When Moisture Attacks and the Impact to Your Building Envelope
In September 2017, two category 4 hurricanes and one category 5 hurricane devastated Florida, Texas, Puerto Rico, the U.S. Virgin Islands and more with a total cost of up to $475 billion in damages. During the 2016-2017 rainy season, SF Gate reported that California received more rain in just a few months than the state had seen in the previous five years – combined. And, according to The Weather Channel, by January 2017, Bismarck, North Dakota had already received 31 inches of snow above average, and had exceeded the entire average season’s worth of snow. It’s hard to deny that we’ve been seeing more volatile moisture events, and it begs the question as to whether they are the new normal.
Not surprisingly, the significant amounts of precipitation that come with these extreme weather events has obvious catastrophic and in some cases, even irreparable, effects to buildings in which we live, work and play. But what about the damage the inconspicuous moisture that accumulates inside these buildings as a result of these events (as well as ventilation issues, poor insulation, air leaks and more) can cause ongoing, not only to the structure itself, but also to our health?
Thanks to common problems with moisture control, simply breathing indoors can harm us. There is a strong association between exposure to damp indoor environments and adverse health effects, according to the Institute of Medicine (IOM) of the National Academy of Sciences. It’s terrible to think that moisture might be lurking in the background unnoticed while being detrimental to the health of a building’s occupants over time. This hurts our pocket books, too – moisture-related health problems and building damage can be extremely expensive. Berkeley Lab estimates that the annual asthma-related medical costs attributable to exposures to dampness and mold total approximately $3.5 billion in the U.S, so cutting back on moisture issues could help reduce costs from having to visit the doctor.
In many ways, moisture control is one of the unsung heroes of any building. The truth is, it’s fundamental to the proper functioning of any building. In addition to protecting occupants from adverse health effects, controlling moisture also protects the building and its mechanical systems and its contents from physical or chemical damage. Yet, moisture issues are common.
A little bit of water makes for big problems
Moisture-related problems are common in U.S. buildings. Between 1994 and 1998, the U.S. Environmental Protection Agency (EPA) Building Assessment Survey and Evaluation (BASE) study collected information about the indoor air quality of 100 randomly selected public and private office buildings in the 10 U.S. climatic regions. The BASE study found that 85 percent of the buildings had been damaged by water at some time, and 45 percent had leaks at the time of data collection. A 2007 study in ASHRAE journal found that, out of 17,000 construction defect claims, 69 percent were the result of moisture-related defects in building enclosure systems.
Moisture-related issues such as damp and moldy indoor environments can lead to increased cases of upper respiratory problems, including coughing, wheezing and asthma aggravation, among others, according to the EPA. There’s also evidence that high levels of building moisture can lead to dyspnea (shortness of breath), lower respiratory illness and asthma development.
As a result of such high levels of damage, moisture-related problems are also costly – American businesses can spend as much as $9 billion annually repairing and litigating damages from moisture intrusion.
Managing moisture through better design
For commercial and residential buildings alike, one of the best ways to address moisture-related problems is to attempt to prevent them from happening in the first place. Designing building enclosures to reduce water intrusion is the best place to start. Then it’s important to look at water condensation – make sure exterior enclosures are airtight by using continuous air barrier systems around the entire enclosure. To be effective, these systems must reduce air leakage into the exterior enclosure assemblies during cold weather, and leakage of outdoor air into the exterior enclosure or interior wall, ceiling, and floor cavities during warm weather. Air sealing an enclosure makes it easier to manage indoor-outdoor air pressure relationships with practical airflow rates.
Meeting minimum R-values in accordance with the International Energy Code will help ensure the building is up to standards. Meanwhile, managing the flow of heat and water vapor through all enclosure assemblies can help avoid condensation on materials inboard of the drainage plane. Insulating materials must also be used to manage heat flow to keep the surface temperature of low permeability materials inside the enclosure above the expected dew point. A continuous thermal barrier also is necessary to reduce condensation on the interior surfaces of exterior walls and ceilings during heating conditions. The insulation layer must be continuous to reduce condensation due to thermal shorts. Areas of high concern include metal framing, concrete slab edges and angle iron ledgers.
Focusing on foundations and walls
Foundations and walls are vulnerable to moisture problems. During warm weather, water may condense on foundation materials because the materials are cooler than the outdoor air. Likewise, crawl spaces and basements have more extensive contact with cool damp or wet soil than slab-on-grade foundations. That’s why many moisture problems can be avoided by properly designing the foundation. This can be done by specifying insulating materials for the outside of foundation walls that can tolerate exposure to the earth. Extruded polystyrene (XPS),high-density expanded polystyrene (EPS) foam boards, or closed-cell spray polyurethane foam (SPF) insulation can be successfully used to insulate outside surfaces of foundation walls. Given wet materials don’t maintain the same R-values it’s essential to understand that using water-resistant materials plays a major role in the performance of a building’ design. Water absorption is commonly measured for these types of materials through standardized testing, such as ASTM C272.
Moisture control is an important aspect of designing an integrated building enclosure. Failing to properly design walls to manage moisture, as well as failing to transition walls with other building enclosure components – such as the roof and foundation – can lead to serious moisture-related damage. To fix these damages, multiple building components may need to be replaced, which is not only extremely difficult to accomplish due to the façade making components inaccessible, but costs a pretty penny in high repair fees, too.
Designing exterior walls to manage excessive rainwater will help mitigate this and is a great start. Monolithic, conforming materials such as a liquid flashing solution to seal around common problem areas like windows, doors, outdoor intakes, exhaust, ducts and other penetrations, can help achieve the water tight barrier your building needs. Exterior walls must also reduce condensation. Cool surfaces within the building envelope can lead to water vapor condensing. Avoiding this condensation can be attempted by controlling the temperature with continuous insulation.
It’s important to understand these issues clearly. Moisture-related issues – which is an even larger concern if recent weather events are any indication – impact the health of building occupants and can be mitigated with a design that minimizes water intrusion. Beyond damages from weather, we see from multiple studies that buildings often unknowingly have leaks and need to be repaired immediately to minimize further issues and higher costs due to repairs. It’s also necessary to pay attention to the foundation and use a design that minimizes condensation from wreaking havoc on crawl spaces, basements and walls.
Staring in the eye of a natural disaster serves as a reminder that buildings need to be designed with the impacts of moisture in mind. Designing a more resilient building will not only help to prepare for unforeseen issues, but will help the building to continue to thrive over time.