Canadian Woodworking

Installing crown moulding – part two

Author: Roger Knapp
Photos: Roger Knapp
Illustration: James Provost
Published: December January 2010

Sloped ceilings are quite popular in houses – adding crown moulding really adds to the value and the beauty of the home.


Unfortunately, many installers do not attempt this part of the moulding project because of the challenges that the sloped ceilings present. In this, part two of the crown moulding series, I will demonstrate how I calculate and install crown moulding on sloped ceilings and vaulted/cathedral ceilings. You will see that the combination of horizontal and vertical turns are not at all difficult and can be achieved with great success.

Let’s begin with the tools required. Along with the tools listed in part one (Oct/Nov ‘09, issue #62), you will need a tall sturdy ladder to safely reach the peak of the ceiling. You will need to reposition your crown stop on your mitre saw so the moulding can be placed right-side up. If you have a shop-built stop, as I used, all you need to do is drill holes to reposition the jig so that the moulding is positioned right side up with the top flange against the fence and the bottom flange against the stop.

Once you have your crown stop repositioned I recommend you take the time to cut four patterns that you will keep at the saw for reference. Make them about 4″ long and use a 20° mitre setting for the cuts. Label them accordingly:

Vertical surface – right inside

Vertical surface – left inside

Vertical surface – right outside

Vertical surface – left outside

Making use of these patterns will avoid the confusion during the saw set-up for the compound mitre cuts. Woodworkers using a compound mitre saw and cutting the moulding on the flat will also find these patterns indispensable.

Let’s look at the differences between the horizontal crowns that were installed in part one of this series and the crown that will be installed on a sloped ceiling. With the horizontal crown we measured the corner of the walls to determine the angle of the cuts. Now, with a sloped ceiling, it is the ceiling turn or (ceiling corner) that is measured to determine the angle of the cuts. I use the term ‘ceiling turn’ because I think it best describes the crown changing angle on a vertical wall surface. The ceiling turns can occur as an inside or outside angle and are always measured with an angle finder. Because we are measuring the ceiling turn angle, the cuts are performed with the moulding set right side up in the saw. To make this clearer, take a pair of the patterns you have just cut and hold them together to close the joint and you will see that the bottom flanges are on the same plane.

Standard crown is designed to fit to a wall that has a flat ceiling, and when it is placed to a sloped ceiling there is a large gap where the top flange contacts the ceiling. To correct this, the back of the crown must be reshaped. You need to measure the angle of the sloped ceiling to the wall. Then cut the back of the top flange with a block plane or rasp to create the same angle as the slope. The bottom flange is never modified, and remember, it is critical to maintain the correct spring angle when the crown is held against the wall. What needs to be noted is that the modified crown rests higher up the wall and the crown depth block cannot be used to locate the position of the lower flange. I find that a short piece of the modified moulding placed against the wall, held at the correct spring angle, can be used to locate the lower flange and then pencil mark the wall.

In the lead photo you can see that I have installed the horizontal moulding and I had the crown turn the corner and run it up the sloped ceiling. This joint is a combination of wall and ceiling turns and is accomplished by cutting and installing a wedge-shaped transition piece between the horizontal and sloped crowns and is performed as follows.

In the illustration I have laid out the pieces. Joint B/B is a typical 90° wall inside corner for the horizontal moulding and is cut upside down on the saw. Now we need to calculate the angle for Joint A/A, which is a ceiling turn for the sloped ceiling moulding and must be cut right-side up on the saw.

Of course, most saws do not have a 74° mark on the mitre saw scale so you subtract 74 from 90 (90-74=16°) The reason you subtract 74 from 90 is because both angles are measured from the fence and you want a reading from the “0” position on the scale. 16° is the mitre setting on the saw.

It seems like a lot of math, but it works. Just make sure you measure the ceiling slope angle accurately in the first step and make the calculations as described and it will work out. The transition piece has no length and must be cut to point. Make the cuts for joint A/A and remember that this is a ceiling turn joint and must be cut in the “right-side up” position.

Glue the transition piece to the horizontal crown with fast-setting glue like five-minute epoxy, as nailing would surely split it. Fit and install both crowns using the normal installation procedure, making sure to maintain the spring angle to ensure a tight fit at the transition piece. You can use this procedure any time the wall meets an upward or downward slope ceiling. Only the mitre cuts will change to accommodate an inside or outside ceiling turn.

The last joint is the peak of the cathedral ceiling. This is a ceiling corner joint and again the crown needs to be placed right side up on the saw. Accurately measure the ceiling angle and divide the measured angle by two and this is your mitre setting (this is Joint C/C in the illustration).

Occasionally you may find a situation that is not covered in this article, and when  it happens simply apply what you know about “inside” and “outside” wall and ceiling turns, make some test pieces and you will find a solution is quick at hand.

Make it easier
 Cut patterns used to set up compound mitre cuts at the saw for a ceiling turn.

Get the numbers right
 Example of measuring ceiling slope with angle finder.

installing crown moulding

Make some changes
 Back of crown is modified to fit tightly to a sloped ceiling.

Proper transition
 The transition piece is cut to a point and is glued to the horizontal crown.

Do the Math

• Measure the slope of the ceiling (mine was 122°)

• Now subtract 90° from the wall/ceiling slope (122-90=32°). This is the acute angle of the horizontal line to the slope of the ceiling. What we want is the ceiling rake angle so you must subtract that result from 180 (180-32=148°)

• Now the mitre is ½ of that measurement (148÷2=74 1/2°).

• This is the mitre cut for joint A/A.

Installation tips

• For safety reasons, cut the transition piece from a crown that is at least one foot long.

• For safety reasons, if you choose to cut away the back of the upper flange for the horizontal crown at the table saw, instead of using a block plane, make sure it is done in a safe manner as there will be a lot of the saw blade exposed.

• Backing strips may not be required behind the horizontal crown because the slope puts the crown much closer to the wall top plates.

• Always use the crown moulding templates as a guide to help you envision the joint and to make the cuts at the correct compound mitre angles.

• If your mitre joint is not tight at top or bottom it is likely that the spring angle is not maintained and you need to twist the crown to close the joint. (It is worth mentioning again because this is the most common cause of a poorly fit joint.)

• Avoid smudge marks on your hardwood crown moulding by staining and sealing the surfaces before cutting and installing. After installation, nail holes can then be filled without fear of filling the surrounding pores causing blotchiness.

• Whether you used a crown made of MDF or stained hardwood, apply DAP paint-able caulk along the length of the moulding where it contacts the wall and the ceiling to fill the gaps and produce a finished look. I first apply a 1/16″ bead of caulk along the moulding and then take a vinyl scraper and pull it at a 45° angle to force the caulk into the gaps and create a smooth joint. My scraper is 1″ x 2″ and the corners have a radius of 1/16″.

Finish off with a little filler and paint and then join everyone together to admire your work.

Crown Buildup

In the wood moulding industry there is a term called crown buildup. This is when the installer is looking for something exceptional in the form of a wider and more ornate crown for a room with a high ceiling and to possibly complement other existing trim work. This buildup is accomplished by adding case and base trim to the crown to create a combination that is unique and personalized to fit the decorative needs of the room. Crown moulding and base trims come in numerous sizes and shapes and their combination is only limited by your imagination. So, if you wish to create a unique look I would encourage you to Google “crown moulding buildup” for ideas and then visit your local wood moulding store.

Part three of this series will deal with making and installing crown moulding on a curved wall. The procedure can also be used to make a crown for a curved cabinet case.

Related Articles:

Installing Crown Moulding: Part One

Installing Crown Moulding: Part Three

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