Building Basics for an Open Rail Balustrade
By Larry Walton, Photos by Mark Walton
If you’ve ever seen a saloon gunfight in an old western movie, it more than likely involved a couple of cowboys falling through a handrail. In their search for revenge, the next of kin should begin with the carpenter whose guardrail couldn’t withstand some rousing piano music let alone the lean of a wounded cowboy. We must build better open rail systems if we are going to keep cowboys and our own family safe.
Open rail balustrades often occupy prominent positions front and center where guests are greeted, which is why the intricate woodwork they require are well worth the time and expense. They also perform very important safety functions.
Open rail systems come in lots of styles and sizes. In broad terms, the systems are either open tread (where balusters sit directly on the tread) or knee wall (where balusters sit on a little curb wall that covers the ends of the treads). Both of these styles can be over-the-post systems, which provide an unbroken handgrip throughout all of the landings and turns of the staircase. Or they can be post-to-post systems, which end each rail section at a newel post and resume on another side of the post.
Regardless of the style, there are important safety standards that open rail balustrades must meet. These have to do with strength to prevent failure, rail-size guidelines to provide usable grip, opening sizes to stop little heads and torsos from passing through, and proper elevations that prevent bodies from falling over the top.
With these major considerations addressed, there are plenty of stylistic options to consider in newel post designs, rail shapes and baluster types. Rails can terminate into a wall, into a rosette or into a half-newel fastened to the wall. Balusters can be dowelled at the base on a flat wall cap or sit in a plowed shoe rail, which itself can sit on the wall cap or be suspended parallel with the handrail. Baluster tops can be in a plow on the underside of the rail or they can act as dowels that penetrate the drilled bottom of a rail.
In many ways, our featured project is about as simple as an open rail balustrade can get. This post-to-post balustrade (with only one post) has square balusters, a plowed handrail and a shoe rail built on a knee wall.
When it comes to baluster spacing, be sure to make it according to code. This generally requires spacing tight enough that a 4-in. ball must not be able to pass through at any point.
I use two methods to calculate baluster layout. In Method One, you can calculate the baluster spacing by measuring the level run, and dividing it by the desired spacing plus the thickness of a baluster (e.g. 4″ space plus 1-5/16-in. baluster = 5-5/16) to get an estimate of the number of balusters. Then, multiply the number of balusters by the hypotenuse of a rake cut of a single baluster and subtract that number from the total length of the rail (measured on the rake or along the bottom). This is the total space filled by the fillet blocks. Divide this total by the number of fillets, which is the number of balusters plus one. This gives you the fillet lengths.
For an odd number of balusters, start installing with a baluster at the center. For an even number of balusters, start at the center with a fillet. Use the fillets to space the next baluster. Keep testing the balusters as you go to see that they are plumb and adjust as needed.
In Method Two, I estimate baluster spacing, try it with some scraps to see if the spacing measured on the run (level) is close to the maximum allowed by code. I make adjustments, mark the top edge of each baluster location at even increments, set the balusters and manually adjust each fillet to fit. If you cut them a little oversize, you can hold each fillet alongside where it lives, mark it and cut it to fit. This actually goes pretty quickly and there are no surprises when you get to the end of a run with too big or too small a space at the newel or the wall.
Here is an overview to complete this project:
- Determine the rail height to meet code requirements as a guard rail.
- Mark two points that determine a straight line that is parallel to the rake of the stairs and is at rail height.
- Cap the knee wall so it is parallel to the rake of the stairs with a vertical face that is plumb.
- Use the handrail layout line and the face of the knee wall to determine the length of the newel post.
- Cut and solidly anchor the newel post so it is plumb in both directions.
- Fit and attach the shoe rail and handrail.
- Install the balusters spaced to code requirements and cut to fit the shoe and hand rails when installed plumb.
- Cut and install fillets and trim boards.
- Fill, spackle, sand, caulk, prime and paint.
Side Note 1
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Side Note 2
Plugging Counter Bore Holes
We used this plug cutter to cut plugs for the newel post with matching material.
It’s a bit tricky to learn to use this type of plug cutter without a drill press, but it can be done freehand.
After cutting the plugs, we used a small screwdriver to snap them off as deeply inside the hole as possible.
When gluing the plugs into place, we turned the grain the same direction as the newel post and drove them in almost flush. We wait for the glue to dry before sanding the plugs flush with the newel post surface.
After the glue in the plugs dried, we sanded them flush with the face of the newel post.
Side Note 3
Fine-tune Knee Wall Framing
We made this jig of 1×4 by ripping the vertical piece so it matches the top of the knee wall framing plus the thickness of the wall cap.
We used a small scrap of wall cap material to test the knee wall in relation to the jig to see if it ran parallel to the stair nosings.
On all of our jobs you will find a supply of these flat shims that are 1.25″ x 3.5″ of varying thickness.
We used the jig and a scrap of wall cap material to determine which flat shims to use.
We used 1/4″ crown staples to fasten the flat shims to the knee wall framing.
We then used a straight edge to bridge between the flat shims at both ends of the knee wall. The gaps between the wall framing and straight edge were filled at 16-in. increments. The result is framing that is flat and parallel with the stair nosing.
We also used the jig to mark the top edge of the stair skirt, which will serve as the trim board along the inside of the knee wall.