SAN FRANCISCO – Over the last 20 years, moisture damage in some North American commercial buildings has become a serious problem. Fortunately, a design guide is now available to keep indoor humidity at bay. The resulting book is 480 pages long, and took 100 years to write.

Well, not really. In fact, ASHRAE admits that during the first 100 years of its history, “Humidity control in commercial buildings received much less attention than temperature control.”

It’s easy to see why. Temperature is not only easier to control than humidity, it is more visible. Building tenants and homeowners know when they see 70∞F on their thermostat that it is an understandable definition of their comfort. Many fewer know much about proper levels of relative humidity. Just as with indoor air quality, few building tenants are willing to pay more for something they have a hard time grasping the intricacies of.

Building practices since the 1970s are also contributing to increased mold growth. “Tighter, warmer, with more furnishings” is how one researcher described this trend. There is reduced air infiltration into our buildings because of added insulation and tighter fitting doors and windows, which saves energy, but also which can lead to a build-up of humidity and other pollutants.

There are other factors which also contribute, but some of these are on a more individualized per-building basis. For instance, oversized cooling systems continue to be a sporadic problem.

News reports stated that Farmers Insurance Group is choosing not to renew homeowner policies in Texas this year because of a dramatic increase in mold claims, which increased from 12 in 1999 to more than 8,000 in 2001. Meanwhile, in Louisiana, the state’s insurance commissioner has been asked to rule on whether insurers can exclude mold claims from their coverage. Schools and a state-owned office building in New Orleans are the subject of recent mold claims and investigations.

“Design Guide for Humidity Control in Commercial Buildings” was funded jointly by the U.S. Department of Energy and the Gas Technology, and comes from ASHRAE research project 1047-RP. To better control indoor humidity, and to curb any resultant mold growth, the authors encourage hvac designers to:

Focus on adjusting the humidity of any incoming ventilation air Install dedicated humidity control equipment that operates independently of the cooling and heating equipment. Seal up all duct work and air handlers to avoid pulling untreated outdoor air into building cavities.

Construction claims from mold

Microbial growth is a major cause of IAQ problems, according to ASHRAE. In one study of 695 buildings over 10 years, microbial growth accounted for 35% of the IAQ problems encountered. And more than 50% of construction claims against architects, engineers and construction firms were due to moisture and humidity problems, according to a study of 5,000 claims.

The book asks and answers two basic questions for readers:

“What humidity level leads to growth of mold and mildew;” and “How high does the humidity have to be held to prevent electrostatic shocks?”

Proper use of humidity control through equipment, maintenance and design can avoid these mistakes, according to ASHRAE. Fourteen chapters of the new volume focus on applications designed to help the hvac designer ask the right questions for a particular building before the design process begins.

Two chapters describe various types of humidification/dehumidification equipment along with their strengths and weaknesses; the use of passive desiccant wheels is also covered.

Importance of sealing ducts and the use of humidity sensors is reviewed in a section on instruments and controls. “Some of the most notorious moisture damage in commercial buildings is caused by suction from leaking ductwork and air handlers. Duct suction pulls untreated, humid air from outdoors into cool building cavities, where moisture condenses to feed mold and corrode the building structure.”

Calculate the moisture load separately from the cooling and ventilation loads. Whenever possible, control the dew point rather than relative humidity.

Calibration of humidity sensors is important, and should be done after installation and prior to commissioning. Most hvac and controls contractors are not in the habit of doing this, and factory-calibrated sensors may be fine in most cases, with +/- 5% RH considered adequate. However, if a building owner has a more defined need, “it is absolutely imperative that all humidity sensors be capable of adjustment after installation, so that their signals are reliable indicators. If sensors are not calibrated in the field before commissioning, it won’t really matter what dehumidifier and humidifier capacity is installed — the system will not work as the designer intends.”

Molds can produce toxic substances called mycotoxins. Some mycotoxins cling to the surface of mold spores; others may be found within spores. More than 200 mycotoxins have been identified from common molds, and many more remain to be identified, according to the EPA. Some of the molds that are known to produce mycotoxins are commonly found in moisture-damaged buildings.

Although some mycotoxins are well known to affect humans and have been shown to be responsible for human health effects, for many mycotoxins little information is available.

Colin Young, in a presentation at ASHRAE IAQ ’01, said that while a 1989 NIOSH (National Institute of Occupational Safety and Health) study revealed that only 5% of IAQ complaints were related to microbiological contamination, more recent studies have shown that there is an association between bioaerosols and increases in IAQ complaints.

