Black attic mold on roof sheathing (C) Daniel FriedmanAttic & Roof Mold ContamiHow to Find & Test for & Remove Mold in Attics

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Attic & roof mold contamination causes & cures:

Not all attic mold is toxic or harmful. It is also not the case that all attic mold needs to be cleaned or removed. It is not the case that all attic mold is going to enter the living area or otherwise be a problem for building occupants.

On the other hand some attic mold contamination can enter air handling equipment, ductwork, or occupied space and can be a risk to occupants. How do we determine the difference beween actionable attic mold and cosmetic mold? What must be done to clean up or remove attic mold contamination, and how do we prevent attic mold growth?

This article series on attic and roof mold contamination gives detailed step by step procedures and advice on how to find, test for, remove & prevent future mold contamination in building attics and roof cavities.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Is attic mold a health risk or indoor air quality problem?

Photograph: toxic mold on pine tongue and groove roof sheathing - © Daniel Friedman

Toxic attic mold: The photo at the left was identified as a toxic mold that probably should be removed, although the ease of movement of mold spores from an attic down into a living area varies widely from building to building.

Uncertain attic mold: The photo at the very top of this page shows where you may find mold growing on the attic side of ceiling drywall, particularly below roof leaks or in areas of ice dam leaks at a building eaves.

Article Series Contents

We pulled back the fiberglass insulation to expose this small area of mold growth. What about the white mold-suspect material observed on the rafters? Is that mold? If so is it a problem?

The answer is, "it depends." In addition to testing to see what this material is (presuming there is a large area of it), we'd also evaluate the chances of particle movement between the attic and the living space before deciding on an appropriate approach to this moldy attic.

Photograph: typical mold on attic side of ceiling drywall after a roof leaks - © Daniel FriedmanThis article discusses attic mold in the following order:

It is simply not the case that all attic mold is toxic. It is not the case that all attic mold is harmful.It is not the case that all attic mold needs to be cleaned or removed. It is not the case that all attic mold is going to enter the living area or otherwise be a problem for building occupants.

It is however the case that attic mold indicates damp conditions or leaks and therefore some further investigation or thought are in order.

Be sure to use the links at the end of this article to review other examples of mold found in attics on tongue-and-groove roof sheathing, brown mold and very dark brown, black-looking mold on attic plywood, and the risk of hidden mold in attic insulation.


Also see our photo guide to finding attic moisture and mold at How to Inspect Attics for Condensation & Moisture - to Detect & Correct Attic Condensation, Frost, Ice Dam Leaks & Attic Mold

How to Evaluate the Risk of Toxic Attic Mold

White attic mold (C) Daniel FriedmanHere are some comments about air and particle movement in buildings and thus the chances that attic mold will be transported from that area into the living space.

Is Mold Sealed-Up in Building Cavities Hazardous?

When attic (or other building) surfaces or insulation contain a large reservoir of toxic or allergenic mold, AND if the area were inaccessible, say because the space is too small to enter, then it may be necessary to remove some portion of roofing to give access for remediation, particularly if there is evidence of transmission of problem mold from that space into the living area.

While some experts (Burge et als.) have opined that there is no important toxic mold spore movement from these "almost sealed" building cavities into occupied space, and thus that mold in building cavities is not a problem, our direct field inspection and test results, as well as client interviews and live field tests performed with clients have demonstrated that that assumption is not reliable, and that in at least some buildings, certain easily airborne mold genera/species such as Aspergillus sp. may move throughout the structure and may be a health concern for some building occupants.

The movement of mold-spore laden air in and out of building cavities and between building areas is not reliably predicable from a visual inspection, nor from simple air tests.

Simply turning a building fan on or off, opening or closing a window, turning up the thermostat, and many other conditions can change how air is moving in buildings.

Air Does Not Always Move Up and Out of a Structure as Building Science Would Suggest

Finally, building air sometimes moves contrary to what building science would lead us to expect. For example we assume that warm air rises up through buildings, passing out through roof ventilation. But direct measurement in some buildings has shown that warm air (including from a moldy attic) can sometimes flow downwards into the occupied space. Two examples that we have frequently observed in the field:

  1. Air conditioning the upper floors of a hot building can cause a sufficient volume of chilled air to flow downwards (by gravity, through stairwells) at a rate that draws warm air down into the occupied space from an attic.
  2. Use of a ceiling-mounted whole house fan to attempt to exhaust hot building air, combined with inadequate exit ventilation out through the attic or roof space can pressurize the building attic, blowing attic air (possibly warm or moldy) downwards into some building areas, air passing through openings cut for ceiling light fixtures, wiring, plumbing, or duct work.

This article is part of our series: MOLD in BUILDINGS which describes how to find mold and test for mold in buildings.

Readers of this article series about black, white, green and other colored mold on attic and under-roof surfaces should also be sure to read INSULATION MOLD CONTAMINATION TEST where we describe the risk of non-visible problematic mold hidden in building insulation.


Continue reading at ATTIC MOLD CAUSES or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


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