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The 4" Rule
Many building codes specify that a 4" ball must not be able to pass between Balusters. Therefore, if you are using turned Balusters, they may need to be a bit closer than 4" at their unturned portions to satisfy the 4" rule.

Traditional Spacing
Traditionally, Balusters are spaced fairly closely. How close a matter of personal taste. Also, the smaller the Baluster, the closer together they are normally spaced.

4'' On Center Spacing

Our general rule of thumb
The space between unturned portions of Balusters should be about 1-1/2 times the width of the Baluster.

Example
If you are using 2-1/2" wide Balusters, the space BETWEEN their unturned portions would look nice at 3-3/4", which would be about 6" on center spacing for that size Baluster.

Exception
Balusters over 3" (actual) in size are typically spaced closer than our Rule would indicate. For example, 5-1/2" Balusters would typically look right with only 2-1/2" of clear space between their unturned faces. That's true because, for these larger Balusters, the actual open space between their most deeply turned points would be approaching the 4" rule.

On Center Spacing
6'' On Center Spacing

Carpenters normally think in terms of "on center" spacing when installing Balusters. That is, they want to know how far it is from the center of one Baluster to the center of the next.

A very common spacing is 6" on center and that's usually what we recommend. This is partly a matter of personal taste, but if the spacing is too great, it can create sufficient space between pairs of Balusters to trap a child's head, or even to permit them to slip through. You should check your area's building code requirements on this point.

Most of our 80 porch drawings illustrate Baluster spacing options. The chart on each of those pages indicates the Baluster depicted and its o.c. spacing.

Even Spacing
Spacing between Balusters should always be equal and the distance from the ends of the Railing to the center of the closest Baluster will look well balanced at one-half the distance from the center of one Baluster to the center of the next.

Your chosen on-center spacing probably will not work perfectly for each balustrade section. If you're close, the differences can be adjusted by allowing slightly more or less space from rail ends to the center of the beginning and ending Balusters. However, varying your first and last Baluster center positions by very much can create visible differences on each side of a Porch Post!

8'' On Center Spacing

Modify the On Center Spacing
The solution is usually to slightly change your chosen on-center spacing from one Balustrade section to the next. Normally, a small increase or decrease in this distance will bring your first and last centers an acceptable distance from the ends of the Railing. A little experimentation will get it! And for you mathematicians, here's a chance for you to put your knowledge to practical use.

10'' On Center Spacing

Determining Quantity Needed
Despite all of the above, it will usually work fine to determine the total length in inches of all of your Balustrade sections and then divide this number by the on center you have chosen. For example, if you have three Balustrade sections totaling 180", and you've chosen 6" for your ideal on-center spacing. Dividing 180 by 6 = 30. Thus, if you order 30 Balusters, you should have enough. (You may want to add one or two for good measure.) If you don't believe the math, get a tape measure and mark it off, remembering to start and end with one-half the on-center distance.

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