Have you ever wondered where inventors go for approval when they have developed something new for the construction industry? For instance, many new man-made decking products are replacing traditional wood, but are they as safe, cost-effective and durable?

The Canadian Construction Materials Centre (CCMC) provides testing and evaluation services for companies developing new construction materials. Based on the test results, CCMC issues an approved product qualification document that is widely accepted by code officials in all regions of Canada.

Building regulations in Canada are under the jurisdiction of the provinces and territories, which use the national construction codes as a basis to establish acceptable performance thresholds in building construction. In 1988, the National Research Council of Canada (NRC) established the Canadian Commission on Construction Materials Evaluation (CCCME), a central national evaluation service, on which building officers across the country could base their decisions regarding the use of building products. CCCME receives administrative, financial and technical support from the Canadian Construction Materials Centre (CCMC), which is located at NRC's Institute for Research in Construction (IRC).

CCMC recently began evaluating composite exterior decking and railings since more and more of these products are sold at local building centres. Composite extrusions are gradually replacing wood in the construction of decking and railings, and are also used to build exterior balconies and decks in residential construction.

Composite extrusions may consist of a wood-blend-based material and plastic (e.g., polyethylene, polypropylene) or may be made of plastic material and cellulose-based fibres derived from wood residues or agricultural waste. While the wood or cellulosic fibre content of these composites varies among products, content (by weight) in the order of 50-60 per cent is typical. Extrusions can be manufactured in solid or hollow cross-sections of various sizes and shapes. The nominal dimensions of many of these extrusions are similar to those of the sawn lumber traditionally used for the construction of exterior decks and railings.

As structural components, these composite decking and railing products must be capable of resisting the loads they will experience under normal use. They must also be capable of maintaining their structural capacity under the environmental loads that they will be exposed to over their service life, such as UV radiation, high and low temperatures, and moisture.

The structural design of products made of known materials, such as wood and steel, are based on established material properties and calculation procedures. These new products are made of non-traditional materials which do not have easily predictable physical and mechanical properties. So, when Canadians set out to build a deck, how can they be sure that these new products are suitable for their intended use and that they conform to the applicable building code requirements?

To answer this question, CCMC developed technical guides for the evaluation of exterior decking and railing products that contain less than 50 per cent plastic (by weight):

• Wood thermoplastic composite lumber (WTCL)

• Solid cross-section

• Cellulosic/polymer composite extrusions of hollow cross-section.

The technical guides contain evaluation requirements related to the physical properties and degradation-resistant mechanisms of the composite material and to the structural performance of the decking and railings as installed. Evaluations are not endorsements, warranties or guarantees, but provide specific information on the most appropriate usage and the construction limitations for the product.

Since it is impossible to produce evaluation protocols that would address all physical, mechanical and design characteristics of each proprietary product, the guides are modified as needed on a case-by-case basis to address the performance of each element and component of a product that CCMC is asked to evaluate.

For instance, the evaluation report (CCMC 13125-R) for one WTCL exterior decking product, Trex Wood Thermoplastic Composite Lumber Decking, intended for exterior use installed over traditional wood framing, was completed in June 2003 and the product will be re-evaluated in three years.

CCMC is presently working on the evaluation of other composite products intended for the construction of exterior decks and guards. Results are available by contacting CCMC directly or using the online Registry of Product Evaluations.

Published: June 1, 2004

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