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    
    
RISE DEGREES N/12  
    
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....

THIS IS HOW TO MAKE THE BASE CUTS WHEN INSTALLING THE CUPOLA ON ASYMMETRICAL
HIP ROOF, SLOPING FRONT TO BACK. (IF YOUR ROOF SLOPES GO LEFT TO RIGHT YOU’LL BE
CUTTING THE FRONT AND REAR BASE COMPONENTS INSTEAD AND TRIMMING THE SIDE COMPONENTS.)


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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