Stairways- baluster arrangement- Part 3
This is my third installment on stairs and stair design. In this article, I'd like to discuss baluster arrangement. There are several ways balusters can be arranged on a stairway.
But first let me define a term. Rake or rake angle is the angle of the handrail above the horizontal plane. This angle is easily established by knowing the rise and run of your stairs. If, for example, your rise is 71/2 inches, and your run ( tread depth) is 10 inches, then your rake angle is 7 1/2 over 10.
I should also insert at this point that balusters can be installed two per tread or three per tread. The number of balusters per tread is not only a matter of preference but in many communities a matter of meeting the code. In most communities the building code requires that a 4 inch sphere cannot be inserted between two balusters. And so, in some circumstances you might be able to get by with two balusters per tread. But probably, more often than not, with a small baluster and a deeper tread you will need three balusters per tread.
The image on the right illustrates the 4" test with two balusters per tread. The reasoning behind the 4 inch code is that a four iinch sphere is smaller than a childs head and so the constraint is a safety code to prevent a child from getting his or her head from getting lodged between two stair balusters.
Angled top horizontal bottom: In this baluster arrangement the bottom of the balusters are horizontal or parallel with the treads. The top of the balusters follow the rake angle or the angle of the handrail.
The difference in the length of the balusters should be one third of the riser height for three balustes per tread and one half of the riser height for two balusters per tread. For a 7 1/2" rise and three balusters per tread the difference in the length of the baluster would be 2 1/2" (7 1/2" / 3 = 2 1/2"). So the second baluster would be 2 1/2" higher than the first and the third baluster would be 2 1/2" higher than the second.
Angled top angle bottom: This particular arrangement has the tops and the bottoms of the balusters following the rake angle. Notice that although the overall length of these balusters varies, the "turning length" of the balusters is the same.
Horizontal top horizontal bottom: The tops and the bottoms of the balusters in this arrangement are horizontal or parallel with the treads. This is my least favorite of the arrangements but some of my customers like this particular pattern. The image on the right is such an arrangement with two balusters per tread.
Knee wall: This is similar to the second arrangement with the exception that the balusters do not attach to the treads. Instead there is a small wall that rises above the treads and so the bottom of the balusters are cut at an angle and the tops and bottoms of the balusters follow the rake angle of the handrail.The length of these balusters are all the same.
In this section I thought I would talk about alternating balusters which is a little different from the above discourse. An alternating baluster arrangement is one in which the balusters alternate between spiral and plain. The image to the right is an example of alternating balusters. This particular job was for a customer in Washinton State based on a historc home - the Silas Dean Home. The baluster arrangement is is angled top and angled bottom.
It should be noted that if you are going to use this design technique, the profiles of the balusters should be identical. (Note the top and the bottom of the balusters). The only difference between one and the other is the spiral (or lack thereof) of the baluster. See the image on the right.