There are some great replacement windows available today, but to complement the design of older houses they usually need exterior trimming. Plain or fancy, there are a few basic considerations in the design of appropriate trim.
Unless manufactured with a wood exterior, most new windows are made with a thin siding-stop type frame and a hidden attachment fin. This works fine for installation, but to replicate the style of traditional homes, there should be exterior trim on the top and sides as well as a visible sloped sill at the bottom. The old wooden windows were secured in place by the trim, and if the house is to look authentic or well-designed, the trim should look substantial.
The width of the window trim should be proportionate with other trim on the house. If the corner boards and eave trim are wide, then most likely the window jambs would also be wide. If other areas of the house are elaborately developed, then the window trim should also show more panache. It’s probably not wise to make the window trim too fancy if the rest of the house architecture will not visually support it.
When you get close to a historic house or reconstruction, you can see that the trim is quite substantial compared with today’s homes. This creates heightened shadow lines and texture on the façade, imparting a greater sense of character and permanence.
Generally, the older the historic style of the house, the thicker the trim pieces will be. Availability of wood and the cost of milling surely played a role, but it is unlikely that the Pilgrims would have used a 3/4-inch trimboard on their homes. Eighteenth century homes in Newport, R.I., have window jambs more than 2 inches thick. (The clapboards were thick, too.) In Williamsburg, Va., they are about 11/2 inches thick, but in postwar homes they run only about 7/8 inches thick.
More classically inspired houses often used backbands and cornices to enhance the windows, but a historic home would never have a cornice above the window unless there were also jamb trimboards and a sill. Backbands and crown moldings can add shadow, texture, and substance to the ensemble but should be used carefully. If there are shutters, these should lay atop the side trim as if they could close over the sash opening.
The proper use of window trim can elevate a mundane façade to an elegant composition. In the hands of a master, it can create an unforgettable image of harmonious proportion and diligent craftsmanship.
—Dick Kawalek, a registered architect for more than 30 years, is founder of Kawalek Architects, in Cleveland; firstname.lastname@example.org.