Performance & Durability
Wood-frame construction combines dimension lumber or engineered wood products and structural wood panel sheathing to make wall, floor and roof assemblies that can be built quickly and efficiently. The assemblies are tough, durable, easy to connect and easy to insulate. About a million new wood-frame homes are built every year in North America.
Companies and universities across North America are constantly improving the materials and techniques that make wood-frame construction such a success:
- Wood trusses for roofing applications that can accommodate virtually any roof shape or loading. Designed and manufactured under exacting factory conditions, they offer quality, performance and flexibility.
- Engineered wood products such as I-joists and laminated veneer lumber (LVL) that provide consistent engineering properties, dimensional stability, higher strength-to-weight ratio and reliability.
Wood-frame construction can be adapted to any energy code requirement so wood houses, offices, schools and other commercial and industrial buildings can keep energy bills for heating and cooling low.
2x4 or Light Frame Construction
Figure 1 demonstrates a typical arrangement of framed members.
Light framing is the use of closely spaced members of dimension lumber size combined with sheathing to form structural elements of a building. The structural elements provide rigidity, support for interior finish and exterior cladding, and a cavity for the installation of insulation. Light framing is the most common method of residential construction in North America. It is also a form of construction which can be used on a larger scale for commercial and public buildings.
Light framing makes use of dimension lumber (generally sawn lumber 38mm (2" nom.) wide and up to 286mm (12" nom.) deep) and manufactured wood products of comparable size to build structural frameworks. These main structural members are used in concert with sheathing elements to provide rigidity for walls, floors, and roofs. Typically, light frame members are spaced no further apart than 600mm (2').
For some loading configurations, engineered wood products such as light frame trusses, prefabricated wood I'joists, or other structural products such as laminated veneer lumber (LVL), parallel strand lumber (PSL) and glulam may be used as framing elements. Where large or clear spans are a requirement, light framing members may be used in combination with heavy beams or columns to transfer loads directly to foundations.
Frame construction, by using small repetitive members and fasteners, develops a redundancy of design. This means that alternate paths of load transmittal become available when the primary path fails. For this reason, frame construction is not prone to sudden failure and is recognized as a good construction technique for resisting, for example seismic and wind forces.
Post and beam construction
Post and beam construction is a method of construction which uses large, widely spaced members to provide structural support. It is a principle method of wood construction which offers the designer the possibility of combining function with the unique beauty of wood.
In light framing construction, the framing serves as structure, as exterior sheathing and interior finish support, and as the insulation cavity. The sheathing and framing together resist lateral loads or racking.
With post and beam construction, the columns and beams support vertical loads, intermediate framing is required to support exterior sheathing and interior finish and provide space for insulation, and diagonal bracing or other support is required to resist lateral loads.
Post and beam construction uses timber, glulam, and parallel strand lumber (PSL) for beams, columns, girders and purlins for structure, and decking for floor and roof sheathing. Using these large members, post and beam construction can be used to create dramatic and appealing appearancesinside and outside a building while providing the degree of fire safety for Heavy Timber construction allowed by North American building codes.
Timber framing is the traditional form of post and beam construction. The origin of timber joinery in North America predates the availability of metal fasteners and of sawmill produced lumber. Therefore large hand hewn and hand sawn timbers were used, joined together by mortice & tenon connections, secured with hardwood pegs, or merely by joint geometry.
Timber framing has enjoyed a revival in recent decades where the technique has been used to create distinctive home designs. Enough is now known about wooden joinery, that it is being used more frequently in commercial projects. It is a method of construction which is more labour intensive than contemporary post and beam construction but which offers a finished appearance demonstrating wood construction and workmanship in an artistic form.
Contemporary post and beam construction and timber frame differ in the following ways:
Post and Beam:
- Timber, glulam, parallel strand lumber (PSL) and laminated veneer lumber (LVL) are used for main members
- Shop preparation of connections is possible
- Metal fasteners are used for speed, economy, and strength
- Hardwood or softwood timber is used for main members - usually in a 'green' state, or of a high moisture content. Recycled or radio-frequency kiln dried timber is also available to reduce movement and checking in the timbers as they dry out. Both these options come with higher cost considerations. Glulam can also be incorporated into timber framing.
- Precise shop preparation of joints is almost always required.
- Fastening is based on the interlocking of members by friction fit, by the use of hardwood pegs, and where employed, traditional joining techniques.
Whether modern materials and connections are used to create wood post and beam construction or whether the historic and traditional timber joinery is used to join members, the resulting product can be functional and striking.
Log homes are manufactured by a number of British Columbia companies, and include traditional horizontal log work, log post and beam construction and variations of both. Log post and beam construction typically uses large-diameter wood for vertical posts, (round or squared) which support horizontal beams. Many British Columbia softwood species are used for log homes, including cedar, pine, spruce and fir.