Click to the right for the section you are interested in:

1.  Basics of Crown Molding on Vaulted Ceilings:

Putting crown molding in corners that involve vaulted ceilings requires considerable insight and careful planning. It should be tackled only by someone who is familiar with putting up crown on regular flat ceilings! I don’t profess to be an expert in this area, but I have done some experimenting that I want to share with you.

Don’t be discouraged but be aware of some of the following problems:

To be sure, some of these problems can be resolved with some of the following ideas. However, keep these limitations in mind when you are considering your project. And if you don't understand the first and second comments, read on.

Let's try an experiment: Visualize putting a 2x4 along a wall that intersects with a ceiling that slopes upwards. The top of the 2x4 rests against the wall/ceiling corner, and there is a gap between the ceiling and this "molding". To eliminate the gap, you rip the 2x4 at an angle that corresponds to the vault angle. Now it fits snugly to the ceiling but is higher on the wall.

This same wall makes a 90° turn and you put a 2x4 against the sloping ceiling. You don’t need to rip this board; it fits fine. But where the two meet in the corner, you have a mismatch! You need to either trim the sloping 2x4 or cut and insert a triangular piece as shown with the dotted line below.

Now look at other wall-to-ceiling intersections (such as a beam along a sloping ceiling) and see how a simple board can create gaps and/or mismatches. It should be quite clear that to solve this mismatch becomes more complex when you substitute crown molding for the flat board!

2.  Intersections:                                                                

Intersections of vertical walls and sloping ceilings come in several different configurations. Let's take a closer look and try to classify them in more detail.

In Part 1 Crown on Horizontal Ceilings we referred to type A-1 and A-2 intersections. Now we are dealing with class B-1 through B-5. Here are some of them graphically as well as a photo of such situations. Each needs to be dealt with individually.

• B-1. Horizontal run meets vaulted run, sloping upwards, inside corner b between 0 and 180 degrees)
• B-2. Horizontal run meets vaulted run sloping upwards, outside corner (b between 180 and 360 degrees). Example: outside corner of columns.
• B-3. Horizontal run meets vaulted run sloping downwards, inside corner (b between 0 and 180 degrees). Example: inside corner of beam.
• B-4. Horizontal run meets vaulted run sloping downwards, outside corner (b between 180 and 360 degrees).
• B-5. Two vaulted runs turn in the same plane. Note this is the same cut as A-2, a downwards turn.

See photo above: 

Next series:

See photo below:

This is an example of an alcove with a flat ceiling that joins a vaulted ceiling. The intersection to the left is an inside corner (wall angle equals 135°). It is a type C-2 intersection. To the right is a type C-3 (wall angle greater than 180°).

Note that the list is by no means complete. We can add more as the occasion arises. However, this outline should help to identifying the more common corner joints you will encounter. When you prepare a plan view of the project record these intersections and think about how to tackle them during the design stages. Again, you will find that each of these different intersections require a new approach.

Vault Angle

We need to define one more parameter: the vault angle q. This is the angle the ceiling makes with a horizontal line. It should be determined at several locations using the wall angle gauge, for instance, and averaged. Make the measurement from wall to ceiling and subtract 90º.

In addition to q, the length along the vaulted ceiling needs to be measured. Of course, in this case it is not the plan view dimension, but the actual length of the intersection of wall and ceiling. You will also find that for most intersections you may need to make measurements along the wall. I explained this in Part 1, but let me repeat the sketch to show you. It is an important point.

3. Resolving the Dilemma of Vaulted Ceiling Intersections:                                                                

Intersections of vertical walls and sloping ceilings come in several different configurations. Let's take a closer look and try to classify them in more detail.

In Part 1 Crown on Horizontal Ceilings we referred to type A-1 and A-2 intersections. Now we are dealing with class B-1 through B-5. Here are some of them graphically as well as a photo of such situations. Each needs to be dealt with individually.

The dilemma I refer to is that when the same crown molding comes together from two different directions and with different angles from the horizontal, the parts will not match. Something has to be done to make the joint smooth and uniform.

To be sure, ceilings with a very small vault angle can be treated with lots of caulk and "popcorn" type of ceiling finishes. There is a book on the market that shows just that. I doubt, however, that you will find many ceilings with a 20° angle and the old fashion popcorn finish. On the following pages you will see my models where the angle is 30º and the only "filler" was paint to make contrast for the photographs.

I present you with four methods that can be considered. They all have their limitations and problems, but I leave it up to you to choose which is best for your installation and skill levels.

Each of these methods has a sub category (case) that depends on the type of intersection.

