There are a lot of misconceptions about mold and how it grows. Unfortunately, those myths can lead to additional problems in the home when you don’t take action. One of the greatest myths is that mold only grows on organic surfaces like fabric, paper and wood.

Mold will grow on any surface – even flat, smooth surfaces like glass. Even steel is susceptible to mold. That means that no area of your home is really safe. As long as there are spores present, which are always in the air, and there’s particulate matter and moisture, then mold can grow.

If mold spores are always present, then how do you control it? Through proper ventilation.

How Air Movement and Moisture Impacts Mold Growth

For Michigan homeowners, all the necessary things mold needs to grow are present in your house. That includes mold spores, moisture, food sources and a surface to grow on. The only way to control the growth of mold is to maintain the level of moisture in your home and properly ventilate it so that the air is constantly moving

Controlling moisture is typically done with dehumidifiers and eliminating any leaks and standing water around the home. Good ventilation is a little trickier.

Your home may seem to be properly ventilated with windows and vents in the right places, but the air might not be moving as well as you think.

Proper Bathroom Ventilation

Installation of ventilation in your bathrooms is a must. The small enclosed space of the bathroom coupled with all the moisture (especially a full bath) makes for quick mold growth. Thankfully, installing vents and fans in the bathroom is fairly simple.

The challenge is making sure the fan is venting properly.

It’s not uncommon for homeowners, and even some contractors, to take a shortcut and vent the bathroom directly into the attic. This pushes a high volume of moisture into a space designed to trap and insulate your home. If you trap moisture in that space you’ll have a high volume of mold growth rapidly throughout your insulation, wood and duct space.

Make sure any bathroom vents and fans are enclosed and vent through the attic and straight out the roof.

A bathroom without ventilation is like a fireplace without a chimney. That moisture needs to vent up and completely out of the home.

Proper Kitchen Ventilation

Like bathroom ventilation, kitchen air needs to vent to the exterior of the home. If the stove is on an exterior wall, it can be much easier to install a vent hood that pushes moist air directly outside. With interior kitchens, or stoves built into inner walls, it may be easier to vent to the roof.

In this situation, like the bathroom, you want those fans or vent hoods pushing the moist air, smells, and food particles up and out rather than into the wall or attic spaces.

You also want to choose the right hood for your appliance. This is because many vents simply filter and recirculate the air. This can help protect surrounding cabinets but may not be effective in eliminating potential mold growth.

  • For standard or conventional cooking equipment (less than 60,000 Btu for gas or electric cooktops), specify 100 CFM for every 1 foot of width of cooking surface. For example, a 30-inch cooktop requires 250 CFM.
  • For high-performance gas cooking equipment (more than 60,000 Btu), use 1 CFM for every 100 Btu. For example, 60,000 Btu requires 600 CFM.
  • If the cooktop contains a grill, add 200 CFM to the total required.
  • If the hood is rated at more than 300 CFM, the project may require a make-up air damper depending on local codes.

If quiet operation is paramount, consider specifying an oversized blower. For example, 300 CFM might be adequate for the cook’s needs, but a range hood rated at 400 CFM produces less noise at a lower speed while providing 300 CFM. For even quieter operation, choose a hood model with a remote blower. Finally, select an HVI-certified hood to ensure that the CFM and Sone levels match the manufacturer’s claim.

For duct work leading through the attic to the exterior of the house, make sure that the duct is equal to or greater than the size of your good. Increase the duct size to improve airflow, and keep 90-degree elbows at least 2 feet apart to prevent air dams. Gentle duct transitions can also prevent air dams and turbulence that impact ventilation and can lead to moisture being trapped.

Proper Attic Ventilation

Roof ventilation varies depending on the climate, but it’s the same whether or not you’re venting the entire attic or just the roof deck.

For cooler climates, like Michigan, the purpose of ventilation is to maintain a cold roof temperature to avoid ice dams created by melting snow. The vent also moves moisture from the conditioned living space up into the attic and out of the home.

During warmer months, the ventilation expels solar-heated hot air to reduce the cooling load on your central air condition systems.

A few tips for attic ventilation that come from the Building Science Corp on roof venting:

  • Make sure your duct work is properly sealed so you’re not venting warm moist air into the attic space
  • Air seal any ceiling penetrations, like recessed lighting.
  • If your home has a roof deck from a vaulted ceiling or conditioned attic space, make sure it’s vented
  • Check for good airflow with soffit vents

Keeping Mold Out of the Basement

Because of its location either partially or fully underground, basements need good ventilation to deal with the moisture that collects naturally below ground. An unventilated basement is prone to musty odors and mildew from condensation. If it’s allowed to collect, it can form into small puddles that become breeding grounds for more mold spores.

It’s difficult to keep air moving and properly ventilate a basement, so it’s best to focus on keeping moisture levels down. Dehumidification is a must, and can typically be achieved with one or more dehumidifiers.