A year ago, I had the idea of adding a cupola to the garage, the least attractive building on the property. Adding a cupola, punctuated by a wind vane, would significantly improve its appearance.
Reasonably priced cupolas are available online, in several styles and sizes. Costing between $200 and $850, they come complete with copper roof and wind vane. I am sure there were not this many options available last year when I looked. Not that it would matter, of course, because even the more expensive ones aren’t built exactly the way I’d like. Besides, it’s more fun to build my own.
Handyman magazine publish an article about building a cupola in 1999, and I found a copy of the article online, with the plan. The plan was simple and very close to what I imagined, so that became my starting point. It just needed a few improvements that I like to incorporate into all my projects:
- Lighter construction
- Reduce the amount of material (& cost)
- Increase strength & durability
For example, rather than cedar 4×4 corner posts, mine would be built from a pair of 2x4s with a miter joint. And I wanted to use tongue-in-groove joins to assemble other pieces, reinforced with construction adhesive.
During the analysis and planning, I learned there is actually a rule for determining the size for a cupola on a building. A cupola should be between 1 and 1.5 inches wide for every foot of unbroken roof-line (8.3-12.5 cm per meter) . In the cupola design I was using, the overall dimensions of the cupola are also dependent on the dimensions of the vents on each side. And since my roof-line indicated a cupola 40 inches square (102 cm), I’d need louvered dormer vents big enough to match.
For louvered vents, the Buy-vs-Build decision was most definitely to “buy.” I’ve made louvered vents before and it’s not that easy. While I looked for vents of the right size and price, the final design and construction had to wait . In the end, the 18-24 inch squares I wanted were just too expensive. I could afford the 12 inch squares, but I had to discard the the rule-of-thumb for cupola size. So in the final design the base of the cupola was 26 inches square (about 66 cm), somewhat less than what was called for by my roof-line. There’d be no blue ribbon for architectural proportion.
With louvered vents obtained, and the exact measurements, I could begin cutting and assembly. Each of the side panels were made of 1×4 stock. I used treated lumber for these and all other exterior wood parts.
To give the side panels more strength, I wanted to join the planks with tongue-in-groove joints. To do that, both sides of the joint were grooved with a router. Then I applied constructions adhesive to each groove and placed a rectangular wafer into one of the grooves before pressing the sides together. Not only would the panels be stronger, the joins would reduce warping over time, and the individual pieces would remain in alignment.
The 2x4s used for the corner posts were fastened with galvanized finishing nails and reinforced with construction adhesive. I also added grooves to each edge where the side panels joined them. Again, this would make the cupola stronger and last longer.
The soffit and the sill (top and bottom plates) were cut from treated 2×6 stock. I cut the 45 degree bevel along the full length of each 2×6, then cut the miter edge for each of the eight individual pieces. The soffit and sill pieces were slightly longer then the base size. I measured 26 inches along the inside edge of the bevel, so the remaining beveled edge would extend out beyond the box, like a cornice. The soffit and sill were attached to the box using deck screws – basically, heavy-duty wood screws with a coating to prevent corrosion.
The roof assembly was the most important take-away from the Handyman design. The curvature of the rafters give the finished roof a distinctive shape, typical of many of the best cupolas. To get the length just right, I actually cut the rafters a little bit long, holding each in place to test the fit, then shaving off any excess from the top angle. The angle on each end of the rafter was also important for achieving that unique appearance. Instead of 45 degrees, the rafters each have a 55 degree angle on one end, and a 35 degree angle on the other. The makes the roof a little shorter than it is wide.
For the plywood decking, I made a template by tracing the concave edges onto a piece of cardboard pressed against the rafters. Then I simply traced the pattern on the 3/8 inch plywood. I attached the plywood triangles with 1 inch screws.
The roof would eventually be covered with tar-paper, then asphalt shingles, and a small pyramid-shaped cap made from aluminum flashing.
The “saddle” is a box made from 3/4 inch plywood on which the cupola will be mounted, tailored to fit the pitch of the roof. I fastened 2×3 boards to be used as “cleats” inside the box on both of the angled sides, and pre-drilled 6 holes for the screws to attach the saddle to the roof. Cleats at the top were made from excess 1×4 boards, and would be used to attach the cupola box to the saddle.
The entire saddle was covered in aluminum flashing, pre-painted white, and attached with tiny nails . Although the seam is sealed with caulk, I put it on the side of the saddle so it would point away from the prevailing weather. I did the same with the flashing cap at the top of the roof. All of these steps are to keep rain out, preventing moisture damage to the wood. After finishing the saddle, it was time to go up on the roof.
A cupola isn’t just an architectural embellishment, it is a functional device used to vent heat and moisture out of the building. After finding the center of the roof-line, I placed the saddle into position, leveled it, and traced it with chalk, and ‘Yes’, I actually cut a hole in the roof. The garage roof had no ridge vent, in fact, no ventilation of any kind except the garage doors. So the moment I opened the hole hot air came billowing out.
A heavy bead of roofing cement was used on each of the angled footprints to seal out rain. However, I left the the down-hill sides unsealed, just as the Handyman article suggested…to provide a way for rain to run out should any get inside.
Three inch deck screws were used fasten the saddle to the roof, running through the cleats, the shingles and into roof decking. After running a heavy bead of caulk along the top edge of the saddle, I placed the cupola box on top of that, and used deck screws to fasten those components together (after pre-drilling).
The 1 inch boards I used for the top cleats were such a small targets to hit with a screw. In retrospect, I should have used the same 2×3 stock I used for the bottom cleats. Still, I managed to obtain a strong bond without piercing the crisp, white flashing on the saddle.
Another heavy bead of caulk was applied to the top of the cupola box before setting the roof. This time I used 2 inch deck screws to attach these components together. I applied another bead of caulk to the inside of each vent and attached them using 1 inch galvanized screws.
The idea of building a cupola actually occurred quite a long time ago. In fact, my wife and I have had the weather vane for about 8 years (such is my to-do list). The sold brass weather vane was a gift from my wife’s parents, and it was about to find its proper place at long last.
After a few more minutes to attach the mounting bracket and seal it with roof cement, it was time for the crowning element. The weather vane looked right at home, as the arrow pivoted in response to the western wind. Finished at last.
I checked it from the ground while I put away the tools…nice. Later, looked from the kitchen window…turned out really well. At the end of the day, on the back deck with wine glass in hand I sat to admire this bit of my own handy work. It looked every bit as good as I’d imagined. That’s when I noticed one the letters on the weather vane was upside down. 😐