Framing a Round Tower

Framing a Round Tower, continued

Some of the shortening bevels were extreme angles, but they were easy to cut with a swing-table adapter (Pairis Products, Phelan, Calif.; 760/868-0973, www.bestconstructiontools.com) mounted on a wormdrive saw. I modified mine to accept a Linear Link chainsaw blade (Muskegon Power Tool, North Muskegon, Mich.; 800/635-5465, www.linearlink.com), made for timber framing or gang-cutting rafters.

The interior ceiling was flat. We framed it with 2x8s, starting with a triple 2-by cross member and filling in with radial joists fanning around like spokes on a wheel.

We sheathed the underside with plywood to tie everything together and resist deformation when we craned the roof into place. The plywood also provided full nailing for the interior crown molding.

Compound-Curve Sheathing

To sheathe the roof, we paneled each rafter bay individually using 1/2-inch cdx plywood. We cut it to bend parallel to the face grain and used separate panels to cover the lower and upper curvatures. This way, we weren’t fighting the plywood into a double inside and outside curve. I patterned the first set of panels by screwing blank stock directly to a bay and marking the rafters’ centerlines. The rest of the panels were cut from tracings of the patterns.

We’d taken care to cut the rafters uniformly and space them equally, so the panels fit well with only minor adjustments needed. We applied a bead of construction adhesive to the rafter edges and used ringshank nails to hold the plywood down tight to the curves. We expected to have to bevel the rafter shoulders prior to sheathing, but it wasn’t necessary.

While the roof was still on the ground, we applied the circular fascia board. I didn’t want to back-kerf and bend a solid wood fascia or invest a lot of labor in a glue-laminated member. Instead, we used cellular PVC Azek (Vycom, Moosic, Pa.; 866/549-6900, www.azek.com). It wrapped easily around the roof’s diameter. We used a double layer of 3/4-inch material, solvent-welded between layers and at the bevel-lapped butt joint.

Shingling in the Round

Like the rest of the roof, the turret roof was finished with Grade A 18-inch “Perfection” western red cedar shingles, installed over a self-adhering bituminous membrane. On top of the membrane, we applied Cedar Breather underlayment (Benjamin Obdyke, Horsham, Pa.; 800/346-7655, www.benjaminobdyke.com), a stiff nylon matrix that allows air to circulate under the shingles, and shingled directly over it, using hand-driven stainless-steel ringshank nails. The ever shrinking, concentric rings of the turret roof shingling required each shingle to be quite narrow and trimmed to a taper. This was a slow process. Our roofing sub had four of his guys working on this one little roof for three days, cutting, block-planing, and fitting shingles of increasingly smaller size as they neared the top. We saved some time by culling out all the narrowest shingles from the bundles and designating them for turret use. To cap the dome, Fred Sr. will fabricate a round, copper “beanie.” The final touch will be a lead-coated copper finial, purchased from a specialty supplier.

John Seifert is a principal owner of Seifert Construction in Mattituck, N.Y.