NASHVILLE, Tenn. - Dry buildings do not tend to grow mold. Dry buildings do not happen of their own accord; they must be planned by everyone on the building team.

"Environmental consultants are suggesting that HVAC systems in buildings may cause mold growth," said George A. Jackins, P.E., as he kicked off a seminar titled "Mold: Where Do We Stand Now?" during the Annual Meeting of the American Society of Heating, Refrigerating, and Air-Conditioning Engineers.

"Why are we still talking about mold?" asked Jackins, who is with Engineering Resource Group Inc., Birmingham, Ala. "Mold is here to stay."

The battle isn't over yet, he said, referring to the HVAC community's efforts to provide humidity control. "Our industry has a terrific problem that needs to be dealt with."

How Water Gets In

During his presentation, "Designing for Moisture Management," Lew Harriman of Mason Grant, Portsmouth, N.H., asked audience members why they should be concerned about mold.

Buildings are designed to be strong, he pointed out. "They don't fall down often," he said. "They do grow mold." Mold claims reached up to $12 billion in 2003, he stated.

It's a well-known fact that mold cannot grow without moisture, he continued, explaining that hygroscopic enzymes surround the mold spores. Mold growth, therefore, is not a question of humidity, but how much actual moisture gets to that food source. Condensation and leakage are the main culprits.

Water does get in, he said; rain comes in through cracks, humid air through the ventilation system, and HVAC systems fail to dry the air. This moisture migrates and mold grows.

"Over the last 40 years, we are seeing more fragile building envelopes," Harriman said.

"There is no second line of defense," he said, and a lot of water is able to directly hit the exterior walls. Walls can't get rid of moisture. A major problem is ignorance in the conceptual design phase of building development, he indicated.

How To Fix It

The architect, Harriman said, needs to design a dry building. In other words, the structure needs to shed water instead of collecting it.

The HVAC designer needs to design ventilation that dries the building. "This is profound," Harriman said: "Spend more money" instead of spending less and adding moisture, he advised.

The builder and contractor need to keep building materials dry during construction, and make sure that any potential leaks are sealed appropriately.

"When moisture gets in anyway, design walls that drain water," Harriman said, "and ventilation that keeps the building dry."

Outside the building:

  • Keep rain off walls with the use of overhangs, awnings, etc.

  • Keep water away from the foundation by sloping the landscaping appropriately.

  • Make flashing effective.

    Inside the building:

  • In some climates, contractors and HVAC designers need to consider offering the building owner dedicated ventilation dehumidification systems for drying the supply air.

  • Beware of duct leaks. Unsealed exhaust ducts draw in air through the building cavity, which draws exterior air through the walls, Harriman explained, pulling air into the building from the outdoors.

    Unrealistic Expectations

    "The owners flat don't spend what they need to spend," stated Rodney H. Lewis, P.E., of Rodney H. Lewis Associates Inc., Houston. "If you don't maintain filters and drain pans, you are going to have a mold problem." His talk was titled "You Can't Design It Like You Used To."

    Lewis himself has been an expert witness in mold litigation, which he said is "mushrooming." Settlement expectations are increasing, he added, while the cost of construction is going downward. To top it all off, training is inadequate.

    He listed some unrealistic building owner expectations:

  • Tight temperature control.

  • Tight humidity control.

  • 100-percent reliability.

  • High efficiency/low operating costs.

  • Silent operation.

  • No maintenance. ("They generally do not spend any money on maintenance anyway," Lewis said.)

  • No mold. ("We live on Earth," he said. "There is a lot of mold here.")

    Project cost pressures include:

  • Poor owner budgeting.

  • Poor contractor budgeting. ("I have never seen a budget from a general contractor that is adequate," Lewis said.)

  • Inadequate contractor estimates.

  • Value engineering.

  • Energy costs.

  • Maintenance costs.

    Then there are other variables, such as architects who seem to love vinyl wallpaper. "That group is not trained," in IAQ risks and materials, Lewis said.

    In order to fix these problems, he advised the following:

  • Select and specify systems that control humidity.

  • Check other consultants' work for potential IAQ problems.

  • Communicate with the building owner.

  • Document all key directions and recommendations.

  • Document the design intent.

    Publication date: 08/16/2004