Not counting things like geodesic domes and igloos, all houses have at least four outside corners. These are important design elements, and the treatment they receive can have a big effect on a structure's appearance. Let's take a look at three common corner details used with wood siding: corner boards, woven corners, and mitered corners.
The simplest and most popular approach to finishing outside corners is installing corner boards. There's good reason for this: Corner boards provide a visual break from the horizontal lines of siding, in much the same way that corner pilasters and columns do. The effect can be reinforced by painting or staining the corner boards a different color than the siding.
To achieve a pleasing sense of scale, corner boards should be sized with both the width of the siding and the overall height of the structure in mind. As with actual columns, increased height calls for added heft. The 4-inch corner boards that look just right on a single-story house sided with narrow clapboards may seem much too light and wimpy on an otherwise similar two-story house.
As strong visual elements, corner boards should also stand proud of the siding. This is most often done by using 5/4 trim stock. For an even stronger effect, the corner boards can be padded out to create a slot that encloses the ends of the siding or the edges of the shingles (see figure below). This detail also provides some margin for error in fitting the siding, because there's no visible butt joint between siding and trim.
Corner boards are often omitted on ranch and prairie-style houses, which emphasize horizontal lines rather than verticals. The simplest way to turn the corner when using lap siding or cedar shingles is by constructing a woven corner (see figure above).
In a woven corner -- also known as a laced corner -- each successive course of siding is mated with its counterpart on the adjoining wall. Traditionally, this involved fitting each course of siding, marking the overlap, and removing the marked piece to make the sloped cut corresponding to the bevel of the opposite course. A quicker and easier method of doing the same thing is to nail both courses in place before cutting off the excess material with a router.
When either approach is used with clapboards or lap siding, the end grain of every other piece of siding is left exposed, so the wood must be carefully sealed to prevent it from absorbing moisture. And with either shingles or siding, accurate coursing is essential, because there's no intervening corner board to conceal any slight irregularities in alignment.
A more elegant corner treatment that eliminates exposed end grain is the mitered corner. This can look great, but it's more time consuming than constructing a woven corner. (Coursed sheet-metal corners were once used to conceal end grain without the need for mitering, but they're seldom seen nowadays.)
To guarantee tight joints, mitered corners are laid up from the corner itself outward, using the same general approach a mason takes in building a brick wall. Once the corners are complete, the intervening field is filled in to finish the job (see figure below). --Alan Freysinger is an architect in Milwaukee. This article originally appeared in REMODELING's sister publication, THE JOURNAL OF LIGHT CONSTRUCTION. To order a subscription, call (800) 375-5981 or visit the Web site at www.jlconline.com.