My business, Narragansett Housewrights, provides custom
millwork and architectural components to builders here in
southern Rhode Island. Last year, my best customer, Baud
Builders, gave me the job of building a screened pavilion for a
shingle-style waterfront home. The pavilion swept out in a
curving wing from a corner of the building, terminating in a
conical roof supported on a semicircular colonnade.
I only take on projects that I can build in the shop and
deliver to the site in sections for assembly. If I had built
this one according to the architect’s framing plan, it
wouldn’t have been transportable (see Figure
1). So I came up with an alternative method that I
believed would also cut the build time by half. We bid the job
accordingly, and after much discussion got approval from the
architect and engineer to proceed.
Figure 1. The roof framing consists of
five modules assembled on site, beginning with the half cone
(top left). The four major modules all bear on the perimeter
architrave beam and a steel moment frame at the cone’s
midsection. The fifth, nonstructural module (bottom right)
completes the top and back of the cone.
I typically skip shop drawings and begin instead by making a
simple model, in this case a section of the conical roof
(Figure 2). This gives me a fast, simple way
to view the critical components at full scale in three
dimensions. Basically, I cut short pieces of each element in
the structure and stick them together with hot-melt glue.
Figure 2. Full-dimension components, quickly glued
with hot-melt adhesive, provide a reliable, accurate way to
check a proposed assembly. Note the crown molding and the
plastic soffit vent material.
I envisioned the overall framing as four independent
truss-framed modules joined together in the finished assembly:
a half-cone, two sloping side modules, and a flat-topped center
section. My trusses are nothing more than 2-by members
connected with plywood gussets.
I designed the conical module around a series of identical
triangular trusses fixed in a radial pattern around a central
“hub.” The roof sections connecting the cone to the
main house use a similar system of trusses arrayed along their
respective framing lines.
The trusses’ tails bear on a curving architrave, a
custom-made structural beam supported on six 4x6 posts
concealed within hollow architectural columns. One of these
columns was pre-existing and provided a point of departure for
the new layout.
Moment frame. Two of the architectural columns
surround steel posts, part of a welded moment frame needed to
resist wind-racking and uplift. The roof modules fully encase
the horizontal steel member, a W8x21 hot-dipped-galvanized
Templated construction. To make sure that site and
shop layout remained consistent with each other, I cut two
identical sets of plywood templates to outline the architrave
and pinpoint all the column locations. I brought the templates
to the job site and laid them out on the masonry deck, then
took lots of triangulated measurements off the building
(Figure 3). I recorded these directly on the
templates. Back at the shop, I used the triangulations to snap
accurate layout lines on the floor so that I could position the
templates exactly as they were on site. Meanwhile, one set of
templates remained at the job site for locating and pouring the
new column bases.
Figure 3. Identical plywood layout
templates ensured a perfect match between site and shop
efforts. The square cutouts pinpoint column centers.
Curvy architrave. I made the architrave in three
segments — the first with a 28-foot radius, the second a
semicircle with an 8-foot radius, and the third a straight
length of LVL. To make the curved beams, I glue-laminated 11
layers of 3/8-inch plywood underlayment bent around shop-built
forms. I used Excel One, a spreadable polyurethane adhesive
excelglue.com), and a
boatload of bar clamps. The adhesive sets up in about five
Because plywood doesn’t bend with smooth, perfect
uniformity, the laminated beam had a somewhat irregular face.
To compensate, I used a router on a long trammel arm to cut
slightly wider, perfectly accurate top plates from 3/4-inch MDO
(medium-density overlay) plywood. We centered the plates on top
of the beam segments and glued and screwed them in place.
Later, after on-site assembly, I gauged the Azek fascia off the
plates’ edges and shimmed the inner and outer pieces in
Conical framing. I began framing the semicircular
conical section by building a hub, a 2-foot-diameter
half-cylinder made of staves cut from an LVL beam
(Figure 4). It’s glued together with
West System epoxy (866/937-8797,
added mechanical strength, I bound the staves with four
perforated steel straps. The staves — which are 1 3/4
inches wide on their outer face — provide faceted
surfaces for attaching the 2-by trusses.
Figure 4. The cylindrical hub at the core of the
conical roof section is made from staves of resawn laminated
veneer lumber (top). Each stave corresponds to a truss in a
radial array (bottom left). The trusses are attached to the hub
with structural screws. Intermediate lookout blocks provide
firm backing for a cellular PVC fascia (bottom
We set the trusses on the semicircular architrave and screwed
them to the hub from the back, using 4-inch Timberlok screws
one each into the top and bottom chords.
The truss tails landed at about 20 inches on-center. To create
more solid backing for the curved fascia, we glued and screwed
lookout blocks on 6-inch centers to a length of 1-by cedar,
then nailed this assembly to the truss tails, effectively tying
We then sheathed the back of the half-cone with a single layer
of 3/8-inch plywood, cutting holes between the webs for access
and air circulation. We added cleats on top of the plywood to
catch the lower-pitched abutting roof sections. (It would have
eliminated compound valleys and simplified construction if the
cone and the connecting roof were the same pitch, but I lost
that argument.) I left the top of the cone flat, about a foot
short of the peak, to be filled in after the adjoining sections
were framed and sheathed.
Flanking sections. We framed the side sections using
matching sets of triangular trusses, tacked to the architrave
and supported on temporary legs on the inside. We tied the
bottom chords together with a running 2x4, then sheathed the
inside vertical face with five layers of 3/8-inch plywood,
glued and stapled (Figure 5). The laps between
layers are offset and all the joints are centered over the
framing. We followed by screwing through the plywood into each
truss with 3-inch Timberlok screws. The layered plywood unifies
the trusses and becomes a laminated structural beam that
carries the inside edge and center module of the truss
assembly. One end bears on the steel I-beam and the other end
is notched to bear on the top plate of the house.
