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cdrew23
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# Posted: 25 Mar 2015 12:54pm
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Seeking opinions for best way to frame a 12' tall wall for a shed roof cabin with 4 in 12 roof. Overall cabin size is 12x12. Wall will have 2 levels of windows, see photo for reference. What headers would you recommend? Planned to construct with 2x4 studs 16" oc.
Also, this was planned to be balloon framed, what kind of bracing is needed? Full length joist for loft between load bearing walls necessary?
Thanks in advance.
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OwenChristensen
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# Posted: 25 Mar 2015 08:20pm
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Not too sure of all you're asking, but of course the back wall will be 8' high. I'm not sure if you have snow load concerns, but here in MN. we'd probably want at least 2x8 rafters on 16'' centers. Then notch them to fit on top the walls with maybe three inches of wood passing over the walls to the faicia. Header wise only the high wall and the back wall will have load. That big window looks like it might be 7' long a double 2x10 would be needed here.
Wall bracing is only needed if you aren't using 4x8 sheets of plywood or OSB siding.
Owen
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Don_P
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# Posted: 25 Mar 2015 09:12pm
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I agree with most of that. The upper end of the rafter would be better unnotched and running over angled top plates on the top wall. The "re-entrant corner" in something like the upper notch concentrates stress and can cause the rafter to split. The ame scenario, I was under an 1820's house over the weekend that had heavily notched joists, most were split from that corner. I'm guessing double jacks and double king studs along the windows on the tall side.
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cdrew23
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# Posted: 27 Mar 2015 01:26pm
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Thanks for the help. As far as framing the large wall goes, please look at the attached photo and give me some feedback. I want to build it right, but not overbuild if possible. My current layout seems headed in the overbuit direction - what can I do differently to improve design? Thanks again
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OwenChristensen
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# Posted: 27 Mar 2015 09:43pm
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Well you don't need a header on the lower windows and you don't need to stack all the studs in the corners. Matter of fact, it would be better if left a space for insulation. A extra stud 4" from a corner is for nailing inside wall finishing, not for strength. Another thing done is to use waste blocks of 2x4 for filler between corner studding.
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Don_P
Member
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# Posted: 27 Mar 2015 11:38pm
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Is the loft floor coming into that header?
I would put double kings and double jacks under the upper header at that wall height.
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cdrew23
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# Posted: 30 Mar 2015 11:38am - Edited by: cdrew23
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Thanks so much for the feedback. The loft floor wasn't intended to come into that header.
Check this updated rendering, assuming there will be blocking with 2x4 scraps at both ends between the 2 2x4's. Is this looking better? I removed the second header, the other is a built up 10" header 8' long. Made sure to include double king and jack studs on this one.
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OwenChristensen
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# Posted: 30 Mar 2015 07:17pm
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That's better. You still don't need to use two under and two along side the headers, but that's only four extra 2x4's.
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Don_P
Member
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# Posted: 30 Mar 2015 08:07pm
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Now I'll open a can of worms. Why aren't you platform framing this section?
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soundandfurycabin
Member
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# Posted: 30 Mar 2015 09:50pm
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How will those lower windows be fastened? If they are three independent windows using nailing flanges with only a single 2x in between, you'll likely either have to trim the flanges or overlap them, which might be ok but I've never seen it done. A double 2x should give plenty of nailing surface.
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cdrew23
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# Posted: 31 Mar 2015 08:02am
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Didn't plan on platform framing since the upper section would only be 4' long, seemed like a weak point if they were separated. Also, that window wouldn't fit in the top section with the necessary header in a 4' wall .
The windows are salvaged, most are wood, and do not have flanges. Speaking of which - any advice for properly installing old windows like this?
Thanks for the help.
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Don_P
Member
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# Posted: 31 Mar 2015 07:51pm
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Quoting: OwenChristensen You still don't need to use two under and two along side the headers, but that's only four extra 2x4's.
Check table 502.5(1), I'd be willing to bet it'll take double jacks. The double king is me, I've had it specced by engineers on tall posted longer span beams, cheap insurance.
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cbright
Member
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# Posted: 1 Apr 2015 03:37pm
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If I were you I'd spend the little extra and frame at least the front wall with 2x6... Wouldn't hurt to do the rear also, Might cost $100 more and be super solid.
I built by 16x13 with 2x6 throughout. My front wall is 12' and the rear 13'. Nothing is tying them together other than the side wall, but since it is a fairly small building and built so solid there is very little play in the finished building.
I thought about tying my loft floor (at 8') to the front wall, but it wasn't needed... and still could be done if I ever detect that things are spreading apart.
See my place here.... http://www.small-cabin.com/forum/6_3652_0.html
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Don_P
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# Posted: 1 Apr 2015 11:17pm
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There should be a ledger well attached to that wall that the loft floor ties into, brace whenever you can, that floor acts as a stabilizing horizontal beam... a diaphragm, a pretty rigid plate. That said it braces the tall studs in that wall as well as the side walls where it ties to them.
I was curious so did a little math. A 12' 2x4 column in a braced (sheathed) wall maxes out at about a 1239 lbs, if there is a bracing floor at the 8' level the max allowable load would go up to 2556 lbs, laterally bracing the studs to the loft floor doubles their vertical load carrying capacity. If there is a vertical and side load like wind suction and a head of snow, the load difference would be even greater.
The built up ends of the headers. in single king double jack with the floor tied at 8' the max load would be 7667 lbs although the control would be the jack's crushing into the header at 3035 lbs
With double kings if goes to 10223 lbs vertical but the control is still the 3035 lbs at the header/jack bearing. Each additional jack increases that bearing capacity 1759 lbs.
When I quickly checked an 8' built up column of 2 jacks and a king, so laterally braced at the loft floor, and applied a 1900 lb vertical load to the column with a 20psf horizontal wind load, the column was just failing, this is the midwall header column. Adding another king brought that back to 78% of max combined stress. I doubt it would give trouble in either configuration, with that floor positively connected, unless you have higher than 50psf snow or very high wind. Bearing in mind that in that kind of wind a 50 psf snow load sitting on the roof is going to be mighty unlikely. In that same scenario of combined vertical load and side load, an 8' 2x4 stud would be capable of a 300 lb vertical load with 200 lb side load... now remember with no side load the same stud is capable of 2556 lbs in just vertical loading, combined loading is a big deal. Hopefully this also explains why you want to grab that bracing element whenever possible especially on an exterior wall. It isn't the slow gravity load that would give you warning, it is the pop of a bad wind that gets a tall slender column.
Rambling, but hopefully more grist for the mill.
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