When engineered wood trusses were first introduced to the construction industry as a new innovative building component, their benefits as an environmentally friendly product were largely over looked. Using engineered wood roof trusses allowed builders to cut down on the overall cost of their roof structures and provided much more flexibility in their home designs. The principles that provide for these benefits also make engineered wood roof trusses a very environmentally desirable product.
The strength of the steel connector plates used to hold the truss joints together and the engineering principles in using triangulation of the truss webs allow trusses to span large distances using very light framing members. A truss can be designed at 2’-0” O.C. intervals to comfortably span a 50’-0” opening using only 2”x4” top chord, bottom chord and web members. (1) Dimensional lumber is not capable of achieving this type of span even using 2”x12” material.
In a comparison study using a 40’-0” x 40’-0” (1600 square feet) bungalow with a 5/12 sloped gable roof, engineered wood trusses designed to be spaced at 2’-0” O.C. intervals required a total of 2128 board feet of lumber. When using the ‘traditional’ framing method of 2”x8” rafters, 2”x6” ceiling joists and 2”x6” collar ties all spaced at 16” O.C. intervals, a total of 3576 board feet of lumber was required. The results showed that engineered wood roof trusses use 40% less lumber than a ‘stick framed’ roof of the same size. This also didn’t take into account the extra material required in the ‘stick framed’ roof for roof beams or extra floor framing material to support the internal bearing points as traditional ‘stick framing’ cannot span 40’-0” without internal bearing.
Not only do engineered wood roof trusses use less lumber than traditional ‘stick framing’, the lumber used in trusses has a smaller cross section (typically 2”x4” or 2”x6”). This means the lumber used for most trusses can be harvested from smaller diameter trees. Generally smaller diameter trees are from younger forests requiring less grow time to replenish. Typically the 2”x4” and 2”x6” material used in truss production at Leduc Truss comes from Spruce and Pine trees harvested in Alberta and British Columbia between 30 years and 40 years old. This compares with the average lifespan of a residential house being built in Canada today which is expected to exceed a lifespan of over 80 years. Leduc Truss only purchases lumber from mills with accredited reforestation programs. This means that the lumber used comes from sustainable, managed forests that have been logged in a responsible manner.
Wood is a natural insulator. Due to its cellular structure, wood traps air resulting in low conductivity and offers good insulating properties. Other commonly used framing materials conduct heat faster than wood. High conductivity causes thermal bridging leading to an increase in operating energy used for heating and cooling of buildings. (2)
Life-cycle assessment (LCA) is the recognized international approach to assess the environmental merits of products or processes as set out in the ISO 14000 series of standards. Based on LCA, wood products have proven to be one of the most environmentally responsible building products.
Wood is a natural building material that requires a relatively small amount of energy to process it. Of the major building materials, wood requires the least amount of embodied energy to produce. (2)
Wood is a renewable resource and Canada is a world leader in forest conservation, protection and sustainable use. Only one quarter of Canada’s forests are managed for commercial use, yet annually Canada harvests less than one quarter of 1% of its forests. (2)
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(1)Based on Edmonton, Alberta area snow load for a residential truss design using 5/12 slope and 7” heel.
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(2)Canadian Wood Council ‘2004 The Span Book’ 2.1, 2.2, 2.3
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