Mold in Attics . . . Why Should I Care and What to Do About It?

It’s true, mold in attics rarely affects the indoor air quality in homes, so what’s the big deal?  Why is it a reportable issue, why does it scare homeowners and what can be done about it?  This is a common issue for homes in the Pacific Northwest, so I wanted to take a moment to address it because there’s also a lot of hype and misinformation out there about mold.

Black or White Staining in Attic?

If your attic sheathing doesn’t look like “new construction,” and is visibly black or white stained like this picture, you likely have a ventilation issue that needs to be addressed and mold remediated.

Why does attic mold rarely, if ever, affect indoor air quality in homes?

It’s due to the simple fact that warm air rises; in a house, this phenomenon is known as “Stack Effect.”  Air rises from the lower levels of the home and up through the attic.  Mold spores don’t have wings, e.g., they can’t “fly” against an upward flow of air from stack effect within a house, so it’s extraordinarily rare for attic mold spores to show up on indoor air quality mold tests.  Therefore, it really isn’t a per se health concern.

Why is attic mold a reportable issue?

Attic mold, left unchecked, can grow and lead to structural deterioration of attic sheathing and roof structural elements.  There’s an underlying moisture issue that needs to be resolved because mold requires moisture to grow and spread.  Mold in attics is scary to most would-be buyers and homeowners; mold staining in attics is an issue that will come up each and every time the home is inspected into the future.  And, the longer one waits to address it, the more expensive repairs and remediation become.

Why does attic mold scare homeowners and would-be buyers?  

There’s a ton of great information out there about mold, but there’s also a lot of misinformation and hype out there too.  The bottom line is that mold requires elevated moisture, or high humidity, to grow and spread.  If you can see mold, it’s likely mold.  In my opinion, you don’t need to pay for an expensive mold inspection.  There’s a source of moisture that needs to be addressed and the mold removed or remediated by a qualified professional.  Deal with the moisture and it won’t come back, it’s that simple, because mold requires moisture to grow and thrive.

Here’s a picture of a properly remediated attic- neat and clean- which protects your investment in the home and is desirable to current and future homeowners (no visible mold!). I recommend using TAN-colored paint (see why below).

Whenever a buyer or homeowner sees mold- whether it be in a sink base cabinet, crawl space, basement, ceiling or attic doesn’t really matter- they’re very concerned about it.  Under the right conditions, mold can present within twenty four (24) hours of a moisture event; yes, twenty four (24) hours!  Identify the source(s) of elevated moisture, make necessary repairs, remove/remediate any visible mold and you should be good to go (mold stained sheetrock is typically replaced).

What can I do about mold growth in my attic?  

Technically, I recommend consulting with a qualified mold remediation contractor to deal with mold in attics.  There are many out there- and bids vary greatly- so it’s important to do your due diligence.  In my experience, mold remediation of most attics costs around $3000+-, depending on the extent of remediation and repair required.  Try to get 2-3 bids if you can.  It’s definitely a fixable issue that protects your investment in the home; the goal is to leave the attic in a state that’s desirable (no visible mold) to the homeowner and future home buyers.  Visible mold isn’t desirable to anyone!

CONTINUE READING BELOW for details on contractor best practices:

(#1) Identify and repair the attic moisture problem(s). This is the crux of the problem that needs to be addressed first! 

  ***WARNING!  Don’t let your contractor remediate mold growth in attics without FIRST identifying and repairing the moisture problem as the mold will simply come right back!***
  • Restricted Vents? – Look for restricted soffit vents in the attic, stuffed with insulation or with deformed cardboard baffles.  Check other attic vents, if present (e.g,. ridge vents, roof vents, gable vents), and make sure they’re unrestricted and properly installed.  It’s not uncommon for wasp nests to restrict vent screens, or for the plywood sheathing at the ridge to not be cut back sufficiently to allow the upper ridge vent to perform its intended purpose.
  • Attic Vent Ducting – Look for bathroom and kitchen vent fans’ ducting that discharge directly into the attic area; ducting should be extended to the exterior entirely.  No exceptions!
  • Roof Leaks? – Look for roof leaks, paying particular attention to penetrations through the roof like chimneys, plumbing vent pipes, skylights, etc.
  • Is the attic sufficiently ventilated?  Sometimes, when you change the dynamics of a home, mold can present in attics.  I’ve seen this happen, for instance, when a roof was replaced and the roofing contractor changed the ventilation dynamics or when new attic insulation has been installed.
  • Vent Fans Working Properly & Actually Used? – Make sure that bathroom and kitchen vent fans are functioning satisfactorily and are used every time.  A good, simple DIY test is to hold some toilet paper up to the vent fan and see if it “sticks.”  If so, you’re basically good to go.
  • Look for sources of air leakage between the home and attic.  This can happen at recessed light fixtures, plumbing vent penetrations into the attic and at interfaces between walls and ceilings in the home, for instance.  Discolored insulation is a good clue for leaking air as insulation acts as a filter, becoming discolored in areas of air infiltration.  Leaking areas can typically be caulked from within the attic to prevent warm, moist interior air from entering the (cold) attic where it may condense and create elevated moisture conditions conducive to mold growth.
  • Install an Attic Vent Fan? – Some homeowners like install a vent fan in the attic- oversized so you can run it on low and not hear it- controlled by a humidistat.  In this way, you’ll have extra insurance against potential future elevated moisture conditions because the fan will turn on when/if elevated moisture conditions present.
  • Improve indoor ventilation within the home.  It is generally recommended to ventilate a home 8 to 12 hours a day.  Ventilation can be scheduled by using a 24-hour programmable timer set for at least two periods.  Part of the ventilation time should be scheduled during the night, when people are sleeping.  Programmable timers are readily available at hardware stores and can replace the fan wall switch; many homeowners put their laundry room vent fan on a timer.  In fact, programmable vent fans are required for new construction.

#2) Dry out the existing moisture.  This can be done with heaters, fans, dehumidifiers, etc.  If the mold growth in the attic is pronounced, you may see it presenting atop attic insulation; replacement of insulation may be necessary if this is the case.

(#3) Fog the attic with a mildicide.  This is typically done with an ULV fogger and sprayed throughout the attic area.  This method effectively kills any current mold growth, but it doesn’t address mold staining on roof sheathing and structural elements.

(#4) Encapsulate mold staining with a TAN-colored mildicide paint.  Why tan?  I recommend tinting the mildicide paint a tan color because any future black or white mold growth will visibly show up on tan paint.  If one encapsulates attic mold with a clear sealant- like many mold remediation companies do- future home inspectors and homeowners won’t have any idea if the visible black/white mold staining in the attic is current or historic!  In short, you’ll need to address the issue again and again which is a great frustration.  If the attic is tan colored in the future, it will be obvious on future inspections that the issue has been satisfactorily addressed.  If it’s tan, you’re good to go.  If it becomes stained black or white, there’s still some work to be done.  Some mold remediation companies warrant their work for a period of time.

Of course, further evaluation by a qualified contractor is advised for all homeowners and this document isn’t meant to be entirely comprehensive, but I hope the above information gives you some hints, great advice and perspective about attic mold and best practices for dealing with it.  It’s a common issue for homes in the Pacific Northwest.  If you have any questions, please don’t hesitate to contact me.  And, you have my full and express permission to share this information with friends, family, colleagues and clients.  In fact, please do!