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Introduction

Design of durable structures is the result of careful planning and understanding of loads and forces that will likely act upon a building during its lifetime. If these key elements are not taken into consideration, the designer may compromise the ability of the structure to remain fully functional over extended periods of time.

Building codes establish minimum requirements for structural strength, safety from fire, and other hazards. To this end, the American Forest & Paper Association (AF&PA) provides several design standards and construction guides. AF&PA's National Design Specification® (NDS®) for Wood Construction, and the related Wood Frame Construction Manual for One- and Two-Family Dwellings, provide standards and guidelines for structural design and construction of wood-frame buildings. Likewise, AF&PA's Design for Code Acceptance (DCA) series provides building code accepted methods for complying with fire safety provisions of the codes. Yet, building codes do not address all of the issues that promote long-term durability of buildings and structures. This document describes practices to control moisture and protect a building from infestations of living organisms, which can influence the long-term durability of buildings, as can structural loads and fire exposures.

Design of durable structures begins with an understanding of moisture loading and how it interacts with building materials. The designer must be concerned with sources of water, how it is transported, and how it can be controlled and removed. Moisture flows within a building must be managed to prevent water accumulation or storage that may lead to premature deterioration of building products. Quality control is also extremely important in constructing building envelope assemblies to resist the negative effects of moisture.

In many areas, there may also be a risk of insect infestation. In particular, termites may attack wood frame structures and, in turn, reduce the life expectancy of the building.

When properly designed, wood frame structures will resist damage by moisture and living organisms. Recommendations for control of moisture and protection against decay and insect infestations are contained in this document. Many of the recommendations are established practice among architects, engineers, and builders.