Figure 5. A worker installs bevel-edged blocking
between the trusses to provide nailing for the roof sheathing
at the top edge, where the roof line transitions to a flat
midsection. Here, the trusses have received the first of five
layers of 3/8-inch UL plywood, forming a structural beam that
supports the center module.
The porch-roof assembly joins the main roof at an acute angle
(Figure 6). Instead of trying to calculate the
angle mathematically, we extended the plywood on the truss
module far enough to allow us to project and scribe the
intersecting profile. To do this, we built a plywood mockup of
the main roof and placed it on the building line snapped on the
floor. We then used a long straightedge to transfer the pitch
to the face of the plywood on the truss assembly. We allowed an
extra inch of tolerance for fitting and shimming, then cut the
plywood and reinforced it with framing.
Figure 6. A plywood mockup of the
existing roofline furnishes the correct cut angle for the roof
Center section. With the three sloped sections
completed, we next framed the roof’s flat-topped center
section (Figure 7). This was a simple matter
of custom-fitting sequential trusses to the existing gap.
First, we made a batch of hold-offs to represent the eventual
five layers of plywood sheathing we’d be laminating over
the two sides. We screwed the hold-offs to the vertical 2x6
truss members, notched to receive the 2x4 top and bottom
chords, and back-screwed them from inside the abutting roof
sections for easy removal later. Then we cut the horizontal top
and bottom chords to fit between the verticals and applied
3/8-inch plywood gussets to both sides of each truss.
Figure 7. The center roof module fills the
progressively widening space between the side modules (top).
Hold-offs, back-screwed to the upright truss members, reserve
the space that will be occupied by five layers of plywood once
the center module is framed and pulled free for access (bottom
left). With the sheathing and cap completed, the modules were
ready for transport to the job site (bottom right).
As we worked our way back out of the gap, we shimmed a series
of shop dollies beneath the bottom chords. This allowed us
— after removing the screws — to roll the completed
center section clear and apply the plywood layers to its two
With the framing completed, we sheathed the roof segments with
a double layer of glued and stapled 3/8-inch UL plywood. On the
conical surface, we cut pie-shaped segments and staggered the
joints between layers. To introduce a slight, water-shedding
crown to the flat roof section, we ran 3/4-inch rippings at
mid-span across the top chords and bent the plywood over
Finally, I made the cap and completed the back of the cone. I
made the cap from wedges of solid framing lumber, cut to the
roof pitch and then band-sawn to radial tapers. I glued the
wedges together with thickened, gap-filling West System epoxy
and sanded the contours smooth after it hardened.
Valley lines. I used a simple method to determine the
compound valley line where the cone overlaps the abutting roof.
First, I set the cap in place, its back half supported down to
the flat roof section by an offcut from the hub. Then, pivoting
a long straightedge around the cap, I projected the
cone’s pitch down onto the connecting roof and marked the
valley line. Allowing for the thickness of the sheathing, we
stepped back from the line and custom-fitted 2x4 framing in a
radial pattern between the hub and the valley. With the
sheathing applied, this last module ended up looking like a
huge bat in flight.
Site assembly. We loaded all the components onto a
truck and hauled them to the site. On installation day, with a
crane standing by, we cut back the existing roof overhangs and
exposed the top plates where the new roof would connect
(Figure 8). We set the steel I-beam with the
crane, and a welder completed the moment frame. Meanwhile, the
crew set and bolted the architrave beams on the columns. By
late morning, we were ready to set the roof sections, beginning
with the cone. We’d already outlined the MDO
plate’s location on the underside of the truss chords,
making it easy to accurately re-establish the overhangs on
site. We secured the cone to the architrave with 3-inch
Timberloks, screwing up through the plate into the bottom
Figure 8. The architrave is supported on 4x6
pressure-treated posts within the architectural columns,
notched to 4x4s where they pass through the beam (top left).
The only straight section in the architrave is made with
doubled LVL lumber (top right). Welded brackets support the
beam at the moment frame (bottom).
We installed the remaining roof modules in the same manner. By
late afternoon, we had all the structural pieces set and bolted
together. Last but not least, we hoisted the “bat”
onto the cone, nailed it in place, and called it a day
(Figure 9). Later, I went back with a
reciprocating saw and notched the plate to install hurricane
ties between the beam and each truss.
Figure 9. While the welder put the finishing touches
on the moment frame, the crew set the roof modules around the
architrave (top). Each module included a recess to encase and
bear upon the moment beam (middle left). Metal plates tie the
architrave to the steel posts (middle right); wood post
locations were tied together with plywood overlays. A slight
built-in tolerance allowed the center module to drop in without
resistance (bottom left). The “bat” module defines
the valleys and completes the cone (bottom right).
To complete the structure, the site crew filled in a few jack
rafters between the truss assembly and the existing roof, then
sheathed the underside with 3/4-inch plywood. This plywood,
glued and nailed, serves as a tension diaphragm tying the
bottom chords together to prevent the structure from spreading
and settling. It was later covered with a beadboard
All I had left to do was install the curved crown moldings, a
detail that gave me an unexpected run for the money (see
“Bending Crown”). Altogether, the work described
here required 600 man-hours, or five weeks for a three-person
Mike Rand runs a specialty millwork shop in Narragansett,