Curved Stairs: Add Eye-Catching Value To Your Home
By Mike Wark
If you’re looking to add some unique flavour to your home or deck, adding a set of curved stairs will bring some serious elegance and style to your next home renovation project. If well designed, curved stairs provide more than just their functional purpose, offering a focal point of design, and a centerpiece of master craftsmanship and artistry. While at first glance, they may appear complex, the design comes down to simple math and a little creativity. Here’s a look at the process.
Step 1: Calculating the Numbers and Laying Out the Stringers
As with any stair, building curved stairs involves calculating the unit rise and run (height and length) of the treads and risers. Similar to straight flights, unit rise is calculated by dividing the total rise of the stair by the number or risers. However, unlike straight flights, curved stairs actually have two unit runs, based on the inside and outside radius of the stair. This is calculated by drawing out a full-sized layout of the stair, based on a radius point set at a given distance from the inside edge of the stair. Oftentimes, the inside unit run is taken as the minimum measurement allowed by building code, which is 150mm (6 inches), but can be calculated by using the radius to find the inside total run of the stair (a percentage of the circumference, based on the total degrees turned by the stair), and dividing this by the number of treads. The outside unit run is found in a similar manner, using the outside radius. Once these numbers are established, we can move on to lay out the stringers, which is done the same as with a straight flight, using a framing square to transfer the unit rise and run to the outside stringer plies.
Step 2: Forming the Curved Stringers
Once the outside stringer plies are laid out, it comes time to form the stringers to the curvature of the stairs. In order to achieve the desired strength to support the treads and risers, as well as the curve in the stringer, it is necessary to laminate multiple layers of thin plywood together, glued and clamped, and bent around temporary curved walls built in place to support the stairs until the treads are installed, held in place with finishing nails. The on-centre stud spacing on these walls should be no more than 6-8” to ensure a tight curve, and joints in the outer layer of plywood should land on studs.
On a recent stair built for a local theatre company, we used 4 layers of 3/8” plywood per stringer, laminated and held in place along temporary walls. As you can see, make sure you have plenty of clamps!
Step 3: Cutting the Stringers
Once the glue has dried, the stringers can be removed from the temporary walls, and cleaned up using a belt sander to ensure top and bottoms of the plies are flush. Finishing nails used to hold the outside plies to the walls can be cut off with an angle grinder or broken off. After clean-up, a circular saw or jigsaw is used to cut along the layout lines on the outside plies of the stringers, to form the support surfaces for the treads and risers. Once the stringers have been cut, they can be clamped back onto the temporary walls for installation of the treads and risers.
Step 4: Installing Treads and Risers
With the stringers in place, treads and risers now be installed for the curved stairs. It is a good idea to start at the top and work your way down, first installing the top riser, followed by the next tread down, which is glued and screwed to the stringer. By this method, the bottom of the riser is covered by the inside edge of the tread, creating a seamless corner junction. In addition, the stiffness of the riser acts in the same fashion as a beam, providing shear strength between the two stringers, and reducing bounce when weight is applied to the stair.
If the stair will be open on one or both sides, it will be necessary to first install the risers, then remove the temporary walls and support the stair with temporary posts from below, so that a side-nosing on the treads can be accommodated.
Step 5: Finishing and Install
Following installation of the treads and risers, the stair can be removed from the temporary walls, finished with stain, painted, optional veneer on the stringers, or endless other options, and installed in its final location, and handrail installed. With that, you can enjoy your beautiful stair that will receive compliments and catch eyes for years to come!
Mike Wark is a guest contributor, and a construction carpenter with Homestead
Custom Carpentry, a general contractor specializing in home renovations, serving the
Central Alberta region. Before entering the field of construction, Mike earned his B.A.
in Political Science from Carleton University, and is currently working towards his
Project Management Professional (PMP) designation, with a focus on construction