On Center - Construction Measurements

On center represents an equally spaced measurement. For example the floor joist in the picture below are 16 inches on center and are equally spaced. The most common measurements in the construction industry are 16 inches on center and 24 inches on center.

Using A Tape Measure For Layout

If you need to lay out a long wall, you should always use a tape measure. One time my father was building a large Mini Storage Complex. I decided to use a custom made layout stick which had three equally spaced 16 inch on center marking blocks that were connected to a stick.

By the time I got to the end of a 20 foot wall, I was off 1/2". This wasn't going to work, especially on some of the walls that were over 60 feet long. That's when I switched from using the layout stick, to a tape measure and never went back.

Shear Panel Wall, Roof And Floor Layout Tip

Today we need to leave an 1/8 of an inch gap in between our plywood, to accommodate for lumber expansion. This wasn't a problem 15 years ago, but it is today. Make sure that you adjust for the 1/8" gap, when laying out any structural shear walls or floors and roof sheeting.

To accomplish this, you will need to add 1/8 of an inch to every 4 foot measurement along the wall, floor or roof.

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