Corner Boards and Exterior Trim
Most siding materials require vertical corner boards as well as trim boards around windows and doors. Roof edges require trim boards of various types, including fascias, sofÞ ts, frieze boards, and moldings, the exact patterns depending on the style and detailing of the building . For most sidings, the traditional
choice of material for these exterior trim components is pine.
For wood shingles, unpainted cedar or redwood may be preferred. Plastic and metal sidings are trimmed with special accessory strips of the same material. Fiber-cement siding may be trimmed either with wood or with Þ ber-cement boards made for the purpose.A high-appearance grade of pine is usually chosen for wood trim boards. Traditionally, the boards are back primed before installation with the application of a prime coat of paint on the back side. This helps to reduce cupping and other distortions of the trim boards with changes of humidity. Fully preprimed trim boards are also available at most lumberyards. Many historical styles require trim that is ornamentally shaped.
The shaping generally takes place at a mill, so that the trim pieces come to the site ready to install As appearance grades of lumber have become more costly, substitutes have been introduced to the market, including boards made of high-density plastic foams, wood composites of various kinds, and lumber that has been cut into short pieces to eliminate knots, then reassembled end to end with Þ nger joints and glue. These products tend to be more consistently straight and free of defects than natural, solid lumber. Some of them are not only produced as ß at boards, but also molded to imitate traditional trim. They must be painted and are not suitable for transparent Þ nishes. Many are also available pre-primed or preÞ nished.
Wood is widely used outdoors for porches, decks, stairs, stoops, and retaining walls . Decay-resistant heartwoods, wood that is pressure treated with preservatives, and moisture-resistant wood/plastic composite planks are suitable for these exposed uses. If nondurable woods are used, they will soon decay at the joints, where water is trapped and held by capillary action. Fasteners must be hot-dip galvanized or stainless steel to avoid corrosion. Wood decking that is exposed to the weather should always have open, spaced joints to allow for drainage of water through the deck and for expansion and contraction of the decking. Plastic composite planks are durable and attractive, although some are not as strong or stiff as wood, and may require more closely spaced joists for support.
Sealing Exterior Joints:
After the completion of exterior carpentry work, exposed gaps between siding, trim, frames of doors and windows, and other exterior materials are sealed with joint sealant to protect against the entry of water. Exterior sealants must have good adhesion to the materials being sealed, remain permanently ß exible, and be unaffected by exposure to sunlight. Paintable sealants can be installed before nish painting and then painted over to match adjacent surfaces. Other sealants, such as most silicones, cannot hold paint. These are selected from a range of available premixed colors and then applied after Þ nish painting. Sealant materials and sealant joint design are discussed in detail.
Exterior Painting, Finish Grading, and Landscaping:
The Þ nal steps in Þ nishing the exterior of a light frame building are painting or staining of exposed wood surfaces; Þ nish grading of the ground around the building; installation of paving for drives, walkways, and terraces; and seeding and planting of landscape materials. By the time these operations take place, interior finishing operations are also usually well underway, having begun as soon as the roofing, sheathing, windows, and doors were in place.