By Erin Bouttenot Technical Manager, IAQ Lab, Northeast Laboratory Services and Ron Lessard, CIH, CSP Foresight Enviornmental Health Services, LLC

Few words are scarier to homeowners than “mold.” Yes, mold can be serious. But it doesn’t have to be terrifying. Consider this your primer on mold, mildew and fungi. Armed with a biological understanding of what makes mold thrive as well as tips on how to prevent it from growing out of control in your home, mold doesn’t have to be a nightmare.

What is mold?

Mold is a naturally occurring organism that is found everywhere, both indoors and outdoors. It can take a variety of forms: mushroom caps, fuzzy spots on rotting food or dying plants, or speckles on various surfaces in your home. Mold is the ultimate recycler; it breaks down organic materials and turns them into nutrients. Without mold, our forests would be piled high with dead trees and debris, bodies and feces of creatures would be everywhere, and our roadways would be littered with rubber from tires. This makes mold a very important part of our everyday life. I’m using the term mold, but, really, mold, mildew and even yeast are all different types of fungi and they behave in similar ways.

How and where does mold grow?

No matter the type or where you find it, all molds and fungi need two things to grow: organic material and moisture. Organic material is material that is—or once was—alive. Our buildings are built from and filled with organic material that can serve as mold food: wood, drywall, ceiling tiles, wallpaper, carpet and fabrics. Even if we were to remove all these organic products from our homes, there are still other materials the mold can grow on, such as dust and dirt. Moisture is the second, and arguably the most critical, element needed for mold to grow. Organic materials can be found in any climate, but how many mushrooms do you see in an arid desert compared to a wet Maine forest? That’s because our forests have a lot more moisture in them, which allows for many varieties of mold to grow. The same thought process can be applied to a home. Often our living rooms are dry spaces, but bathrooms and basements tend to be more humid. This is why you are more likely to find, and smell, musty odors in these wet areas of a home rather than the dry ones. Follow the moisture to find the fungus.

What can mold do to my health?

Lots of media attention is given to the possible health effects of mold. But, if you find mold growing in your home or building, don’t panic. The Centers for Disease Control and Prevention (CDC) states that exposure to damp and moldy environments may cause a variety of health effects, or perhaps none. Think of mold exposure like spring allergy season. Some people experience slight irritation if they breathe in pollen; others have major difficulties breathing. Then there are those who have no symptoms at all. Mold affects human health in a similar manner, where the chance and type of health symptoms varies from person to person. Some people are more sensitive than others or have sensitivities to specific types of mold, much like people have sensitivities to certain plant pollens.

Common symptoms for those who are sensitive to mold include nasal stuffiness, throat irritation, coughing or wheezing, eye irritation, or, in some cases, skin irritation. People with fungal allergies may have more severe reactions, and mold is a common trigger for those with asthma. Immune-compromised people and people with chronic lung illnesses, such as obstructive lung disease, may be susceptible to more serious lung infections when they are exposed to mold.

“Black mold” or “toxic mold”: It’s just mold

There is a lot of confusion around mold color, especially black mold, and whether certain species of mold are “toxic” to humans. Molds come in many different shades and colors, and while some of them create a byproduct called mycotoxins, the molds themselves are not toxic. Regardless of the color or species, mold growing in your home may not be healthy for you and can cause physical damage to your home. Treat all molds the same, regardless of color or type, and work to resolve and repair the problem.

What does mold do to my property?

Indoor mold can also lead to property damage in several ways. The most obvious effect is building decay, like you see on collapsing roofs or rotting window frames. Mold can also lead to permanent staining on materials and produce a musty odor, both of which can be difficult to remove from textiles such as carpeting. All these issues are why addressing mold growth quickly is important to preserve our building materials, finishes and furnishings and to protect homeowner health.

The importance of water

The good news is that water and mold issues can be easily prevented. Since all mold needs water to grow, eliminating excess moisture will prevent mold growth. No moisture = no mold.

