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What Causes Attic Mold & How to Remove it

Attics are one of the most common areas of mold growth in the home.  Attics tend to have the perfect conditions for mold growth (hot, humid, and an abundant food source with the wood sheathing).  Furthermore, most homeowners don’t ever go up in their attic, so the mold problem is allowed to grow undisturbed – often for years!

Lots of folks first learn about their problem right before they sell their home.  The buyer’s home inspector notices the mold in the attic right before the closing date, which causes both buyer and seller to panic, often putting the whole deal in jeopardy.

How to know if you have an attic mold problem

But the good news is that this “attic mold panic” scenario can all be avoided by quickly checking your attic annually for mold and dealing with it promptly if you do find a problem.  

What are the tell-tale signs of an attic mold problem?

  • Dark black staining on wood surfaces — If the wood in your attic shows any black discoloration, the problem has moved beyond moisture; you have mold that should be removed.
  • Attic feels excessively hot or stuffy — Attics should feel breezy if they are properly ventilated.  When an attic is stuffy, that indicates you have a ventilation problem, which often results in mold problems.
  • Frost buildup on the underside of the roof sheathing in winter — When it’s cold enough outside, water vapor in an attic with improper ventilation can freeze on the underside of your roof. This makes it especially easy to spot.
  • Wet insulation in the attic — Not only is this a sign that you may (or soon will) have a mold problem, but when insulation gets damp or wet its ability to insulate becomes significantly diminished, costing you extra money to heat/cool your home.
  • Water dripping from smoke detectors, light fixtures, bath fans — This is a sure sign that the floor (or attic) above you has a level of moisture that needs to be addressed.
  • The smell of mildew in the attic — Trust your nose. A musty or moldy smell in the attic means there’s a moisture problem somewhere.

What causes attic mold?

We in the mold industry like to say that “mold problems are moisture problems.”  In other words, you cannot have a mold problem without a moisture problem.

Generally speaking, attic moisture problems that lead to mold growth are most often caused by:

  1. Blocked or Insufficient Ventilation
  2. Improper Exhausting of Bathroom Fans or Dryer Vents
  3. Roof Issues/Leaks

Let’s take a look at each one of these three causes individually so you can make sure you or a professional fix the source of the mold problem.

Blocked or Insufficient Ventilation

The most common cause of attic mold, by far, is blocked or insufficient ventilation of the attic space.  Attics usually have a passive ventilation system in which outside air comes in through the soffit/eave vents at the bottom, warms up in the attic, and escapes through the can or ridge vents at the top (because hot air rises).  That cycle creates a nice, breezy airflow and a well-ventilated attic. See this illustration:

attic ventilation and circulation

However, we often see the soffit/eave vents blocked with insulation, thereby destroying the whole passive ventilation system.  And when that system is destroyed, warm and humid air in the attic will stagnate, and often condense along the cold wood sheathing in the winter, causing wet wood and subsequent mold growth throughout much of the attic.

mold in the attic

We also see mold growth in attics if there are not enough vents installed.  Check your local building codes for what’s required in your area, but in general, 1 square foot of venting is needed for every 100 square feet of attic space. 

Any home inspector worth their salt will check a house’s attic ventilation system. To pass an inspection, and to ensure that an attic stays cool and dry, make sure there’s a proper system in place that’s unblocked by insulation.

Knowing the proper signs of attic mold, and how to prevent it to begin with, can save you a major headache during the sale of your home.

Improper Exhausting of Bathroom Fans or Dryer Vents

Dryer exhaust vents, kitchen exhaust fans and bathroom exhaust fans are designed to pump moisture OUT of your home. So make absolutely sure that they terminate outside your home and NEVER in the attic. Also plumbing stacks in the attic can be a source of condensation, which can lead to attic mold growth. Plumbing stacks can also emit hazardous gases, so make sure that they too do not terminate inside the attic.

Roof Issues/Leaks

Roof leaks will often lead to a small, localized area of attic mold near where the leak is occurring.  Below are a few ways to check for possible roof leaks:

  • Check for areas of dark discoloration/staining of wood (e.g. rafters, sheathing, joists, attic side of fascia boards, etc.).
  • Check roof valleys (i.e. where two roofs join at an angle), which are highly susceptible to roof leaks.
  • Observe vents, plumbing stacks, chimneys, attic windows and any portion of the attic/roof where dissimilar materials join each other (including flashings). These places are hotbeds for potential moisture intrusion.

How to get rid of an attic mold problem

In addition to fixing the moisture problem that caused the mold problem, you also need to get rid of the mold properly.

To do so, there are three options:

  1. Removing attic mold yourself (DIY)
  2. Fix the moisture problems only but leave the attic mold behind
  3. Professional attic mold remediation

Option #1: Do it yourself (DIY)

Attics are probably the most dangerous area of your home. They are extremely dangerous even for experienced mold technicians who have done countless attic mold removal jobs. One wrong step and you could fall through the floor joists and cause yourself serious injury.

Besides falling through the ceiling, you can also step on a protruding nail, hit your head on a rafter or nail, run into nesting animals or electrocute yourself, among many other dangers if you are not careful.

