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Build a cupola, with maintenance-saving features, for about $150 -- less than half the cost of a similar manufactured model.
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1. Bevel 2x6s on a table saw. To cut the pieces that will form the sill of the cupola, bolt a 1x6 to the saw’s fence (to keep the workpiece from tilting), set the blade at 19 degrees and position the fence 3/4 in. from the blade. To bevel the soffit parts, set
the blade at 45 degrees and the fence 4-1/4 in. from the blade. To make bevel cutting easier, we first cut 2x6s into 30-in. sections. When all eight pieces are beveled, sand them and then miter the ends at 45 degrees. Save the beveled cut-offs from the sill and rip about 1/4 in. off them. You’ll use them later to complete the slope of the sill (Photo 4).
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2. Assemble the sill and soffit frames by screwing temporary plywood scraps to the undersides of the 2x6s. Don’t cover up the corners—you’ll need to drive screws through them later. And make sure that the sill and soffit frames are
perfectly square.
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3. Then screw the sill to the corner posts. Drill pilot holes and drive four 3-in. screws into each post, two on each side of the miter joint. The inner edge of each post should meet the inside corner of the sill.
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4. Assemble brick mold frames between the posts. Predrill and countersink the holes before driving screws. You may have to draw the posts together or spread them apart to make the top piece of brick mold fit. Screw the bottom and sides of the frames to the posts and screw the top piece to the sides. Remember to fasten the beveled cut-offs to the sill with nails and construction adhesive before you install the brick mold.
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5. Screw the vents to the backsides of the brick mold frames with 1/2-in. self-tapping sheet metal screws. Then attach the soffit to the corner posts just as you attached the sill.
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6. Mark and cut one rafter, then use it as a template to mark the other three. To mark the curve, we put a section of plastic door stop molding in a bar clamp and tightened the clamp until the curve was right. Any thin piece of wood will work, but we used plastic because it doesn’t have knots or any other imperfections that lead to an inconsistent arch. Use a protractor ($5 at home centers) to mark the correct angles at the ends of the rafters.
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7. Join the rafters using a 6-1/2 in. piece of 2x2 as a hub. Screw the hub to two of the rafters, and fasten the other two by driving 3-in. screws through the rafters into the hub. Center the rafter assembly on a 26 x 26-in. piece of 3/8-in. plywood and drive 1-1/4 in. screws from below through the plywood and into the lower end of each rafter. Cut a hole in the plywood base so the roof can dry out if water gets in.
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8. Fasten the 3/8-in. plywood to the rafters with 1-1/4 in. screws. Begin at the middle, driving the screws at an angle. There should be a gap (about 1/2 in. wide) between the pieces of sheathing. When the sheathing is done, center the roof on the vent housing and drive four screws up through the soffit into the roof’s base. You can remove the roof later to make it easier to carry. Important: Be sure to cut the roof sheathing so that the grain runs horizontally across each piece. Plywood bends more easily across the grain than with the grain.
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9. Shingle the roof beginning with a "starter strip," a full shingle nailed to the roof upside down. The starter strip should overhang the plywood by about 3/4 in. With the starter strips in place, begin nailing on the 4-in. wide shingles. As with the plywood roof sheathing, leave a gap between the shingles at the ridges. Glue the lower edge of each 4-in. tab down with a dab of roofing cement.
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10. Nail the ridge cap shingles over the ridges. Lay heavy beads of roofing cement along both sides of the ridge. To make the shingles conform to the curve of the ridge, we cut them 5 in. long. The first shingle on each ridge must be cut to match the corner of the roof. The corners of the stiff shingles may stand up at first, but a few hours in the hot sun will make them lie flat.
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11. Cap the roof by folding a 9 x 14-in. piece of flashing around the peak. Hold the flashing in place while you mark it for cutting. When the cap is cut, fold it back into its pyramid shape, squeeze a large blob of roofing cement into it, press it onto the peak and drive one roofing nail through the side of the cap that has the overlapping seam.
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12. Construct a roof pitch gauge by laying two boards over the ridge of your roof and screwing them together.
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13. Mark two sides of the saddle using your roofpitch gauge. Place the point of the gauge on the center line about 4 in. from the top of the saddle and align the legs of the gauge with the inside edges of the saddle. Then cut out the V-shaped notch that will straddle the ridge of the roof. For the saddle’s construction, see the downloadable plan.
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14. Wrap flashing tightly around the saddle and fasten down the seam with self-tapping
screws. To crease flashing around corners, use a hammer and wood block. When the saddle is wrapped, fold down the overhanging flashing along the top and bottom edges. At the V-notch, cut the flashing, fold the flaps into the saddle and secure each flap temporarily with one screw. All of this is a lot easier if you have a helper. And be sure to wear gloves—or plan to visit the emergency room for stitches!
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15. Fasten the saddle to the roof with 2x2 cleats. First lay a bead of roofing cement on the roof along each sloped side of the saddle. Then fold the four flaps down over the cement (cut them back if they extend over the roof hole). Drive 2-in. screws through the 2x2s into the saddle and 3-in. screws into the roof. Seal the gap at the ridge with roofing
cement and caulk around the upper edge of the saddle. But leave the two low edges of the saddle unsealed so any water that gets in can drain out.
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16. Fasten the vent housing to the saddle by driving 3-in. screws through the sill into the 2x2 rails inside the saddle. Be sure the housing is centered on the saddle before you drive any screws.
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17. Drive 2-in. screws through the soffit into the roof’s plywood base. Then caulk over the screwheads and touch them up with paint.
Good article, but there are some possible problems that aren't addressed. 1. The cupola should be properly grounded with a Class I or Class II lightning protection cable, extending from a U.L. approved air terminal to a properly installed ground rod. Check local codes. 2. The 3" screws that are shown anchoring the cupola are insufficient for the wind loads on this size cupola. Use through bolts. 3. When you open a hole in the roof, blow in rain can enter too through louver blades.