Calculating headers in a tall balloon frame wall
Hi all,
I’ve heard that header sizes are calculated differently in a balloon frame wall vs a platform wall, but I can’t find anything in the IBC to back that up. Is there a prescriptive path to sizing headers in a balloon frame wall?
In my situation, I have a 17’ tall 2-story wall, where the 2nd-floor diaphragm is supported by post and beam and does not share any gravity load with the exterior walls (but does provide lateral resistance). Main studs are 24”OC, with roof trusses stacked on studs. Here is a framing plan of the south wall using the header tables for platform walls. I’m surprised at how much extra lumber would be required in a balloon frame with the additional tall jack/king studs. Does this look like a reasonable framing plan?
Is it possible to lift a wall this size with 1 or 2 people using framing jacks?
Thanks for the help,
Adam
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In my jurisdiction this wall would require engineering, due to 1) height of studs and 2) concentrated loads on lintels (headers). I would also have questions about the independent floor system and how it provides lateral resistance. So if you are applying for a permit, expect these questions.
Depending on local climatic data (wind, snow, seismic) you may be required to have a ceiling diaphragm (plywood), large mechanical hold-downs at openings, and blocking. Sheathing may need specific nailing patterns.
I would not want to lift these walls, jacks or no.
Great thanks for that. Good to know about these questions. I’ve asked an engineer to redline these drawings for me, and then stamp them once those issues have been resolved.
I was actually considering a plywood ceiling finish, perhaps this can be structural as well.
The floor system is constructed with 6x12 beams at the perimeter, these will be fastened directly to the blocking between studs with the schedule tbd. These beams will be exposed, so whatever fastening method I use will have to be hidden, while still allowing a continuous smart vapor retarder. Hopefully this can satisfy seismic requirements.
It sounds like I either need a crane, or I’ll have to separate the wall into shorter sections.
I appreciate the advice,
Adam
My reply above was largely based on not knowing what or why is bracing the walls, so i treated it like nothing was there. Your engineer may be comfortable with what you are doing.
May I ask why you are building this way and not with a conventional platform frame?
You wont need a crane, a zoom boom or excavator would lift the wall well if the pick points are carefully chosen.
Sure it’s a fair question. We happen to have a lot of Doug fir Timbers that were milled on site, but not enough for a full timber framed structure. So we went with this hybrid design, plus we really like the aesthetic of timber post and beam.
Adam,
Lintels are lintels. They are sized by the loads they take, and don't care how high the wall is. What may very is the number of jack studs necessary.
If I were framing that wall I would move all the lower level lintels up above the upper windows, which would both reduce the number necessary, and eliminate the point loads from the top ones onto the ones below.
With the windows located where they are you will probably end up with two engineered shear-panels on the ends of the wall. Typically something like this: https://www.strongtie.com/wswh_strongwallwoodshearwalls/wswh_shearwall/p/strong-wall-high-strength-wood-shearwall
Thanks for that idea, moving the lintels to the top would definitely save lumber. However, if I’m correct, these lintels would have to be sized larger (to accommodate the longer span of several windows together). Thus either the top row of windows have to drop a bit to make room, or the top plate has to be higher. Not a dealbreaker, just being aware of any design changes I need to make.
Adam
Adam,
You have a few choices:
- Move the headers you show on the first floor up to the second. They then support the loads over six windows rather than three, and can stay the same size.
- Extend the headers to cover the two small upper windows next to them. The three headers now carry the loads of all the windows, and again they can stay the same size if you leave the jack studs in their present position about 1/3 way along the span.
- Because there is so little wall left between them all, use one long header (an LVL?) over all the windows, but again leave all the intermediate jack studs (which would have been at each end of the shorter spans). This option also has no effect on the depth of the header necessary.
If you have raised-heel trusses, you can also set those headers above the top-plate. The advantages of this are:
- Less thermal bridging.
- All your studs would be the same height (no jacks).
- Without the headers the wall would be much lighter to raise.
- It would also allow you to raise your upper windows as high as you wanted.
You would need to use hangers on the trusses though.
Always nice to have a stack of fir timbers around. Will your timber frame have lateral bracing with knee braces or such? How will the footings and foundation be designed to take loads from both the exterior wall and interior posts?
One of the challenges of an exposed timber floor system is running electrical, plumbing and mechanical. If you have T&G on top of your floor joists you can run 2x4 strapping on top of this to create horizontal chases for water lines and electrical, but this will not fit ducting.
Cool project!
I recently built and lifted this 18’ wide by 20’ high wall made from LSL studs. I used wall jacks extended to the highest setting and supported the wall while I repositioned the jacks to get more height. This was definitely sketchy, I would not recommend trying to lift a wall as large as you are describing with a couple jacks and 2 people.
Please read the IRC Code book, either one, under R602.3 Design and Construction, you'll see that not even a 2x6 12" o.c. wall will do, and especially a 44' wide wall. Headers may require additional bracing or attachments. You really need to hire an Engineer. You may end up with 2x8s at 8" o.c., manufactured studs, special bracing, etc. Building in the PNW, you maybe required to engineer for specific seismic and wind forces, or other local conditions.
ADD: I just looked at a job I designed in TX, where the wall is 21'x34' with a porch brace on the outside. The Engineer required 2x8 LSL studs @ 8" o.c., with Simpson straps and bolts imbedded in concrete, straps to the stud/header connection and tight nailing pattern. I'll be willing to bet your wall maybe designed much tougher.