What exactly is excess water? Most of our building materials contain and can safely store some amount of water. For example, the wood in our homes typically contains about 6% of its weight in water, but it can hold up to 16% of its weight in water before water becomes “excess” and available for mold growth. In contrast, drywall can only store about 1% of its weight in water before water becomes “excess” and available for mold growth. This is one reason why drywall is usually one of the first places we see mold growth in a home.

How to find indoor water intrusion

Where do we look for excess water? Some water sources tend to be obvious, such as plumbing leaks and overflowing drains. Outside water can leak through our roofs, walls and foundations and around windows, doors and other openings in the building. These leaks can sometimes be less obvious until they become persistent.

Excess water can also start out as water vapor. Water vapor itself isn’t a problem, but if the vapor contacts a surface that’s cool enough, it can condense into liquid water and that liquid water can become excess water (see “Does a house need to breathe?” on page 53). Water vapor is always present in indoor and outdoor air. Air moves through the building enclosure from inside to outside and vice versa and, when it does, it carries water vapor with it. Typical places where air moves through the building enclosure include:

■ Gaps around windows, doors and other openings in the enclosure.

■ Gaps around electrical switches, receptacles, and ceiling fixtures.

■ Gaps in building sheathing and siding.

Water vapor can also slowly creep through the building enclosure by a process called diffusion, but air leakage can carry far more moisture into the enclosure. As water vapor moves through the building enclosure, it can come into contact with surfaces that are cool enough to cause it to condense into excess water for mold growth. Water vapor can also condense on other cool surfaces such as:

■ Uninsulated cold water pipes

■ Cool objects in uninsulated basements

■ Interior surfaces of windows and window trim in the winter

HOMEOWNER TIP: Maintaining the relative humidity in your home between 30-50% year-round will significantly reduce the likelihood of water vapor condensing on surfaces and causing a mold problem.

How to find a mold problem in your home

Just like you, your home will benefit from an annual check-up. Take a walk through your home once a year and look for signs of both moisture and mold. Moisture inspections are quick and easy to do and have great health and structural benefits. Simply check your home for wet spots, condensation, leaks or water stains (often an indicator of past leaks). Insects and insect damage may also be a sign of water problems.

Your nose can be just as good a tool as your eyes. Mold often creates a musty odor. As you enter each new area, take a sniff. Follow the smell and you may find the source!

If during your inspection you find liquid water, even something as small as an infrequent drip from a pipe, quick action is needed. It takes just a day or two for mold to start growing where excess water is present. The sooner you address a moisture problem, the less likely it is that mold growth will occur. If left unaddressed, the mold will continue to spread and damage more materials in your home.

Do I need to test?

Mold testing is not like testing for other indoor pollutants, such as radon or asbestos. Because individuals react differently to mold exposure, science is unable to set standards for mold tests; we just don’t know how much mold is too much mold to cause health problems.To complicate matters further, your mold test results will always indicate that you have mold, because mold is everywhere, both indoors and outdoors. This can be very confusing and unhelpful towards solving your concerns. Generally, your annual moisture inspection may be all the testing you need. If you see mold or smell mold during your inspection and can clearly identify the source of the moisture problem, you can assume that you have mold and can take action to fix the problem. If you suspect hidden mold, or someone in the home has a sensitivity to a certain type of mold, consider professional testing and analysis.

What should you do if you find a mold problem?

Don’t wait. The longer a moisture problem remains unaddressed, the more likely it is that mold will continue to grow, causing both expensive property damage and putting homeowner health at risk.

FIXING A MOLD PROBLEM IS A TWO-PART PROCESS:

1. Find and fix the moisture problem that is causing the mold growth. Without this critical first step, mold will just regrow, even if you clean and replace the moldy materials.

2. After the moisture problem is resolved, do proper cleanup and repair of the contaminated area. All mold removal and repairs, whether done by a savvy DIY homeowner or a mold remediation professional, should follow available best practice guidance to prevent spreading mold spores around the home, leading to a much larger problem. The U.S. Environmental Protection Agency (EPA) publishes a free guide, “Mold Remediation in Schools and Commercial Buildings,” that provides excellent information for approaching mold problems of all sizes, including homes. A word of caution: Very large mold problems are best left to professionals.

