Energy efficiency and durability are two goals that have recently gained higher priority among building envelope specialists and architects. Often, these two goals have negative impact on each other. When steel is exposed to humidity corrosion prevention and control are unquestionable requirements. At design time and/or when planning for maintenance and durability simulation tools are needed to assess the potential for corrosion and its impact.

Recently, a number of hygrothermal simulation tools have been created that provide good predictions of the local temperature, relative humidity, and moisture contents in building envelope systems. While this information is invaluable, there is a need to include corrosion prediction in the cost, benefit, and risk analyses of particular envelope systems.

In this paper, we describe the development of a multivariate corrosion model derived from the ISO-9223 standard amenable to be incorporated or interfaced to existing hygrothermal simulation codes. We also describe the approach followed to generate time-dependent corrosion estimates from the yearly-averaged values and to account for temperature effects. For illustration, we present results obtained by simulating the time-dependent hygrothermal conditions and predict corrosion build-up of a building structure subject to typical interior and exterior conditions.