Crown moulding with angled ceiling

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Spanish Is it possible to take an out-of-kilter ceiling into account? November 22, 2003

Question
I've seen the discussions on finding angles for cutting crown flat and for cutting it "upside down and backwards," etc.

However, these only take into consideration the walls being 90 degrees or something other than 90. What about when a room has a ceiling that rises/slopes with say, a 2.5 degree angle? Is there a formula that can take that into consideration?

I understand many would say that putting crown around a room like this would be a design error.

Forum Responses
(Cabinet and Millwork Installation Forum)
From contributor A:
If I understand your theoretical room correctly, then it is indeed a design error. Not because of personal taste, but rather because you physically cannot make a right angle turn from a sloping crown to a horizontal plane crown. The result of making such a transition is that the horizontal crown needs to be a wider profile version of the slope side version. For example, if a 3 1/2" face crown is traveling down the sloped ceiling, the perpendicular wall with a horizontal crown will end up being in the neighborhood of a 4" face. Just picture trying to make that inside corner joint and you should be able to see this. The top edge of the crown in the horizontal plane will need to be pushed out from the wall further than normal since it has to meet up with the top edge of the sloped crown, which is rising up the wall as it moves away from the corner. Hence, a similar but larger profile is required.


From the original questioner:
I think I realized the problem here shortly after I first took the job, and then talked myself out of it somehow, thinking - nah, it has to be able to be done somehow! Then, I found a website with a solution which looked a bit strange and complicated and was hoping it wasn't the only solution. I think I'll play around with it and see if I can get it to work.

This way it looks like it can be done and with the same size moulding all around.

In essence, it seems that the way to get around the problem of the end profiles being different lengths due to the ceiling slope or vault, is to make a very small third piece that fits in the corner. It comes off the wall with no slope as if the line of the adjoining wall was horizontal too. To make there be no gap at the top on the sloped ceiling, this small piece is cut to a point at the top where it meets the piece on the "normal" wall. Then, from this small piece, it is possible to join to the piece of crown on the sloped/vaulted ceiling.

Doubt I made that clear, but it's what it looks like in the pictures, and there are clearly still some angles to figure out.


From contributor A:
We run into this on curved crown pediments on cabinet work at least once a year. Some architect will draw it up for a customer with the arched front moulding going all the way to the sides of the cabinet, and then the same crown profile turning and going back along the sides to the back of the cabinet. It doesn't work. You have to have horizontal "wings" transition off the arch before making the 90 degree turn to the back.

From contributor A:
Oddly enough, just this morning we ran into this issue again in the shop.

Upon closer examination I'm coming to the following conclusion... I'd appreciate anyone who has examined this issue to submit their thoughts as well.

If coming down at an angle such as a roof rake edge and turning back 90 degrees so as to make an outside corner, I'm of the opinion that the profile of the horizontal moulding will be smaller than that of the rake edge moulding.

If coming down the ceiling edge of a vaulted ceiling and turning in o0 degrees so as to make an inside corner, I'm of the opinion that the profile of the horizontal moulding will be larger than that of the rake edge moulding.

We are starting a crown moulding in Bubinga that goes on the top of a compound curve top of a corner cabinet (curves out and up). It will be up to the shop that has sent this piece to us to make to miter the straight wall ceiling crown into the ends of this curved crown which is coming down at an angle much as a cathedral ceiling crown situation. I'm pretty confident that if they want to miter it they will have to make the wall crown a larger profile, or change the profile they want us to cut so that it is about 1/2" smaller.

Any other thoughts on this?


From contributor B:
I work for a company that does both millwork and mouldings, and we make custom rake crowns all of the time that work with the horizontal crown moulds. The rake crown has the same profile, but is wider. The width varies according to the pitch.

From contributor C:
On the regular wall (not raked), hold the crowns bottom flat area tight against the wall (just as it is normally installed) and move it up until it is tight against the ceiling. Mark the top and bottom edges on ceiling and wall. Now move to the rake wall. Place crown on the wall and roll until the bottom edge lines up with the bottom edge mark on standard wall. Again mark the top and bottom edges. The intersection of these marks will be your miter setting. Adjust bevel setting to close face of moulding. Should use same settings throughout room - inside or outside miters. I know this is the super low tech/quick and dirty approach but it works quite well. I've installed lots of crown (we have a lot of lake houses around here with vaulted ceilings and window walls) on these ceilings.

