Pushing the Building Envelope Can Cause Mold Problems

The building envelope is the physical separator between the interior and the exterior environments of a building.  The control function is at the core of good performance, and in practice focuses, in order of importance, on rain control, air control, heat control, and vapor control.  Uncontrolled moisture indoors can cause major damage to the building structure, as well as to furnishings and to finish materials like floors, walls, and ceilings.

Uncontrolled moisture can trigger mold and bacteria growth, which not only damages the building structure, but can lead to health and performance problems for building occupants.  Mold is usually not a problem indoors unless there is excess moisture.
Primary causes of indoor moisture problems in buildings include:

• Inadequate HVAC equipment sizing
• Inadequate fresh air dehumidification
• Inadequate building pressurization/ventilation design
• New construction related debris obstructing the HVAC System evaporator coils
• Inadequate Test & Balance
• Use of building materials that are previously wetted
• Poor control of rain and snow resulting in roof and flashing leaks
• Wet or damp construction cavities
• Lack of energy saving (ESCO) environmental controls
• Moisture-laden outdoor air entering the building
• Condensation on cool surfaces

It is extremely important to prevent uncontrolled moisture from entering the building envelope through window and door openings, seams, footings, roofs or other openings. In virtually all areas of the country, provide an exterior weather barrier to prevent moisture from entering construction cavities. Wet or damp construction cavities (e.g., spaces between interior and exterior walls), attics, chases and plenums are major sources of mold and can contribute significantly to indoor air quality problems. Moisture can damage the structure and degrade the performance of insulation, increasing energy and operating costs.

Water also enters construction cavities through a process of moisture migration. Moisture migrates from the warm and humid side of the construction assembly to the cold dry side of the construction assembly. Air pressure differentials can also drive moisture into interior and exterior walls, creating mold-favorable environments, and they can do so in both heating climates and hot, humid climates. In hot, humid climates, even slight negative interior pressures can pull hot outdoor moisture into chilled wall cavities during cooling periods if the building envelope is not properly designed and constructed. Similarly, during heating periods, positive pressures can push warm, moist air from indoors into chilled exterior walls. In either case, this uncontrolled moisture can lead to mold growth that impairs indoor air quality and damages building materials.

Therefore, buildings in the north should not blow and buildings in the south should not suck. For hot, humid climates, a slight positive (blow) pressure in the building is recommended, and in northern buildings a slight negative (suck) pressurize in the building will help. However, in mixed climate areas, using positive or negative pressures can create problems as the weather changes. Ultimately, the most reliable solution is the proper construction of the building envelope.

For a professional assessment of your building envelop and indoor air quality baseline conditions call the building science experts at Pure Air Control Services 1-800-422-7873 

About Pure Air Control Services, Inc:

Alan Wozniak founded Pure Air Control Services, Inc. in 1984 as a small mechanical contracting firm. Today, Pure Air Control Services sets the industry standard for indoor environmental quality diagnosis and remediation  while servicing more than 500 million square feet of indoor environments in over 10,000 facilities.

Pure Air Control Services nationally performed services include: Building Sciences Evaluation; Building Health Check; an AIHA accredited Environmental Microbiology Laboratory; DIY IAQ Screen Check test kits, Environmental Project Management; and Mold Remediation Services, among other indoor environmental services.

The company’s expanding client roster includes the General Services Administration (GSA); Federal Aviation Administration (FAA), Allstate Insurance; Carrier Air Conditioning; Naval Air Warfare Center, Orlando; and Naval Air Station - King's Bay, Georgia, US Postal Service (USPS) and many other Fortune 500 companies, school boards, and city, state, and county governments, making Pure Air Control Services one of the most reliable IAQ industry leaders.

For more information on Pure Air Control Services, Inc and its indoor environmental IAQ services offering please contact Alan Wozniak at (800) 422-7873 x 802 or visit www.pureaircontrols.com.