Forensic Analysis of Roof Deterioration Due to Condensation

Abstract

Corrosion of the structural steel roof deck of large warehouses resulted in several invasive forensic investigations to determine the cause and mechanism of the corrosion. The warehouse roof investigation presented in this paper is one of many similar warehouses located near the Gulf of Mexico and along the Southern Atlantic Seaboard experiencing corroded roof decks when constructed using fiberboard roof insulation made from sugarcane fiber called bagasse. Consensus exists among individuals studying this phenomenon that the fiberboard became saturated with water, which dissolved formic and acetic acid from the fiberboard. The steel deck corroded when it came in contact with the acidic solution. There was little consensus regarding the mechanism by which water intruded into the roof assembly. Invasive investigation of the low-slope roofs of buildings with various types of insulation (including bagasse fiberboard) and observation of physical commonalities between the instances led to the following conclusion: Water in the roof assemblies did not result from leaks through a compromised roof membrane but rather from humid air infiltrating the roof assembly and condensing on the underside of the roof membrane.