If you are blocking for structural strength (not fire protection or nailing surface), wouldn't it be better to put the 2x4s sideways, oriented the way they would be in a built-up header?
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1Can you be more specific about the type of blocking you are referring to. Is this between joists or studs? What structural support is it providing?– BMitch ♦Aug 27, 2015 at 2:39
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Well, it's sort of a general question, but I was picturing the blocking between studs. And I guess the answer to what structural support is being provided is probably the answer to my original question--I pictured it providing support against lateral forces, like a shear wall does, but perhaps that's just not what it is for.– Phil EsraAug 27, 2015 at 20:01
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2The blocking between studs you see running horizontal and flat is typically fire blocking, required when you get above 8' ceilings in most locations. When installed vertically, it's usually for a nailing surface (cabinets, railings, drywall joints). Structural is occasionally a shear wall with a diagonal brace, or the blocking between joists.– BMitch ♦Aug 28, 2015 at 1:22
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3 Answers
it doesn't matter, because the stresses on between-stud blocking is 100% horizontal compression. The vertical orientation of the deep face absolutely doesn't matter...though having it horizontal, spanning the full width of the studs would help to prevent torsion/twisting forces, and thus would be ever-so-slightly preferred.
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I am talking way out of my depth here--apologies--but: in the case of a cripple wall in an earthquake, for example, the way I imagine it, the "taller" the horizontal bracing, the more resistance there is to the wall folding up under lateral forces like a collapsed cardboard box. Right? I guess framing traditionally has been more focused on static loads? Aug 27, 2015 at 17:17
Horizontal blocking IS used with 2x lumber on edge for non-structural reasons: grab bar blocking, plumbing fixtures (notably freestanding wall sinks) and kitchen cabinets.
Its usually shifted to the front of the wall, just behind the drywall. For sinks, 2x6 is usually used, allowing a range of mounting heights, ditto for grab bars in baths and showers.
One time for a steel stud wall in a basement, I used an entire sheet of 3/4 plywood over the studs and under the drywall. It let me freely mount upper and lower cabinets for a bar area.
In the case of a 2x6 "wet wall" (used for plumbing, especially drains), the blocking can be "let in" in a continuous piece for additional strength, spanning several stud bays.
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2While this is technically true, I don't think this is the type of "blocking" the OP is referring to. The OP is taking about blocking that's installed to strengthen a wall/floor, and to prevent deformation of the framing members. While it's true blocking can be used to make mounting things to the wall/ceiling easier, that type of blocking is not intended as structural blocking. As @dwoz points out. structural blocking has to span the entire depth of the framing member, to prevent twisting. Aug 27, 2015 at 10:58
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1Your first sentence should read "Horizontal blocking IS used with 2x lumber on edge for nonstructural reasons" Aug 27, 2015 at 11:00
Gravity.
Everything pulls down. So props that hold things up resist gravity. Vertical members hold things up.
Headers are spans that sit on things (jack studs) that hold things up. The header isn't the support, the studs (hopefully tied eventually to foundation elements) are.
So, vertical members, including vertical blocking, are the real support. But if you need to support over a gap where you can't put a vertical member, the horizontal header conveys the weight to the sides, where vertical support takes over.
