Common Examples of Non-Storm Related Moisture Intrusion

It is that time of year when memories of snow loads and frozen pipes are distant, having been replaced with thunderstorms, hail, and hurricanes.

It also is the time of year when discoloration of ceiling finishes, delamination of trim, and other distress to interior finishes is noticed. One might wonder: Is the distress relatable to last week’s hail storm, or last month’s heavy rain with high-velocity winds?

For this distress to result in covered damage, often the question becomes “Was there a storm-created opening that allowed moisture to penetrate the building envelope? Storm-created openings often are somewhat straightforward. They typically result in missing shingles, punctured roof membranes, or broken windows.

But what if there is not such an opening? Where did the distress come from? The answer can be more subtle and, in many conditions, could be a latent condition that has existed since construction of the building. The following are some common examples of moisture intrusion related distress and their non-storm related causes.       

Condensation. When hot, humid air drops in temperature, it releases the water that it is carrying. In much of the country, summer brings just the hot and humid conditions that make up half of this equation (coincidently this also corresponds with hail and hurricane seasons). The other half of the equation is the cool, dry luxury of air conditioning. As long as the two do not mix, there is not a problem. The problem occurs, however, when the warm and humid air makes contact with a cool air-conditioned surface.

An example of this air leakage through the building envelope is noted in Photo 1. Hot, humid ambient air leaks through the exterior wall of a courthouse and hits the air-conditioned concrete surface cooled by the return air plenum. The result is a continuous source of substantial water infiltration even when it is not raining.

In many cases, the air conditioning actually accommodates and treats much of the humidity and condensation-related infiltration. What if a wall finish, like vinyl wallpaper, prevented this from occurring? With similar air leakage through an exterior wall assembly, the hot, humid air would condense on the cool back side of the wallpaper, trapping the moisture and preventing it from being absorbed and conditioned in the air-conditioning system. Over time, this becomes a problem because the wallpaper has, in effect, become a vapor barrier on the wrong side of the wall. In a warm climate, the vapor barrier should be on the outside of the wall, if used at all. Too often, the specific climate is overlooked when specifying finishes for national retail, restaurant, and hospitality chains.  

Ventilation. A properly ventilated attic space serves a couple of purposes. First, it exhausts hot air and helps with cooling costs while also prolonging the life of the shingles. Ventilation also serves to mitigate humidity against the issues previously described. Building codes are fairly specific about attic ventilation, but often it is not done properly. Vents are located incorrectly or are undersized; soffit vents get plugged with insulation; or ventilation is circumvented with a well-intended but counterproductive mechanical fan or louver.

With all of the issues that can go wrong with attic ventilation, at least we don’t have to worry about ventilating vaulted or cathedral ceilings, right? Wrong. Except for very specific construction, most codes require that vaulted and cathedral ceilings have the same ventilation as a ceiling with an attic. If there were any way to quantify this, it could very well be the most common construction-related defect ever.

Following Hurricane Ike, a cathedral ceiling with tongue and groove joints was discovered to have discolorations of the ceiling finish. An inspection of the roof found no missing shingles or other storm-created openings. The inspection also revealed that the roof assembly was not equipped with ridge vents, soffit vents, or any other means to ventilate. After close observation of the discoloration (see Photo 2), it became apparent that lack of ventilation created a condition where hot, humid air trapped within the system escaped through the tongue and groove joints, condensing on the relatively cool surface of the ceiling finish and causing discoloration. 

Maintenance. “It never leaked until this storm.” If the drains get plugged or overwhelmed on a low-slope roof with a continuous parapet, the water level during a particularly rigorous event can rise to a point where it bypasses the flashing, resulting in water infiltration (see Photo 3). This could quite possibly be the first time that a particular sequence of events came together with a heavy rain causing water infiltration during the service life of the facility. Still, this is a latent defect coupled with a maintenance issue resulting in the observed distress.

In summary, moisture-related distress can go unnoticed until an event creates reason to investigate further. Storm-created opening distress can be relatively easy to diagnose and develop a scope of repairs for. The latent conditions that also result in moisture intrusion through other mechanisms can be more challenging to discover and remedy.