Wind Resistance

Wood has inherent characteristics, such as its light weight and flexibility, which make it an ideal material in areas prone to high winds.

The elements of a wood-frame building that enable it to withstand lateral loads are the shear walls and diaphragms. However, in order for either to be effective, all of the related components—including framing, structural panel sheathing and inter-element fastening details—must be designed and installed correctly.

For the structural system to work, a roof diaphragm must act to transfer lateral loads to the shear walls and the shear walls themselves must transfer this load to the foundation. The effectiveness of the entire system is only as good as the quality and quantity of the connections. Thus, the key to constructing a building that can resist lateral loads is understanding connections and the proper transfer of forces.

In hurricanes, the loss of roofing materials and sheathing is the leading cause of structural failure in wood-frame buildings. The central reasons behind these failures are improper connection detailing between structural systems and inadequate fastening of sheathing to supporting members. Most local building codes require a minimum of 33 fasteners for a standard 4x8 panel installed over roof supports 24 inches on center (o.c.). Fasteners, such as 8d common nails or other code-approved fasteners, should be placed a maximum of six inches o.c. along panel edges and 12 inches o.c. at intermediate supports. Following Hurricane Andrew in Florida, damage assessment teams found roof sheathing panels with as few as four fasteners. Once the roof sheathing has been pulled off the roof framing, the load path is interrupted and the diaphragm ceases to function.

Source: Design Concepts: Building in High Wind and Seismic Zones – APA – The Engineered Wood Association, 8 pages

More information

• Designing for Wind Resistance - WoodWorks
• ANSI/AF&PA NDS-2005 – National Design Specification® (NDS®) for Wood Construction – American Wood Council/American Forest & Paper Association standard, 268 pages
• ANSI/AF&PA SDPWS-2005 – Special Design Provisions for Wind and Seismic standard with commentary – American Wood Council, 44 pages
• ANSI/AF&PA WFCM-2001 Wood Frame Construction Manual for One and Two-Family Dwellings with commentary – American Wood Council/American Forest & Paper Association standard, 320 pages
• Considerations in Wind Design of Wood Structures – American Wood Council, 9 pages ( 113KB PDF)
• Diaphragms and Shear Walls – APA – The Engineered Wood Association, 32 pages
• Introduction to Lateral Design – APA – The Engineered Wood Association, 20 pages
• Retrofitting a Roof for High Wind Uplift – APA – The Engineered Wood Association, 8 pages
• Roof Sheathing Fastening Schedules for Wind Uplift – APA – The Engineered Wood Association, 4 pages
• Wind-Rated Roofs: Designing Commercial Roofs to withstand Wind Uplift Forces – APA – The Engineered Wood Association, 12 pages