You're assigned a water damage claim, and the residence is dark and damp. A thin veneer of fungal growth covers selected contents and the walls. However, your observations and interview with the insured yield no evidence of a recent water release. Is there a hidden water source? Did the air conditioning fail for an extended period of time? Don't be confounded; you may have encountered the modern equivalent of a cave.
Caves are commonly cool, dark, damp environments. Unknown to owners of condominiums, apartments and houses, cave-like conditions can be created by their lifestyles. When you encounter these conditions with no apparent water loss, think moisture mismanagement.
Air conditioning systems are sized to meet a calculated heat load. The heat load consists of two elements: the sensible heat load and latent heat load. When conditions alter the amount of either type of load, the effectiveness of an air conditioning system to cool and dehumidify decreases, and the living conditions deteriorate. The climatic region can affect an A/C's functioning and lead to fungal growth.
In hot, humid climates, cool, damp interior conditions can occur when the sensible heat load is lowered in an effort to decrease energy costs and improve privacy. Hurricane shutters, landscaping, tree cover, covered porches and neighboring buildings reduce the sensible heat load outside the home. Drapes, curtains and shutters can nearly eliminate the penetration of light and heat inside the home, but as a consequence, the relative humidity increases. In the short term, these elements provide privacy and a lower electric bill, but in the long run they create a disparity between the design capacity of the air conditioning system and the actual heat load. The greater the disparity, the shorter the operating or "run time" that is required for the air conditioning equipment to lower the temperature and meet the thermostat's set point. The less the air conditioner operates, the less dehumidification occurs within the home, creating a living space that is cool and damp.
When these conditions occur, the moisture content in gypsum board paper, leather goods, and wood gradually rises to the point where microbial growth is supported. The rate of moisture absorption is slow, often requiring months or seasons to manifest fungal growth and characteristic odors.
In cold, humid climates, buildings are likely to experience cool and damp conditions when the latent heat load exceeds the intended design capacity, especially during the winter months when residents try to retain heat and diminish exterior ventilation. When these efforts are coupled with cooking and bathing, the retention of latent heat prevails. Residents with ineffective bath and kitchen ventilation, limited make-up air, and overall poor air circulation experience elevated humidity, excessive window condensation and microbial growth. This problem is usually recognized after several years of occupancy when the building materials and home contents have experienced several wet-dry seasonal cycles and the moisture content is optimal to support fungal growth.
The cave effect can be manifested in a wide range of locations; the most common is the north-facing, lower floor condominium or apartment. By all appearances, north-facing units constructed with large sliding glass doors allow diffused, ambient light to enter during the day without the harsh impact of direct sunlight (Figure 1). This seemingly pleasant circumstance has a hidden liability—little or no sensible heat gain. What is initially perceived by the owners or tenants as a utility bill "wonder" is gradually replaced by the frustration of damp sheets, window condensation, and moldy shoes and garments (Figure 2).
Unoccupied units located adjacent to occupied units are also susceptible to moisture. When a subject unit shares an adjacent wall, ceiling or floor with an air-conditioned unit, a portion of its sensible heat load is transferred to the adjacent unit. In this circumstance, unoccupied units may experience a diminished sensible heat load and consequentially less dehumidification; as a result, the thermostat in the subject unit reaches the set point temperature less frequently.
Large apartment and condominium complexes can also suffer from HVAC uniformity. If you inquire about the size of air conditioning systems in units with one, two and three bedrooms, you will often discover that they are strictly sized. For example, one-bedroom units will be equipped with a 1.5-ton unit, two-bedroom units with a 2.5-ton unit, and three-bedroom units with a 4-ton unit. So, despite their orientation, north-facing units with the same floor plan will have the same cooling capacity as those units that face south, east or west. When evaluating an apartment or condominium with moisture problems, one of the first tasks is to determine the direction the most prominent fenestration faces. The best candidates for moisture management problems in large multi-family complexes are those located on the first floor, with exterior windows or doors that are covered, shaded or north-facing.
Building attributes also diminish sensible heat load. Hurricane shutters, reflective window coatings, extended balconies and overhangs, covered hallways, concrete stairwells located in front of an entry, screened lanais, and shade trees can block sensible heat load and change the performance of an air conditioning system. Don't ignore the contribution of these elements when evaluating water damage claims.
