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Instructions for Cupolas

The History of Cupolas

The word cupola originates from Latin, meaning "small cupo" or little dome. Historically, it originally referred to the small dome typically sitting atop cathedrals which allowed light to enter the sanctuary. While many of those cupolas are still in existence, we are more familiar with the cupolas we see on homes, barns and stables as well as some prominent government buildings.

The first recorded use of cupolas was their widespread presence atop most Islamic architecture around the first part of the 8th century. They often topped minarets (a tall, slender tower attached to a mosque), and would have one or more projecting balconies from which the muezzin or “crier” would call the faithful to prayer. They were typically placed over the center sections or corners of mosques and as time progressed, cupolas were placed on domestic dwellings in the Middle East and India.

It has been speculated that the Moors (a mixed race of Arabs and Berbers from North Africa) brought cupola architecture to Spain. The influence of Islam reputedly advanced its spread throughout the rest of Europe as seen in the rounded domes of churches throughout Bavaria and Austria. The 17th and 18th century architectural style specifically highlight the “onion dome” as seen in St. Petersburg. Not only exceptionally decorative, the incline of the dome allows the snow to slide off the cupola, preventing caved roofs (still a common hazard in that part of the world).

Once cupolas were integrated into English domestic architecture, their spread to America was inevitable. Evidence of the cupola design is apparent if one observes American architectural design, particularly during the post-Revolutionary Federalist era, i.e., the Capitol Building in Washington D.C. Around this period, Americans wishing to distinguish themselves from their neighbors began to place cupolas on their residences and surrounding outdoor structures, such as barns or stables, posts and lanterns.

The design started to change slightly as people became more aware of the actual benefit of cupolas: allowing clear light and also covered ventilation pieces. Once the practical benefits were discovered, the cupola trend really took off. If you travel through America now – particularly around the New England area – you will find hundreds upon hundreds of cupolas still adorning homes, barns and other structures.

For years, cupolas have been an example of aesthetic design and practical utility. They are a classic, timeless accent to private homes and surrounding structures as well as public and government buildings. It’s glorious to see the past still sitting pretty atop the world’s finest buildings and maybe, on top of yours.

How to Select a Cupola

Cupolas can be described in many ways, however in modern times, they are typically classified as Functional or Ornamental designs.

Functional cupolas follow original traditional features and are equipped with vents that enable air to circulate through the roof they are mounted on. Functional cupolas are unequalled as passive vents for maximum air circulation because of the natural thermal chimney effect that they create. Functional cupolas can also appear quite ornate and always add a dramatic sense of detail to any shed, garage, home or shop.

Ornamental cupolas can also greatly enhance the look of any structure but do not vent the roof they are mounted on. This group of cupolas usually come equipped with windows and not vents. In most cases, ornamental cupolas can also be illuminated at night to create an eye catching effect. In some communities, larger illuminated cupolas can become well known landmarks.

In all cases, cupolas of any type increase the perceived value of any structure.

After deciding on your preference for an ornamental or a functional cupola, the size of the cupola you purchase is critical. Cupolas are typically described by the size of their base. A cupola may be an 18" by 18" model or a 36" by 36" model as common examples. A good rule of thumb to follow is to consider a cupola that offers 1 inch of base for every foot of building. In other words, an 18" by 18" cupola will look acceptable on a roof line of up to 18 feet. For a 24 foot roof line, a 24" cupola is appropriate and so forth. It is always better to install a slightly oversized cupola as opposed to one that appears too small on your roof. If for example, you have a roof line that is 21 feet, it's better to install a 24" cupola as opposed to an 18" model.

Lastly, consider your budget. Although 8 sided cupolas look impressive, their intricate construction costs substantially more. About two thirds of all cupola purchases are for standard 4 sided models.

How to Install a Cupola

Determining Roof Slope

You can purchase an angle finder at your local building supply store for a few dollars. When placed on your roof, it will indicate the angle of the roof in degrees, a 4/12 roof for example would have a slope angle of 15 degrees.

A simple angle finder


Make sure that the angle finder rests squarely on a shingle if you have a shingled roof, and not across layers of shingle rows. This will not give you an accurate reading of the roof pitch.

Record the roof pitch angle and prepare to cut the base components to fit your particular roof.....

If you do not have an angle finder on hand, a yardstick as well as a four foot level will also work for you.

1) Place apiece of masking tape 6 inches from the end of your level and then 36 inches away from that mark, at the other end of the level.

2) Place the level on the peak of your roof and when you have it level, measure the height (or rise) of your roof at the opposite mark three feet away and down the slope of the roof. The measurement will give you the rise over a 3 foot distance of run. 

In the previous diagram, the rise measured is 12 inches. Therefore the angle of the roof is:

12 inches/36 inches times 45 degrees = 15 degree roof.

This is also a 4/12 roof in our case.

When you determine your rise over a 36” run, use this simple formula to determine the roof angle:

(Rise in inches)/36 inches times 45 degrees.

We use 45 degrees since a 12/12 roof has an equal rise over run and thus the multiplier of 45 degrees is (1)....

Here is another example of  rise over run calculations:

An 18” rise over a 36” run has an angle calculated using our formula:

18/36*45 degrees =  a slope of 22.5 degrees This is also a 6/12 roof

Roof Slope Calculations over 36" run    
12 15 4.00  
14 17.5 4.67  
16 20 5.33  
18 22.5 6.00  
20 25 6.67  
22 27.5 7.33  
24 30 8.00  
26 32.5 8.67  
28 35 9.33  
30 37.5 10.00  
32 40 10.67  
34 42.5 11.33  
36 45 12.00  
N/12 is roof slope expressed as standard rise    
over 12 foot run    

Now that you’ve determined the roof angle, you can nor cut your base to natch your individual roof. Remember that if your roof is not symmetrical front verus back, or side to side you’ll need separate angles for each roof....


Mark the center of the side base components and temporarily assemble the four base components. Turn the base on its side and use a skil saw to make the angled cuts. NOTE THAT THE CUT STARTS AT THE FRONT OF THE FACE OF THE FRONT AND REAR COMPONENTS.  Since the skil saw blade is round only cut until the two cuts meet at the peak, and then finish the cuts with a hand saw.  This will prevent over-cutting on the faces of the side components.

Now disassemble the base and on a table saw, tilt the blade to match the slope angle and cut the bottom edge of the front and rear base components.

Cut the bottom edge of the front and rear at the slope angle


Start the cut at the FACE of the front and rear base components.

Finish the angle cuts with a handsaw to prevent over-cutting and use a skil saw or table saw to cut the bottoms of the front and rear base components.

At this point you should have the roof, vents and lower vent brackets assembled. Also you should have the base assembled and cut to match the slope of your roof profile.

You can determine exactly where your cupola will be installed. Traditionally, they are mounted on center at the peak of the roof. Although this cupola can offer functional venting, you may add openings in your roof to create a venting effect or, simply install the cupola as a purely ornamental enhancement.

If you decide to make the cupola a functional vent, create four 6 by 6 openings between rafters.

Mark where you will place the cupola and then install 8 3” by 3” by 1” metal “L” brackets using 3/4” wood screws. Make pilot holes to prevent cracking. See diagram for positioning of “L” brackets.

Just prior to installation, run a thick bead of white caulking on the underside of the base to enhance the seal and then screw into place.

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