Sourcing local wood building materials: Trim
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By Lee Burnett and Chris Briley
Almost all of the wood shown in this portage lake home is northern white cedar, including the porch checking, ceiling, siding and the trim on the door and windows. Photo courtesy of Maine Cedar Store.
Picking the right material for exterior trim is a balancing act between durability, maintenance, cost and, of course, good looks. The decision is made more difficult by requirements for moisture handling in high-performance construction.
Wood has long been the preferred choice for its natural good looks, but its use has waned under the relentless marketing of more modern materials. Some of these modern materials are even quite good, but most are more expensive than locally grown and widely available pine.
EASTERN WHITE PINE
This is the tried and true choice. Pine is affordable and universally available. It is also lightweight and easily worked. Modern-era pine grows faster, and hence is less rot-resistant, than the old-growth pine that has lasted for centuries on older homes, but that can easily be overcome by careful installation and proper painting. Factory-primed pine is a very good option. For the very best performance, specify pine that is sawn across the growth rings. This “vertical sawn” or “rift sawn” wood is more dimensionally stable and hence will hold paint better and resist weather longer. The milling is discernible by looking at the butt end of a board. If the growth rings run perpendicular to the board faces, it is vertical sawn. By contrast, flat sawn wood, which is more common, is discernible by a pattern of concentric arcs. (In the installation of flat-sawn trim, be sure the end-grain arcs are smiling (facing up), as wood tends to cup in the opposite direction of the arc.)
NORTHERN WHITE CEDAR
More expensive than pine, this species of wood is usually used as trim when a natural finish is desired (and usually when northern white cedar is being used in a similar fashion for siding). White cedar is a local wood here in New England and as such represents a lower carbon footprint than its red cousin from the west. Being a cedar, it is naturally rot-resistant if it is able to dry. Sealing the trim (on all sides) will also increase its durability. Bleaching oils can also provide protection while allowing the wood to age naturally.
FINGER-JOINTED RADIATA PINE
This is growing in popularity as it is even less expensive than eastern white pine trim. It’s made from many small off-cuts that are glued together to look like a single piece of wood. It typically comes pre-primed to hide the joints. But joining wood is imperfect, as the uneven movement of joined wood tends to “telegraph” the shape of the joint through wood. Radiata pine is grown almost exclusively on plantations – chiefly in Australia, Chile and New Zealand. The heartwood, which is normally the most rot-resistant part of a tree, is rated as nondurable to perishable.
WESTERN RED CEDAR
Western red cedar has been the traditional go-to choice for durability and beauty in high-end residential construction. Western red cedar is naturally rot-resistant with or without a preservative stain. On the West Coast, where it is grown, it has a low carbon footprint, but the cost of shipping it across the country gives it a higher carbon footprint on the East Coast.
FIBER CEMENT
Pine will weather well in the elements, if it is properly primed and painted. The pine clapboards and trim on this house in Springvale were installed in 2003 and show no signs of deterioration. Photo by Lee Burnett.
This has become a popular choice because it combines the performance of masonry with the look of painted wood clapboards or shingles. It’s essentially a masonry product made from cement, cellulose and sand. Fiber cement trim is heavy, requires special tools and procedures to cut and machine and presents a dust hazard to those cutting the material. Typically, it explodes into a cloud of silica dust when it hits the saw blade. A respirator is a must. James Hardie Building Products has introduced a low-density product that handles and installs more like wood trim. As a cement product, this trim family is very high in embodied energy and embodied carbon.
PVC
Plastic is hyped as “no maintenance.” Plastic trim may resist weathering better than unmaintained wood — in the short term. But when it fails, it fails catastrophically and must be replaced (long after the builder who hyped PVC is gone). Its weakness is in its thermal expansion. Long runs of trim need to accommodate this expansion with caulked expansion joints that should be maintained over time. Good builders can make this look good but to the trained eye, it still looks a little like cheap plastic. Its true downside is the material itself. PVC is toxic to make, toxic to dispose of and difficult to recycle. It also has a sizeable carbon footprint compared to local wood.
TORREFIED WOOD
Torrefication, or thermal modification, dries wood beyond the usual kiln-dried condition. It’s done under higher heat and in an oxygen-free environment to prevent burning. The result is a wood much more resistant to rot without the use of toxic chemicals. Torrefication can transform cheaper, less desirable species – such as poplar or soft maple – into woods that rival tropical hardwoods in durability and beauty. Some treatment plants capture the smoke escaping the wood and ignite it in the kiln so that after a while the wood cooks itself. For this reason, the wood has a relatively low carbon footprint. We recommend torrefied trim if you are already using torrefied wood as siding.
ACETYLATED WOOD
This is another process that improves the durability of wood in a benign way. Acetylization essentially pickles wood in an industrial vinegar-type solution called acetic anhydride. It does not contain copper or biocides that can leach into the environment as in pressure treated wood. The sole supplier, Accoya, has burnished the product’s green credentials by obtaining an “environmental product declaration,” Forest Stewardship Council sustainability certification and other certificates for maximum credits in LEED building certification. We recommend acetylated wood trim if you’re already using it in siding.
GOOD DETAILING AND SEALING
Wood trim often gets a bad rap that is undeserved. If one takes pine trim and only paints the exposed side, then installs it hard up against some sheathing or tar paper, then fails to install cap flashing, that trim is going to absorb moisture, dry unevenly and move and twist with the change of relative humidity. Any paint you put on it will fly off in a matter of years. Sealing all sides, flashing the top, and allowing it to properly dry and evenly acclimate to changing weather can make that wood last for generations (and the paint applied to it for a decade or two or three). If you’ve sensed a preference for wood from the authors, it shouldn’t be a surprise. If detailed correctly it’s a real winner in terms of environmental impact, appearance and durability.
Lee Burnett is the project director of Local Wood WORKS, promoting sustainable forestry and high-value wood products. He organizes conferences and tours and maintains their online Maine Wood Guide at www.localwoodworks.org
Chris Briley is a partner and principal architect at BRIBURN, specializing in energy-efficient, environmentally friendly design. He is a founding board member of PassivhausMAINE, a blogger at greenbuildingadvison.com and co-host of the Green Architects’ Lounge podcast.
This article appeared in the Fall 2020/Winter 2021 edition of Green & Healthy Maine HOMES. Subscribe today!