CNC Railings at the Marguerite ADU

Construction has just wrapped up on the Marguerite ADU, contemporary accessory dwelling unit we designed in Southeast Portland. In this post we’d like to share the design and fabrication process used in making the guardrails at the stair and loft. Being makers—in addition to designers—was a lot of fun, and we’re really excited about how the project turned out!

Stair railings are a great place to get creative. While they have some basic functions they have to perform, like keeping people from falling off the stairs, they present the designer with a wide wide variety of aesthetic and material possibilities. Because this ADU is primarily one large room, the guardrail serves the additional role of being a partition between the living and sleeping spaces. We wanted a design that was both unique and substantial.

First iteration of the railing design

The idea to use a CNC milled plywood panel came pretty early in the design process, but the details of both the pattern and how the guardrail would be constructed continued to evolve through the design process. Initially we were planning to mount the panels to the faces of the posts, but were torn about which side of the posts to mount the panels on. In the end, we decided to mount the panels in grooves cut into the posts so that they would be symmetrical on both sides.

Final railing design

When it came time to make the panels, we decided to hire the ADX fabrication team to do the CNC milling and some of the rough woodwork. We would then put some finishing touches on the components in the office and would work with Right Arm Construction, the project’s general contractor, on the installation of the panels themselves. Right Arm temporarily installed uncut versions of the vertical posts, and precise measurements were taken so the panels could be fabricated to the correct size. While we had a very accurate 3d model of the design, the tolerances on the panels fitting into the grooves were tight enough that we knew we couldn’t just rely on the dimensions in our model—we would have to measure the as-built conditions before cutting the panels.

Setting the posts for one final measurement before cutting the panels

After measuring the posts, we translated the design into a 2d CAD drawing that incorporated the as-built conditions, did our final tweaks of the pattern, then prepared the files that ADX would use to cut the panels.

Production CAD file

After the posts were measured, they were dismounted and taken to ADX so the grooves could be cut on their table saw. We had them stop a little short so we could finish the ends of the grooves by hand, getting them to precisely the right length.

Something new (CNC milling), something old (mallet and chisel) 

Once the pieces were all set, we took everything back to the sire for a test fit of the panels. It was good thing we did, as two of the panels needed to be remade for a perfect fit. After recutting those panels, and a second test fit, we handed off the panels to Right Arm, who finished the installation.

It looks pretty sharp, if we do say so ourselves! We’re excited to do more of this type of work, where we get to get our hands dirty making custom design elements. Overall the process was quite successful, though there were some challenges involved in coordinating the offsite fabrication of the panels to fit perfectly with the site-installed vertical posts. Next time we’ll work towards something with an equally compelling design, but with a more forgiving installation process.