Cupola Roof
DEAR TIM: I'm going to build a cupola on top of my garage. The roof is not too steep, so I think I can manage to do this safely. I've got all sorts of questions about cupola designs and general questions. What is the best cupola roof to have? I've seen hip roofs as well as fancy sloped hip designs. Can you do just a standard gable roof on a cupola? What other tips can you share about installing a cupola? Bradley G, Lexington, KY
DEAR BRADLEY: Congratulations on this exciting upcoming project. Cupolas add a touch of class to a structure. Drive around New England where I live and you'll see quite a few on barns, stables, garages and even houses. You have perhaps two of the most viewed cupolas in the world just west of you in Louisville, KY at the Churchill Downs race track.
You may think this is a strange dog house or a playhouse. It's actually a cupola for a garage! It's over 6 feet tall and built on the ground. Photo Credit: Tim Carter
The first thing you need to do is draw up a very accurate scale drawing of your garage. All you really need is a front elevation and maybe one side elevation. The next step is to draw the cupola as an overlay using translucent paper that allows you to see through to the garage elevations. You need to get the scale of the cupola correct.
To help you get the scale right, try to locate some historical photos of buildings that have cupolas on them. Look for photos that are taken straight on so you can do your best to determine the proportions of the cupola to the main structure. If you make the cupola too small or too large, it's going to look horrible.
The next step is to decide whether you want the cupola to be decorative or functional. Many old cupolas were designed to ventilate the structures they adorned. The latest cupola I saw is going to be a magnificent lantern that's going to saturate a garage with all sorts of natural light.
This cupola is going to have a window on each face to allow natural light to stream into the garage below. It's going to be perhaps one of the most decorative skylights I've seen in my career.
If you just want your cupola to be decorative, that means you don't have to cut a massive hole in your existing roof. You can frame the cupola on top of your existing roof, but be sure you have solid blocking under the outside walls of the cupola. This blocking will transfer the load of the cupola to the roof trusses or to the roof rafters.
Most cupolas I've seen have a hip roof. These are pretty easy to frame. The most decorative cupolas I've seen have four gable roofs that meet in the center creating four unique valleys. This roof structure can be made by creating a simple gable roof on one axis of the cupola and then creating two gables roofs that overlay on top of the standard gable roof.
Be sure to get up to speed on flashing the gable to the existing roof of the garage. This is not that hard, but the sill flashings need to be soldered at the lower four corners of the cupola. Don't rely on caulk to seal flashing. I prefer to use 40-pound tin-coated steel for my flashings. It's easy to bend and solders like a dream.
Cupolas are very exposed to the weather. If you're going to use regular wood to frame it and clad the exterior, I'd highly recommend that you pre-paint all the finish wood before you cut it. Any cut ends need to have paint applied to them before they're nailed into place. This will really help extend the life of the cupola.
Many cupolas have decorative weathervanes that enhance the look of the tiny house. These weather vanes need both vertical and horizontal support. You'd be shocked at how the wind can cause these to bend if they're not supported.
Think about how you can include a piece of treated lumber inside the cupola that spans over two of the exterior walls of the cupola. I suggest treated lumber in case the hole around the weathervane leaks and water drips down the shaft of the weathervane. You don't want this piece of wood rotting over time.
I'd drill a hole part way into this treated piece of lumber that accepts the vertical shaft of the weathervane. Make the hole diameter in the wood just one-eighth inch larger than the diameter of the shaft so the weathervane is always plumb.
Many weathervanes have steel center support shafts. It's vitally important these are painted well before installing them. I'd recommend a great metal primer and at least two coats of metal finish paint before the vane is dropped down into the cupola.
Be sure the entire shaft is painted, even the length that's not exposed to the weather. You don't want rust seeping through the bottom of the cupola staining the roofing materials.
Perform periodic inspections of the cupola to ensure it's standing up to the weather. Don't underestimate the beating it will take from Mother Nature.
You can discover a cupola design video that discusses the scale and size of cupolas. Just type "roof cupola video" into the AsktheBuilder.com search engine.
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