In fact, Young concluded that “biological contamination is a commonly encountered occupational and environmental, as well as public health, issue. Health care and safety professionals should be cognizant of recognizing symptoms consistent with biological exposures… Furthermore, periodic and preventive maintenance of building components so as to avoid water intrusion may be as important as early recognition and treatment of health effects secondary to biological contamination.”

Time to clean the ducts

In a new guide, Mold Remediation in Schools and Commercial Buildings, the Environmental Protection Agency advises: “Do not run the hvac system if you know or suspect that it is contaminated with mold. If you suspect that it may be contaminated (it is part of an identified moisture problem, for instance, or there is mold growth near the intake to the system,) consult EPA’s guide ‘Should You Have the Air Ducts in Your Home Cleaned?’ before taking further action.”

Also still under debate is the safety and effectiveness of using biocides in mold remediation. According to the EPA, “It is necessary to clean up mold contamination, not just to kill the mold. Dead mold is still allergenic, and some dead molds are potentially toxic.” Use of a biocide, such as chlorine bleach, is not recommended. It doesn’t completely rule out use of biocides by professionals, if done with the proper care and guidelines.

The National Air Duct Cleaners Association (NADCA) tells consumers on its website ( that “Heating, ventilation, and air conditioning systems have been shown to act as a collection source for a variety of contaminants that have the potential to affect health, such as mold, fungi, bacteria, and very small particles of dust. The removal of such contaminants from the hvac system and home should be considered as one component in an overall plan to improve indoor air quality.”

Frequency of duct cleaning depends on several factors, according to NADCA, including whatever there are:

  • Smokers in the household.

  • Pets that shed high amounts of hair and dander.

  • Water contamination or damage to the home or hvac system.

  • Residents with allergies or asthma who might benefit from a reduction in the amount of indoor air pollutants in the home’s hvac system.

  • After home renovations or remodeling.

Prior to occupancy of a new home.

Ductmate Industries, E. Monongahela, Pa., supplies High Temperature Sandwich Access Doors to McDonald’s Corporation, among others. McDonald’s planned to build or rebuild nearly 600 restaurants in a single year, with the Franke Corporation installing over 60% of the kitchen systems.

Ductmate’s access doors met standards set forth by NFPA96 and installed in just minutes. They also make it easier for the duct cleaners later on, speeding up the process by giving easy access to the ducts.

McDonald’s traditional three hood design typically requires at least one access door per hood. The access doors Franke was using were labor intensive, requiring both welding and excess screwing to install – at least 15 minutes per door, after the welding equipment is in place. A typical McDonald’s restaurant is up and running 60 days after groundbreaking; a complete renovation takes only 20 days. It takes Franke Corporation 100 man-hours to install an entire McDonald’s kitchen, and another 15 or 20 minutes can make a big difference when you are under such strict scheduling.

The U.S. Environmental Protection Agency offers the following checklist for mold remediation

Investigate and evaluate moisture and mold problems

  • Assess size of moldy area (square feet)

  • Consider the possibility of hidden mold

  • Clean up small mold problems and fix moisture problems before they become large problems

  • Select remediation manager for medium or large size mold problem

  • Investigate areas associated with occupant complaints

  • Identify source(s) or cause of water or moisture problem(s)

  • Note type of water-damaged materials (wallboard, carpet, etc.)

  • Check inside air ducts and air handling unit

  • Throughout process, consult qualified professional if necessary or desired

    Communicate when you remediate

  • Establish that the health and safety of building occupants are top priorities

  • Demonstrate that the occupants’ concerns are understood and taken seriously

  • Present clearly the current status of the investigation or remediation efforts

  • Identify a person whom building occupants can contact directly to discuss questions and comments about the remediation activities

    Plan remediation

  • Adapt or modify remediation guidelines to fit your situation; use professional judgment

  • Plan to dry wet, non-moldy materials within 48 hours to prevent mold growth

  • Select cleanup methods for moldy items

  • Select Personal Protective Equipment – protect remediators

  • Select containment equipment – protect building occupants

  • Select remediation personnel who have the experience and training needed to implement the remediation plan and use Personal Protective Equipment and containment as appropriate

    Remediate moisture and mold problems

  • Fix moisture problem, implement repair plan and/or maintenance plan

  • Dry wet, non-moldy materials within 48 hours to prevent mold growth

  • Clean and dry moldy materials

Discard moldy porous items that can’t be cleaned.