Interior Trim: Scale & Proportion

By Bud Dietrich

A dining room showing the high plate rail detail favored by Prairie School architects.

For thousands of years we have had rules that govern dimensions of trim pieces.  These rules, chronicled in books by the likes of Vitruvius, can insure that any trim we install is both functional and pleasing.  So rather than just putting up the standard 2 ¼” colonial casing and 3 ¼” colonial baseboard, let’s take a look at some of these rules to see how we can adapt them to our homes.



The 7 percent solution.
 A baseboard height that’s approximately 7% of the wall height provides for a solid and definable base without being too big.  The overall proportion of baseboard to wall height will be comfortable and pleasing. So in a room with a 9 foot high ceiling, a baseboard that’s about 8 inches tall works.

The 50 percent rule.
 Generally, vertical trim elements such as door and window casings should be smaller and have less heft than baseboards. So I've found that a good rule of thumb for sizing window and door casings is to keep them at about 50 percent of the height of the baseboard.
The 50% rule is a good starting point for sizing a crown as well.  However, there are many variables, such as profile and whether or not there will be a picture rail that go into the sizing of a crown.

Given these variables, sizing a crown isn't as straightforward as you might think. I like to purchase foot-long pieces of different sizes and profiles and construct mock-ups of the crown in the room. In fact, because most trim is readily available and inexpensive, this is a really good process to use for selecting all of your trim elements.

The rule of thirds. Installing a chair rail, with or without wainscoting, will divide the vertical plane — the walls — into multiple areas. If you want to make the room feel taller, place the chair rail one third of the way up from the floor.  If, on the other hand, you’d like to make the ceiling feel lower, place a rail higher up in the wall and finish the area above the rail differently than from below the rail. This was a favorite trim detail for the Prairie School architects such as Frank Lloyd Wright, as illustrated in the dining room at the top of this post.




02/02/2014