The incorporation of sustainable materials into project construction requires knowledge of the product's building life-cycle impact (LEED MRc1), environmental impacts (LEED MRc2), raw material sources (LEED MRc3), material ingredients (LEED MRc4), and the manufacturing, fabrication, and shipping processes required to get that material to market. In addition, LEED v4 has changed the evaluation process for Materials and Resources criteria, requiring more rigorous technical standards for qualifying sustainable materials and resources by including:

• The entire life-cycle assessment of the material/resource

• A comprehensive Environmental Products Declaration (EPD) through full disclosure of impacts and ingredients for the material/resource

• Adherence to higher standards such as GreenScreen™, the European REACH (Registration, Evaluation, Authorization, and restriction of Chemicals) program, and others

Sustainable and Renewable Resources and Materials

This article will provide examples of products that qualify as renewable materials/resources by green building and sustainable design criteria. Some of these products are obtained directly from renewable resources (forest products) while others are produced by processes that mimic non-renewable natural resources rather than deplete their supply. One product utilizes living renewable plant resources as part of its function to manage stormwater and provide energy-efficient roofing for buildings. Using any of these products on a project can assist in enhancing the healthy living environment and sustainability of the project.

Renewable Wood

Wood has been used for centuries as a construction material. It is considered a sustainable building material as it is harvested from a renewable source (forest land) and has a “low embodied energy”¹ due to the following factors:

• There is minimal non-renewable energy used in the harvesting and production of timber and in its construction use.

• Due to its natural thermal properties, structures built of wood rely less on carbon-emitting appliances for heating and cooling.

• Many wood products (especially hardwoods) have a service life of 50 or more years and require minimal maintenance.

• Wood can be readily recycled, thus providing a low carbon footprint.

Forests play a key role in natural water-carbon-nitrogen cycles. For years, many wood products were treated with chemical preservatives to increase their durability and provide added protection from rot and insects. Most of these chemical preservatives later proved to be toxic to both human health and the environment and their use was discontinued. In an effort to provide wood products with increased durability and longevity, timber companies began to harvest South American and Latin American hardwoods such as Ipe, Cocobolo, Bocote, and Parota. The harvesting of these woods has begun to deplete stands of tropical rainforests. Although many of the South American woods are certified through the Forest Stewardship Council (FSC) and are thus considered responsibly harvested, other woods are harvested illegally or do not meet FSC criteria and certification.

Thermally Modified Hardwoods

Thermally modified North American hardwoods are used as exterior tiles for roof decking, ground-level decking, and as wood components for landscape site furniture such as benches, chairs, and tables. These wood products do not require chemicals to enhance their durability or resistance to decay as the thermal heat process provides this durability. Thus, the product is ecologically and environmentally safe.

Thermally modified wood tiles, built onto adjustable paver pedestals Photo courtesy of Tournesol Siteworks

These thermally modified North American hardwoods are domestically sourced from red oak and ash trees that are currently harvested in Wisconsin. Red oak and ash are the preferred species because of their consistency in durability and color. The natural durability of the red oak and ash is enhanced through the thermal heating process, creating a product that is a Grade-A wood with a 25-year Class 1 durability level and a resistance to decay that is comparable to South American hardwoods.

Detail of bench made from thermally modified North American hardwood Photo courtesy of Tournesol Siteworks

The thermal wood process was originally developed in Finland and the U.S. company that provides the thermally modified wood product utilizes special kilns fabricated in Finland. These kilns provide high temperature heat with steam, and the process changes the chemical composition of the wood, making it highly resistant to rot, decay (EN-350-2 Standard), and pests as the resin and sap content are essentially cooked out of the wood. The thermal process also creates a very aesthetically pleasing dark-colored wood product.

The thermally modified hardwood is FSC certified, harvested, processed, and finished. The wood decking products have a Class B fire rating based on ASTM E-84-10 standard test method for surface burning. (Note: the wood decking products must be treated with fire retardant to achieve a Class A fire rating).

Thermally modified North American hardwood products are lighter in weight and easier to cut and work with than many of the South American hardwoods such as Ipe. Red oak and ash are easy to cut and easy to use in construction. In addition, the cell structure of the red oak and ash changes during the thermal modification process, making the wood resistant to warping, twisting, and other moisture-related movements and thus providing long-term dimensional stability.

Thermally modified North American hardwood products have been used for both decking and benches at the Patagonia Clothing Company headquarters in Ventura, California. The company embraced the use of the reclaimed wood as it closely reflects their own corporate ethos. The project designer suggested this product specifically because of the qualities of thermally modified North American hardwood. The Patagonia Clothing Company is pleased with the overall performance of the wood over the first year (the benches were installed winter 2013), and the company is planning to add additional benches to the project site.

Thermally modified North American hardwood products are a sustainable and renewable resource in that they are sourced and harvested in the U.S. from forest crops that can be replanted and they are 50 percent lighter than South American hardwoods so there is less energy (as well as less cost) used in processing and shipping. They also meet LEED MR Criteria through FSC certification and lack of toxic chemical content.