Bathroom Ventilation Ducts & Fans – Pt II
The most serious consequence of an improper ventilation setup is the potential accumulation of mold in attics or crawlspaces. Health problems caused by mold are related to high concentrations of spores in indoor air. “Spores” are like microscopic seeds, released by mold fungi when they reproduce. Every home has mold. Moisture levels of about 20% in materials will cause mold colonies to grow. Inhaling mold spores can cause health problems in those with asthma or allergies, and can cause serious or fatal fungal infections in those with lung disease or compromised immune systems.
In order to grow, mold fungi require that the following conditions are present:
Improper Install on Bathroom Vent.
- Oxygen
- Temperatures between approximately 45° F and 85° F
- Food. This includes a wider variety of materials found in homes
- Moisture
If insufficient levels of any of these requirements exist, all mold growth will stop and fungi will go dormant. Most are difficult to actually kill.
Even though mold growth may take place in the attic, mold spores can be sucked into the living areas of a residence by low air pressure. Low air pressure is usually created by the expulsion of household air from exhaust fans in bathrooms, dryers, kitchens and heating equipment.
Improper Ventilation
Ventilation ducts must be made from appropriate materials and oriented effectively in order to ensure that stale air is properly exhausted. This is something that is carefully observed during a Fronline Home Inspection.
Ventilation ducts must:
- Terminate outdoors. Ducts should never terminate within the home or attic.
- Contain a screen or louvered (angled) slats at its termination to prevent bird, rodent and insect entry.
- Be as short and straight as possible and avoid turns. Longer ducts allow more time for vapor to condense and also force the exhaust fan to work harder.
- Be insulated, especially in cooler climates. Cold ducts will encourage condensation.
- Protrude at least several inches from the roof.
- Be equipped with a roof termination cap that protects the duct from the elements.
- Be installed to manufacturer’s recommendations.
The following tips are helpful although not required. Ventilation ducts should:
- Be made from inflexible metal, PVC, or other rigid material.
- Have smooth interiors. Ridges will encourage vapor to condense, allowing water to back-flow into the exhaust fan or leak through joints onto vulnerable surfaces.
Above all else, a bathroom ventilation fan should be connected to a duct capable of venting water vapor and odors into the outdoors. Mold growth within the bathroom or attic is a clear indication of improper ventilation that must be corrected in order to avoid structural decay and respiratory health issues.
Source: InterNachi
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