When American Constructors began a 106,000-square-foot elementary school for Round Rock School District, near Austin, TX, there was a general concern about the development of mold and mildew during the project.
American Constructors had built many schools in fast-growing central Texas. Based on years of experience, the company set goals to maintain targeted temperature and humidity levels during construction without using the newly installed HVAC system.
With outside air temperatures about 30°F during winter, the climate-controlled space inside needed to be kept near 60°F and relative humidity was to average below 30% RH.
“Many insurance carriers no longer will ensure contractors against the effects of mold, mildew, and water-related damage,” said construction project manager, Corey Taylor. “Our goal was to reduce moisture in the building during construction, and thereby eliminate the cause of mold problems.”
Variations in levels of humidity and temperature in the Austin area, especially throughout the winter months, can create challenges for contractors. Using the traditional method of direct-fired heaters, it is often difficult to maintain conditions that minimize mold or mildew. As a result, humidity rises, allowing condensation to form on surfaces throughout the building interior, such as metal studs and wallboards.
If this happens and moisture is trapped inside walls during finishing work, the building becomes a candidate for mold problems. High humidity levels inside the building also slow the drying time of materials like joint compounds, fireproofing, and paint. “Unless joint compound is sufficiently dry, we can’t sand or paint. And if the moisture content in concrete is not sufficiently low, we can’t apply the floor coverings,” Taylor said.
To solve the moisture problem and preclude the possibility of mold growth, American Constructors turned to Polygon. After reviewing construction plans, Polygon recommended a temporary dehumidification system to be phased in as work progressed. The system was a combination of desiccant dehumidifiers, indirect-fired heaters, and fans used to move the warm, dry air through a distribution network of lightweight flexible ducts.
The system was a great improvement over using heat from direct-fired heaters or the HVAC system because it dried the air, as well as heated it. The dry air precluded the possibility of condensation forming on structural materials, usually the principal cause of dangerous mold growth in new buildings.
We were able to minimize dust throughout the construction site by introducing outside air rather than recirculating inside air. Having an alternative source of heat eliminated the need for an early start-up of the building's HVAC system. This was preferred by the building engineers, who specified no use of the HVAC system until the building was turned over to the owner.
According to Taylor, maintaining consistent temperature and humidity levels using the HVAC system during construction in winter can prove difficult. “In the Austin area, running the heating unit to control humidity is tricky because there are many days when it is not cold, and heat makes it uncomfortable to work. As a result, the workers open the windows,” Taylor said. “If the heat isn’t running, the indoor areas become humid. Should a cold front arrive, that humidity condenses on the floor and walls.”
“Working with moisture-laden materials sends humidity upward, but then the dehumidifiers quickly reduce it. For example, after wallboard texturing, the humidity climbed from 30% RH to 70%RH because of the moisture in the compound, but by the next morning, the dehumidifiers had lowered the conditions to under 50% RH and then returned humidity to the maintenance level of 30% RH,” Taylor said.
Initially, the construction firm only sought help to deter the possibility of mold growth during construction. However, the project team soon discovered that removing moisture shortened the drying times of concrete, wallboard compound, and substrate surfaces. With predictable drying rates, project managers could schedule the painting and installation of ceramic tile and flooring material without weather-induced moisture delays.
Taylor added that the architect’s concern about moisture and its effect on finished products was completely addressed by Polygon's temporary climate control solution, and hassles with subcontractors and manufacturers over the effective date of warranties were avoided.
A Flexible Approach
The Polygon system was partially installed when some of the buildings were enclosed. As the entire structure was closed in, we expanded the system to meet growing humidity and temperature control needs. As a result, there was no cost for unnecessary equipment on site.
Removing moisture eliminates mold growth and eventual contamination of the building. By dehumidifying throughout the project, mold concerns were never an issue.
Materials such as paint, drywall compound, surface texturing, epoxy, and concrete all dried at their maximum rate. This allowed work to proceed faster and scheduling to be dependable.