Vaulted Ceilings and Crown Moulding
By Joseph Fusco
Revised

Watch the video part 1
Watch the video part 2

 

A few years ago I wrote a piece on doing crown on vaulted (rake) ceilings (Photo1). I applied a technique where I used two of the same profiled moulding's but at different scales. Even though this approach is “technically correct” it almost always proves problematic.  First there is the issue of finding or making the moulding that’s needed and there is a fair amount of mathematics involved in order to get things just right. Like I said in my original article; this technique isn’t for the faint of heart.

Well with that in mind I set out to do something that a lot of other carpenters have done and that’s to use a transition piece as opposed to two different sizes of crown. The transition is made from the same identical crown and requires far less fancy calculations. As a matter of fact I’m going to show you a way to use as little math as possible.

The methods I illustrate here are for cutting the crown moulding transition piece in place on the mitersaw, if you are going to cut on the flat these methods would not be applicable.

For those who need to cut on the flat I describe a method so you can transpose your in position numbers to flat numbers at the end of the article. There is also a short video Tip-It™.

The first step is to mark some lines on the corner where the crown goes up the rake wall from the regular wall. You can easily do this by holding a piece of crown against the regular wall and then the rake wall. If you hold the moulding square against the regular wall and just touching the vaulted ceiling you will notice that at the top of moulding where it meets the ceiling there is a gap (Photo2). This gap is due to the  ceiling being sloped and not “square” to the wall. All standard crowns are milled to “bed” between a wall and ceiling that meets at 90°. That’s why some are called 38°/52° and 45°/45° crowns. The wall and ceiling angles on the crown form a 90° intersection.  There are two ways to handle this, the first being just to caulk or plaster it and the other is to remove some of the material on the top backside of the crown. The gap size is a function of the roof pitch so ceilings with low pitches might fare well with either caulking or plastering whereas on steep pitch ceilings the crown would need to have material removed. You can use a plane, belt sander, tablesaw or grinder to remove the material and which method you choose will depend on what’s most comfortable to you. Once again, you’d have to decide what’s best in your particular situation. If you decide to remover material from the crown, you should first do it before scribing the line at the bottom of it. If you scribe it before, the location will change as the moulding will move "up" to touch the vaulted ceiling changing the location of the level line and thus the intersection point.

Having made your decision, place a piece of crown (un modified) against the vaulted ceiling and the rake wall below it so the crown beds to the wall and ceiling at the correct spring angle, then scribe lines along the top and bottom of the moulding. Then from the bottom part of the moulding the you scribed on the regular wall, draw a level line across from the corner level until it crosses the line you drew on the bottom of the crown on the rake wall (Photo3). The moulding on the rake wall may go past the level line intersection in some cases depending on the slope of the ceiling. Don't worry about it.

The lines that you scribed show the relationship of the moulding's on each side of the corner (Photo4). This will help you layout the cut for the transition piece. This transition comes out of the corner level with the bottom of the moulding against the rake wall and its inside corner cut is the same as any inside corner cut on a standard ceiling (a 90° corner with a 45° miter cut).

Holding the transition piece with its inside corner cut (already cut with a 45° miter and cut upside down and backwards in the saw) into the corner and along the level line, you can see where it intersects the bottom scribed line on the rake wall. Marking this point in conjunction with the top of the inside cut will give you the angle you now need to cut the outside corner cut with (which is cut with the transition piece seated in the saw as it sits on the wall) to make the transition from level to rake moulding (Photo6). It's important to mention that the miter cut from transition piece to rake piece is treated like an outside corner cut.

 

 

The location of the mark at the top of the moulding will vary depending on how your moulding is profiled. Usually there is a shoulder that forms a plumb edge; you’d want to mark the angle line starting just below that edge (Photos7&8).

Now the purpose of doing this is to avoid having to measure the angle of the vaulted ceiling directly.  Another way to avoid measuring the ceiling would be if you knew what the pitch of the ceiling was to begin with. In my case I knew that the roof pitch was a 9/12 which is ~37°. The way you derive that is by using the simple formula; vault_angle = Tan^-1(9/12). You would then take half that angle to get the miter angle which would be ~18.5°.  If you didn’t know the roof pitch off hand and for some reason you didn’t want to layout the line, you could always use either a bevel square or angle finding device like the Bosch Digital Protractor. Though even with the use of such a device you’d still have to subtract 90° from the displayed angle to deduce the vault angle. Diyer’s may not what to invest the money for such a device although it’s well worth it if you plan on doing a lot of crown moulding.

Another simple method of finding the pitch angle is to use a bevel square and level (or level line) in combination (Photo9). This is an improvement over the more traditional method of using the bevel square to measure the vault directly. That method required you to first measure the entire vault, determine what that angle was than subtract 90° from it. By using a level or level line you eliminate the need to subtract 90° because the level does it for you. What's left is a way to read the angle that’s produced and that job falls to your compound miter saw (Photo10).

The job of determining the vault angle is pretty straight forward with just one twist, you need to rotate the bevel square on the miter saw to get the correct angle. If you were to place the bevel square with either side up against the fence you’d be reading the complement of the vault angle. Furthermore, since most vault angles are less than 45°, it would mean that it’s complement would be great the 45°, which is beyond the capacity of most saws to measure. The simple solution to this is to place a square block against the saw fence and then place the bevel square against the block effectively rotating it 90° (Photo11). Then swing the saw table until the blade is aligned with the saw slot to determine the vault angle. Dividing that angle in half would than produce the miter angle. You’d than set your saw to that angle to cut the outside corner of the transition piece holding it “right side up” in the miter saw.

So, you’d have to take all those steps to determine the vault angle if you didn’t want to just lay it out. It’s clear to me that laying it out is both a simpler and faster method. As stated above once you mark both locations on the transition piece, it’s than just a matter of setting the saw to cut the miter correctly. Just like almost everything else in this work, that’s pretty easy as well.

Draw a line connecting both marks you’ve made on the transition piece making sure to start just below the profile at the top and extending to the “inside” mark at the bottom (Photo12). If you draw a straight line on the bottom of the moulding from back to front, you want to align the line with the back tic. Once you have drawn the line place the piece in the mitersaw “right side up”. Swing the table of the saw until it aligns with the bottom tic mark and that the saw blade aligns with the location at the top of the moulding. Once this is done the transition piece is in the correct position to cut the miter. You can than cut the piece (Photo13).

Cutting the crown moulding that goes up the rake is now just a matter of positioning it correctly in the saw and making the miter cut. Since you now know the miter angle, swing the table to the other side of zero to the same angle. Place the moulding “right side up” and cut the corresponding outside miter cut (Photo14).

It’s important to note that I was cutting a transition piece for a rake way going up to my left. The piece was cut by being on the right side of the saw blade a Photo12 illustrates. This means that the “save” piece for the moulding going up the rake is on the left side of the saw blade as Photo14 illustrates.

Once you have all three piece cut that make up the complete transition from corner to level to rake there is still a little work left before they will all fit nicely together on the wall. The first being that you most likely will need to remove a bit of stock from behind the moulding going up the rake and then you need to cut a bit off the top profile of the moulding going into the corner. The reason for this is that if you don’t the moulding going up the rake will interfere with the moulding going into the corner.

In reality you are making a small cope cut on the moulding going into the corner to allow the rake moulding to pass by it as it goes into the corner.

Once you have complete this, with just a little bit more “finessing” you should be able to fit the transition quite well.