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ENVIRONMENTAL HAZARDS - INSPECT, TEST, REMEDY
MOLD: A COMPLETE GUIDE to TEST CLEAN PREVENT
ACTIVITY of MOLD in BUILDINGS
AGE of MOLD - Old is the Mold?
AIR CLEANER PURIFIER TYPES
AIR FILTERS for HVAC SYSTEMS
AIR TEST SAMPLING CASSETTE STUDY
AIRBORNE MOLD COUNT NUMBER GUIDE
AIRBORNE PARTICLE ANALYSIS METHODS
ALLERGEN TESTS for BUILDINGS
BROWN HAIRY BATHROOM MOLD
BIBLIOGAPHY for ENVIRONMENTAL HEALTH, MOLD, IAQ
BLACK MOLD, HARMLESS COSMETIC
BLACK MOLD, TOXIC & ALLERGENIC
BLEACHING MOLD, Advice about
BOOK MOLD, Moldy Book Cleaning
BOOKSTORE - ENVIRONMENTAL
CACTUS FUNGI / MOLD
CAR MOLD CONTAMINATION
CARPET DUST IDENTIFICATION
CARPET PADDING ASBESTOS, MOLD, ODORS
CARPET FUNGICIDAL SPRAY
CARPET STAIN DIAGNOSIS
CARPET & other STAIN TESTS
CARPET TEST PROCEDURE
CARPETING & INDOOR AIR QUALITY
CHAIN OF CUSTODY - TEST SAMPLE
CLEARANCE INSPECTIONS - MOLD CLEANUP
DIRECTORY of MOLD / ENVIRONMENTAL EXPERTS
DIRT FLOOR MOLD CONTAMINATION
Disinfecting Buildings with Bleach
DO-IT-YOURSELF MOLD CLEANUP WARNINGS
DUST ANALYSIS for FIBERGLASS
DUST, HVAC CONTAMINATION STUDY
EFFLORESCENCE, Salts & White / Brown Deposits
FEAR of MOLD - MYCOPHOBIA
Fiberboard Insulation Sheathing Mold
FIBERGLASS INSULATION MOLD
FIND MOLD, ESSENTIAL STEPS
MOLD in BUILDINGS
FIRE DAMAGE vs MOLD DAMAGE
FLOODS IN BUILDINGS-mold
FOXING STAINS on books & papers
FUNGICIDAL SPRAY & SEALANT USE GUIDE
GAS DETECTION INSTRUMENTS
GAS EXPOSURE EFFECTS, TOXIC
GAS EXPOSURE LIMITS & STANDARDS
GAS TEST PROCEDURES
HOUSE DUST ANALYSIS
HOUSE DUST COMPONENTS
HUMIDITY CONTROL & TARGETS INDOORS
LAB PROCEDURES MICROSCOPE TECHNIQUES
LIGHT, GUIDE to FORENSIC USE
MEDIA BLASTING for MOLD REMOVAL
METHANE GAS SOURCES
MICROSCOPE DIGITAL PHOTOGRAPHY
MEDIA BLASTING for MOLD REMOVAL
METHANE GAS SOURCES
MICROSCOPE DIGITAL PHOTOGRAPHY
MILDEW ERRORS, IT's MOLD
MILDEW REMOVAL & PREVENTION
MOISTURE CONTROL in BUILDINGS
MOLD: A COMPLETE GUIDE TO MOLD
MOLD EXPERT, WHEN TO HIRE
MVOCs & MOLDY MUSTY ODORS
MYCOPHOBIA, STAINS MISTAKEN for MOLD
MYCOTOXIN EFFECTS of MOLD EXPOSURE
ODORS GASES SMELLS, DIAGNOSIS & CURE
RENTERS GUIDE TO MOLD & IAQ
ROBIGUS & Wheat Rust Fungus
SMELL PATCH TEST to Track Down Odors
STAINS on & in BUILDINGS, CAUSES & CURES
THERMAL IMAGING MOLD SCANS
TRAPPED MOLD BETWEEN WOOD SURFACES
UV LIGHT BLACK LIGHT USES
VAPOR BARRIERS & CONDENSATION
VENTILATION in BUILDINGS
Volatile Organic Compounds VOCs
WATER ENTRY in buildings
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: MOLD in BUILDINGS 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.
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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.
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).
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>
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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Frequently Asked Questions (FAQs)
Question: can a basement flood or wet crawl space cause attic mold contamination?
My mother's home has mold in the attic and I am wondering if the mold could be caused by two floods she had in her basement.
The first caused extensive mold damage in the basement. Could you please advise. - G.D. 7/30/2013 /P>
Yes basement flooding can contribute to or even be the primary cause of an attic mold problem. In most buildings moisture moves upwards through the building naturally on rising warm-air convection currents, from basement or crawl space up to the attic or other under-roof space like a cathedral ceiling. Most of that air and moisture movement is through various openings or penetrations that may be visible in the living area (openings around a ceiling light fixture for example) or hidden within building wall cavities (openings around wiring or pipes for example). (Details: Air Bypass Leaks, Thermal Tracking )
Combining a wet basement with poor attic ventilation makes attic mold still more likely. (Details ATTIC CONDENSATION CAUSE & CURE )
When I make a field investigation of a building that has an upper floor or attic mold problem I inspect the entire property, inside and out, to identify both construction methods/materials and actual leak evidence as sources of water or moisture indoors. That always includes a look at the basement: even if we know there is a moisture problem in the attic. We need to know if the wet attic conditions are due to a roof leak, ventilation defects, or an in-building moisture source such as a wet basement or crawl space.
Why doesn't the basement or crawl space moisture also cause mold contamination on lower building floors? Well it can; but consider also that speaking generally, as individual building details vary widey, moisture moves upwards through the building to accumulate in areas where it is trapped. If warm moist air is not trapped until it reaches a poorly-vented attic, then that's where it may be most noticed.
HUMIDITY LEVEL TARGET - how dry does the building interior need to be
Questions & answers or comments about the underlying causes of mold in building attics .
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
Mold Contamination Testing, Cleanup, Prevention: references & products
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.