INTRODUCTION

The building envelope is usually considered to include facades, windows, and roofs. The first portion of this chapter deals with building walls and facades and the second part with windows and nonmasonry curtain walls. Roofs and roof terraces are not included in this chapter.

Prior to the 20th century, building walls served not only to keep out the weather, but also to support the building's floor and roof loads. Within the last 100 years the function of supporting the structure has usually been relegated to a structural skeleton, with the wall serving only to enclose the building. The building wall's primary role has become that of shedding water and containing occupants, furnishings, heat, etc. The wall also supplies light and vision via windows, and it defines the architectural character of the building. As buildings grow in size and complexity, and as economic pressures lead to thinner, less costly wall systems coupled with greater performance expectations, the potential for building envelope problems and failures increases.

In light of the role of forensic structural engineering, which involves the application of engineering principles to investigate and resolve causes of failure, to provide information for the development of repairs, and to aid in the jurisprudence process, the intent of this chapter is to provide information on principles of investigation and analysis and on common failures associated with various building envelope systems.