What do the following four contractors have in common?

The most significant commonality between these four cases is that a subsequent investigation demonstrated that the sources of excess moisture in these buildings were located at the buildings’ interior, not the exterior.

Finding Solutions?
In case #1, the only evidence offered against the roofer was that one of the roof drains was positioned directly above the damaged area down at the first floor and destructive testing at this roof drain had found a small area of plywood decking with elevated moisture content. These observations were deemed sufficient to initiate a claim against the roofer alleging harmful health effects to the first floor tenants due to mold proliferation within an interior wall.

After months of legal maneuvering, permission was granted to the defense expert to open this interior wall, exposing the drain piping that serviced the roof drain. Both the surface of the piping and the adjacent framing and wallboard were observed to be clean and dry, with no evidence of any past leakage from above. Permission then was granted to open a similar section of the interior wall at the second floor unit—where the plastic drain pipe was found to have been punctured by a nail used to secure the wood baseboard trim. During winter rains over several years, leakage at this puncture had migrated down the wall to the lower unit. Despite evidence fully exonerating the roofer of any responsibility for this interior damage, plaintiff’s attorney then issued a revised demand for $10,000 to settle the claim.

Case #2 is a similar story in which plastic drain leaders from the roof gutters had been concealed inside wood-framed deck columns. Staples used to secure the stucco’s metal lath to the OSB sheathing had punctured the hidden drain piping, which abutted the back side of the sheathing. The stucco contractor arrived at the project after the columns had been sheathed—should the contractor be blamed for not determining the exact positioning of the unseen piping?

Case #3 resulted from a failure to connect the clothes dryer ducts to the corresponding vents at the exterior walls properly. At almost every vent, warm moist air was being pumped into the wall cavities. The resulting damage was particularly severe near the vents. Yet after a multi-day investigation, the plaintiff’s expert concluded that this damage had resulted from rainwater infiltration from the exterior due to the siding contractor’s failure to ensure proper spacing of the nails used to secure the vinyl siding.

Case #4 represents a common problem in residential buildings during winter months in some parts of the country—condensation of water vapor that is migrating, via diffusion and/or air convection, from the warm humid interior toward the colder, dryer exterior. The surging popularity of fiber-cement siding systems, which have very low vapor permeability ratings, has increased the likelihood of such vapor condensation in exterior walls of homes that have relatively high levels of interior humidity.

Different Perspectives
Sometimes the severity of the condensation damage makes the problem obvious to all observers; however, as discussed with Case #4, what about minor wintertime condensation over the course of a multiyear period that results only in rusty nail heads and minor staining of the sheathing? Do these conditions constitute a level of damage that necessitates total replacement of the siding and sheathing? If so, why blame the siding contractor for vapor migration from the interior?

Case #4 is significant because it highlights a differing perspective between building envelope scientists and some construction defects professionals who limit their litigation work to representing plaintiffs. North America’s leading guru of building envelope science is Dr. Joseph Lstiburek of the Westford, Mass.-based Building Science Corp., whose publication Vapor Barriers and Wall Design includes the following guidance:

Dr. Joe’s ‘no harm, no foul’ perspective of acceptable building envelope performance is reasonable, obvious and consistent with ASTM E 2266-04 Standard Guide for Design and Construction of Low-Rise Frame Building Wall Systems to Resist Water Infiltration.

However, many attorneys and their experts will cite minor surface staining after years of service at otherwise undamaged sheathing or framing as proof, ipso facto, that the building envelope must be reconstructed.

These four examples demonstrate that each investigation must be approached with an open mind. Most good construction professionals understand the numerous routes by which rainwater can infiltrate a poorly-constructed building envelope, but this knowledge should not blind them from also evaluating every reasonable possibility that the primary source of the observed moisture or mold damage is located within the building interior, not at the exterior envelope.