Question about bracing/sheer wall on a 2x4 wall 12' tall.

[phalynx]

On my next project, 135, I am constructing a building that is 20x32 with 12' walls.  I want to use 2x4's for the walls as it won't be used 24x7 and the extra insulation isn't warranted.  I was planning on using 5/8" T-111 for the siding vertically.  Would it be enough for sheer strength for the building? 

The plan as it is constructed as follows unless someone hits me over the head and says NO:

4 4x6 beams spaced 6'6" apart resting on concrete blocks every 8'.  On top will be 2x8x20' 12 o/c with 3/4" T&G plywood subfloor.  2x4 walls 12' high with Tyvek and T-111 4x8' sheet panels nailed vertically. 2x8x20' ceiling joists.  2x6x12' for rafters and a sheet metal roof like my shop.

thoughts?

[rocking23nf]

I personally would not use 4x6 for my beams, a 6 inch board just isnt very thick in my opinion, and the cost different to go to a 10 inch board is minimal, plus you could use less boards.

But im not a licenced builder or inspector, but I have done some contruction including my own cabin and decks.

[John_M]

A couple of questions I have is what is the pitch of the roof and is there going to be a loft floor?

If there is a loft floor, you might not be able to "let in" a ledger board.  That would take out too much of the 2x4....you would have to use jack posts to hold up the joists!

[phalynx]

No loft floor at all.  This will be open to the roof.  No sheetrock on the ceiling.  One giant open room 12' tall.  It will be used as a multi purpose room for photography and video shooting/editing.  Roof will be 3/12.

[Don_P]

No storage in the attic? 2x8's on 16's will work for ceiling joists.
The floor joists could be 2x6's on 16" centers, wall studs can be 2x4, they are maxed out at 12'. Shear isn't the problem, out of plane buckling in a tall thin wall is probably going to be the main concern.
Midfloor girders are supporting 6.5'x8'x50psf=2600lbs. A double 2x8 would deflect less than a 6x6, 4x6 fails.
Edge girders are supporting (3.25'x8'x50psf)+(11'half roof width plus 1' overhang x8'x (snow+10psf dead load))... don't know the snow load for your area. If its 10psf or under and if we call the walls 5pf you'll come in around 3500 lbs on each 8'girder span. A triple 2x8 is working there. ...IMO

[phalynx]

Thanks Don.  I was thinking I could double up the concrete blocks to make it every 4' for the support beams.  The 4x6's were much cheaper than the 2x8's but math may win out on this.  I want the floor to be stiff as moving around on the floor may make the camera shake and that's a no no.  That's why I was looking at 12" o/c.  Concrete floor is ideal but just isn't going to happen out here.  There is no snow load in our area.  We barely get rain. 

My concern with the shear was wind load on the 2x4 walls wanting to twist the building.  We are in a bunch of trees and don't get a lot of direct wind load but I also don't want to walk outside to see a pile of rubble..

[Don_P]

Securing the building down to something that can handle the sail area of the wall would be the first priority for wind. The 2x4's are at their height limit for 90 mph so 2x6's wouldn't hurt. In wind its usually about the connections.

On the floor the girder is as big a problem vibrationwise as the joist, awesome joists on a bouncy girder will still bounce, so don't skimp there if stability is key. An old rule of thumb comes into play "deeper is cheaper". In deflection calcs, depth is squared while width is not, you build stiffness fastest and usually cheaper by making beams deeper.