Humidity in a house is primarily caused by excess moisture entering or being generated indoors combined with poor ventilation that prevents proper air circulation and moisture removal. Key causes include:
- Daily activities that produce water vapor: Showering, bathing, cooking (boiling water, stove use), and drying laundry indoors release significant moisture into the air, raising indoor humidity levels
- Heating appliances: Gas heaters, especially unflued ones, produce water vapor as a byproduct of combustion, adding moisture to indoor air
- Poor ventilation: Insufficient air exchange traps moisture inside, causing stale, humid air and condensation on cold surfaces like windows and walls. This lack of ventilation also promotes mold growth
- Structural issues: Moisture can infiltrate through wall pores, poorly constructed foundations, leaks in water mains or appliances, and inadequate air sealing, allowing dampness from outside or soil to enter the home
- Environmental factors: Living in coastal, rainy, or humid climates naturally increases indoor humidity due to higher outdoor moisture and evaporation
- Other factors: Open crawl spaces, disconnected or improperly sized HVAC systems, and malfunctioning bathroom exhaust fans can exacerbate indoor humidity problems
In summary, indoor humidity results from moisture generated by everyday activities and appliances, combined with moisture intrusion and inadequate ventilation or air sealing that trap this moisture indoors
