Trimming does not have just a structural function, it is also used as finishing around openings and as protection for joints, edges and ends. Most exterior trim is made of wood or wood products, but vinyl and aluminum trim have become popular as well. Many older homes are traditionally designed with decorative sheet-metal cornices, which are also considered part of the trim. Sheet-metal trim, however, will rust and deteriorate if not properly maintained and kept adequately painted.
During an exterior house trim inspection, check whether all wood trim that is exposed to the weather is decay-resistant so that it does not rot. Some types of preformed trim are factory-treated with a water-repellent preservative to make them water- and decay-resistant, but not all types have this quality. More often than not, they are not treated and the joints, which really absorb water, start to rot. When the trim is cut to size during construction, the ends or miter joints must be treated to become water-resistant.
If there is a wood trim, pay particular attention to the joints that are vulnerable to decay. All non-treated wood continually exposed to moisture is susceptible to decay and will eventually rot. A house with a wide roof overhang at the eaves and gables will provide greater weather protection of the sidewalls and trim than one without roof projection beyond the walls.
In addition, the trim around the edge of the roof is particularly vulnerable. The Asphalt Roofing Manufacturers Association recommends the installation of a metal drip edge along the eaves of a roof deck, but in practice this is usually omitted. The drip edge is designed to allow water runoff to drip free from the underlying trim. Otherwise, water will curl back under the shingles, wetting the edge of the roof sheathing and trim.
Lastly, an exterior house trim made of wood should be inspected for cracked, loose, missing and rotting sections. If the trim is painted, check to see whether the paint is peeling and flaking in sections or whether the trim needs repainting for weather protection.
In older Tudor-style homes with timbers embedded in the stucco siding, check the timbers at the stucco joints for signs of decay, especially if the joint is horizontal. In time, the joints tend to open slightly, thus allowing water to penetrate. With non-wood exterior house trim, check for loose, missing and deteriorated sections.