UPDATED: November 11, 2021
“Indoor mold is the culprit behind an epidemic of headaches in the United States,” as stated in the article Mold Insurance: Crafting Coverage for a Spreading Problem. The article by Julia R. Barrett goes on to say “if these aren’t literal headaches – they certainly are figurative ones, as a result of the nightmare of cleaning up mold contamination and converting the associated costs.”1 A quick Google News search for “apartment mold” returns about 83,500 results with numerous reports from across the country made within the past few weeks.
According to the Journal of Property Management, “a growing problem for building owners and managers is the occurrence and recurrence of mold. Mold spores fester indoors and can be found anywhere from low-income tenant apartments to multi-millions dollar office suites.”2 The book Toxic Mold Litigation states that “news reports of mold infestation and new mold-related lawsuits continue to appear with regularity.”3 The author Raymond C. King, explains further that “mold claims are likely to be a staple of property-damages, bad-faith, and personal-injury litigation for some time to come.”3
The Insurance Information Institute says that “the national cost of mold is difficult to track because most insurers don’t separate mold from water damage claims, but the latest estimates clearly show that mold is a multibillion dollar problem.”4 At the center of the debate is the issue of responsibility between landlords and tenants. By educating both landlords and tenants we can implement moisture removal solutions to help maintain healthy living conditions and reduce high humidity and mold growth in apartments.
Use Moisture Management to Lower Relative Humidity
• Excess moisture can originate from leaks, ventilation, and occupant activities such as cooking, cleaning, showering & even breathing
• Leaks (weather or plumbing) are the result of a building failure and must be corrected immediately – responsibility for leaks usually falls on the landlord
• Water is in the air – the amount depends on various factors. The principles of water vapor are typically poorly understood by landlords and tenants.
• Maintaining appropriate levels of moisture (water vapor) inside apartments is the responsibility of both the landlord and the tenant.
“The most common surface moisture-related problems, regardless of climate, are mold, mildew, and condensation. The single most important factor influencing these problems is relative humidity near surfaces.”5
-Joseph Lstiburek and John Carmody, Moisture Control Handbook
Excess humidity can cause condensation in apartments.
Condensation occurs when moisture in the air “condenses” into liquid water on a cool surface. The surface temperature at which this occurs is known as the “dew point”.
In cases involving water leaks, tenants should promptly notify the landlord that water is leaking into the unit. By doing so, the tenant is acting to protect the structural integrity of the dwelling while helping to prevent problems from unwanted moisture that is not removed promptly. More frequently than physical leaks is the presence of excess moisture in the air (high relative humidity). A common example might be unwanted condensation on windows.
In the Moisture Control Handbook, Joseph Lstiburek and John Carmody state, “condensation can provide an environment for the growth of mold, mildew, and other biological pathogens. In addition, it can lead to the deterioration of building materials if it is allowed to collect.”5 The concept of condensation is important. Condensation occurs when moisture suspended in the air (water vapor) “condenses” into liquid water on a cool surface. The surface temperature at which this occurs is known as the “dew point” temperature. Dew point can be controlled by controlling BOTH room temperature and relative humidity (RH).
According to the Moisture Control Handbook, “the same strategies that control mold and mildew growth also control condensation on surfaces – increasing surface temperatures and reducing vapor pressures (moisture levels) near surfaces.”5
“To control mold growth in our homes, we must control excess moisture and water!”
– Kathleen Parrot, Ph.D., Mold Prevention6
“In order to grow, molds require:
• A food source.
• Appropriate temperature.
• Adequate moisture.”6
“Mold spores are present everywhere, in outside air as well as indoor air.”
-What You Need to Know About Mold 7
The following excerpt from Mold: Causes, Health Effects and Clean-up explains how water affects the construction process:
“Mold, especially mold spores are everywhere outside. Mold is on everything we build with and everything we bring into a building. Remember we build outside. We turn a piece of the “outside” into the inside as the construction process progresses. Therefore mold will also be inside. And remember it’s often wet outside. What’s worse is that construction is also a wet process. It is not possible or practical to have a mold free building. Just like it is not possible to have a mold free outside. We just don’t want a lot of mold inside and we don’t want any mold that is actively growing. We especially don’t want a lot of mold or mold that is growing where you can breathe it.”8
Moisture is the only factor that can be sufficiently controlled.
Temperature control is affected by mechanical limitations, ambient environment, and tenant preference. Oversized HVAC systems are common in multifamily housing properties. It is important to note that conventional air conditioning systems operate based on sensible (temperature) input. Water vapor removal by air conditioning systems depends on how long the air conditioner runs and is secondary to the primary function which is temperature control.
Water vapor removal by air conditioning systems depends on how long the air conditioner runs and is secondary to the primary function which is temperature control.
A good example of this scenario would be senior housing properties. These apartments are typically smaller than the average family housing unit. The smallest conventional split air conditioner supplies 18,000 BTUs of cooling (or 1.5 tons) which may be more cooling than is required. For many senior apartments, this means the tenant is forced to decide between “overcooling” and setting the thermostat to a lower temperature in order to dehumidify. More often than not, senior occupants choose not to run the air conditioner which prevents moisture trapped inside from condensing over the HVAC condenser coils and causes the relative humidity to rise.
