I was just measuring the back of one of our bureau drawers, and noticed something odd. The drawer back is about 38â…œ” wide—and the tape measure has a little diamond mark at that point. There are other diamonds, all multiples of approximately 19.1875″.
What is the significance of 38â…œ”?
Janet
Replies
The significance is of 19.2"
The significance is of 19.2" goes into 96" exactly 5 times, meaning that with floor joists or studs spaced that far apart plywood or sheet rock will both start and end evenly on a joist or stud. It is a way to save on framing lumber or increase r-value of a wall. So, 38.4 or approximately 38 3/8 is one of the multiples. You will also see similar marks, likely with a different color or shape, every 16" to make framing to that, more common dimension, easier.
For the furniture, in may well be pure coincidence,
We call them cubits.
Seriously?
No not seriously, though undoubtedly there was somewhere at sometime a definition of cubit that happened to be 19.2 inches or there abouts. But really it derives from the 96" length of a sheet of plywood sheathing .
What I don't know is when or why the 16" joist spacing standard that fits 4x8 sheets so well came into use. Likely the accident of some building code, or some engineering standard promoted by lumber manufacturers.. I do know that by 1932, standard spacing for studs was 16" o.c. even though it was still common to use solid lumber for subfloors and exterior sheathing, and use lathe and plaster, not drywall, for interiors. The 1932 edition of Ramsey and Sleeper, doesn't mention plywood.
Among framing carpenters, we call them cubits out on job sites, sort of a joke, we have lots of names that aren't quite what you would find in a technical manual. We think its funny to hollar out, "are you puttin them by the cubit, Jake?" whereby Jake lays his arm down from elbow to middle finger and yells back, "just about perfect". It impresses customers and greenhorns that we are such precise craftsmen.
The "black diamond" centers are normally used for engineered products, mostly floor trusses and TJI joists. They are not typically used for conventional framing lumber. The 19.2" spacing only works well when you are laying 4'x8' sheets the long way. The odd number doesn't work well in other situations, such as board sheathing, 12' drywall or when using batt insulation.
I've only used cubits, for floor framing. This on center spacing, along with the thicker T&G subflooring sheets commonly used today, meet or exceed the strength and deflection criteria for floor framing. It also saves a member every eight feet compared to the more common spacing of 16" OC for standard framing lumber. Engineered products are often significantly more expensive than the same spec framing lumber but they can handle heavier loads at longer spans and are uniform, straight and fairly light weight. In some cases, they can eliminate the need for support posts and carrying timbers.
Hammer,
Beautifully explained. Articulate. Nice...
Zolton
Hammer time! Can't touch this.
Wow. Was that twenty years ago?
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