Recently, my friend Nick Ridge and I took on a job in
Northern California that had an interesting challenge —
an elliptical staircase with a self-supporting inside stringer.
To make things trickier, the major axis of the ellipse
paralleled a back wall that ran at an angle to the two side
walls (A) enclosing the staircase. I had to figure out a way to
size the ellipse so that it hit the walls at three unknown
The architect's drawing was of little use and I couldn't figure
out a way to do the layout with math, so I resorted to the
tried-and-true caveman method — trial and error —
in hopes of eventually finding the correct-size ellipse to fit
the space. Working in an open area elsewhere in the house so
that the proliferation of trial lines wouldn't confuse us
later, I snapped out the wall layout and started drawing trial
ellipses. I got lucky: On the second try, I found the right
focus points for drawing the ellipse that fit the space.
After drawing the outside and inside curves of the stair, we
did a quick check to make sure the stairs would meet code:
First, we drew a third ellipse 12 inches in from the inside
edge to define the "line of travel." Using a 50-foot steel
tape, we measured the total length along the line of travel and
divided by the specified number of treads (11) to make sure the
treads were wide enough at that point. The result — 9 5/8
inches — was better than the 9-inch minimum required by
the local code.
We used the same procedure to check the tread width along the
inside of the curve and came up with 63/16 inches —
slightly better than the 6-inch minimum requirement.
Next, we divided the inside and outside ellipses by the number
of treads, then snapped lines between the marks to define the
Time to Cut
We could now use the floor layout as a pattern to cut all the
various pieces. We used 1 1/4-inch plywood for the treads, and
11 1/4-inch TimberStrand rim board for the risers. The plan was
to attach 2x4 cleats to the front of each riser to support the
Cutting all the pieces took a while because, unlike standard
circular-stair parts, each tread — as well as every angle
on the end of the risers — was unique. We took the angle
cuts directly off the floor layout with a protractor, then
adjusted the circular-saw bevel accordingly for each cut. We
cut both the risers (B) and the 2x4 tread cleats (C) this
To mark the treads, we positioned sheets of plywood over the
floor layout, then redrew the inside and outside elliptical
curves using the same focus points as before.
Next, we made the elliptical wall plates for the perimeter
walls out of plywood. With the treads in position on the floor
(D), we laid out the wall studs — which would also
support the outer end of the risers — to fall either in
front of or behind the line of each riser assembly, depending
on the situation.
When I'm framing a standard circular staircase, I can easily
position the studs exactly parallel to the riser so they can be
sandwich-nailed together. It wasn't so easy with the elliptical
stair: While some of the studs fell parallel to the incoming
riser, others had to be rotated slightly to give good support
but not affect the drywall nailing. In some cases, the angle of
the studs was so severe we had to make vertical cheek cuts on
the end of the riser.
At the corners, we were able to run the risers long and connect
to the studs of the rear wall as well (refer back to B), which
greatly strengthened the staircase.
With the perimeter curved wall in place, we calculated the
riser height and laid out a floor-to-floor story pole to mark
where the top of each riser assembly would be nailed to its
appropriate supporting stud. We then used the riser marks on
the perimeter studs as a reference to precut temporary support
studs for the inside of the ellipse.
At last we moved on to the fun stuff: putting it all together.
We started by attaching the 2x4 cleats to the risers (E), then
worked our way upward, nailing off each riser assembly to the
correct perimeter stud. We tacked the temporary support at the
inboard end and added the tread on top, completing each step
before moving on to the next (F).
To make sure we stayed exactly on our floor layout below, we
plumbed down with a level at the end of each tread.
Once all the treads were in place, we began the process of
applying overlapping layers of 1/8-inch plywood to build up a 1
3/4-inch-thick structural stringer. Nick first installed pieces
of 3/4-inch plywood in the end of each riser-tread assembly,
with the stair's slope along the bottom edge. This would give
us a smoothly ascending line to use as a guide when we cut the
bottom of the stringers after the glue-up.
We found that 1/8-inch wacky wood worked well in the tightly
curved sections at the top and bottom (G), while standard
1/8-inch door skin was more than flexible enough for the middle
part. We used Weldwood plastic resin glue and plenty of screws
and clamps, applying layer after layer (H).
When the glue had set up, Nick went to town with a jigsaw and
circular saw to put a finish edge on the bottom of the stringer
and cut out the triangular sections on top (I).
Later, finished oak treads would be cantilevered beyond the
stringer by the trim guys for the traditional open-staircase
look. But for our part as framers, we only had to remove the
temporary riser support studs, take a moment to admire a
once-in-a-lifetime project, and move on to our next
adventure.Will Holladayis a roof-cutting
specialist and the author of A Roof Cutter's Secrets.