Cleaning Up Smaller Mold Problems in Your Home

Homeowners can easily manage smaller mold clean-up projects on their own. Follow these practices when dealing with surface mold due to condensation less than ten square feet in size (common on bathroom ceiling, exterior wall in a closet, exterior wall behind furniture, boxes and shelving).

■ Correct the problem that caused condensation.

■ Wash the mold area with soapy water and rinse thoroughly. Allow the surface to dry completely.

■ Repaint if needed; superficial discoloration may remain.

■ If the mold has penetrated below the surface (as on gypsum board) remove involved material and approximately one foot of uninvolved material in all directions. A general rule is to remove the gypsum board from one stud cavity on each side of the area that has mold growth and one foot above and below the area that has mold.

■ Wear personal protective equipment (PPE): N95 mask, rubber gloves and eye protection.

Larger mold problems and mold in wall cavities require careful containment, removal and repair. In these cases, consider hiring a mold remediation professional.

Doing an Annual Indoor Moisture Inspection

Follow this simple two-step process to properly prevent mold growth in your home. Preventing leaks and moisture problems and fixing water damage quickly are the keys to preventing mold growth.

STEP 1. MOISTURE MAINTENANCE AND REPAIRS

Perform these simple tasks to help prevent moisture problems:

1. Repair any leaks that let water into the home.

2. Ensure good drainage around the home.

3. Repair any plumbing leaks, including tightening clamps on washing machine connections. Vent all dryers to the outside.

4. Insulate cold water piping.

5. Install kitchen and bath fans that are vented to the outside. (Low-noise fans have a better chance of being used.)

6. Seal, caulk and replace broken glass on old windows to minimize air leakage or replace with new windows.

7. Replace any drywall, insulation, carpet/pad and (if necessary) wood surfaces that have been wet for more than two days.

8. Provide dehumidification in chronically damp areas, such as basements and crawlspaces.

9. Remove carpets from uninsulated basement slabs.

STEP 2. ANNUAL MOISTURE INSPECTION

Check the following areas for wet spots, condensation, leaks or water stains (often an indicator of past leaks). Insects and insect damage may also be a sign of water problems.

■ Plumbing under sinks and in the basement

■ Windows and doors

■ Around tubs, showers, sinks and toilets

■ Roofs and attics

■ Ceilings and walls

■ Carpets

■ Washing machine connections

■ Basements and crawlspaces

A properly maintained and dry home will create a healthier indoor environment and reduce the likelihood of costly repairs.

Preventing moisture problems during new construction and renovations

It’s critical during new construction and renovations to prevent future moisture and mold problems by following best building practices. When most people think of foundations, walls and roofs, they think about their structural functions. But, in addition to their structural contributions to a building, foundations, walls and roofs have four other functions:

■ Provide a drainage plane (prevent outside rain/melt water from entering the building enclosure and interior spaces)

■ Provide thermal control (prevent heat from moving through the building enclosure from the inside out and vice versa)

■ Provide air control (prevent air from moving through the building enclosure from the inside out and vice versa)

■ Provide vapor management (prevent water vapor from being trapped and condensing within the building enclosure)

Each of these functions typically requires the installation of several different products that are incorporated together into systems. Builders must understand how each building product fits into the system and must install the products relative to the others so that effective systems are produced. These four systems must also be designed and constructed to work together and for the climate in which they are located.

For example, a very well insulated wall in a very cold climate will require much more robust vapor control than a wall with less insulation in a mild climate.

WANT MORE ABOUT MOLD?

This article has only scratched the surface of information and guidance available to homeowners on mold. If using the internet to explore strategies to solve mold problems in your own home, limit your research to sites that are science-based, thoroughly researched or peer-reviewed. Here are some recommendations:

A Brief Guide to Mold & Moisture in Your Home (US EPA)

Resources on Building Science and Moisture Problems in Homes and Other Buildings

Guidance on Mold Repairs: EPA Mold Remediation in Schools & Commercial Buildings

General information on mold, mold testing, mold inspections, prevention and repairs and indoor air quality