In spite of its inherent drawbacks—it burns, it rots, it expands and contracts with moisture—wood has been a material of choice for centuries for everything from large structural members to fine millwork.
We use wood in many different forms: as solid pieces of lumber milled and finished to the shape we need, as thin veneers shaved off a log, or as wood fiber, glued together into engineered panels and other shapes.
Forest management and FSC
Environmental damage and resource depletion from centuries of logging North American forests have made us much more sensitive to the need for careful forest management: harvesting timber in a way that protects wildlife habitat, recreational opportunities, aquifer recharge, and the long-term interests of local communities.
These concerns led to the practice of independent certification of well-managed forests, and a system of labeling wood products from those forests so specifiers and builders can use wood with some confidence that the forest it came from is not being abused. Tree farms or plantations may be one legitimate alternative to logging in natural forests, as long as those forests are not being cleared and converted to create more plantations.
In GreenSpec we look to the Forest Stewardship Council (FSC) certification as the most responsible indicator that wood products of all types come from well-managed forests.
Salvaged and reclaimed wood
For most building materials, the terms “salvaged” and “reclaimed” apply only to materials that have been previously used and then collected for reuse. This definition applies to wood products as well, especially large timbers from old structures that are remilled for use as structural members or flooring.
With wood products, however, there are also logs that have been salvaged from river bottoms, or from forests that have been submerged by reservoirs. Some foresters even refer to cleanup operations after a forest has been damaged by logging, fire, or storms as “salvage.” These kinds of salvaged wood don’t count toward LEED credits, but might still be a good option. Be careful, though: some salvage operations, particularly river-bottom salvage, can cause habitat disruption.
Glues and binders
The most common binders used to make panel products, such as plywood, oriented-strand board (OSB), particleboard, and medium- or high-density fiberboard (MDF or HDF), use formaldehyde as a primary ingredient. Panels designed for indoor use are especially problematic, because the urea-formaldehyde resin that holds them together is less stable and offgases carcinogenic formaldehyde.
Alternative binders are available and increasingly common, thanks to growing awareness of the issue and recent regulations (led by California) restricting allowable formaldehyde emissions. Look for products that meet California’s CARB Phase II requirements for having no-added urea-formaldehyde (NAUF).
Preservative and other treatments
To prevent wood from rotting in applications where it can get wet, and from burning, we treat it with chemicals, some of which are toxic—although use of the worst heavy-metal formulations has been largely eliminated in buildings over the past decade. Less-hazardous alternatives are available for many applications.
Insulated panels and sheathing
Most insulation products are covered separately in Division 7, Thermal and Moisture Protection, but those integrated with wood, such as structural insulated panels (SIPs, also known as stressed-skin panels), are listed here.
SIPs are useful for creating building envelopes with continuous insulation (spanning across structural members that otherwise short-circuit the insulation) and with minimal air leakage. Some sheathing products also have integral insulation that provides similar benefits.
Both virgin and recycled plastic construction products are increasingly used to make construction products, including boards and trim intended to replace wood in outdoor applications such as decking and fencing. GreenSpec doesn’t favor using virgin plastic in this way, especially the ubiquitous PVC, but recycled plastic products can be a good choice. There are also wood-plastic composites that offer some advantages over either wood or plastic alone.