Causes of Mold in Attics
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What causes mold in attics or roof cavities?
How do we diagnose the cause of moldy roof decks?
How do we get rid of and prevent roof mold or attic mold?
The relationship between wet basements, wet crawl spaces, and attic mold.
Where to look for mold in a building attic
Questions & Answers about the underlying causes of mold in building attics
References

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What causes mold contamination or growth in attics and cathedral ceilings? Here we explain the causes of moldy attics or roof mold in buildings, and we discuss the relationship between other building moisture sources (such as a wet basement) and attic and roof mold contamination.

This document gives advice on how to find and deal with mold in building attics and roof cavities; We discuss when and how to clean up attic mold - how to get rid of attic or roof mold.

This article is part of our series: FIND MOLD in buildings, HOW TO which describes how to find mold and test for mold in buildings, including how and where to collect mold samples using adhesive tape - an easy, inexpensive, low-tech but very effective mold testing method. The page top photograph of dark mold found on the attic-side of plywood roof decking was contributed by David Grudzinski, a Cranston RI professional home inspector and member of ASHI and NACHI.

ATTIC MOLD CAUSES

What causes mold growth in attics? Understanding why we get mold contamination in roof spaces helps define the steps necessary to prevent attic mold, cathedral ceiling mold and similar problems.

Black moldy attic (C) D Friedman D Grudzinski

As this moldy attic photo (courtesy of David Grudzinski) also shows, mold on roof decking or roof framing may be quite extensive.

If you look closely at the buckling plywood in the upper right of this photograph, you may notice some cracking that might indicate that the plywood roof decking is actually delaminating and badly damaged.

If that proves to be the case, this mold cleanup job will be simplified, but more costly as roof decking may need to be removed and replaced.

When we see an attic with extensive visible mold on wood surfaces, we also suspect that the fiberglass insulation may also be mold contaminated, or may become so during any mold cleanup job in the area. See INSULATION MOLD for details.

What Causes Attic Mold?

Cleaning up moldy wood surfaces, removing moldy attic insulation, will be a costly but wasted step if we don't understand and correct what caused these conditions in the first place. Below we describe the combination of two critical factors that make for a wet, moldy attic: inadequate roof ventilation and an indoor source of un-wanted or excessive building moisture. A third source, roof leaks, is more obvious and should also be considered in any building inspection for leaks, moisture, or mold.

Inadequate Roof Ventilation

David pointed out in his emailed comments that the attic of this home was not adequately vented. We don't see good, continuous intake ventilation at the house eaves or soffits (the lower roof edges.) We also did not see good roof exit venting along the ridge of the building.

Our example photos (below) show characteristic rust stains around roofing nails in a poorly-vented attic (below left), and the absence of those stains around roofing nails in a well-ventilated attic (below right). Even our poorly-vented attic (below left) was not as severely wet and moldy as the attic in Grudzinski's photos (above).

Attic roof stains around roofing nails (C) Daniel Friedman

Our photo of frost on the under-side of an attic roof deck (left) shows another clue of inadequate under-roof ventilation that may be visible if the building is located in a freezing climate.

Regardless of its source, moisture entering the attic from anywhere is trapped in this space - contributing to mold growth and longer term to building rot or perhaps even inviting insect attack on the structure.

If the moisture levels were low, no mold problem may have occurred. But if we combine poor roof ventilation with high moisture levels, we've asked for trouble with mold and rot.

Insulation improvements as well as attic ventilation improvements are discussed at INSULATION INSPECTION & IMPROVEMENT, and at ROOF VENTILATION SPECIFICATIONS we give specific details on good attic ventilation.

Indoor Moisture Sources Causing Attic Mold

Poor insulation & bathroom, dryer, or kitchen fans not vented outside: Mr. Grudzinski also observed that the moldy attic in this home was fed moisture from a combination of poor insulation, and two bath fans that were venting directly into the attic rather than being directed outside. "Poor insulation" means increased heat flow into the attic in cold weather.

Our photo (left, from a different home) shows a rats nest of bath vent fan ducts that the building owner emptied into a building attic. These vents should have been conducted to outside the building.

"Heat flow" into a cold attic means warm moisture-laden air flow from the occupied spaces in the home below is moving into the chilly or cold attic space. This airflow not only increases the cost of heating the home, but it brings up moisture from below into the attic area where water condenses out of the warm air onto cold attic surfaces.

Wet basements or crawl spaces mean wet moldy attics: At BASEMENT MOLD WATER IMPACT another series of photographs by Mr. Grudzinski demonstrates how a wet (rotting, moldy) sub-basement served as a moisture source that was almost certainly a major contributor to if not the main cause of the moldy attic shown in our page top photographs here.

At ATTIC CONDENSATION CAUSE & CURE and at ICE DAM PREVENTION we describe problems caused by inadequate roof ventilation that include not just attic moisture and mold, but ice damming and even leaks into building ceilings and walls. 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

Toxic attic mold: The photo at the left was identified as a toxic mold that probably should be removed. Lots of protruding nails through a roof deck preclude wiping or scrubbing.

