Is Attic Mold Dangerous If Nobody Goes Up There?

Is attic mold dangerous if nobody goes up there? For most households the exposure is lower than with mold in a basement or bedroom, because the attic is outside the heated part of the house and air mostly moves up into it, not down from it. It still should be removed. Health Canada's guidance is that mold growing in a home should be cleaned up whatever the type, and attic mold tells you moisture is getting somewhere it should not.

Is attic mold dangerous to the people living below?

In winter, a heated house acts like a chimney. Warm air rises and pushes out through gaps in the top-floor ceiling, and cold air is drawn in low down. That upward flow works in your favour. Air and spores in the attic are mostly carried out through the roof vents, not into the hallway.

That is the general rule, and there are exceptions. Some houses have direct pathways that move attic air into the living space, and then the attic is no longer separate.

How attic air gets into the house

• Ductwork in the attic. Furnace or air conditioning ducts and air handlers above the ceiling can pull attic air in through leaky joints on the return side.
• Summer air conditioning. On hot days the flow can reverse. Cool indoor air sinks and leaks out low, and warm air is drawn in from the top, including through ceiling gaps.
• A loose attic hatch. A hatch with no weatherstripping, especially in a bedroom closet, lets air and dust drop whenever a door slams or an exhaust fan runs.
• Pot lights and ceiling fixtures. Older recessed lights are open to the attic.
• Strong exhaust. A big range hood or a dryer running in a tight house pulls replacement air from wherever it can find it.
• People. Anyone who goes up for storage or to run a cable disturbs the growth and carries it back down on clothes.

What mold exposure can do

According to Health Canada, indoor mold can irritate the eyes, nose and throat, cause coughing and wheezing, and make asthma and allergy symptoms worse. Some people react more than others. Those with asthma, allergies or weakened immune systems, along with infants and seniors, are more susceptible.

We remove mold. We do not diagnose anyone. If someone in the house has symptoms that concern you, see a doctor and mention that mold has been found. Do not assume the attic is the reason, and do not assume it is not.

The risks that have nothing to do with health

For most people the bigger cost of leaving attic mold is to the house and to its value.

• It spreads while the moisture continues. A patch above a bathroom fan becomes a full slope over a few winters.
• The wood can deteriorate. Mold itself feeds on the surface, but the dampness that supports it also supports wood decay. Plywood delaminates and OSB swells and softens if it stays wet for years.
• It will be found when you sell. Home inspectors look in the attic. Discovered during a conditional period, it becomes a negotiation with a deadline attached.
• It usually comes with wasted heat. The same air leaks that carry moisture into the attic carry heat you paid for.

Who should stay out of the attic

Until it is dealt with, treat the attic as off limits for casual trips. Anyone with asthma, allergies or a weakened immune system should not go up at all. If you have to look, wear a properly fitted N95 respirator, do not touch or brush the stained wood, and close the hatch behind you. Move stored items out only if they are in sealed bins that can be wiped down. Cardboard boxes that have sat under moldy sheathing are better bagged at the hatch than carried through the house.

How urgent is it?

Attic mold is rarely a drop-everything emergency. It took seasons to develop and a few more weeks will not change much. Three situations move it up the list: there is ductwork or an air handler in the attic, someone in the home is in a susceptible group, or the house is going on the market. In those cases, deal with it now.

For everyone else, a sensible plan is to have it removed and the moisture source corrected within the season, before another winter of condensation adds to it. Start by checking whether your hatch seals tightly and whether any ducts run through the attic. Those two details tell you how separate your attic really is from the air you breathe.

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