Allowable Mold Levels For Indoor Air Quality


Some questions have been raised regarding the levels of mold in the lumber used in one of our truss projects. The issue of indoor air quality is up and coming. Do you have any information regarding standard allowable values? And how can we test for these contaminants?


It is not practical for a non-professional to test for the presence of biological contaminants. However, due to potential health consequences, if contaminants are suspected in a home, an investigation should be conducted to remove or control them.

Left unchecked, mold can grow and cause health problems for sensitive people. Because there are no standards for “normal” levels of mold, tests are not usually conducted. When tests are done, however, they compare types and levels of molds in the house with molds in the outside air.

An important thing to remember is that moisture content levels in lumber need to be over 19% to support mold and fungi growth and cause decay. Normal installation conditions for wood framing usually fall well below this (8-11% yearly average moisture content in the US).

For information on mold prevention in wood components, see SBCA’s TTB – Mold on Wood Structural Building Components and TTB – Builder Advisory on Mold. For general information on mold remediation, visit the US Environmental Protection Agency website on indoor air quality.

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