Got Mold? Here's What to Do

To home builders, mold is a nasty four-letter word. It's a problem begging for prevention. Even in relatively dry Denver, we're struggling with rising risk related to mold.

Consider four recent items. First, in late April, a mold-related lawsuit against a Denver builder went to court. Partway through the jury trial, the case settled. According to one participant, lawyers on both sides learned about each other's arguments and tactics through this process. He expects lawyers will put builders back in front of a jury empanelled on a different mold case within 12 months.

Second, the Tri-County Health Dept. (Adams, Arapahoe, Douglas) recently held a meeting with code officials to present information about mold-related problems reported to them. Tri-County is exploring whether changes need to be made to the code to help prevent mold formation, especially beneath structural wood-decked basement floors.

Third, the Metro Denver RBA's Council of Professional Remodelers recently sponsored a luncheon seminar on mold. The meeting sold out three weeks in advance of the session. There were no empty chairs.

Fourth, during a session on mold presented by engineer Steve Easley on Builder Product Night, the large crowd learned that NAHB has never gotten more calls on any one subject than they have received recently on mold.

The trend lines aren't good. In the residential sector, don't expect the spotlight to leave mold overnight. So do everything you can to get informed about the issues and preventative steps.

The Energy and Environmental Building Association is publishing a paper this month called "Water Management Guide" (www.eeba.org). A key part of its message: Controlling rain and groundwater entry are keys to controlling mold. Pick up a copy.

The paper's principle author is engineer Joe Lstiburek with Building Science Corp. (Westford, Mass.). He and colleagues Terry Brennan and Nathan Yost also authored a very readable set of short papers about mold (www.buildingscience.com). Here is their take on the mold fundamentals.

More mold today?

Are huffy TV crews and mold-chasing lawyers to blame for the recent ramp-up in concern about mold? Not really. We've always had huffy journalists and lawyers, says Lstiburek. What has changed is the moisture balance in our buildings.

First, homes don't dry out as fast as they used to because we insulate better and build tighter. "Repeated wetting followed by repeated drying isn't a problem," said Lstiburek. "Today, buildings are still getting wet, as they always have, but they're slower to dry."

Second, today's homes are built with more moisture-sensitive materials. Mold likes processed wood - paper, particle board, hardboard, even OSB - more than it likes lumber. "Paper is nature's most perfect mold food," said Lstiburek. "Even old mold with no teeth can chow down on paper. So where were the adults when someone decided that covering drywall with green paper would prevent bathroom mold problems?"

Third, we've reduced a home's "hygric buffer" capacity - its ability to soak up and store some amount of moisture that enters the building shell by design flaws or imperfect workmanship. Compared to decades past, we're using less masonry and more paper-faced drywall in our homes. Masonry absorbs more moisture than wood, wood more than drywall. Steel can't absorb water. Finally, we circulate a lot of air more frequently in today's buildings than in 30- to 50-year-old homes. And because most ductwork leaks, different parts of the home get pressurized or depressurized. When that happens, we can pull unwanted moisture from where we don't want it (crawlspaces, attics, the humid outdoors) and deliver it where we don't want it (vulnerable building elements like rim joists and closed cathedral ceilings).

"These four practices have changed the dwell time of moisture in our buildings," said Lstiburek. "So building elements that get wet are staying wet longer. We need to alter our designs and workmanship to adjust for those realities."

Four basics

Mold is a type of fungus that's everywhere. In the air, under a pile of leaves, on a slice of bread - we're all exposed to mold every day. There are thousands of different types of mold. Molds were around before we arrived and they'll be here after we're gone.

Mold spores, the invisible "seeds" that can spread mold, need four conditions to grow. They need moisture or high relative humidity (70-80 percent). Add a food source - dirt, wood or organic material - plus oxygen and temperatures between 40 and 100 degrees F, and it's off to the races.

"Wood will start decaying when it reaches over 28 percent moisture content by weight, and will continue decaying until it drops below 20 percent," said Lstiburek. "So keep wood below the `off switch' - 19 percent or less. And since mold will grow on wood at 16 percent moisture content, keep wood below that `off switch' too - 15 percent or less."

Testing

If you smell mold, you probably have it, so look around for the source. Terry Brennan (Camroden & Associates, Syracuse, N.Y.) says to look for wet spots in attics, in crawl spaces and in walls with plumbing or under windows. If you see mold, you definitely have it, so why bother to test?

"I generally don't recommend air sampling for investigating mold problems in buildings," said Brennan. "There's a poor return on the money spent." Reason: mold concentrations in the air vary dramatically with time. Air sampling costs between $50 and $100 per sample; consultants often take a half-dozen to a few dozen samples.

Brennan is researching the value of drilling and testing air samples from enclosed wall cavities that might be hiding mold. He'll be covering one side with rigid plastic, the other side with drywall, then raising moisture levels within the wall cavities and matching visual observations with air samples obtained through small holes. The take-home here: we don't have enough information yet to have confidence in testing procedures.

Response keys

If you find mold, carefully assess the problem before any cleanup. Identify the source of moisture that's causing the problem and isolate that source. Identify the extent of contamination and any safety precautions needed during remediation; follow the New York City Dept. of Health's "Guidelines for Mold Remediation." Either clean off the mold with soap and water or remove the damaged materials, realizing that removal will cause the release of more mold spores than simple cleaning. Dry out the assemblies. Replace any structurally damaged materials. For cosmetic purposes, paint over any stained exposed surfaces.

Health effects

When testing a person's blood pressure, we know the risk threshold. For mold exposure, such a threshold hasn't been established. To further muddy the water, people have widely differing reactions to different levels and types of mold.

"If mold were as bad as some press reports, most of us would already be dead," said Lstiburek. "We would have to ban farming and forestry, outlaw composting, and require respirators when you mow your lawn. That said, some molds cause problems, and toxic molds can cause serious problems. But today, the science is really quite thin and we mostly have stories - anecdotal evidence."

Dr. Nathan Yost, formerly with the American Lung Association and now fulltime with Building Science Corp., also seeks to "counter the hysteria that any mold is like plutonium. Exposure to a little mold is not a problem."

But Yost is quick to cite studies showing that the incidence of asthma in young children more than doubled over the last two decades. That trend is primarily an urban phenomenon. Since ethnic mix, racial background and geography apparently aren't key variables, the air within our homes is increasingly viewed as a suspect.

"The mold-asthma connection is really the heart of the mold worries," said Yost. "Mold can trigger asthma. What is not proven is whether exposure to mold can lead to the development of asthma. The more we study asthma and mold, the more we discover about how mold affects us. It is beginning to look as if some of these mold effects are not particularly nice."

Prevention

Simply stated, don't let your house get wet. No moisture, no mold. If building elements in a home do get wet, they need a way to dry, either to the inside or outdoors, depending on climate. Careful design and good workmanship make this possible. Over the next couple of months, this column will cover the best practices in EEBA's "Water Management Guide" to help keep buildings dry and mold at bay.

Steve Andrews consults with builders for E-Star Colorado and writes on energy issues (sbandrews@att.net). E-Star (www.e-star.com), is a nonprofit home energy rating system that works with both new and existing homes statewide.

A different version o f this article first appeared in the February issue of Professional Builder Magazine.

2008 Built Green Colorado

Home Builders Association of Metro Denver, 9033 E. Easter Place, Suite 200, Centennial, CO 80112
(303) 778-1400 fax: (303) 733-9440  info@builtgreen.org

Last Updated: 10/05/2007