What Causes Attic Mold & How to Remove It
Learn how to remove attic mold and what causes it to grow.
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 from the wood sheathing). Furthermore, most homeowners don’t ever go up in their attic, so the mold problem is allowed to grow undisturbed – sometimes for years!
Jump to a section below and learn about the best way to remove attic mold:
What can happen if you don’t treat attic mold?
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.
It’s better to be proactive and fix it before you are ready to sell. Then the mold could possibly be discovered during a home inspection which can lead a buyer to decide to walk. If the buyer decides not to walk, they are 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.
Signs of attic mold
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.
Here are the main signs of attic mold:
Dark stains on plywood
Mildew smell in your attic
Hot and stuffy attic air
Frost buildup or roof sheathing
Water dripping from smoke detectors and ceiling fans
Dark stains on attic plywood
If the plywood in your attic shows any black discoloration, the problem has moved beyond moisture. If your attic plywood is stained you have mold that should be removed. Don’t hesitate to contact a professional ASAP.
Mildew smell in your attic
Trust your nose. A musty or moldy smell in the attic means there’s a moisture problem somewhere. If you suspect that you smell mildew anywhere in your home, especially in your attic, you may have a mold problem and should check it out right away.
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.
Hot and stuffy attic
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 of roof sheathing
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.
Water dripping from smoke detectors, light fixtures or bath fans
This is a sure sign that the floor (or attic) above you has a level of moisture that needs to be addressed.
Main causes of attic mold
Ventilation issues in your home
Mold that is caused from improper bathroom or kitchen fan exhaust
Roof issues and roof leaks
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.
Common ventilation issues in attic
Blocked soffit or eave vents
Often soffit/eave vents are blocked with insulation, thereby destroying the whole passive ventilation system.
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.
Not enough vents
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.
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. At some point, you will probably need to go to your attic for something. Perhaps you use it for storage. Maybe it’s infrequent, 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.
Improper bathroom or kitchen fan exhaust
Dryer exhaust vents, kitchen exhaust fans and bathroom exhaust fans are designed to pump moisture OUT of your home. So make 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 gasses, so make sure that they do not terminate inside the attic.
Roof issues that cause mold in your attic
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.
Wait before replacing your 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).
Removing mold from your attic
DIY mold removal
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. If you think you have mold in other areas of your home, check out our guide of resources for killing mold at home.
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.
Hiring a professional to remove mold
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.
Some techniques a mold professional may utilize:
Mold killing chemicals
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 anti-fungal 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.
Abrasive blasting to remove mold
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
Attic Mold is Common but it Doesn’t Have to Cost You Thousands
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.
Attic mold is caused by moisture and mildew 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!
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