Why Use Prefabricated Wood I-joists?
Quite simply, Prefabricated wood I-joists are environmentally sensitive products. The design of prefabricated wood I-joists allows a manufacturer to utilize smaller diameter, faster growing, and generally lower quality trees and still produce a quality product. Secondly, when compared to other building materials, production of wood materials uses less energy and produces less carbon than materials such as steel and concrete.
Resource Utilization
Prefabricated wood I-joists belong to a family of wood products known as an engineered wood products (EWP’s). Other EWP’s include Glulam Beams, Structural Composite Lumber (SCL), finger jointed lumber and Structural Panels. SCL includes products such as Laminated Veneer Lumber (LVL), Parallel Strand Lumber (PSL), and Laminated Strand Lumber (LSL). Structural panels include products such as Oriented Strand Board (OSB) and plywood.
Prefabricated wood I-joists are made from EWP’s. The flanges are typically SCL or finger jointed lumber while the webs are either OSB or Plywood. All of which are classified as EWP’s. All of these components can be produced from fast growing, small diameter, low quality trees. In addition, EWP’s are able to utilize tree species once deemed as “weed trees”. Therefore, it is possible to make a structural product with a depth that is greater than the diameter of trees from which the components are produced.
The question becomes, how can we produce a high strength high quality product from such resources? The flanges are designed to resist bending forces and provide stiffness while the web is designed to withstand shear forces. The design of prefabricated wood I-joists utilizes the geometry of the I-shaped cross section to maximize the benefit of the high strength and stiffness components; therefore, efficiently utilizing the wood fiber.
Effects of Wood Production on the Environment
The forest product industry has been criticized by environmental groups especially in the timber harvesting practices such as clear cutting. Not only are clear cuts perceived to be a blight on the landscape, but the practice is also criticized for contributing to the “Green House Effect”.
The perceived environmental impacts of wood has helped to make other material such as steel and concrete more acceptable in residential construction. However, when one compares wood to other building materials, wood is a more environmentally friendly material in that less carbon is released and less energy consumed in the production of wood products than other materials. (See Tables 1 and 2).
Table 1 — Carbon Released and Stored in the Manufacture of Building Materials
| Material | Carbon Released (kg/t) |
Carbon Released (kg/m3) |
Carbon Stored (kg/m3) |
|---|---|---|---|
| Rough Sawn Timber | 30 | 15 | 250 |
| Steel | 700 | 5320 | 0 |
| Concrete | 50 | 120 | 0 |
| Aluminum | 8700 | 22000 | 0 |
Source: Presented in Ferguson, I., LaFontaine, B., Vinden, P., Bren,L., Hately, R., and Hermesec, B. 1996. ‘Environmental Properties of Timber” Research Paper commissioned by the Forest & Wood Products Research & Development Corporation.
Table 2 — Fossil Fuel Energy used in the manufacture of building materials.
| Material | Fossil Fuel Energy (MJ/kg) |
Fossil Fuel Energy (MJ/m3) |
|---|---|---|
| Rough Sawn Timber | 1.5 | 750 |
| Steel | 35 | 26,600 |
| Concrete | 2 | 4800 |
| Aluminum | 435 | 1,100,000 |
Source: Presented in Ferguson, I., LaFontaine, B., Vinden, P., Bren,L., Hately, R., and Hermesec, B. 1996. ‘Environmental Properties of Timber” Research Paper commissioned by the Forest & Wood Products Research & Development Corporation.
To further demonstrate, here are some facts about timber harvesting:
- 35% more wood is grown than what is harvested.
- More wood is lost to wild fires, pests and disease than is harvested.
- 0.40% of all productive woodland is harvested each year in Canada.
- Unlike ores that are mined, wood is a renewable resource.
Clearly, the effects of wood production on the environment are minimal when compared to other materials. Furthermore, it can be argued that with re-planting more carbon is taken out of the environment than we contribute.
Conclusion
Prefabricated wood I-joists provide a way to more efficiently use our wood resources while still providing high strength and quality products. The other benefit is that when compared to other products, wood and EWP’s are more environmentally friendly when compared to other materials.
