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Beating Mold: Understanding and Controlling Humidity - Part II

By
Home Inspector with Diadem Property Inspections - Serving Southeast Michigan

You may be interested in Part I of this post. But continuing on... here are some of the problems when indoor humidity gets out of control.

High Humidity and Indoor Air Quality

  • Fungi (that means mold!)
  • Bacterial growth
  • Viruses
  • Biological growth
  • Asthma
  • Volatile Organic Compound (VOC) off-gassing
  • VOC chemical interaction
  • Wet windows
  • Rotting sills
  • Damage to pictures, books, furniture
  • Dust mites
  • Uncomfortable living conditions



"Humidity promotes mold growth and dust mite population growth. Both are significant indoor allergens and can set off allergic sensitivity..."

--American Academy of Allergy Asthma and Immunology


Problems With Low Humidity Levels

  • Static electricity (ouch!)
  • Dry skin, itchy skin, skin disorders
  • Sore throats
  • Bloody nose or nose irritation
  • Germs spread easier
  • Respiratory infections
  • Viruses and bacteria
  • Uncomfortable living conditions

In very dry environments, the mucous membranes in the nose and throat dry out. That leads to a really yucky feeling and leaves us more susceptible to colds and respiratory illnesses.

As far as nasty things like bacteria go, staphylococcus and streptoccoccus (try saying that ten times fast!) die 20 times faster at 45% RH than below 20% RH.

In addition to the health concerns, in super-dry conditions, the body feels chilled, even at higher thermostat settings. So people can burn more energy and get no benefit.



So What Is The Recommended RH Range?

 

Under most conditions, the International Indoor Air Quality Commission recommends RH levels should be kept around 45% - 55%. This gives the best mix of comfort and air quality. Most building and air quality authorities believe 45% is the optimal RH in a structure.

Sources of Humidity

Here's some fascinating math: in a 1,000 SF house at 70 degrees F inside, adding only 5 pints of moisture can raise the RH from 15% to 60%!

Wow! So what could produce that much water vapor? Here are some culprits, many of which we rarely think about as contributing to high RH:

 

  • Showers (a family of 4 can produce 1 quart of water vapor per day)
  • Cooking (can produce up to a gallon of moisture a day)
  • Breathing (1 person typically produces 6 cups of moisture per day!)
  • Humidifiers (no kidding!)
  • Aquariums
  • Plants
  • Unsealed crawlspaces
  • Improper ventilation (like bathroom vents terminating in the attic instead of outside)
  • Water infiltration
  • Leaky ductwork

 

 

Posted by

 

Jason Channell     Twitter - Home Inspection LinkedIn Twitter - Home Inspection

Diadem Property Inspections
(888) 699-8710

Learn more: michigan-indoor-air-quality.com

Learn more: HouseSleuth.com

Michigan Builder's License 2101198700
Environmental Solutions Association 3818 -- Certified Mold Inspector & Assessor, Certified Allergen Inspector
International Indoor Air Quality Commission CC1983 --  Indoor Environmental Certified Consultant

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Comments (5)

Dan Edward Phillips
Dan Edward Phillips - Eureka, CA
Realtor and Broker/Owner

Hi Jason excellent post and advice on maintaing humidity in the home!

Aug 23, 2010 05:33 PM
Jason Channell
Diadem Property Inspections - Serving Southeast Michigan - Troy, MI
The House Sleuth

Thanks very much, Dan.

Aug 23, 2010 05:35 PM
Tim Lorenz
TIM LORENZ - Elite Home Sales Team - Mission Viejo, CA
949 874-2247

It is hot here now but we do not get much humidity.

Aug 23, 2010 06:56 PM
Not a real person
San Diego, CA

I'm in the same situation as Tim, maybe because we're just 60 miles from each other. However, as I learned the first time I went to Palm Springs and was subject to temperatures of 116°F, there's nothing in California that is anything remotely like the heat and humidity that I was subjected to while growing up and living in Texas.

Aug 23, 2010 10:31 PM
Rosalinda Morgan
Brookville, NY
"The Rose Lady"

In Long Island, it is hot and humid in the summer.  However, I'd rather have that than dry condition because my skin gets so dry and itchy otherwise. 

Aug 30, 2010 08:35 AM