Crown Moulding Widths and Cathedral (Rake/Vaulted) Ceilings.
by Joseph Fusco

If you would like to try this there are some things you need to know first. You can't use the same size moulding to trim the horizontal ceiling section as the vaulted (rake) ceiling section. The trim along the "rake" wall will have to be larger then the trim along the horizontal (level) ceiling section and have a different wall angle, but have the same profile. This profile will need to be scaled to coincide with the smaller eave crown. Since this is the case, this is a fair task to accomplish to say the least. The discussion that follows details how to determine the information need to perform the task.

To being I'll use a level (eave) crown of 3-5/8" wide that has an angle of 38/52° and a rake angle of 45° as an example, I'll go through the steps needed to calculate the rake crown width and the miter and bevel angles needed to cut both crowns.

Eave crown basic information for example:

1. Width = 3-5/8".
2. Wall angle 38°
3. Vault/Pitch angle = 45°

1. Calculate wall length of crown using the basic information on the Eave crown moulding.

a. Wall length = Width * cos(Eave wall angle)

i. Wall length = 3.625 * cos(38)

(1) Wall length = 2.8565 or 2-55/64"

2. Calculate Wall projection using basic information on the Eave crown moulding.

a. Wall projection = Width * sin(Eave wall angle)

i. Wall projection = 3.265 * sin(38)

(1) Wall projection = 2.2317 or 2-15/64"

3. Calculating the Wall length of the Rake crown.

a. Wall length = (cos((angle of eave crown) (-) (angle of roof slope))) * (eave crown width)

i. (cos((38) (-) (45))) * (3.625)

(1) (cos(-7) * (3.625)

(a) (cos(.9925) * (3.625)

(i) Wall length = 3.5979 or 3-39/64"

(ii) What is unique about this measurement is that it’s the same as the “width” for the Eave crown.

4. Calculate the Rake crown width.

a. Rake Crown Width = sqrt(2.2317² + 3.5979²)

i. Rake Crown Width = sqrt(17.9253)

(1) Rake Crown Width = 4.2338 or 4-1/4"

(2) It should be stated here that this would be the minium width that this crown could be. Since there is no advantage in making it bigger it is best to use the measurement.

5. Calculate the wall angle of Rake crown.

a. Rake Wall Angle = Tan-1(Wall projection / Wall length)

i. Rake Wall Angle = Tan-1(2.2317 / 3.5979)

(1) Rake Wall Angle = Tan-1(.6202)

(a) Rake Wall Angle = 31.81°

6. Calculating the Miter cut Angle for the Rake crown.

a. This is simple. Rake Miter = Vault/Pitch Angle - Eave wall angle

i. Rake Miter = 7°

7. Calulating the Miter cut Angle for Eave crown

a. This is fairly simple too.

i. Eave Miter = Tan-1(2.2317 / 3.5979)

(1) Eave Miter = 31.81 °

(2) This is the same as the Rake crown wall angle.

8. Lastly the Bevel cut angle is 45°.

 

 

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