Where to Look For Mold in Attics

Attic mold contamination inspection, where to look: this article explains how and where to inspect or test for mold in building attics and roof cavities.

Page top photo: mold on attic side of ceiling drywall and on rafter and roof decking in the lower roof area of a home with inadequate under-roof ventilation.

How to find attic mold contamination

This brown mold on plywood roof sheathing visible in an attic is an indicator of wet or damp attic conditions.

It's also a strong suggestion that there is no functional under-roof or attic ventilation in this building, and the risk is more than mold: over time such moisture can delaminate or even rot the roof sheathing, leading to more-costly repairs.

Watch out: My carpenter's assistant Donna S. and I (DF) were beginning work on an older New York home when she walked across the roof deck and fell right through into the attic below - the roof sheathing was that damaged. From above, before the crash, there was barely a clue of the underlrying damgage: it wasn't a roof leak it was condensation moisture in the attic.

It is common to identify Cladosporium sphaerospermum or perhaps Aureobasidium pullulans in these conditions, though without a lab test we don't know what this mold is.

And certainly other mold genera/species may be found in buildng attics. Of the millions of mold genera/species there are about two-hundred, of various colors and various health risks, that are commonly-found in buildings.

The black staining on the plywood roof sheathing visible in this modern attic is a clear indicator of very humid or even wet attic conditions.

When you view the larger copy of this image (click photo for larger image) you may notice that insulation was pushed out into the building eaves where it blocked any intake venting.

This black staining is probably mold.

Though we can't assert that this mold is harmful, we can conclude that the attic has been too wet and that roof venting is not working on this building.

Inspect attic insulation, insulation kraft paper facing, and the attic side of ceiling drywall

visible in the attic floor, particularly in areas below roof leaks.

It is useful to distinguish between a real roof leak or ice dam leak and more trivial drip stains from attic condensation.

Attic condensation and the resulting drip marks on the attic floor or on attic insulation, as shown here, is not itself likely to wet the attic insulation nor the surfaces below it enough to cause a big mold reservoir.

However, attic condensation is evidence of wet or very humid attic conditions.

Therefore I'd take a close look at the roof sheathing and framing

If attic insulation has been wet 

and especially if the insulation has been exposed to other moldy conditions, even if the insulation itself looks ok it may be mold contaminated.

Some types of building insulation readily harbor mold contamination even if it's not visible (such as fiberglass insulation).

Other types of insulation such as cellulose, seem to resist mold growth (possibly because that material is usually treated with a fire retardant chemical which may also be fungicidal.)

The drip spots you see on attic flooring and insulation

in this photo are from attic condensation which formed on protruding roof shingle nails in the attic where it formed frost in cold weather, then melted and dripped onto the attic floor.

This indicates poor attic venting and possibly humid conditions.

How do we know these are from attic condensation and not a roof leak?

Because of their distribution throughout the attic and because their spacing, if you look up (I did in this attic) matches the distribution of the roof shingle nails protruding through the roof sheathing.

But there probably was not enough leakage to cause a mold infection of the insulation or drywall below.

Spot checks for visible mold in the most-likely or most-dripped-on area may be all that's needed.

Look for mold around roof leak areas

 & water stains in the attic: at the eaves where shingles are more worn or where ice dam leaks may occur in freezing weather, at roof penetrations for chimneys and plumbing vents

Attic or Under-roof Condensation Drip Marks: Some "leak stains" you may see on the attic floor or on insulation are not really due to leaks from above. You may be looking at more trivial drip stains from attic condensation.

Attic condensation

and the resulting drip marks on the attic floor or on attic insulation, as shown above - not itself likely to wet the attic insulation nor the surfaces below it enough to cause a big mold reservoir.

However, attic condensation is evidence of wet or very humid attic conditions.

Therefore take a close look at the roof sheathing and framing in an attic that has been moist or humid even if there have been no roof leaks.

The mold shown in the attic photograph above was identified in our forensic lab as Aspergillus sp. on attic mold visible on pine tongue and groove roof sheathing near the building eaves.

Also notice the condensation stains at the shingle nail, more evidence of a history of attic moisture which was a factor in this mold growth.

This article is part of our series:

MOLD in BUILDINGS which describes how to find mold and test for mold in buildings

For an easy, inexpensive, low-tech but very effective mold testing method

see TEST KIT for DUST, MOLD, PARTICLES: INSTRUCTIONS

Reader Question: what should we do about moldy fiberglass insulation?

(Sept 7, 2012) Wendy said:
Our 35-year-old house has unfaced fiberglass insulation in the attic. It has black mold all over the underside of the fiberglass insulation. How should we take care of it?

Reply:

Watch out: it is easy to mistake harmless black or gray building dust deposition on fiberglass insulation for "mold contamination". Air bypass leaks will leave dark or black marks on fiberglass insulation just like the marks shown on the pink fiberglass insulation in our photo at left.

On the other hand, insulation that has been wet or insulation that has been exposed to high levels of building mold contamination from other sources is at particular risk of mold contamination even if it looks clean.

And kraft or foil-faced fiberglass insulating batts that have been wet may produce mold growth on the paper facing.

See INSULATION STAINS - AIR BYPASS LEAKS and also

see STAINS on INDOOR SURFACES, PHOTO GUIDE

Watch out: for mold-contaminated building insulation in attics (or other building cavities) where there have been leaks or high moisture levels.

See INSULATION MOLD CONTAMINATION TEST

...

Continue reading at ATTIC MOLD, WHAT IT LOOKS LIKE or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

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• ATTIC MOLD, WHERE TO LOOK
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• ATTIC MOLD, HARMLESS COSMETIC?
• ATTIC MOLD ROOF TEAROFF
• ATTIC MOLD ENCAPSULANTS
• INSULATION MOLD CONTAMINATION TEST - risk of non-visible problematic mold hidden in building insulation.

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