Interior Trim Glossary

By Bud Dietrich, Originally Published in Houseplans.com

These are the basic elements that make up interior trim.

What’s casing?  Where does an apron go?  Why would we want to install a base shoe? In addition to the question of style, these and more are the questions we all come across when thinking about how we’ll be trimming out the interior of our new home. So here’s a glossary -- keyed to the illustration above -- explaining what the most common trim parts are and where each is installed.

Generally, casing is the vertical and horizontal trim that wraps door and window openings and is typically made up of three pieces; the jambs, head, and apron.  When we speak of casing an opening we are talking about installing the final trim pieces around that opening. Casings come in many styles, profiles and sizes. Sometimes a window opening is picture framed which is when the same casing profile is installed at the head, jambs and apron.  On the other hand, the illustration shows a distinct difference between these pieces, resulting in a more three dimensional casing option.


A baseboard, or a skirting board as it’s called by the British, is the bottom most trim piece.  It gets installed at the intersection of the wall and floor.  A baseboard provides a durable material that can more easily withstand furniture and more banging into it.
To eliminate any gap between floor and wall and to provide some extra protection to the wall, we can install a base shoe, or simply a shoe.

Just as there’s a piece of trim to cover the gap at the wall / floor intersection, there’s a piece to cover the gap at the wall / ceiling intersection.This trim piece is the crown molding or simply the crown. These pieces can be quite elaborate or very simple, depending on the style you’re aiming for. Also, the profile of a crown can vary widely.  Concave, convex, ogee shaped, composed of several pieces, etc. are all available for a crown. Again, the style you’re looking for will dictate what crown, if any, you select.

Other trim pieces that are common are the picture rail and chair rail.  These pieces traditionally served to provide added protection to the wall finish. While the chair rail protects the wall from getting banged up by the backs of chairs, the picture rail provides an easy to use place from which to hang pictures (no more banging nails into the wall).


When looking at what trim you’ll use, an important consideration is to be consistent throughout.  The baseboard, casing, crown, etc. should all come from the same style family.  So don’t mix a Ranch, or clamshell, baseboard with Colonial casing as the overall look will be confused.

January 31, 2014