If you have the unfortunate experience of having to deal with attic mould, know that you’re not alone.  Attic mould is very common and is dealt with by tens of thousands of families every year.  Attics are one of the most common areas of mould growth in the home.  Attics are apt to have the right conditions for mould development — hot, humid, and an abundance of sheathing.  Additionally, most home owners don’t ever access their attic, so the mould problem is allowed to grow undisturbed.

attic mould

How to know if you have an attic mould problem

Here are some key indicators that often reveal mould in an attic:

  • Dark black staining on wood surfaces— If the wood in your attic shows any black discoloration, the problem has moved beyond moisture.
  • 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 mould 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 identify.
  • Wet insulation in the attic— Not only is this a sign that you may (or soon will) have a mould 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— A musty or mildew smell in the attic means there’s a moisture problem somewhere.
dark wood stains
wet insulation
frost buildup
water leak from light

What causes attic mould?

Mould problems are mainly moisture problems.  You can’t have mould if you don’t have moisture.

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

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

Blocked or Insufficient Ventilation

The most common cause of attic mould, 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 or eave vents at the bottom, warms up in the attic, and escapes through the can or ridge vents at the top.  That cycle creates a nice, breezy airflow and a well-ventilated attic.

However, if the soffits are blocked with insulation, the whole passive ventilation system is interrupted.  When that system is interrupted, 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 mould growth throughout much of the attic.

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

Knowing the proper signs of attic mould, and how to prevent it to begin with, can save you a major headache during the future 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 mould growth.

bath ventilation

Roof Issues and/or Leaks

Roof leaks will often lead to a small, localized area of attic mould 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.
roof leaks

How to get rid of an attic mould problem

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

Attics are probably the most dangerous area of your home. They are extremely dangerous even for experienced mould technicians who have done countless attic mould removal jobs.  One wrong step and you could fall through the floor joists and injure yourself.  Besides falling through the ceiling, you can also step on a protruding nail, hit your head on a rafter or nail, or run into nesting animals or many other dangers if you are not careful.

Furthermore, breathing can be very difficult in attics due to the space being confined and even doubly so when the small confined attic space is filled with mould spores.

It’s not likely the weekend handyman is going to do these things properly with his/her first attic mould removal job. The last thing you need is for a job to be done incorrectly.  Therefore, we only recommend attic mould remediation be done by mould professionals.

Professional attic mould 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 mould related health symptoms.

If you hire the right professional, you will obtain peace of mind that the job was done right, and you can regain the clean healthy air in your home.  Professional mould remediation companies follow industry guidelines when removing attic mould.  The most common type of remediation is chemical based – using powerful cleaning agents to kill the mould, and then covering the attic with powerful antifungal sealers that will prevent mould from growing back.  Chemical based mould remediation is highly effective and usually costs the least, so it’s the most popular option.

You can easily find mould remediation professionals by searching online for “local mould remediation companies” or “flood restoration companies near me”.

Another method that’s highly effective, but usually much more expensive, is abrasive blasting.  In this method, the mould 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 labour hours. Therefore, this method is much less popular.

mould remediation

Cost to remediate mould in the attic

Typical mould remediation of areas such as crawlspaces in the home can cost between $500 and $4,000 depending on the extent of the mould and the type. Most homeowners can expect to pay around $2,000 for remediation of areas such as crawlspaces, attics, or basements where mould is most commonly found.

If you have mould in your basement, click here to learn more.