How to Miter Vaulted Coving

Figure how to miter cove molding for a vaulted ceiling using a tape measure, some type of calculator and a compound miter saw. Use a tape measure to find the distance from the top of the wall to the peak of the vaulted ceiling. Measure from the wall to the center of the peak, an imaginary horizontal line; make this measurement on a floor or holding the tape level.

Divide the horizontal distance by the sloped measurement, for instance 8 feet from wall to peak horizontally and 12 feet from wall to peak on a slope. Use a scientific calculator to translate those measurements into specific angles. Start by dividing 8 by 12, then use the "sine" key on the calculator to calculate the angle at the peak, 83.6 degrees; divide that by 2 to get the angle to cut each side of the molding.

Simplify the calculation and be more precise by looking up a scientific calculator on the Internet; several versions are available, free. Enter the basic figures, for example 8 feet horizontally and 12 feet diagonally, and the program will produce the precise angles, both at the vaulted top and against the wall, 41.81 degrees at the top and 48.19 at the bottom.

Lay the cove molding upside down in a compound miter saw, with the edge that will go against the ceiling flat on the saw table and the side that will go on the wall against the back fence. Use a table with the saw or look up one on the Internet -- building supply stores usually have them -- to determine any special bevel or tilt for the miter, which will vary with the type of cove. For example, an 85-degree peak with a 90-degree back will require a miter of 37.66 degrees and a bevel adjustment of 31.42 degrees for a perfect corner.

Make test miters with short pieces of cove molding. Cut the prescribed miter angle and bevel on the ends of two strips and fit them into molding intersections. Test both the peak, where two vaulted slopes meet, and the sides, where a sloped vault meets the wall top. Adjust the cuts if necessary until the corners are perfect.