Wood Products on the Job - Structural Applications
Roof Systems
The design of roofs varies considerably in North America — as it must to meet conditions that range from the snow loads of Alaska to the wind loads of the Florida coast. Wood-frame construction is a highly versatile construction method that can be suited to any load condition.

Wood trusses have surpassed lumber rafter roof construction in frequency of use. Trusses are accurately engineered and fast to install. In addition to lumber rafters, wood I-joists are used for roof framing.

Span tables for wood rafters are based on anticipated loads. In the same way, truss manufacturers and wood-I joist manufacturers use design software, based on local conditions, to design roof members.

The wood-frame roof is a system where the framing members, including plywood or OSB sheathing, transfer the vertical loads to the wall framing and improve diaphragm resistance against racking from lateral loads like wind.

As in the case of shearwalls, nailing patterns are extremely important for high wind areas where suction from wind pressure can lift panels of roofing away from the roof.

Concentrated Loads
Whenever the arrangement of framing members is interrupted by openings like windows and doors, headers, lintels, beams and columns are needed to transfer the loads around the opening to the support system below.

In addition to door and window openings, modern home buyers prefer open areas and high, cathedral style ceilings. That means few supporting walls, columns and roof structures can be used. Taking their place are engineered components designed to handle the increased loads.

Several wood products are used for beams and columns including built-up lumber (nail-laminated) beams, glulam, laminated veneer lumber, parallel strand lumber, girder trusses and wood I-joists.

Often, the design of beams and columns is not included in the prescriptive solutions provided in the building codes and the services of an engineer are required. However, preliminary sizing can be done using software such as WoodWorks® or Beam Check.

Timber Frame Construction
Prior to the advent of sawmilling in North America, construction was typically made with hand sawn or hewn posts and beams. In the past 25 years, there has been a revival of this traditional timber frame construction.

Timber Framing Resources
Island School of Building Arts
Timber Framers Guild

Column Capacity Charts for Download
Typical Glulam Beam Capacities