Depending where you live, there are a few alternatives. First, a good majority of the houses on the Cape were built in the ’80s, and the predominant type of trim was #2 raw Northern white pine boards. The knots were sealed and painted after the trim was installed. This left the end grain and backside of the trim susceptible to water damage from wind-driven rain. In the past 20 years, there have been many improvements not only with the introduction of superior products, but also with the installation methods.
The first product we would suggest is a product called Bodyguard, which is a wood product that is naturally bug resistant and pre-primed; it comes in nominal widths and thicknesses. The most important thing to remember when installing this product is to prime with an oil-base paint, preferably the end sealer that Bodyguard manufactures, on all end joints or cut edges. This will prevent water from wicking into the trim board, which allows premature decaying to begin. It is also a good idea to use stainless-steel nails whenever possible, because of the harsh environment on Cape Cod. The nail holes should be filled, and seams and cracks caulked, and painted with two coats of a premium latex paint.
The second product that we recommend is cedar trim boards. This product also comes in nominal widths and thicknesses. It is somewhat naturally bug and decay resistant. If trim is to be painted, we recommend that all raw wood sides, ends, and edges be pre-primed with an oil-base paint. Then after installation, preferably with stainless-steel fasteners, fill nail holes with an oil-base putty, caulk joints and cracks, and give two coats of a premium oil-base paint.
Both of these trim products are widely used in both residential and commercial applications, and are usually accepted by most historical boards.
The third product is a PVC-type trim board, such as Azek. This comes in nominal widths and thicknesses, cuts the same as a wood product, and is applied in the same way as wood trim. The benefit is that you don’t have to paint any part of this product: It will not decay or be eaten by bugs, and it lasts forever. When installing, an adhesive should be used to connect end joints, and a caulk that is recommended for PVC should be used to fill nail holes and cracks. Stainless-steel fasteners are preferred for application. This product can be painted, usually with two coats of a premium latex paint, and is treated just like wood trim. With this product, there is expansion and contraction depending on the temperature. If it’s not installed correctly, it will show cracks and spaces at the butt joints. Always follow the manufacturer’s installation instructions. If you live in a historical area, seek approval by the historical board to use this product (most boards don’t accept the use of PVC).