Furthermore, respiration and breathing can be very difficult in attics due to their usually being small and hot confined spaces and even doubly so when the small confined attic space is filled with mold spores.

Lastly, even if you avoided all the dangers mentioned above, attic jobs can be complicated and require things like negative air setup, containment, creating temporary flooring, and other variables that take time and experience that can only be accrued from many attic jobs to learn and do properly.

It’s not likely the weekend warrior is going to do these things properly with his/her first attic mold removal job. The last thing you or anyone else wants is for a job to be done incorrectly, putting you and your family at risk for future exposure or risk major injury.  We have advised and helped many DIYers fix minor mold problems on their own over the years in other areas of the home (e.g. basement & crawlspace mold, bathroom mold). But attic mold is a different story due to the safety risk and difficulty of the job. Therefore, we only recommend attic mold remediations be done by mold professionals or highly capable DIYers in good physical condition.

Option #2: Fix the moisture problems only but leave the attic mold behind

Sometimes you may hear someone argue that mold in the attic doesn’t really matter because it’s not a livable space of the home. We disagree with this argument for a number of reasons:

  • Mold in the attic will likely kill a real estate transaction and scare away potential buyers if it’s not fixed. If you ignore a mold problem in your attic, do not expect the next buyer of your house to do the same when it will inevitably be discovered during the home inspection. Home sellers take a major risk of buyers walking away if mold is discovered. Better to be proactive and fix it before you are ready to sell then let it be discovered during a home inspection when a buyer may simply decide to walk. If the buyer decides not to walk, he or she is almost certainly going to want it fixed before closing (or receive a big credit at closing / price reduction) and it’s pretty much a guarantee that the bank will require that the attic mold is remediated before giving a loan to the buyer.
  • Air can be depressurized and pulled down from the attic into the livable space. This means it is possible for moldy attic air to enter livable spaces from the attic and affect the health of the occupants.
  • Mold problems are indications of water problems. Water and mold problems in the attic can deteriorate wood in the roof sheathing, joists, etc. and eventually cause wood rot and reducing the life of your roof.
  • At some point, you will probably need to go to your attic for something. Perhaps you use it for storage. Maybe it’s infrequently, but you’re exposing yourself and others (if the attic is open) to moldy air if you enter an attic that has a mold problem.
  • For all these reasons, simply fixing the water/moisture problem and not the mold problem in an attic is a bad idea.

Option #3: Professional attic mold remediation

Attics are too dangerous to try to fix on your own and even if you avoid the dangers, attic jobs are complex and there is a good chance someone with little experience will do the job improperly and potentially expose themselves and their family to mold related health symptoms. In addition, fixing the moisture/water problem while leaving the mold behind is like putting the finger in the dam because sooner or later you are going to have to remove the mold too.

If you hire the right professional, you will obtain peace of mind for yourself and family that the job was done right, and you can regain the clean healthy air in your home that you and your family deserve. You can also breathe a sigh of relief that you do not have to worry about nasty mold impacting your health and others living with you.

And of course, you can rest easy knowing that if and when you decide to sell your home, the transaction will not be held up or killed by a previously unknown attic mold problem.

Professional mold remediation companies follow industry guidelines when removing attic mold.  The most common type of remediation is chemical based – using powerful cleaning agents to kill the mold, and then covering the attic with powerful antifungal sealers that will prevent mold from growing back.  Chemical based mold remediation is highly effective and usually costs the least, so it’s the most popular option.

Another method that’s highly effective, but usually much more expensive, is abrasive blasting.  In this method, the mold professional will blast off the top layer of wood using a medium such as dry ice, soda ash, or sand.  This method is very impressive, but is usually loud, expensive and requires a lot of labor hours. Therefore, this method is much less popular.

Notice that in this article there has been no mention of taking a wrecking ball to the home!  Most of the time, the only area of the home that has to be treated is the attic and nowhere else. Mold in attics is very common and can usually be dealt with quickly and effectively.  No need to panic and treat your home as if it’s uninhabitable and beyond repair.

Note also, that we did not mention replacing the roof. You almost never need to replace a roof because of attic mold. You may need to replace the roof for other reasons –like the roof is in really poor condition due to age and wear and tear (which lead to mold growth).

You’re Not Alone – Attic Mold is Common

If you have the unfortunate experience of having to deal with attic mold, know that you’re not alone.  Attic mold is very common and is dealt with by tens of thousands of families every year.

Attic mold is caused by moisture issues.  If your attic is well ventilated and has no moisture intrusion, you won’t have attic mold to deal with.

And while it will cost some money to take care of it, know that it can be taken care of, quickly and at a reasonable cost.  Your local mold professional can help. Good luck!

Are you in STL or CHI? Got a mold problem?

or call us at (888) 725-3134
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The Moldman Difference

  • No overstating mold problems
  • No scare tactics
  • No pressure, no hassles
  • 100% focus on mold and water damage
  • Licensed, insured, certified and member of the BBB
  • Thousands of jobs worth of experience
  • 10-year warranty & 100% satisfaction guarantee

Free Estimates • On Time • On Budget

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