Mold growth, provided it is not just cosmetic mold which can simply be left alone, (see Cosmetic Mold) can be cleaned from wood surfaces by blasting, scrubbing, or even simple surface wiping, depending on the surface accessibility and smoothness.

Sanding wood building surfaces such as plywood or tongue and groove roof sheathing, wall sheathing, or wood framing is usually unnecessary and inappropriate.

If you must return wood surfaces to immaculate, pristine looking condition, perhaps for cosmetic reasons where wood surfaces are left exposed to view in a building interior, see MOLD CLEANUP by MEDIA BLASTING and MOLD CLEANUP by MEDIA BLASTING and MOLD CLEANUP with BLEACH and MOLD CLEANUP - WOOD FRAMING & PLYWOOD and finally MOLD CLEANUP HEALTH RISKS

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Technical Reviewers & References

Related Topics, found near the top of this page suggest articles closely related to this one.

David Grudzinski, Advantage Home Inspections, ASHI cert # 249089, HUD cert# H-145, is a professional home inspector who contributes on various topics including structural matters. Mr. Grudzinski, Cranston RI serving both Rhode Island and Eastern Connecticut can be reached at 401-935-6547 fax- 401-490-0607 or by email to Davidgrudzinski@aol.com. Mr. Grudzinski is a regular contributor to InspectAPedia.com - see DECK FLASHING LEAKS, ROT Case Study, and BASEMENT WATER MOLD IMPACT and VERMICULITE INSULATION for examples.

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.

The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.

Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.

Building inspection education & report writing systems from Carson, Dunlop & Associates Ltd

Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
Environmental Health & Investigation Bibliography - our technical library on indoor air quality inspection, testing, laboratory procedures, forensic microscopy, etc.
Adkins and Adkins Dictionary of Roman Religion discusses Robigus, the Roman god of crop protection and the legendary progenitor of wheat rust fungus.
Kansas State University, department of plant pathology, extension plant pathology web page on wheat rust fungus: see http://www.oznet.ksu.edu/path-ext/factSheets/Wheat/Wheat%20Leaf%20Rust.asp
"A Brief Guide to Mold, Moisture, and Your Home", U.S. Environmental Protection Agency US EPA - includes basic advice for building owners, occupants, and mold cleanup operations. See http://www.epa.gov/mold/moldguide.htm
US EPA - Mold Remediation in Schools and Commercial Building [Copy on file at /sickhouse/EPA_Mold_Remediation_in_Schools.pdf ] - US EPA
US EPA - Una Breva Guia a Moho - Hongo [Copy on file as /sickhouse/EPA_Moho_Guia_sp.pdf - en Espanol