Another factor to consider is high-performance design. Trapped moisture has become the unintended consequence of tightly constructed, energy-efficient buildings. While tighter building envelopes drive down the sensible cooling load and save energy by reducing air conditioner run time, they also trap excess moisture, increasing the risk of mold in apartments. In a tightly sealed apartment, moisture accumulates from normal occupant lifestyle activities. As stated earlier, conventional air conditioners do not operate based on water vapor content or relative humidity. The typical apartment HVAC system serves only one purpose, to raise or lower temperature. The following quote from Mold: Causes, Health Effects and Clean-up explains the risk caused by excess moisture:
“Mold requires water. No water, no mold. Mold is the result of a water problem. Fix the water problem.”8
How to Remove Moisture Trapped in Apartments
High humidity can cause moisture related problems in multifamily housing
- Do not use ventilation when outdoor dew point is above 55.9
- Make sure the clothes dryer is vented properly.
- Cook with lids to help contain steam.
- Do not dry clothing indoors on clothing racks.
- Immediately clean up spills and messes.
- Reduce water vapor by using effective bathroom, kitchen, and utility room exhaust fans above common sources of moisture. Verify exhaust fans are actually moving air (hold a tissue below vent to check air flow).
- Confirm appropriate indoor relative humidity level using a reliable digital thermometer/hygrometer.
- Keep relative humidity below 60 percent at all times and use a dehumidifier when necessary.10
Why Dehumidifier Size Matters
Using a dehumidifier for homes is the most reliable way to ensure appropriate levels of relative humidity are always maintained inside apartments.
Whole-house dehumidifiers are appropriately sized for larger, single-family dwellings. While they will adequately remove moisture from apartments, common complaints include excessive noise and heat displacement as well as lack of operational control. If a tenant elects not to operate the air conditioner unit, they are unlikely to operate a dehumidifier. Whole house units are also controlled by a wall-mounted humidistat, similar to a thermostat. Additionally, whole-house dehumidifiers are installed in conjunction with the existing HVAC air handler which requires integration into the mechanical system. Installation of these systems requires a licensed HVAC technician.
Portable dehumidifiers may be less costly, but present other types of challenges when attempting to remove humidity and prevent mold in apartments. They are inconvenient, often require manual emptying, and also rely on tenant cooperation to operate. Is relying on tenants to properly maintain a portable unit worth the risk? In many situations, it is impractical to expect tenants to effectively operate dehumidifiers. The complaints from tenants in regard to portable dehumidifiers range from being too loud, releasing hot air into the apartment, safety hazards, and even the nuisance of remembering to empty the tank.
Moisture Removal Solutions
Currently, there is only one versatile dehumidifier specifically designed for apartments, available in the US. The award-winning, ENERGY STAR® Certified IN Wall/ ON Wall IW25-4 dehumidifier by Innovative Dehumidifier Systems. The IW25-4 puts apartment humidity control directly in the hands of landlords and property owners. Created to provide moisture removal daily, the built-in dehumidifier system includes a tamper-proof cover that can only be removed using a specialty tool. The IW25-4 can be quickly installed inside an interior wall between existing studs or hung directly on wall. Once installed, it operates independently of the HVAC system to condense and remove moisture in apartments quietly and efficiently. Designed for hands-free moisture management the dehumidification system, drains directly into current plumbing lines, or the optional internal condensate pump (purchased separately), installs into the unit to remove collected condensation.
For landlords and tenants who are searching for a cost-effective and efficient solution to remove moisture and prevent mold caused by humidity in apartments, the IW25-4 dehumidifier just makes sense for apartments.
1. Barret, Julia R., Mold Insurance: Crafting Coverage for a Spreading Problem (2003), Environmental Health Perspectives, accessed November 2021 <https://ehp.niehs.nih.gov/doi/pdf/10.1289/ehp.111-a100>
2. Dave, Nitin, and Stephen R. Galati. “What’s mold is new: remediation and proper planning helps remove fuss over fungus. (Feature).” Journal of Property Management, vol. 68, no. 4, July-Aug. 2003, pp. 42+. Gale Academic OneFile, <link.gale.com/apps/doc/A105554759/AONE?u=anon~175b10af&sid=googleScholar&xid=aa5caac5> accessed Nov 2021.
3. King, Raymond C., (2008). Toxic Mold Litigation. American Bar Association, accessed November 2021, <https://mnwaterdamagerestoration.com/wp-content/uploads/2012/03/moldwhitepaper.pdf>
4. Hartwig, Robert P. and Wilkinson, Claire, August 2003, Insurance Information Institute
5. Lstiburek, J. and Carmody, J. (1993) Moisture Control Handbook (Principles and Practices for Residential and Small Commercial Buildings). New York: Van Nostrand Reinhold.
6. Virginia Polytechnic Institute and State University; Kathleen Parrott, Ph.D. 2009, Virginia Cooperative Extension, accessed November 2021,
7. Lstiburek, J. Brennan, J., and Yost N., (2002) RR-0208: What You Need to Know About Mold, Building Science Corporation, accessed November 2022 <https://www.buildingscience.com/documents/reports/rr-0208-what-you-need-to-know-about-mold/view>
8. Lstiburek, Yost N., and J. Brennan, J., (2002) Mold: Causes, Health Effects and Clean-Up, Citeseer, accessed November 2021 <http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.625.1632&rep=rep1&type=pdf>
9. Moisture Science 101, Dan Welkin;
10. A Brief Guide to Mold, Moisture and Your Home, United States Environmental Protection Agency; <https://www.epa.gov/mold/preventionandcontrol.html>