Base molding is the tallest piece of molding in a room and forms the "base" for adding other pieces such as casing and crown molding. Use a 3 1/4-inch base molding for a 6-foot-tall ceiling, a 4 1/4- to 5 1/4-inch molding for a 9 or 10 foot tall ceiling, a 5 1/4- to 7 1/4-inch molding for an 11-foot-tall ceiling and a base molding that is 7 1/4-inches tall or more for a ceiling that is 12 feet tall or more.
The height of the casing molding is always shorter than the height of the base or crown molding. Otherwise, the molding will look unbalanced and out of proportion. Use a 2 1/4-inch casing for a 6 foot ceiling, a 2 1/4- to 3 1/4-inch casing for a 9 or 10 foot ceiling and a 3 1/4- to 4 1/4-inch casing for a ceiling that is 11 feet tall or more. Casing molding used for doors and windows is based on width measurements and is typically 1 to 4 inches wide. As a rule, the wider the door or the window, the wider the molding should be.
Decorative crown molding will have a pattern and ornamentation, such as a dentil design, a leaf pattern or rope treatment. Taller pieces will often include grooves and curves, giving the molding a multi-dimensional look. Alternatively, a flat piece can be built-up with short 1/2- to 1-inch-tall pieces of decorative molding to create a custom look. As a rule, the total height of the crown molding for a 6-foot-tall ceiling should be 3 5/8 inches. Use crown molding that is 4 1/4 to 5 ¼ inches tall for ceilings that are 9 to 10 feet tall; use 5 1/4- to 7 1/4-inch crown molding for an 11-foot-tall ceiling and use crown molding that is 7 inches tall or more for a ceiling that is 12 feet tall or more.
Chair Rail Moulding
The functional purpose of chair rail molding is to protect walls from being bruised and dented by chairs. However, chair rail molding also adds a decorative touch in dining rooms and kitchens and even bedrooms and bathrooms. You can purchase chair rail molding as one solid unit that already has a base cap and smooth edges, or you can create a custom piece with your own choice for the base and the base cap. As always, use the height of the room as your guide to determine the appropriate height for the chair rail molding. The height -- including the base and base caps -- should be between 2 3/4 and 3 inches for a room that is 6 to 9 feet tall, and 3 1/4 to 4 inches for a room that is 9 feet tall or more.