Mold Contamination Testing, Cleanup, Prevention: references & products

The Mold Information Center: What to Do About Mold in buildings, When and How to Inspect for Mold, Clean Up Mold, or Avoid Mold Problems
Aerobiology, Building Science, Microscopy, & Laboratory References, an extensive technical bibliography
Allergens: what they look like in buildings
Associations: Sick House, Sick Building, SBS - Air Quality, Government, Private Associations and Information Resources
Atlas of Clinical Fungi, 2nd Ed., GS deHoog, J Guarro, J Gene, & MJ Figueras, Centraalbureau voor Schimmelcultures, Universitat Rovira I Virgili, 2000, ISBN 90-70351-43-9 (you can buy this book at Amazon) - The Atlas of Clinical Fungi is also available on CD ROM
Atlas of Mold Related Illness: Index of Symptoms and health, physical, neurological, psychological, and other complaint which people suspect may be mold or building-related.
Atlas of Indoor Mold, Online Clinical Mold Atlas, Toxins, Pathogens, Allergens and Other Indoor Particles - Medical Health Effects of Mold (separate online document)
Black Mold that is Harmless Photos of recognizable, usually harmless black mold on wood, bluestain, ceratocystis, ophistoma
Building Floods: quick steps after a building flood or plumbing leak can prevent costly mold contamination
Classes of Mold: what types of cosmetic, allergenic, or toxic mold are a problem? Can mold be cleaned-up successfully?
Clinical Mold References - Detailed bibliography of mold reference texts
"A Brief Guide to Mold, Moisture, and Your Home", U.S. Environmental Protection Agency US EPA - includes basic advice for building owners, occupants, and mold cleanup operations. See http://www.epa.gov/mold/moldguide.htm
"Disease Prevention Program for Certain Vegetable Crops," David B. Langston, Jr., Extension Plant Pathologist - Vegetables, University of Georgia (PDF document) original source: www.reeis.usda.gov/web/crisprojectpages/209797.html
"Disease Prevention in Home Vegetable Gardens," Patricia Donald, Department of Plant Microbiology and Pathology, Lewis Jett
Department of Horticulture, University of Missouri Extension - extension.missouri.edu/publications/DisplayPub.aspx?P=G6202
"Management of Powdery Mildew, Leveillula taurica, in Greenhouse Peppers," Ministry of Agriculture and Lands, British Columbia - Original source: www.agf.gov.bc.ca/cropprot/peppermildew.htm
Environmental Health & Investigation Bibliography - our own technical library on indoor air quality inspection, testing, laboratory procedures, forensic microscopy, etc.
Fiberglass: Mold in Fiberglass Insulation© 2005 comments about a field study in process, & more about health hazards from fiberglass insulation - DJF
Fifth Kingdom, Bryce Kendrick, ISBN13: 9781585100224, is available from the InspectAPedia online bookstore - we recommend the CD-ROM version of this book. This 3rd/edition is a compact but comprehensive encyclopedia of all things mycological. Every aspect of the fungi, from aflatoxin to zppspores, with an accessible blend of verve and wit. The 24 chapters are filled with up-to-date information of classification, yeast, lichens, spore dispersal, allergies, ecology, genetics, plant pathology, predatory fungi, biological control, mutualistic symbioses with animals and plants, fungi as food, food spoilage and mycotoxins.
Fungi, Identifying Filamentous, A Clinical Laboratory Handbook, Guy St-Germain, Richard Summerbell, Star Publishing, 1996, ISBN 0-89863-177-7 (English) (buy at Amazon)
Looking for Mold Procedure: what mold is often found where in buildings - simple technical presentation
Meruliporia: the house eating fungus or "poria"
Mold Action Guide: Step-by-Step Instructions, What to do about mold, mildew, and other indoor allergens
MOLD APPEARANCE - WHAT MOLD LOOKS LIKE Photos of what mold looks like in buildings
MOLD APPEARANCE - STUFF THAT IS NOT MOLD Photos of NOT-mold material that is sometimes mistaken for mold
MOLD ATLAS & PARTICLES INDEX, Pathogens, Allergens and Other Indoor Particles - Medical Health Effects of Mold (separate online document)
MOLD BY MICROSCOPE Mold under the microscope - photo identification of the most common indoor molds found in buildings
Mold FAQs Answers to Most Questions about Indoor Mold, Mold Related Illness, Mold Cleanup, Mold Prevention
US EPA: Mold Remediation in Schools and Commercial Building [Copy on file at /sickhouse/EPA_Mold_Remediation_in_Schools.pdf ] - US EPA
Mold spores in the Home - a Photo ID Library for detection and identification of mold allergens
Mold Test Kits - How to Collect and Send Your Own Mold Sample to our mold testing lab or to any mold lab you wish
Most Common Indoor Molds Found in buildings, A Table of
Mycology, Fundamentals of Diagnostic, Fran Fisher, Norma B. Cook, W.B. Saunders Co. 1998, ISBN 0-7216-5006-6 (buy this book at Amazon)
Ozone Warnings - Use of Ozone as a "mold" remedy is ineffective and may be dangerous.
Rot concerns in buildings-some building mold such as Meruliporia incrassata "Poria" risks serious rot and hidden structural damage
US EPA: Una Breva Guia a Moho - Hongo [Copy on file as /sickhouse/EPA_Moho_Guia_sp.pdf - en Espanol

OTHER IAQ ISSUES: How To Find and Address Other Indoor Air or Indoor Environment Contaminants Besides Mold

Mold or allergens may not be the only or even the main indoor environmental contaminant. Don't let media attention to mold cause so much enviro-scare fear that other, possibly more urgent hazards go un-addressed.

Fiberglass building insulation and HVAC duct work insulation hazards
Sewage and Septic backup contamination in buildings: inspection, testing, remediation, & references to expert sources
Other environmental risks: Asbestos, carbon monoxide, electromagnetic fields, environmental illness, fiberglass, MCS - multiple chemical sensitivity, toxic gases, etc
Indoor Gas Sampling Plan for Residential buildings lists a number of toxic indoor gases which we test for, depending on the building complaint and building conditions
Ozone Warnings - Use of Ozone as a "mold" remedy is ineffective and may be dangerous.
Pet control - if you can't say goodbye to your bird, cat, dog, guinea pig, hamster, tropical fish, then limit the areas they occupy and limit the airflow from that area to sleeping or other areas of the building, use allergenic bedding, eliminate wall-to-wall carpeting, improve housecleaning including use of a HEPA-rated vacuum cleaner. For more details see our article Dog, Cat, and Other Animal Dander - Information for Asthmatics and Indoor Air Quality
Rodents, Mice, Squirrel Control - I find high levels of mouse and rodent dander, fecal dust, and urine-contaminated dust in some buildings, and high levels of these materials in building insulation in those locations. If you have a mouse problem, particularly if mice and their waste (fecals or urine) are contaminating the building HVAC or building insulation, may need both steps to clean up or remove infected materials and steps to stop an ongoing rodent problem. If squirrels are a problem, the cleanup needs to include closing off entry openings into the building. Get some help from a licensed pest control expert.
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