Did the Winter Season Leave You With a Mold Problem?

March 11, 2014
Ross and Witmer

A trip to the attic or an inspection around window frames may uncover a mold problem you hadn’t anticipated over the course of the recent winter. Mold needs warmth, moisture and food for it to thrive and grow. Since mold is nature’s primary composter, anything organic serves as a host for it. The building materials in your attic, including the insulation and anything you store in it, are vulnerable.

If your windows have wood frames, cold temperatures may cause the moisture in the indoor air to condense or freeze on the windows, and as it warms, the frost melts. Left there, mold can start to grow, even around the drywall surrounding the frames of vinyl or metal windows.

How a Mold Problem Gets Started

Mold spores are present on many of the surfaces of your home and in the air. During the winter, warm, moist air escaping into the attic can carry these spores. If your attic insulation is inadequate, the warmth from your home will transfer into the attic, along with warm air, and warm the roof decking enough for the moist air to condense on it and drip down. The organic matter the condensation lands on can serve as a fertile spot for mold growth.

How to Control a Mold Problem

Mold will eventually disintegrate whatever it grows on including wood, fabrics, paper, and some types of paint and glue. Those with allergies may react to even a minor mold problem in your home. Unless the growth is widespread, you may be able to wipe the surface off with a water and bleach or vinegar solution. If it’s on the surface of drywall, it may be easier to remove the infested piece and replace it. Sealing the air leaks between your attic and ceilings will also lower the humidity level, preventing mold growth.


Mold spores can be filtered out of your home’s air supply using a filter rated to remove particulates as small as 2 microns, the smallest mold spore. A filter for your HVAC system with a MERV (minimum efficiency reporting value) rating of 8 will remove fewer than 50 percent of the mold spores in the air, while one with a rating of 12 can trap more than 80 percent of the spores.

HVAC systems use air filters to keep their internal parts clean, but they can also be used to control a mold problem. The filters you buy in the hardware or grocery store may not show a MERV rating, but may provide other information. The packaging, for example, may indicate that the filter traps mold spores and other allergens.

Before you install such an effective filter, check with your HVAC technician or the owner’s manual to see if your system can use such a device. Filters that will trap nearly all the mold spores have a MERV rating of 12 and higher. The higher-rated filters may require serious system modifications to run in your HVAC equipment. They’re typically thicker than standard one-inch filters, and require a stronger blower or air handler to push the air through the dense filtration material.

UV Lights

UV lights inside your air handler will stop a mold problem, especially during the cooling season. Water condenses from the air when the air conditioner runs, and it can foster mold and bacteria growth if it doesn’t drain away or dry fast enough from the evaporator coil or drain pan. UV lights alter the genetic structure of any organic particulate that passes by the light, eventually killing the micro-organism, which is why they’re widely used in health-care settings.

The lights can also be placed in the ductwork to treat the airstream as it moves through the ducts repeatedly through the day. They’ll need changing approximately once a year to maintain their potency. Installing UV lights inside your HVAC system where they’re hidden, but effective, is a good way to remedy a mold problem, along with reducing the population of harmful airborne viruses and bacteria.

Humidity Control

Removing excessive humidity from the air will thwart mold growth, which is possible year-round with a whole-house dehumidifier. You can also lower humidity by using the exhaust fans in the bathrooms and kitchen when steam is present. The ideal humidity range indoors runs from 30 to 50 percent, and an inexpensive hygrometer will help you keep it balanced year-round.

To learn more about a mold problem in your home and the best ways for you to deal with it, contact Ross & Witmer, providing HVAC services for Charlotte, Gaston, Mecklenburg and Union homeowners since 1945.

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