I will concentrate on Method 1 and 4. The other two, or a combination there of, have very limited usage but can resolve tricky problems. Note also that for methods 1 and 4 the molding is oriented with the lower heel flat against the vertical wall.

Method 1. Use of a transition piece(s).           

First notice that the horizontal piece, Part H, has its top heel trimmed in order to eliminate the gap at the ceiling. Now consider the strange triangle piece. If you were to simply butt the two long pieces together in the corner, part S would have its lower heel below that of part H. To take care of this mismatch, Method 1 uses the transition piece. 

To the left we have a standard inside corner where Part H and the transition piece meet. It a regular Type A-1 joint. See Part 1 Crown on Horizontal Ceilings.

For edge 2 we have a type B-5 (or A-2) joint. It is as if the molding is turning upwards. The cut is a function of the vault angle q, the spring angle g, and the wall angle b. Put all three of these values into the spreadsheet Excel Spreadsheets for Calculating Angles) and it will give the miter and bevel angles for cutting the crown lying flat on the miter saw table. Notice the offset, F, in the sketch above. It marks the point where the slanted part stops and it determines where to make the wall measurement. The spreadsheet will provide the value for F, or you could make a mark after cutting the transition piece and holding the parts in place.

This method can be used for vault angles ranging from 0 (a flat ceiling) up to about 45 degrees. The reason for this limitation is that the horizontal molding needs something to bear against at the top. If the angle becomes too steep there will be a large gap at the top. In the sample shown, I removed part of the top edge so it lies against the sloping ceiling. This can be done with a block plane, a band saw, or if you have it available, a jointer. Keep in mind that the calculations for edge 2 depend on this "removal" (it uses the normal profile of the crown as if it were installed on a flat ceiling).

• Case 2. Negative vault angles; ceiling slopes down from a vertical surface.

For example, this could be a beam or wall near the top of the ceiling. It is a type B-2 intersection as shown in  previously. The triangular transition piece looks similar and serves the same purpose as in case 1. However, the top heel need not be removed. Note that edge 2 makes a "vertical" turn, with the turn angle b = 180 –q

• Case 3. Same as case 1 but now the heel is not removed.

Notice, from the sketch below, that in order for the bottom heels to line up, the slanted crown has to be lowered. This creates a gap at the top that has to be filled. For steep vault angles this can amount to as much as ½ inch; more than you would want to fill with caulk. A wooden shim can be used for short segments. To calculate the filler thickness, you have to provide the width of the top heel for the molding you are using.

• Case 4. Heel not removed; use two transition pieces.

The first transition would make a horizontal turn and the second an upward turn to connect the heels. Technically there is no way to do this in one step with the same molding shape.

You might say that this small gap is not worth fooling with and that the molding (Part S) can easily be bent to meet edge 2. The caulking would take care of the mismatch. I would heartily agree in most cases. But the idea of using two pieces can be used when a real problem arises. In particular it leads me into the general situation that:

When two sections of crown molding meet from two different directions and with different profiles, two transitions need to be made.

The following case demonstrates how two transition pieces can solve an outside corner for vaulted ceilings. Again, I would not recommend this! It is difficult and does not really look attractive. But it makes the point that transition pieces can technically have a place.

• Case 5. Outside corner; the crown along the sloping ceiling turns into a horizontal run.

Method 2. Using molding of two different sizes. 

Some of the more common crown shapes are available in different widths. The common Colonial style, for example, comes in seven sizes ranging from 1.63 to 7.25 inches in width. By combining two of these it is often possible to solve vaulted ceiling problems. Because the profile of the slanted piece is larger than the horizontal part , you should put the smaller size on the vaulted wall.
The right combination of the two depends on their widths and the vault angle. The spreadsheet tabulates seven different sizes of crown molding available from Pacific Millwork in MDF and pine. You can have a total of twenty-one combinations; however, only about seven are of practical interest (vault angles ranging from 23 to 44 degrees).

All others would be for very steep angles. You will find this to be a very versatile technique for types B-1, B-3, C-1 and C-2 intersections.

The sample shown to the right was made with two pieces that had widths of 3.63 and 4.25 inches. This would calculate out to be for a vault angle of 31 degrees. My model had a 30º angle. Close enough!

