Your House Will Make You Sick

Mold and Rot are nature’s way of recycling

Mold; like asbestos, lead, and radon, is a potential health risk.

Fear of mold is a hot-button topic

Let’s use Building Science (BS) to distinguish molds’ true effects from the fictions of marketing and conventional wisdom.

Dewpoint is where air’s capacity to hold moisture and temperature intersect. The lower the temperature the less water air can hold

All mold is fungi

Fungi are any member of a kingdom of organisms that lack chlorophyll, leaves, true stems, and roots, reproduce by spores, and live as saprotrophs or parasites.
Molds are the 2nd most diverse organism on earth.
Molds are naturally occurring. They develop outside building enclosures.

With few exceptions mold is ever-present in building enclosures.


Condensation within this duct was caused when warm, moist crawl space air met cooler dry conditioned air

Biblical Mold

High levels of moisture and mold have always been assumed to be unhealthy

In Leviticus the Lord tells Moses and Aaron:
First ask a priest to inspect it. Then scrape the inside walls and throw all contaminated materials in an unclean part of town. If that doesn’t work, the house ”must be torn down — its stones, timbers and all the plaster.”






Too much moisture in crawl caused condensation and subsequent mold on new floor joists

Mold and Health

The term mold allergy is a misnomer: Mold sickness is a reaction to high levels of physical irritation.
Approximately 20% of the public are environmentally sensitive to irritants including mold, smoke and other forms of air pollution. 3% are extremely sensitive.
Exposure to damp and moldy environments may cause a variety of health effects, or none at all. Effects include nasal stuffiness, coughing, and throat, eye and skin irritation. Immune-compromised people and people with chronic lung disease may be more prone to infection.


Poor roof drainage caused black mold on floor framing


Mold toxicity is condition-specific 

Mold is dependent on food sources and environment.
Abundance and diversity are key factors in determining the adverse effects of mold; limited amounts of mold are not harmful to most people.
Passive (inert) molds are not dispersed to air, active (growing) molds are.


Until the science of mold is settled there’s an opening for litigation



Dust in ducting is food for mold. Change air filters regularly

In the three years following the 2001 landmark settlement in Texas, Ballard vs Farmers Insurance, mold claims rose from 114 million to 1 billion dollars.
At some conferences lawyers outnumber mold assessment and remediation contractors.
Fear sells to worried parents and sick homeowners. Remediation is effective only if the underlying causes of contamination are removed.



Stand-alone ducted de-humidifier reduces latent heat. The result: improved comfort and efficiency

Building Science and Mold

“It’s not the heat, it’s the humidity” is fundamentally true.
Mold likes houses; it feeds on building materials and thrives at the same temperature and moisture levels as humans.
Vapor permeability describes a material’s ability to allow water vapor to pass through it. In mixed-humid climates where vapor flows in two directions (inside-out in winter, outside-in in summer) building materials should be vapor permeable.


Vapor-impermeable plastic keeps soil moisture out. Vapor-permeable foam allows vapor to move between crawl and conditioned spaces

Vapor-impermeable materials like vinyl flooring and wallpaper, plastic sheeting and mirrors anchored directly onto walls trap moisture and may cause “black mold”.
Reduced drying potentials of composite building materials and tightly built homes are conducive to mold growth. This is one reason my inspection reports focus on moisture management.

Until conclusive epidemiological studies determine what types and levels of mold are “normal” the science of mold will remain open to interpretation. We’ll know the science is settled when Mold joins Lead, Asbestos and Radon on the website .



Removing mold with soapy water and elbow grease

Latent vs Sensible Cooling Loads

Sensible cooling lowers heat by lowering temperature. Latent cooling reduces heat by reducing the capacity of air to hold moisture.
Oversized A/C systems lower sensible but not latent moisture.
Variable speed A/Cs that cool to lower sensible temperatures increase the potential for condensation. (see psychometric chart)
Properly designed HVAC systems lower both sensible and latent heat.



System humidifiers inject moisture (and the potential for mold) into ducts. Use room plug-in types instead

Mold Solutions

Mold is a moisture problem

Manage moisture is all its forms: latent loads, exterior drainage, plumbing leaks, soil, cooking, bathrooms and laundry.
Set your thermostat no lower than 75-80F.
Install a stand-alone or ducted dehumidifier.
Design for latent cooling when replacing your A/C.
Use vapor-permeable building materials and back-vent (provide an air gap behind) mirrors.

It’s better, and cheaper, managing water before it enters the building. Good site drainage eliminates the expense of installing, operating, and maintaining this sump pumps and de-humidifiers

Build it tight and ventilate it right”
Provide adequate ventilation but don’t overdo it.
Avoid high volume whole house and range exhaust fans.


If you smell mold, you have a mold problem
Mold is a surface phenomenon. It does not cause structural damage unless left untreated.

If you find mold wipe it off and dry it out.

When there is a large area of contamination carefully remove mold-contaminated materials.


Removing dead mold limits aerosolizationthe conversion of mold spores into particles small and light enough to be carried on the air.


Inspection for and removal of mold is preferable to sampling.

Your Problem might be More than Mold

Controlling mold is just one component of healthy indoor air quality (IAQ).
For whole house solutions that limit or eliminate other contaminants contact a qualified Indoor Air Quality contractor.

A note of thanks to Stephen Andrews of Healthy Air USA for help with this newsletter

Inspector Dan


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