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The OC Spacing

October 5, 2018Olen Murriel

The On-Center Spacing Concept in Construction

If you are familiar with architectural plans, construction drawings, and woodworking designs, you must have come across the term on-center. Often abbreviated as 0C : on-center indicates that the dimensions specified apply to the distance between the centers of two different members.

A good example that I can use to explain this concept is when one is framing a stud well. In the framing of the stud wall, the building plan may dictate or require that the studs be placed after every 16 inches on-center against the top plate and the floor plate. This means that there will be a 16-inch interval between the centers of each stud that follow each other. Adherence to the OC measurements specified in the building codes is important in ensuring that the structural elements like the studs, floor joists and rafters are positioned correctly. Therefore, OC provides consistency in the flow and design of the architectural structures.

The Relevance of On-Center Spacing

On-Center spacing is important for many reasons. For starters, the on-center spacing is essential in ensuring that the edge of a sheet good like drywall or plywood is supported and back by an additional inch of wood that allows for screwing into and nailing. On regular occasions, sheet goods have a dimension of 4 by 8. If you have to use 16 inches or 24 inches OC to frame a stud wall, then the edge of the vertical sheet which will be installed will fall over the stud’s center. Therefore, this will be essential in providing additional space for the nailing. This will also mean that the next sheet will get the similar support and backing when being installed.

Another importance of On-center spacing you should look at is that it makes sure that you achieve perfect layouts even when there is a variation in thickness of the construction materials since most of the materials don’t come in precise dimensions and uniform measurements. On-center spacing helps in leveraging on these variations in dimensions given the case that the focus is put on the center off the material. The dimensional differences are thus equally split to both sides. In essence, OC allows you to achieve the right structural appearance regardless of the material thickness which on regular occasions, that is to mean without the use of the OC spacing; it would have been difficult to achieve.


Tips for On-Center Layouts

One of the ways to achieve OC spacing is using unique markings on a standard tape measure. Most of these standard tape measures have markings after every 16 inches, often indicated an arrow, a red mark or a distinctive marking.

For a 16 -inch OC layout, you can use such a tape measure to mark every time you cover 16 inches of space. You then should be careful to position every stud on the same side of these marks. For instance, if you are moving from left to right with your measurement, the studs should be placed on the right side of each mark. However, if you want to start your layout at the end of the well or a corner and you intend to have the first stud covered with a good sheet completely, then OC spacing will be slightly different. Given that the drywall sheet is 48 inches wide and the first edge covers the first stud rather than falling on the center, then the distance from the side of the first stud to the center of the third stud should be 48 inches. This requires you to cut out half the thickness of the first stud at the beginning. You can achieve this easily by marking the 15 % inches mark on the second stud then move to the end of the tape measure up to that mark. The other studs can be labeled after 16-inch intervals.

If you find this hard to comprehend, try doing it practically. The practical approach makes the work more accessible to understand the detail in the concept. It’s easier to get the concept that way.

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