Like many carpenters, I always thought there was no good way to install crown molding on a cathedral or vaulted ceiling. For years, I would just shake my head whenever anyone suggested it. "Nah," I'd say knowingly, "that never looks good." Most of the time I got away with that, but occasionally customers insisted, and it was always a struggle. But I kept my eyes and ears open for a better method, and in the last few years I've discovered several, each of which has advantages and disadvantages.

No matter which of these methods I use, the back of the crown molding installed on the horizontal runs must first be ripped with a new shoulder or foot bevel to follow the sloped ceiling or the wall. Sometimes both angles must be modified (see "Ripping a New Bevel Angle," below). If you fudge the inside corner using just one size of crown, you sometimes have to rip both the top and bottom bevels; if you use two sizes of crown, you only have to rip the top.

Ripping a New Bevel Angle Altering the back of crown molding isn't a job for amateurs. I've seen carpenters make this cut freehand with a circular saw, but I wouldn't recommend it. Running a circular saw at an angle on the narrow edge of crown molding is asking for it. If I'm installing only a few pieces, I use a power plane and just knock down the shoulder until it's out of the way, being careful not to cut anything off the face or top edge of the crown. It doesn't matter how much is removed from the back because only the top face and edge of the molding bear on the ceiling or wall. However, when I'm running a lot of crown, I don't have the patience to make so many multiple passes with a plane, so I set up a jig on my table saw. Take my word for it, this is one operation that requires a jig. Fingers are much too valuable to donate to a job. Besides, it seems like every time I make any jig, I end up having to use it again, and soon. The jig is a simple sled that gets clamped to the table saw fence (see sketch). The crown molding slides on a piece of 1-by beveled at 45 degrees on both edges. Along the front edge of the sled, I attach a 1/2x3/4-inch stop, which keeps the crown from kicking out at the bottom. Tipping the blade provides all the adjustment necessary to cut right on a fillet line. Because the blade comes up through the molding at a severe angle, I use a push stick to shove the last few feet of crown through the jig. Using a jig and a push stick is the safest way to recut bevel angles on the back of crown molding.

Forcing the Inside Corners

This is the first method I learned and the one most carpenters use to solve the problem of vaulted ceilings. To join the inside corners, you just tip the crown on the horizontal runs until it's nearly plumb (see Figure 1). Before making the scribe, a new foot must be ripped on the bottom of the crown so the material will sit flat on the wall. I use two short pieces of scrap to get the right angles. First, I cut the end of the raked piece so that it's close to the spring angle of the horizontal piece; then I rock the horizontal piece toward plumb until the profiles line up best. Crown isn't supposed to be plumb, and that's why this method doesn't look so great. In fact, on ceilings that are steeper than 6/12, forcing the corner looks terrible. It works on a 4/12 ceiling but only after some serious scribing.

Figure 1.To "force" a crown molding corner on a cathedral ceiling, the author tips the molding on the horizontal run closer to plumb. That way, the height of the crown on the horizontal run more nearly matches the height of the crown coming down the rake, though the profiles will rarely match perfectly, especially on steeply sloped ceilings. Rebeveling the back of the crown at the bottom allows it to close tightly against the wall.

For the cut to work, the scribes must be held perfectly level — they can't tip even a little. This requires patience and a good eye. And following an S-curve requires a very steady hand. To make these crazy scribes, I alternate between a jigsaw equipped with a Collins Coping Foot (888/838-8988, www.collinstool.com) and a small grinder (Figure 2). I use the jigsaw to follow and relieve the scribe line, back cutting as I normally would. Then I turn to the grinder to remove even more material from the back of the molding, because these scribes must be severely relieved on the back or the joint won't close up tightly.

Figure 2.To cut the unusual scribes that are required when fudging an inside corner (above), the author uses a jigsaw fitted with a coping foot (above right), as well as a grinder (right), for making extra steep back bevels.

To get a tight fit, arm yourself with lots of patience; it's best to plan on two or three attempts. And be careful on the horizontal cuts: If you remove too much material from a horizontal line, you'll probably have to start over from scratch.

Using Two Sizes of Crown

A couple of years ago, I learned another way to join miters when two pieces of crown molding meet at different planes — by using the same profile crown moldings in two sizes, a larger crown for the horizontal runs and a smaller size for the rakes (Figure 3). Some of the carpenters who visit the Finish Carpentry Forum at jlconline.com have pointed out that craftsmen have been using this method for centuries. The corners still require careful scribing, but the result is pleasing — even on steep-pitched ceilings. However, not every profile of crown molding is available in a variety of sizes like standard S-and-Cove or S-profile crown moldings, which are available off the shelf from many lumber yards in 2 1/4-, 3 1/2-, and 4 1/2-inch widths. Fortunately, if the molding is made in only one size, there's another method.

Figure 3.Using two sizes of the same profile — wider stock for the horizontal run, narrower for the rake — can sometimes work to turn a cathedral corner. The horizontal run still has the same spring angle, so the bottom doesn't have to be rebeveled, only the top, to match the slope of the ceiling.