Because the two parts have different dimensions, they have to be treated individually. The wall angle is still 90º, so the horizontal piece has the standard A-1 cut. The slanted piece, however, should not be cut the same way. It is a compound angle cut and is similar to the rafter example I cover in Part 5 Compound Angle Cutting, except now the "rafter" (or slanted crown) comes from above. It is an inside corner with r = 90º. The angle b has to be calculated in order to get the miter angle M and bevel setting B. The spreadsheet does this for you. Notice that there are numerous cases with different calculations depending on what type of intersection you are dealing with.
Here is an other situation where coping works better. Have the sloped Part S go straight to the vertical wall and cope the horizontal piece

Caulking will be necessary because the shapes are inherently different. But this is not too bad if the right combination of angles happen to fit your vault angle. Even a few degrees difference will not be noticeable. When the angle is off by more than 5 degrees you could still consider this method if you combine it with Method 3: Tilting the crown.

Method 3. Tilting the Crown Along the Vertical Wall:

Another way to make the two parts meet in a corner is to tilt the horizontal part against the wall. This works for small vault angles (20 degree or less). The limit is when the piece is flat against the wall and the vault angle and the crown spring angle are the same. The main problem with this method is that it doesn't look right. The horizontal parts (most of the time the more important and most visible) look like they are glued to the wall. In addition, unless you trim it, there will be a gap along the bottom of the horizontal part that needs to be filled.

The intersection of the slanted part and sloping piece is a very complex matter. It involves how high the horizontal part is against the ceiling (a function of q), how much the part is tilted (a function of the crown dimensions) and the angle b. I have not provided a thorough analysis of this.

When you combine this with Method 2, make some samples and experiment to find the best cutting angles. The spreadsheet provides a few empirical solutions and some suggestions. But here trial and error will dominate. The sample in the photograph above was made by coping the horizontal piece.

Because of its awkward slant and intersection, I would consider this to be more of a last resort or a way to solve a particularly tricky problem, rather than a "Method". When used by itself, it would be limited to short sections and small vault angles. It would not be my first choice unless, again, it is used in combination with Method 2.

Method 4. Modify the corner with a block or other means to avoid the crown parts from intersecting:

When the intersection is complicated or none of the above methods seem appropriate, consider adding a block or some decorative piece to the corner. Don’t fight the misalignment and angles; have the parts mate with something that is easier to deal with. Will you be adding columns, cornices and other decorative designs? If so, try to insert a stop to the crown molding and have it continue on the other side.

Here is one example. A 4x4 block, mitered to angle q, is nailed into the corner. Now the molding can be cut straight across for the horizontal run. The vaulted piece is cut like a type B-5 or A-2; the crown looks like it is turning upwards. A more decorative approach is to add a couple of pieces of the same crown molding to the bottom of the block, as shown below.

An outside corner is a real challenge. Even adding a block can become a bit more involved. I show one example for a right angle turn. Instead of having a very wide block, I took a piece of 4x4 and turned it 45 degrees. Now it faces into the room at an angle. This looks more balanced but requires some extra cutting. The drawing shows that the back was bevel cut on my table saw to provide clearance for the wall. I had to do some extra chiseling to make it fit just right. In addition, the surface that is against the ceiling is now a compound angle cut! Again, see the spreadsheet for calculating the miter and bevel settings for the saw. Some smaller crown pieces were added to the bottom and here is the result:

Now, the straight or horizontal molding has a simple A-1 intersection with b = 135º. The slanted piece, however, is more complicated since it now meets the block at two different angles.
I have included part of the analysis in the spreadsheets (section on compound angle cutting). It involves the rotation of parts from 3D onto a plane (see the second example about rafters). In this case the line AB is our crown molding. As the part is rotated to the right, the effective crown angle, g, decreases by the value of q. In my example, where the crown angle is 52º, g becomes 52 – 30 = 22 degrees. Using the spreadsheet for this case, we get b = 285º and M = -50.1 and B = -17.2 degrees. The minus signs only mean that you have to pay close attention as to how you make the cuts. Here is where your 3D vision plays a role.
Note that the angle M is too large for most miter saws. I used my table saw for this cut. Don’t try to cut the part on the miter saw by rotating it! It is too dangerous. Even with a clamping fixture as one author has suggested, cutting at this sharp an angle can result in some serious injuries. If you don’t have a table saw, use a hand saw, rough cut the miter and use a disk sander, or file it by hand.

Because of these complicated intersections it is again advisable to see how the corners can be modified in other ways. Adding a column or cornice can often help to make the overall design look a lot smoother and attractive.

Disclaimer: The information in this document has been provided to you free of charge and for your consideration only. The author has prepared the information in good faith and believes it to be correct and helpful. However, he takes no responsibility for anyone misusing the data, spreadsheets, suggestions or any other information contained herein. The reader is advised to take every precaution and apply all safety steps recommended by the manufacturer for the use of saws and other tools referenced herein.

Author: Jacob Brentjes, December 2005