Insulation Institute Blog

Mold in a home can create indoor air quality and health issues for the occupants, cost builders and contractors thousands of dollars to fix and result in costly and lengthy litigation. Moreover, increasingly tight construction with less natural ventilation may create indoor environments prone to moisture buildup, one of the key requirements for mold growth.  The best and least expensive strategy for builders to address mold is prevention.  Insulation Institute talked with Certified Indoor Environmental Consultant Mike Lanius of Indoor Environmental Professionals about the prevalence of mold in new construction, ways to prevent it and the single most common error he sees in new construction that leads to mold and what builders can do to prevent it.

How Big a Problem is Mold?

It’s been estimated that up to 28 percent of home builders have mold issues during construction.[1] Lanius says it’s very common for his inspectors to find mold growth in new homes, but the fungus is avoidable. In order for mold to grow it needs, mold spores must be present (and they’re ubiquitous) as well as moisture, a food source and warmth temperatures (generally, warmer temperatures promote greater mold growth). While all three elements are necessary for the proliferation of mold, Lanius stresses moisture regulation in particular, as the average home subjected to 6,000 to 9,000 gallons of water during construction.[2]

“One of the most important things to keep in mind when controlling mold growth in the indoor environment is to control moisture flow and intrusion,” he said. That can be a challenge, given that many building products can absorb moisture and complicate that effort.

Tips on Controlling Moisture to Prevent Mold

While moisture in home construction is inevitable, there are a few simple things builders ca

n do to decrease the likelihood of developing mold during construction:

1. Inspect and test material shipments – For example, experts recommend an average wood moisture content of 15 percent, not to exceed 19 percent for mold prevention. Moisture levels higher than 19 percent in wood are ideal for mold development. “Many species of mold can begin to growth at 65% relative humidity,” he said. “Keeping building materials as dry as possible during the building process is one step that the building contractor can take to help prevent mold growth from beginning to proliferate.”
2. Mandate proper storage practices and train crews – Whenever possible, store building materials under a roof or tarp and off the floor to keep them dry, but avoid cover that’s too tight as it can trap moisture and create fertile conditions for mold buildup.
3. Take caution with the envelope – If the goal is to achieve the lowest level of risk for mold formation, the single best opportunity to do that happens with the envelope. Take caution to properly air seal wall cavities and if needed, allow drying time for the materials before closing up the wall. This is important for products such as wet spray cellulose, which introduces moisture into a wall cavity. This should include carefully monitoring humidity levels on the jobsite.
4. Use commercial dehumidification equipment when necessary – In periods of heavy or prolonged rain, it may be necessary to use commercial dehumidification equipment such as a desiccant or mechanical dehumidifier. If such a device is necessary, follow the proper steps for safe operation. This is relevant when installing some types of spray foam, as high levels of humidity can negatively impact cell formation during application[3]. Airborne moisture can also condense on cold substrates, causing adhesion problems[4].

Post construction, builders should also provide guidance to homeowners about long-term maintenance and care of the home to prevent mold. “Homeowners should know how to maintain HVAC equipment, why it’s important to address any leaks in the home promptly and why ventilation is important to keeping mold at bay,” Lanius said.

Basements – Most Prone to Mold          

While Lanius has said he regularly sees many errors in construction that that can lead to mold growth, one of the most common areas that his company finds mold growth is on the rim joists that encompass the perimeter of the basement (see image at right).

“Most building contractors will insulate the rim joist area with fiberglass batt insulation. During the mold inspection process, we often identify mold growth in this area behind the insulation,” Lanius said.  He said contractors should take care to also use foam board in this area and seal the rim joist with foam or caulk separately, not just fill the cavity with insulation and   keep the joist area dry and completely sealed from outside air infiltration. Keep in mind that the ambient and surface temperature of the rim joist materials also play a part in whether mold growth will begin to develop. If ambient and surface temperature conditions are right, the surface of building materials can reach dew point and this is when condensation will begin to form on the surface of the building material and that moisture can promote mold growth.”

What to Do If You Find Mold

Lanius says having mold remediation can cost the building contractor thousands of dollars and reduce the overall profitability of the building projects. While mold sampling can be expensive and standards for what is or is not an acceptable or tolerable quantity of mold haven’t been set, addressing mold found during construction should be a primary concern, since it can affect human health, according to the U.S. Centers for Disease Control and Prevention[5].

If mold is present during construction, it should be remediated by removing standing water and drying affected areas within 24 to 48 hours. Repairs should be made in the defects that led to the moisture accumulation and should be conducted in conjunction with or prior to mold remediation by a professional mold remediation company.

“Taking the necessary steps to prevent mold from beginning to grow will save the building contractor thousands in unwanted costs,” Lanius concluded. “This is the simplest and the least expensive way to address the problem.”

[1] “The Truth About Mold,” Susan Cooper, 2004 p. 13

[2] http://www.moldchicago.com/new-construction/

[3]http://www.sprayfoam.org/files/docs/2015/Presentations/2E%20Advanced%20Best%20Practices%20for%20Avoiding%20Problems.pdf

[4] Ibid

[5] https://www.cdc.gov/mold/faqs.htm#affect