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We are looking at potentially building a barndominium (a steel building finished inside to use as a residence). After erection of the steel structure and exterior, I will need to frame out exterior walls on the side of the insulation. The steel building itself will be loadbearing and protect from wind and elements; the wall I'm framing will be purely for finishing (providing a place to attach drywall and running pipes and electrical wires)

Much of the house will be two stories and can be build with standard 8' or 10' 2x4s, but the great room will need to be approximately 20' tall leading up to a finished ceiling. I am hoping to frame and install these walls with as little help (or machinery) as possible.

I had planned on 16" OC throughout the home, attached to the concrete pad using a nail gun. For exterior walls I considered a 2x6 top plate attached to the exterior structure for support, though that creates a thermal bridge that I'd rather not have.

How does framing a wall of this size differ from framing a standard 8' tall wall? I've seen 16' long 2x4s at Home Depot; does one simply build the wall the same as an 8' tall one using those? If so, how do I reach the remaining 4' to the ceiling? Is there anything additional I need to do to secure the wall given its higher center of gravity?

  • So this will be a free-standing 20' wall that doesn't connect to a second story (no support in the middle of the wall? I think you wouldn't be able to use 2x4's at that point because of the flex. Interesting question. – JPhi1618 Dec 5 '19 at 19:09
  • @JPhi1618 Yes, that's correct, unless it's anchored to the exterior steel beam, but that creates a thermal bridge which is undesirable. I assume at least one or two anchor points will be required, but hopefully not many, and I'm curious how others approach this. – Nicholas Dec 5 '19 at 20:53
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Structurally I think you have a bigger problem with the two story space than with the taller one story space.

If you put a lot of weight up in the air 10’ or so without anchoring it to something or providing some shear bracing, it could tip over by lateral loads or racking. If you put gypsum board on the walls that will help, but may not be sufficient depending on the upstairs load (weight).

I’d plan on about 20 psf to 30 psf horizontal force on the walls, depending on where you live, because if you open an exterior door during a wind storm that force will transfer to your new walls. The same force will be applied to the 20’ high walls, but it won’t have the weight of the second floor furnishings, people, etc. acting as a high center of gravity.

Even without the wind, you’ll have a tendency for the second floor to rack.

Gypsum board has some horizontal resistance when nailed properly. However, even when it’s nailed properly, it’s horizontal resistance is not close to plywood. If you use the plywood shear approach rather than the 2x4 wall brace approach, be sure to use adequate anchor bolts into the concrete slab floor.

I know you don’t want to install 2x4 braces over to the exterior structural walls because of possible heat transfer, but that is a minor issue compared to the horizontal structural issues.

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On a long 'span' between support points, what will control design is deflection. Typically you want to limit that to better than L/120 with a 5 psf load for non-bearing interior partitions. Assuming your at 24" oc, you'll need a minimum of 2x6. You'll need blocking between studs, and I would believe that some of that blocking will be fire blocking. Check with your local building department. They are there to make sure people are safe, not to cause problems.

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