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Oilersfan
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# Posted: 30 Jan 2013 07:25pm
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I am trying to figure out what I need for wall bracing and the IRC manual is driving me crazy....
I want to design a 12' high wall, 16' long with lots of windows...south facing. The roof is single pitch. So I have a tall wall which add a 1.2 factor. It appears if I install 4' (a guess due to being confused the more I read) OSB sheathing that I would be ok. However can I split up the 4' and do 2' at either ends of the wall? What if I have 2' on both sides of the corner of the wall?
Confused! Please help!
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MtnDon
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# Posted: 30 Jan 2013 08:46pm
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Wall bracing is probably the most complicated section of the IRC, so don't feel bad about being confused.
First, if the wall is 16 ft long a 24" panel at each end is okay according to...
R602.10.2.3 Minimum number of braced wall panels.
Braced wall lines with a length of 16 feet (4877Â mm) or less shall have a minimum of two braced wall panels of any length or one braced wall panel equal to 48 inches (1219 mm) or more. Braced wall lines greater than 16 feet (4877 mm) shall have a minimum of two braced wall panels.
The single 4 foot section could be centered if you wanted one braced panel. Then windows on either side to the corners.
The desired 12 foot wall height may be an issue though. Stud height is limited to 10 feet without bracing perpendicular to the wall in question. If this wall is a side wall, supporting the rafter tails for a gable roof eve that would mean something like joists, rafter ties, something, tieing the wall across the building at the ten foot or lower height. That is simplified but that is what that means. See TABLE R602.3(5) SIZE, HEIGHT AND SPACING OF WOOD STUDS.
Twelve foot tall, unbraced walls are possible, but fall into fotnote (a) for that table...
"a. Listed heights are distances between points of lateral support placed perpendicular to the plane of the wall. Increases in unsupported height are permitted where justified by analysis." Analysis = engineer.
Other elements to be considered with a (tall) wall of lots of windows is the ability to resist winds directed perpendicular to the window wall. The bracing in R602.10.2.3 is about bracing forces that are acting along the line of the wall, not against the face of the wall. Homes you see with a wall of windows are almost invariably the result of an engineers calculations.
With the wall in question also being a load bearing wall (in the case of the roof rafters and eves resting on the wall top) The headers have to be sized and then the loads they transmit down to the floor assembly assessed. With wide expanses of windows it could be possible to overload the studs supporting the header beams or the bottom plate /floor assembly the jack studs rest on. That's just a detail that should be checked.
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MtnDon
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# Posted: 30 Jan 2013 09:12pm
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If the wall in question is not load bearing as in a gable end wall the vertical loading is not an issue unless there is a ridge Beam for the roof. The 10 foot height, unbraced perpendicular rule still applies though. Again, the solution can be engineered. Sometimes a tall gable end wall as in a cathedral ceiling end wall can be braced at the 10 foot height with a beam laid on it's side, to resist the lateral wind forces against the wall face. To do that without guessing requires some calculations.
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MtnDon
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# Posted: 30 Jan 2013 09:14pm - Edited by: MtnDon
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Oops, forgot something I wanted to mention...
The osb/plywood sheathing for a tall wall should be full height of the wall rather than pieced together. 4x9, 4x10 and 4x12 sheets are available but sometimes need to be searched out. Big box stores around here do not carry them.
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Oilersfan
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# Posted: 31 Jan 2013 10:46am
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Thanks for the reply MtnDon. The sheathing issue sounds workable.
I know I am making things difficult with the tall wall design and single pitch roof but learning this stuff is half the fun. Plus I am not ready yet to cave and go with the traditional peak roof just yet...maybe that will come soon!!
I did a bit of research on the tall wall design and found basically nothing but design manuals...awesome. Does it help the situation to build another small 2ft stud wall on top of a 10ft wall? What about sheathing both the interior and exterior of this wall. I am also planning on using 2x6 studs @16" OC. Any ideas to deal with the 12' height?
PS I am a civil engineer but unfortunately my structural design is pretty rusty. If anyone needs a runway built for their cabin let me know. This is right up my alley!!
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MtnDon
Member
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# Posted: 31 Jan 2013 06:34pm
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Quoting: Oilersfan Any ideas to deal with the 12' height?
My understanding of the height being limited to 10 feet without additional supports perpendicular to the load bearing wall stems from the wall being designed to take a 3 second gust of 90 mph wind. It is said that every location in the USA could be hit by a 90 mph gust. Coastal areas in particular higher. So that is what is limiting the design. Then the addition of a lot of windows complicates things. For example a 32 inch wide window means the wind force is transmitted through the window to the studs it is fastened to. That places extra load on them. It is beyond where I am comfortable.
I suspect that studs with greater depth and carefully selected for their straight grain and lesser number of knots would go a long ways in helping. Maybe #1 grade instead of #2, select structural grade if available and you can afford them. though sometimes I can find some mighty nice #2's with some sorting.
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Oilersfan
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# Posted: 1 Feb 2013 10:36am
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I think we are going to go back to the drawing board and bring the tall wall back to 10ft in height. We have a box layout planned so all walls would be load bearing. I am not comfortable entering into the realm of the "tall" wall world without any professional assistance which I really don't want to use for a small cabin in the woods.
The loft might be a little tight but I still can't bring myself to go with the peak roof for our little shack.
Thanks for your help MtnDon. Much appreciated. I will be sure to post some photos starting in the spring. I find others photos and posts are very helpful on this site.
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MtnDon
Member
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# Posted: 1 Feb 2013 11:16am
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Quoting: Oilersfan a box layout planned so all walls would be load bearing.
Maybe I am misinterpreting something; I've done that before with word pictures.
If it is a simple rectangular box with a shed roof (single pitch as you call it) the two walls that support the long sides of the roof sre the load bearing walls. The rafters lay across from the higher wall to the lower wall. The two shorter walls, end walls are not load bearing. They support their own weight, that is all, and that is not considered load bearing. Unless I missed something.
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Oilersfan
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# Posted: 1 Feb 2013 04:16pm
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Sorry I wasn't very clear. The tall 12' wall along with the back wall would be load bearing. The rafters would sit on these walls. I guess I was incorrect in saying the side walls are load bearing.
Either way still looking to stay below the 10ft height eliminate complexity. I did buy some shed plans from townandcountryplans.com a week or so ago so maybe these will "shed" some light on the subject. I know bad joke...but its Friday.
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MtnDon
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# Posted: 1 Feb 2013 05:20pm
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Good luck and yes it is simpler to stay within the prescriptive codes.
Re the bearing walls; I do like to leave things clear for any future readers.
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