My client is questioning the following information in my Section 061000 Rough Carpentry.
“Provide continuous horizontal blocking at midheight of partitions more than 96 inches high, using members of 2-inch nominal thickness and of same width as wall or partitions.”
This language is straight out of MasterSpec.
The architect said the structural engineer and contractor do not think that this blocking is necessary. The blocking will add cost to the project.
I searched the IBC and could not find any information. It might be in NDS or ASCE 7 publication but I do not have them handy.
Does anyone know where this requirement comes from?
This blocking is also used to provide edge support for sheathing and gypsum board installed perpendicular to the framing. It will also help keep the studs straight and plumb. Ignore the last comment if the wall framing uses engineered lumber.
Agreed that this would be a standard of care; another “master spec” states this: “Provide framing and blocking members as indicated or as required to support finishes, fixtures, specialty items, and trim” as a general statement, and supplements that with language regarding specialty items, fireblocking, etc. It doesn’t address wood framing, though, which is where this requirement is stated.
It makes good sense, since more than 96 inches probably means substantially more height and the wallboard might be applied horizontally to maximize use and minimize waste. and you’d want the edge supported. It’s almost a no-brainer.
If the wall is 100 inches, maybe it’s not needed; but I still want to be sure that edges of wallboard are supported. How many walls are over 96 inches? And how far over? Decide if it’s worth the battle.
The only thing I could find is in Section 2308.9.9 (2012 IBC), which requires bridging when sheathing or wall coverings are not applied to both sides and the height-to-least-thickness ratio exceeds 50.
I assume this is for wood stud partitions and not steel stud partitions (which I believe would not require the horizontal bridging, assuming the studs are the proper gauge, spacing, etc).
Years ago when I worked construction over my summer breaks from school I was always told that this blocking was installed in taller walls to resist twisting of the wood studs. They were placed mid-span and not necessarily at potential gyp. bd. seams. It was typically installed in a staggered pattern so you could end nail them in place thru the 2x4s. In this fashion every other block is 1 1/2" off from the adjacent block so it would not provide edge support for horizontal gyp. board.
I am not sure if the information I got was accurate but that is what I was told.
The traditional horizontal blocking, I understand was also an effort to have the whole wall work more as a membrane, so that localized loads/deformations, such as a heavy TV mount, will be distributed to more than one or two studs. You never know how an occupant will eventually use the wall.
To expand on my first comment: I was always told that the blocking was installed to resist the twisting of the wood studs to avoid nail pops, cracked seams, etc. The contractor didn’t initiate the blocking requirements but they provided it on taller walls because they felt that it helped save them the expense of call backs. We typically did it on walls over 10’-0" but I am not sure why it was decided that 10’-0" was the magic number.
Back in the day we always nailed the gyp. bd. and nail pops where a big issue for the contractors. Screw attachment may have solved, or at least diminished, a lot of these problems.
Yes, the blocking is both to resist twisting warp, and also to pull the studs into a more planar condition. Studs are not perfectly straight, so this helps make a better wall, aesthetically. Good carpenters will set studs with all natural cambers in one direction, but you can’t count on that. In addition to all of that, it seems to me the blocking will also help strengthen the wall and help it resist flexure by transmitting forces to adjacent studs better than WB. Mark, I’m sure, will advise if I’m off-base on that.
I believe the 10’-0" requirement had to do with fire/draft stops.
While blocking will help share load between studs I believe it is limited in how effective it is. I believe that plywood or OSB that is continuous over the stud is more effective in this regards.
I do not believe that there is any standard requiring mid height blocking for 2x4 and 2x6 studs.
My guess is that the 96" was introduced based on a perception of good practice. Since there is no documented basis available it makes it hard to change. In these situations individuals are putting forth a lot of guesses. This is why all sorts of weird requirements are in master specifications.