We're builders who normally work along the North Carolina
coast. But when the opportunity arose to build a replica of a
historic lighthouse on the Chesapeake Bay shoreline, we were so
intrigued we decided to extend our usual geographic reach to
take the job.
The area where the lighthouse is located is experiencing rapid
growth, and as newcomers we found it a real challenge to enlist
qualified subs. Consequently, the task of building the central
spiral staircase fell to our framing crew. The plans indicated
the location of the stairwell and the size of the shaft, but we
had to work out the construction details on site.
Framing the Radius Walls
The stairwell is enclosed by a two-story-high 6-foot-square
shaft, which opens up at the third level into the octagonal
cupola that houses the lighthouse's lens.
We started the project by framing the 2x4 walls of the square
shaft, then made a template for the curved plates of the
stairway's cylindrical walls.
To do this, we snapped out a 3-foot-by-6-foot rectangle —
half of the shaft's area — on a sheet of 3/4-inch
plywood, then scribed a pair of tightfitting arcs to represent
the plates. We cut the pattern out with a jigsaw (1) and used
it for the radius plates we'd need for any of the cylindrical
walls that would be exposed on both sides.
For the most part, we used 1 5/8-inch-wide plates and 2x2
studs, though in a few loadbearing areas we used full-width 3
1/2-inch plates. We also made a pattern for plywood "corner
plates" that would support the corners wherever the cylinder
was enclosed by the square walls (2).
Because we would be using vertical 1x4 T&G paneling, we
wanted to provide nailing plates at 3-foot intervals up the
cylinder wall. Using the patterns, we cut enough plates and
inside corner pieces from 3/4-inch plywood to build up double
and triple laminations where needed all the way up the
Then we nailed off the bottom plates on the first floor,
toenailed the 2x2 studs in place, added another plate on top,
and face-nailed the studs. We continued this process to the
top, varying the parts as needed, depending on the stair
layout: Where the stair was enclosed, we used the plywood
corner plates; where the curved wall was visible from both
sides, we used the narrow plates.
The one special-order item required for the stair was the
12-sided laminated oak center pole. We purchased this from a
millwork company in Ohio (Woodsmiths, 800/874-2876), which
shipped it to us in Virginia.
To position the pole, we cut the third-floor sheathing to form
the landing and the stair cylinder at the very top, where the
stair pivots 90 degrees to the right to emerge onto the floor
of the cupola (3, 4). We marked the pole's center point on the
sheathing and, after rotating the pole so that its 12 facets
were in the proper orientation to the tread layout, secured it
with structural screws at top and bottom (5).
The pole's finished length was 21 1/2 feet (6). We received a
28-foot blank, which had been damaged near one end; fortunately
we were able to cut off the damaged part.
Wall Paneling and Stringers
Next we installed the vertical 1x4 T&G paneling (7). We
located the longest vertical run available to begin the
installation and used this as a baseline to work in both
directions as needed. We located butt joints where the stair
stringers would conceal them (8).
Once the stairwell wall was fully paneled, we laid out the
stringer on the cylinder wall, plotting the points where rises
and runs intersected. Using a tall story pole for the rise, we
marked these points at 30-degree intervals around the first
full rotation of the stair. To plot the stair's second
rotation, we fastened a small plywood rip horizontally around
the cylinder wall, level with the second-floor landing, and
rested the story pole on that.
We set a trim nail at each stringer point to give us the line
needed to begin laminating the stringer (9), which we made from
four layers of 1/4-inch plywood strips, secured to the wall
with adhesive and screws and braced with kickers while the
adhesive set (10).
We made the seat and riser cuts on the bottom of the first
piece, positioned it at the base of the stair, then bent it to
the wall while pulling it up tightly against the trim nails. We
followed with layer after layer, working our way up the
cylinder and staggering the joints in successive layers (11).
Since the bottom three layers would be covered, we could use as
many screws as we needed in them.
To avoid placing screws where we might saw through them, we
marked the rise and run on each layer, drawing plumb and level
lines from the points indicated by the trim nails. We secured
the top layer with trim nails and kickers until the adhesive
set. Then we cut out the runs and rises with a circular saw
(12) and finished the cuts with a utility knife, chisel, or
RotoZip (13, 14).
Installing Risers and Treads
The flat facets of the center pole provided a convenient place
to secure a router jig (15) so that we could mortise pockets
for the supporting risers (16).
To precisely locate the jig, we leveled from the stringers,
marking each tread elevation on the pole (17). We made five or
six passes to cut the 1-inch-deep pockets (18), which were 1
7/8 inches wide to allow room for a 5/4 support riser and a
3/4-inch finish riser, with a little play for installation. The
height of the pockets exactly matched the height of the
stringer rise cuts.
After ripping them to the correct height, we installed the 5/4
support risers by pushing them to the back of their pockets
(19) and nailing and gluing them to the pole. On the stringer
end (20), we glued and screwed them.
The treads were made of the same 5/4x6 T&G heart pine used
for the flooring (21). We glued up and sanded these, then
shaped them using templates made from the plywood arcs left
from cutting the plates earlier. We used the jigsaw, files, and
sandpaper to get a good fit at the pole and the wall, then set
the treads in place to mark the front and rear cuts along the
risers (22). We left an extra 3/4 inch along the front of each
tread to allow for the finish riser and a 1-inch
After cutting and rounding the front edges, we glued and
nailed the treads in place.
Once all the treads were installed, we ripped the finish
risers so they would fit snugly between the treads. We cut them
1/8 inch short and slightly beveled the face on the pole end so
we could ease them into the routed pocket and rotate them into
position. When we had the fit we wanted, we applied adhesive to
the backs and nailed the finish risers to the stringer, the
pole, and the support risers.
Twist at the Top
As noted earlier, the top four steps pivot up to the cupola
landing in the opposite direction from the rest of the stair.
The narrow ends of these four treads rotate around the lens
To bend the stringer for this section, we framed a partial
wall that hangs from the cutout floor that restrains the top of
the pole (23). We used curved plywood plates and 2x2s for this
upside-down wall, which radiates from the top landing to the
center pole. Its main purpose was to act as a form for the
final stringer section. Once the final short section of
stringer was laminated and the treads and risers were
installed, we cut off the bottom of the upside-down wall and
capped it underneath (24), then paneled it above (25).
After a thorough sanding, we finished off this utilitarian
stairway with wood filler and paint.
David Brothersis a framing contractor
in Elizabeth City, N.C.