6.4 Exposure to Corrosion and Building Orientation

Both exposure and building orientation affect corrosion rates (exposure classes are described in Section 7 of this Course). Exposed areas such as building exteriors are often coated with large amounts of salt spray and can be expected to suffer high corrosion rates. LaQue (1975) found that the metals on the side of a building facing the ocean corrode much faster than those facing away from the ocean.

Perhaps less obvious is LaQue’s finding that partially sheltered exposures, such as areas under pilingsupported buildings or under decks and walkways, can experience even greater corrosion than open exposures. Tests showed that portions of buildings exposed to rain may undergo lower corrosion rates than sheltered areas because rain can periodically wash away salt accumulations. Sheltered or covered areas, on the other hand, do not benefit from occasional rinsing from rain and therefore accumulate more salt, resulting in higher corrosion rates.

Another effect of exposure and building orientation is related to the duration of surface wetness. Open exposures dry more readily because they are exposed to sunlight, and rapid drying slows the corrosion rate. Partially sheltered exposures stay damp longer and therefore may corrode faster.