Staircase Construction - Baluster Fastening Methods

This hub page, like many of my others, has to do with staircases. However, this one is slightly different in that it gets a little more technical. This hub is more so for the do-it-yourselfer (DIY) or perhaps the professional stair installer. If any of you have been around stairway construction, you may have noticed that there are different ways of attaching balusters to the stair treads. You may have been around remodeling projects that included older stairways. If so, you might have noticed that the method for attaching stair balusters 150 years ago is different than the method that is used today.

In my first graphic above, you will notice that the stair treads have been notched in what is a dovetailed pattern. In this method, the bottom of the balusters are cut with a corresponding dovetail that neatly slides into the notch of the treads. The angle of the dovetail "locks" the baluster in place. The stair return is then applied over the dovetailed section and then fastened to the tread. It seems like a lot of work, doesn’t it? This method did not require any glue but relied upon the skill of the stair installer to make a nice tight fit. Dovetail construction is still used to manufacture drawers, but is seldom used in stairway construction. I have had some customers, though, that were attaching new balusters too old stair treads. And so, they had to cut and dovetail the bottoms of the new balusters to fit the old stair treads.

If you have been around stair construction at all you have seen balusters with dowel bottoms. The graphic on the right illustrates this. Dowel are turned on the bottoms of the baluster. They are typically three quarters of an inch by three quarters of the inch. And so, a ¾” hole is drilled into the stair tread to receive the balusters. Ordinarily, glue and a finish nail are used to fasten the balusters. This method is probably still the most common method used in stairway construction. I have found, however, that it somewhat more difficult to get a really snug fit between the tread and the baluster with this method.   The next two methods remedy this shortfall.

A local stair company introduced me to this next method of installing balusters to the staircase. This method uses a dowel screw. In this case, a pilot hole is drilled into the bottom of the balusters as well as the top of the tread. A 5/16” dowel screw requires a 9/32 inch pilot hole. The dowel screw should go into the tread first and then the balusters can be screwed onto it. Since treads are typically harder than balusters. This installation sequence will ensure that the balusters or not “stripped”.  This fastening method (as well as the one below) really help to tighten the fit between the stair tread and baluster.

By the way, there is a handy dowel screw driver called a hanger bolt driver that can be purchased to fit the particular size of the dowel screw you are using (5/16" is probably the best size to use). A drill guide is also available for purchase for drilling the pilot hole into the bottom of the baluster.

The last method is similar to the dowel screw method. There is a difference, however. The dowel screw that is fastened to the baluster has a wood thread and a machine thread on it. The wood thread goes into the bottom of the balusters. The machine thread goes into a threaded insert that is inserted into the tread. The pilot hole used in the stair tread is larger then the pilot hole for the bottom of the balusters . The threaded insert can be screwed into the tread using a screwdriver or a driver bit specially made for the threaded insert. See photo.

Conclusion:  I hope this has been helpful to you.  I wished I would have known about the newer methods when I first got started .The threaded inserts and dowel screws can certainly be a time saver.  If you have any questions or comments let me hear from you.