A decorative molding can be defined as any continuous projection that is used to enhance the look of a wall. In ancient Greece, they were first used to throw water away from the wall. The contours, measurements, and projections of moldings vary greatly.
Frieze
One type of molding - the frieze (or frieze board) - was first used on the Parthenon at the Acropolis. The frieze is considered a part of the Greek architectural style.
The Parthenon was built for the goddess Athena. The frieze moldings that were used were meant to tell the story of her triumph over Poseidon in becoming the patron of the ancient city which is now Athens.
The frieze panels are a series of designed pediments which are filled with the images of Athena's birth and rise to power. Today, a frieze board is the flat panel just below a crown molding or cornice. Often, low relief is applied to this panel for added decoration.
Today, frieze moldings are most common as a portion of a decorative molding that follows the neoclassical architecture or decorating style.
You need a pretty high ceiling (minimum of 9 feet), and it's a good idea to paint or stain the frieze and the crown molding the same color. The frieze is a good way to visually bring the ceiling down and make the room appear cozier.
Crown Molding
Crown molding is the most popular type of cornice molding. Crown molding is generally a single-piece of decorative molding, installed at the top of a wall, at an angle to the adjoining ceiling. However, I have seen crown molding assemblies of 5 or more pieces in more elaborate settings.
Crown molding often has a profile that projects out on the ceiling and down the wall, adding a rich appearance to a room. It is often used at the top of cabinets or built-in furniture.
Introducing this type of decorative molding to a relatively simple room provides a historic character that the room would not otherwise have. Crown molding is also used in combination with other moldings to add details to fireplace mantels and shelves. (For what it's worth, this is probably my favorite architectural feature).
Crown molding is a form of Cornice Molding. The term "cornice" describes molding installed along the top of a wall or above the window. When this treatment is made from multiple pieces of molding, it is called a "build-up cornice." The other form of cornice molding is the Cove Molding.
Cove Molding
Cove molding is very similar to crown molding, with the same application and function. The difference between the two is in the profile. Cove molding has a concave profile (which bows inward) while crown molding has a convex (outward) profile.
While crown is most at home in traditional settings, Cove moldings are equally comfortable in country, or even contemporary settings. You don't normally see multi-piece assemblies of cove moldings. You can occasionally see it "beaded" at top and bottom for a little accent.
Entries, formal living rooms, formal dining rooms, and master bedrooms usually receive decorative moldings with ornate or traditional patterns.
Kitchens and other more functional areas of the home might be where you will find the simpler design of the cove molding. Over the years, coves and crowns have become much smaller, but most still bear the shapes and styles of the original Greek and Roman designers.
Chair Rail Molding
A chair rail is a decorative molding that divides a wall horizontally, usually about 32" to 36" above the floor. They protect the walls in areas where damage might occur from people getting up out of chairs.
For this reason, the more traditional chair rails will have a nosing in the center, with curved and beveled surfaces that taper back to the wall above and below the nosing.
Today, chair rails remain a common detail in traditional interiors. They serve the decorating effect of unifying the various architectural details of a room, such as door and window trim, and fireplace surrounds.
Chair rail can also be used as a cap for wainscoting or other wood paneling. This decorative molding adds a feeling of detail and charm while achieving continuity in a room by unifying the various decorative elements.
Panel Molding
Panel molding, commonly called a picture frame molding, looks like a large empty frame, and is often part of designs on walls of old Colonial and, Georgian, and Early American homes. The placement of this molding should be above the chair rail height and about 10 to 12 inches down from the ceiling.
The size of this type of decorative molding, measuring 1" to 3" in width, should be proportionate to the ceiling height of the room. Like the other moldings, panel molding adds a feeling of charm and delicate detail to a room.
Wall framing appears at the Georgian period of American architecture, when plaster began to replace wood panels on the walls. Panel molding also is a good way to divide walls into large, aesthetically pleasing units, without the same expense of full wall paneling.
Another application of this versatile molding is to trim openings made by wider planks which are assembled as rails and styles. Often, the centers of these frames are left open. By applying panel moldings around the perimeter of the opening, you create the look of a picture frame.
When this decorative molding is painted in the same color as the surrounding walls, you achieve a sculptural quality to a wall, adding texture and shadows. If moldings are painted in contrasting colors, they can create a striking three dimensional appearance, giving depth and dimension. This type of treatment is popular for staircases and entries.
Baseboard & Base Molding
Baseboard molding protects the bottom of the wall from ware and tear, while hiding openings and other irregularities where the wall meets the floor. Base moldings give the floor line a higher profile, and can be as elaborate or simple as you like.
Whereas it is relatively easy to install chair rail on a level plane, baseboard (like crown) can be tricky if your floors (or ceilings) are not level. For this reason, I recommend getting a professional woodworker for the installation of these moldings.
As one remedy to uneven floors, you can install a "shoe molding" along the bottom front edge to give the baseboard a finished look. Something else you can do with baseboard (as well as with the toe kick of your kitchen cabinets) is incorporate accent lighting.
This isn't in keeping with the pure traditionalist, but it's a pretty nifty way to have accent lighting around the perimeter of a room. You couldn't do this until they created the small LED rope lights of today.
Rope lights come in different lengths and colors, and can be easily installed behind baseboard. Simply make a notch in the back side of the baseboard, at the top, and run the rope lights into the notch.
This is more often used in commercial spaces, but has been added in entries and hallways - especially in contemporary homes.
Flexible Moldings
If you have a curved wall or arch, you can probably have a good craftsman create a curved molding for about 3 times the cost of a straight molding. Or, you can buy a flexible molding for about the same price as the straight one.
These allow you to install moldings onto curved surfaces or arches, without the delay and expense of having them made from wood. The stock profiles (there are hundreds) are identical to the rigid versions and they are compatible as far as paint finish is concerned.
Charles Gueli invites you to ask questions about decorative molding, and take advantage of the resources on http://www.continuous-home-improvement-help.com, where guidance, information and support are always available - helping homeowners make better decisions.
