Tape Measure Diamonds

[doyle]

I have a question about those little diamonds on a tape measure that are at 19.2" intervals. I've heard the term "building on 19's" before, but I'm not sure how often people actually space their framing using this method. Is it usually just used for trusses? I know that over an 8' sheet of roof decking, there would be 5 contact points using 24"on center, and 7 contact points using 16"oc, so the 19's method, would have 6 contact points. This is really only saving one truss (for example) over the 16"oc method. If it's not used very often, why do all the tape measure manufacturers put it on the tape?

[Rich]

From what I know the 19.2 came about from a value engineering standpoint. It's fewer framing members than 16" o.c. but structurally stronger than 24" o.c. You are right that you aren't going to save a lot in the 8' section but when you frame 1000's of feet of wall it definately saves.

[mjpliv]

You will find the 19.2" OC will be used quite a bit in engineered floor systems. When you are paying a premium for these joist systems, you can save a fair amount on a project.

When the floor is specified at 19.2" OC double check your sub-floor material selection. Some are only rated for the 16" inch span. On the same token, a lot of engineered floor systems use 2x3 or 2x4 top and bottom cords therefore the clearspan between joists is reduced.

2x10@16"OC - 14.5" clearspan
2x3 topcord @ 19.2" OC - 16.7" clearspan
2x4 topcord @ 19.2" OC - 15.7" clearspan