easier to distinguish what's what - the codes are common across all photos.
A = 2x4 T crossbar - the knotted/bowed member
B = Ridge, with all "D" rafters/hip ridges tied in
C = cross ties
D = Rafters/Hip ridges
E = 2x4 T base, fastened to "A"

Photo 1036 shows the back/"top" of the T bar ("A") - the knot is not marked, but it's on the right side and about even the right cross tie. You can see that the weight of the ridge is on the "A" member.

Photo 1037 shows the knot (at the end of the red line) and the approx. half-inch gap between the "bar" and the "base" of the T ("A" & "E" respectively). 1038 is basically the same shot, but farther back.

In 1039, the T cross-bar ("A") is supporting the ridge ("B"), and the T base ("E") continues up the side of the ridge "B". again, the knot is at the upper end of the red line.

To complicate matters, if you look back in my previous post, you can see the A/C air handler the the right of my foot in one photo. Fortunately, it's suspended so the plywood in that photo could be pulled up if a temp load support had to be fabricated across the joists.
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Old 07-16-2012, 12:20 AM   #6
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Bowed Rafter Supports


That's actually VERY clean framing. I can't see what you're worried about though. You could probably take out any of those vertical things and it would be fine..The roof was probably already up and sheathed way before those went in. But if you're worried about a bow/knot, add a 2x where ever ya want. It is hard to see the whole picture cuz it is so close up..
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Old 07-16-2012, 08:38 AM   #7
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Bowed Rafter Supports


that all looks fine, a bit of a cluster spot but normal for hip roofs. As copperclad mentions, the vertical 2x was added probably as insurance but I do not recommend touching it,and a knot in wood is totally the norm. As long as the rafters are nailed good to the joists/plates down near the exterior walls the roof framing where it meets up in the peak will stay in place from its own pressure and weight.

Last edited by hand drive; 07-16-2012 at 08:40 AM.
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Old 07-16-2012, 09:04 AM   #8
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Bowed Rafter Supports


When you look at the building code for hip roofs either that support is not needed or it greatly undersize. The code says the point where the hip roof meets at the top must be supported. This would be require a large column going all the way to the foundation. When you do the math you would need a column at each end of the board you have marked B that was large enough to hold up 2/3 the weight of the roof...many 1000's of lbs. Most likely at least a 4x6 or 6x6.

The building code does have a vague exception that lets you use "other" methods of support.

In your case I suspect since the 2 hip roofs are only about a foot apart the board marked B is being used as a structural ridge in compression to transfer the loads between the 2 hip roofs. This in general does not work for longer spans because of the size of lumber involved. What you have is very close to a pyramid hip roof which is one of the strongest designs around.

I suspect the board was used as a construction aid. If it does not go all the way to the foundation all it does it transfer any load to your drywall ceiling. Still I would not mess with it if it is not causing a issue.
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Old 07-16-2012, 11:04 AM   #9
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Bowed Rafter Supports


Hi Bill. I was wondering if you could post some kind of reference regarding this code stating "where a hip roof intersects a post is required."
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Old 07-16-2012, 11:31 AM   #10
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It does not say a lot. It is part of r802.3 "Hip and valley rafters shall be supported at the ridge by a brace to a bearing partition or be designed to carry and distribute the specific load at that point" There are a couple of free articles you can find that show how to calculate the load on the hip rafters themselves as well as the loads at the end points. Unfortunately the best one I have found is article they want you to pay for from www.jlconline.com called "Straight Talk About Hip and Valley Rafters".

You will also find this discussed in some of the timber framed house since they use a special truss to support these roofs. Problem is a building inspector can understand a post at a ridge few will approve any other solution unless a engineer has stamped it.
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Old 07-16-2012, 12:12 PM   #11
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Bowed Rafter Supports


okay.. and then it states "or be designed to carry and distribute the specific load at that point." All conventionally framed/ stick built roof meet that criteria, unless a bearing post of some kind is called out on the plans, which is very rare. In the OP's roof, he has 6 common rafters, and 4 hip rafters, and a 1' or less ridge. So the roof is basically self supporting which is typical in framed roofs. All the point loads are directed at each other. If a bearing post of some kind was called out then that ridge would be a double, triple, or solid ridge, not just a 2x ridge.
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Old 07-16-2012, 12:16 PM   #12
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Bowed Rafter Supports


If the gap in that t-stud bothers you, why not just run a couple screws thru the assembly to pull it closed?
You'd need to clear away the insulation at the bottom and trace out where the loads wind up. But I'd agree that it probably isn't holding a lot of weight.

*not an engineer!
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Old 07-16-2012, 12:34 PM   #13
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or be designed to carry and distribute the specific load at that point

Yes if you have a engineer that says that you are ok and the house plans are approved that is what that statement says. There are a couple of ways to transfer this load....but you cannot just assume a conventionally framed house meets this requirement you must PROVE it meets this requirement.

Just think about how you build a hip roof. How do you get the 2 long hip rafters to stay up. They will not stay their by themselves. You in most cases rest them against the common rafters and common ridge. BUT where does this force go ? How big does the common ridge have to be ? It is actually not that hard to do this calculation but the inspector will require someone who can both do the calculation and have some proof they are qualified to make that calculation.
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Old 07-16-2012, 01:14 PM   #14
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Umm.. They basically do stay up by themselves.. They do however get a few nails into the common rafters. What keeps them up is them pressing against each other. You set your 4 common rafters running north and south that holds up the ridge. Then you set your 2 common rafters that run east and west and that braces the ridge.. You could then install your 4 hip rafters with no nails on top, as long as they are nailed at the wall side.
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Old 07-16-2012, 01:40 PM   #15
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I promise you will never get a set of plans past a permit department of any city with that argument. Just because you FEEL it is true does not make it true.

Do you have any background at all in engineering. Anyone who has any form of engineering degree has had a course or two in structural engineering.

Lets assume you just take the 2 ridge rafter and put just those up with nothing else. How do you hold them up. There MUST be force or you could magically hold them up with a couple of nails at the wall headers.

This force is actually many TONS for the average roof. In the method you propose you ASSUME all this force can be transferred though the ridge board to the hip on the far end. Show me the table in the building code that shows the size of this ridge board. Try to construct your design without a common ridge board ? You think the common rafter pairs will just stand there.

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