high humidity and moldHigh humidity promotes mold growth and can destroy a home or building just as the results of plumbing leaks or water infiltration from the outside.  Mold spores floating in air can take the humidity from the air and start growing on materials and surfaces, including walls and ceiling.

What is relative humidity?

The relative humidity (RH) plays a big part in promoting or inhibiting mold growth.  It is the total amount of moisture air can hold at a given temperature. Warmer air can hold a greater amount of moisture than colder air. The RH is based on two factors – the amount of moisture in the air and the temperature.  Psychrometric Chart. The RH is defined as the ratio of the amount of water vapor in the air at a specific temperature to the maximum amount that the air can hold at that temperature, expressed as a percentage. At an RH of 100%, dew point is reached when moisture condenses on surfaces cooler than the surrounding air.  The following Psychrometric chart shows the relationship between humidity and temperature.

high humidity and mold 2

The extent of mold contamination is directly related to the relative humidity. Below 30% relative humidity very little mold growth occurs, while at 70% conditions are optimum for mold growth. High humidity allows moisture to condense on cool surfaces, such as windows and sills. Moisture can also seep through walls, ceilings, basements, and concrete slabs. To avoid mold problems, it is recommended that the RH be kept under 60% at all times.

Northerners beware of sub-tropical climates!

Let us repeat that mold needs three things in order to grow – a surface to grown on, food (dead organic material), and moisture.  Moisture is the only factor we can control.

There are many northerners who buy a condo in Florida.  They enjoy it for a couple of months in the winter season, then they return to their homes up north, and to save money, they turn off the HVAC system.   To their horror, when they return the next winter, they find their  condo covered  with mold.    Florida realtors should warn their clients to keep the HVAC on all the time, and having a friend or neighbor check their condo once in a while.

In our next segment “High Humidity And Mold Damage – Part 2,” we will explore the various indoor conditions that can lead to mold growth.  A humidity/temperature pen is affordable and quite useful to test the different rooms in your house.  To acquire a pen similar to the above picture,  check our trusted resources.

For more information, feel free to contact us.  We operate a mold assessment company in Central Florida and are authors of this blog and several books on mold.

Written by Charles & Danielle Dobbs – Professional mold assessors, expert witnesses, authors of several books on mold, and mold education bloggers

Charles & Danielle Dobbs - Professional mold assessors, expert witnesses, authors of several books on mold, and mold education bloggers

Professional mold assessors, expert witnesses, and authors of MOLD MATTERS- SOLUTIONS AND PREVENTION, MOLD PREVENTION TIPS FOR THE GREEN BUILD INDUSTRY, and INSPECTION AND SAMPLING METHODOLOGIES FOR TRAINING MOLD ASSESSORS.