Moisture Control Not Rocket Science

Posted on November 24, 2010


In Florida, architects have been beat over the head with best practices for ‘designing for mold’, a.k.a. moisture control. I believe the impetus for this focus is to combat a legal environment where mold has evolved into fertile territory for copious lawsuits based on media attention, public sentiment and asthma prevalence. The topic has been quite prevalent over the past two to five years, popping up everywhere from conferences to lunch-and-learns.

And I take it for granted that the rest of the design and construction community is sick of hearing about mold. But, maybe hospital owners are curious about this crucial aspect of good design. For this reason, I offer a Cliff’s Notes version of what I have gleaned about moisture control.

Moisture, especially in construction, is pretty easy to recognize:  damp / humid air, coatings and glues slow to dry, warped wood, condensation and obviously, mold. Moisture issues arise because of poor water management: water infiltration, high humidity weather, improper HVAC systems, residual moisture from building materials, poor vapor / water barriers and obviously, water sources like plumbing failure.

Water infiltration requires three things:  water, a hole, and pressure to allow water to enter. Eliminate one of the three and water will not be a problem. Similarly, mold requires four elements:  spores, food, proper temperature and moisture. Like water infiltration, eliminate one and mold will not be a problem. The tricky part is to pick which one is most under your control.

For most facilities, moisture is the easiest one to manage. In addition to being a hot button for infection control, air quality is also a key to control mold. For construction, that means not bringing wet materials into a dry building, protecting areas from humidity or moisture intrusion, and keeping water and moldy materials out of a building. These are no-brainers, things that anyone can check on any project.

Add to these measures design lessons like not installing materials that trap moisture in areas that have moisture (VCT on uncured concrete slabs, vinyl wall covering on the inside of exterior walls) and mold is very manageable.

Fortunately, heating, ventilation and air conditioning (HVAC) equipment helps acclimate the interior to an environment that deters mold. Heating helps remove moisture from air, which removes a good deal of mold threat. Ventilation creates air exchanges, which are filtered and properly humidified prior to discharge into a space. Air conditioning keeps temperatures in a range at which microorganisms do not rapidly reproduce; for bacteria, spores and fungi, warmer is usually preferred. Dehumidification, which is built into most HVAC equipment, modulates the moisture content of air, which mold uses to feed and grow.

HVAC is no magic solution because mold can adapt to many interior climatic conditions. Also, HVAC equipment in hospitals uses a lot of energy, and thus are expensive solutions to moisture. As the ASHRAE Journal notes in “Preventing Mold by Keeping New Construction Dry”:

Conventional HVAC systems are not designed to dry out construction-related moisture. The moisture load from wet materials is simply too large and the drying task too complex for systems that are intended for comfort air conditioning.”

Mold must be proactively managed during design and construction first. Also, take note of LEED procedures like flush-outs with outside air, which may stress a building’s HVAC or air quality. Unconditioned air can carry three of the four items mold needs: spores, moisture and adequate temperature.

In conclusion, mold mitigation is mainly common sense. Part of moisture management is timing the project as sensitively as possible to seasons, especially for construction sequencing and dry-in. By observing proper material storage and installation procedures, while managing building envelope assembly, mold likelihood on your project can be rare.