Sensible Heat – When an object is heated, its temperature rises as heat is added. The increase in heat is called sensible heat. Similarly, when heat is removed from an object and its temperature falls, the heat removed is also called sensible heat. Heat that causes a change in temperature in an object is called sensible heat. Both exterior (sunlight) and interior sources of heat (appliances, lights, electronic equipment, etc.) are used to properly size an HVAC unit.
Latent Heat – All pure substances in nature are able to change their state. Solids can become liquids (ice to water) and liquids can become gases (water to vapor), but changes such as these require the addition or removal of heat. The heat that causes these changes is called latent heat. Sources of latent heat in a home include water vapor infiltration and sources created inside the home (e.g., showering, cooking, breathing, bathing).
Water Activity (Aw) – Water activity expresses the tendency of water to escape (become available) when compared to pure water. This unit of measure is similar to the vapor pressure. Water activity is essentially a measurement of water availability in a substrate.
Relative Humidity (RH) – The ratio of the partial pressure of water vapor in an air-water mixture to the saturated vapor pressure of water at a given temperature. RH refers to the amount of moisture a given air mass contains relative to the potential amount the air mass could support if saturated with water vapor (i.e., 100% RH) under the observed temperature and atmospheric pressure.
Xerophiles – Xerophilic fungi grow under conditions of reduced water activity or water availability. They are the first fungi to grow on water-damaged surfaces. These fungi grow and reproduce in conditions of high sugar or salt concentrations that often occur during the early stages of a water loss.
Spelunking for Clues
Not all water-based damage occurs from a sudden event. Moisture retention and conditions that cause the cave effect require sustained conditions of elevated relative humidity over months or years. When fungal growth occurs, it represents the last but most recognizable event in a sequence of gradual water vapor absorption caused by poor moisture management.
The fungal species typically encountered in the domestic cave are Xerophiles, which proliferate with the least amount of water. These pale green to gray fungi grow on walls, leather goods, clothing, closet contents and various surfaces throughout the residence, and are frequently species of the genus Aspergillus or Penicillium. Members of these genera can grow and reproduce within a week or two, relying on moisture from sustained conditions of elevated relative humidity. They grow with minimal moisture requirements (water activity [Aw] = 0.75 to 0.90) and require only atmospheric water vapor to initiate growth. Taking and analyzing samples of fungi growing in a site of loss can assist in the determination of duration.
Interviews on typical lifestyle contributions to microbial growth will also aid the investigative process. For instance, the misuse of hurricane shutters is fairly common, but might not be evident when you inspect a home. The shutters are meant for protection of the home during hurricanes, but some owners keep the shutters closed throughout the six-month hurricane season and often throughout the entire year, thereby creating cave conditions. You won't know about that without asking. Typical temperature settings, use of ventilation in bathrooms and throughout the house, and hidden indicators, such as moist linens, could remain unknowns without a thorough interview.
Here are some steps to take whenever you encounter a residence with microbial growth but no apparent water loss.
- Diagram the orientation (indicate north arrow) of the house, apartment or condominium and the windows.
- Photograph exterior conditions (hurricane shutters, trees, landscaping, balconies, screened lanais and concrete stairwells).
- Inquire as to the occupancy of adjacent apartments and condominiums including those above and below. Are they occupied? If so, at what temperature do the occupants set their thermostats?
- Locate areas of microbial growth on a floor plan and determine if they are predominantly behind furnishings, pictures and drapes. Is the microbial growth diffuse and positioned primarily along the north wall?
- Photograph heavily shaded windows.
- Record the set point temperature on the thermostat and inquire at what times the insured alters the settings.
People and Going Green
The most critical elements that influence the performance of a building are the occupants. Lifestyles that create additional water vapor and/or thermal gradients will elicit a profound effect on the performance of every structure. High-performance or "green" building designs emphasize reductions in energy consumption, solar heat gain, and outside air infiltration. When these strategies are implemented, increases in latent heat load are inevitable unless efforts are made to compensate and keep the interior space dry (< 60% relative humidity). Efforts to save energy must be balanced with efforts to manage moisture, a frequent underlying cause of what look like water-damage claims.
) is a consultant in the Building Sciences Dept. of HSA
. Dr. Ralph Moon
), director of the Building Sciences Dept. with HSA in Tampa
, is a frequent speaker at educational seminars for insurance adjusters.