Most of us think of the attic as a dusty place to store things we rarely use. That dirty old attic also ends up being the place to keep things that we just can’t throw away. We fill it with cardboard boxes full of old papers and books, or perhaps old furniture, clothing or toys from the past. Although having an attic as an extra storage place is great – it can lead to mold. With factors like heat, condensation, humidity, poor ventilation and improper insulation all potentially playing a role in your attic environment, mold growth almost seems inevitable. So take some time and consider the conditions of your attic and make the proper maintenance repairs to prevent potential mold growth.
Factors Contributing to Attic Mold
- Heat: We all know from 5th grade science class that heat rises. In a house, the natural infiltration of air near the bottom of your home helps hot air rise to the top of your house. Once at the top, it needs to ventilate through open windows, ridge or gable wall vents or other openings near the roof. So imagine it’s cold outside and all that hot air is rising up to your attic looking for a place to escape – but it can’t. Many attics (especially older homes) have little, if any ventilation to allow the hot air out. Many attics have been stuffed to the gills with insulation by a home owner who though more is always better. Or it’s been packed to the ceiling with a lifetime of family heirlooms. Either way, the hot air ends up trapped against the attic sheathing, and on the other side of this sheathing, its cold.
- Condensation: I’m sure you’ve seen the buildup of moisture on a cold drink in the summer time. Well that same moisture buildup occurs on your attic sheathing. The trapped hot air is cooled quickly by the cold outside temperature, and you end up with wet sheathing. Wet sheathing equals mold. Pretty simple.
- Humidity: Our old friend humidity adds fuel to the attic mold fire. With enough humid days, the moisture content in your attic sheathing can become damp enough to develop wide-spread areas of mold growth. The most common species we find on attic sheathing (if caused by humidity) is Aspergillus/Penicillium, and although that is a mold found on leaves and outdoor foliage, it still shouldn’t be on your attic sheathing. Remember, mold “in the wild” has one job – decay and destroy cellulose-based matter. Your sheathing, framing, wood furniture, cardboard and paper products are all cellulose-based. In other words – your attic has become a dine-in buffet for mold. Be sure to monitor your humidity levels in your attic to prevent mold caused by humidity.
- Ventilation: Air circulation (or a lack thereof) is probably the most overlooked cause of mold in attics. Soffit vents, ridge vents and gable wall vents can greatly decrease the possibility of developing mold in an attic. But if installed incorrectly or in the wrong combination, they can defeat their own purpose. If your soffit vents are large enough and unobstructed by insulation or stored items – and they can allow air in, up and out through a ridge vent, you’re in good shape. Many homeowners install humidistat-actuated roof fans to vent air out of the attic. That would only be necessary if you had no soffit and ridge vent system – but you do not need both. Attic construction and other factors may come into play, so your best bet is to have a professional who is versed in attic ventilation help you resolve the problem.
- Improper Insulation: Most men I know feel that more is better. Even I have fallen into this mentality, but with insulation – more isn’t always better. It may seem counter-productive to allow air flow into your overly insulated attic – but it’s not. Your insulation has one job – to minimize heat or cool air loss from the floor below. That’s it. It isn’t there to keep the roof or attic walls warm. The recommended level for most attics is to insulate to R-38 or about 10 to 14 inches, depending on insulation type. You shouldn’t be able to see the tops of the floor joists if done correctly.
So you can see that many things factor into whether you do or don’t end up with mold in your attic. If you’re not sure if mold has already developed, have it inspected and possibly tested. A professional mold inspection will differentiate between mold and water staining and if it is mold, your inspector can develop a scope of work for a mold remediation.