From contributor D:
Although I prefer corner blocks, many customers don’t like them. I then use the small extra piece that is coped and mitered. It is easy and quick.

From contributor E:
I think the answer to this question is a little simpler than it appears, as long as the slope isn't more than about a 4/12 pitch. Imagine that you assemble four walls of crown on a bench but exactly as they would be if there were walls. If you pick this square ring of crown molding up, you could tilt it at any angle up to about 30 degrees (before the top rear edge would hit the wall). The only problem with this solution is that technically the crown on the lower and upper level sections wouldn't be at 30 degrees. On smaller slopes I doubt it would be very noticeable. If the level runs are coped into the angle ceiling sections, then the joints will be the same as if the ceiling were level.

From the original questioner:
Thanks, contributor E. I still haven't gotten around to starting this, and your suggestion seems to be worth looking at in my application. I guess the larger the slope, the larger the gap at the bottom of the crown on the lower horizontal run, and the top of the crown on the higher horizontal run.

While the slope in this application is very visible when just looking at it in the room, I measure it to only be a couple of degrees. (I haven't tried to determine the slope in terms of rise/run). Therefore, I've imagined that the third piece in the corners for the above solutions would end up being extremely small, which made me wonder how I'd cut it.

Some day, hopefully soon, I'll get around to experimenting with this in my shop before I actually try to do it.

It seems like you'd want to install the angled walls first, cope or miter the horizontal runs as if there were no slopes and fit them to the angled pieces to determine their slightly altered position on the wall.


From contributor F:
The solution is very simple. Keep the separate pieces of crown oriented to each other as if the ceiling was not vaulted. The only adjustment that needs to be made is at the bottom of the bottom run and the top of the top run. They will be pushed away from the wall (bottom run) and ceiling (top run) by the back of the crown. Just take off the back point (for lack of a better word) with a plane and the crown will fit nice and tight. I have run miles of crown this way and it is the cleanest, fastest way to do it.

From contributor G:
Come on, guys. Don't over-think, don't complicate. You're making two corners. Use three pieces.

From contributor H:
Get a compound saw and a trig calculator and use this:

M is the miter angle
B is the bevel angle
Tan-1 is inverse tangent

M = Tan-1((Tan * (angle of wall) * (Sin * (angle of crown))

B =Tan-1(Sin * M) / (Tan * angle of crown)

Yes, it will work for vaulting areas!


The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor I:
Contributer H seemed to have a few deceprencies with his notation and a division by two missing. Also, I found the miter equation go be reversed but center about 90 degree wall angle. I believe I have properly corrected these errors. Note: If you do the calculations on a spread sheet, remember to convert to and from radian measure.

Miter: Normally a board is cut at 90 Degrees. The miter angle is the deviation from 90 degrees.

Bevel: Normally the saw blade is vertical when cutting. The bevel angle is the deviation from vertical.

C is the Angle of Crown Moulding leaning away from wall - Degrees
W is the Angle between walls - Degrees
M=ATAN(COT(W/2)*SIN(C)) This gives Miter Angle - Degrees
B=ATAN(SIN(M)/TAN(C)) This gives the Bevel Angle - Degrees

The equations for a Lotus 123 spreadsheet would be as below.

Row - Column
- F - G - H
2 - @PI/180 - Degrees to Radians
3 - C - Input - Angle of Crown Moulding leaning away from wall - Degrees
4 - W - Input - Angle between walls - Degrees
5 - M - @ATAN(@COT(G4*G2/2)*@SIN(G3*G2))/G2
6 - B - @ATAN(@SIN(G5*G2)/@TAN(G3*G2))/G2

Install the above into the spreadsheet at F2. Start with the blank box. Convert the text into equations and remove the "Input" words by inserting numbers.


Comment from contributor T:
It can be done. I used to build custom homes that used 4 3/4 crown for drip edge. It does take a third piece. We call those cuts "bastard cuts". Remember, all the faces of your mitres must be of equal length. After that, does it matter?
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