Attic Mold – Questions & Answers

Attic Mold – Questions & Answers

As a mold inspector, attic mold is one of the most common issues that I come across in the field, and not surprisingly the topic of much debate and questions.

In this article I will detail the most common questions and answers regarding attic mold, while providing some advice on how to deal with it.

Why do we get attic mold?

Just like mold found anywhere else in the home, it needs a moisture source, moderate temperature and an organic food source to grow. There are a number of sources that can contribute to this. Due to past construction methodologies, weather conditions, lack of maintenance and mismanagement of the attic space, I have listed the most common reasons below…

Newer Building Materials – Older roofing installations (60-100 years +) allowed for more air and heat to escape, thus reducing the chances for concentrated moisture to develop into mold. However, OSB and plywood (newer materials) are less mold resistant.  The move to manufactured materials rather than traditional wood products, combined with poor ventilation design has resulted in moisture into the attic, while sustaining a perfect environment for attic mold to flourish.

Poor & Missing Ventilation – Attics require proper ventilation to allow air to flow both from the soffits (exterior vents along the perimeter of the home, below the roof line) and out through roof or ridge vents. In addition, air that escapes from the home below (also known as stack effect) will need to be vented as well. When soffit vents are blocked or missing, airflow is not possible. This allows areas of the attic to form condensation, thus, providing the necessary moisture source for mold growth. Other issues include poor vent design, which can cause vents to compete for airflow, especially with gable vents (wall vents in the attic). Attic mold can claim residence anywhere moisture accumulates in the attic.

Improper Attic Ducting: Laundry, Kitchen & Bathroom Ventilation – Often, the ducts inside the attic are made of outdated (plastic) materials, which are susceptible to damage. Damaged, disconnected or unsealed ducts will discharge warm humid air. When this happens, it comes in contact with the cooler sheathing surface, allowing moisture to develop and eventually mold growth.

Inadequate or missing Insulation – Missing insulation keeps the attic cold in the winter and warmer in the summer. This combined with warm air leakage through voids along the attic floor (ceiling lights, attic hatches, fans, electrical conduit pathways & piping cut outs) contributes to moisture and attic mold.

Rainwater Ingress, leaky roof – As the name suggests, small leaks can saturate the sheathing and to allow mold growth.

Low roof slope – When the decking or sheathing is not sufficiently angled, airflow is compromised, so condensation forms more easily along the underside of the sheathing or decking. This problem will be compounded when the soffits are blocked or missing, as mentioned above.

Night Sky Radiation, Condensation – The strange phenomenon looks like patches of dark moisture staining and possible mold growth along the sheathing. In the Pacific Northwest, it seems to appear primarily on the North side of the attic.

This issue is common with newer tighter homes… leaving homeowners frustrated and builders puzzled because it occurs in attics that have actually been designed according to recommended code specifications and proper venting.

According to research conducted by RDH (A Vancouver based engineering firm) this happens when the roof sheathing temperature drops lower than the dew point temperature, resulting from a cold night sky. Frost develops on the roof, even though the temperature is above freezing. The sheathing absorbs the condensation, while the subsequent moisture once again, leads to attic mold. Check out a link to their study here

Does attic mold affect your health?

Fortunately, mold growth in the attic is not usually a health concern. The reason for this is because warm air rises from lower areas of the home, upward into the attic through voids in the upper level ceiling, rather than into the home. This phenomenon is also called stack effect. In addition, we do not spend a lot of time in the attic, so the exposure is limited.

So how do we deal with attic mold once it has been discovered?

It depends on how problematic the situation is. This is a two-part answer. First, you want to call in a professional to find out the source of the problem, so it doesn’t continue.

The next step depends on the nature of the problem and how much actual mold is found. This may involve bringing in a few different professionals, especially if the problem requires more than just mold removal.

Remediation contractors will be able to remove the mold, yet may not install new roof or soffit vents and fix duct work. At times, the repairs may involve a roofer, engineer & remediation contractor to ensure the job is fixed properly.

A word of caution… In my experience, it is always best to bring in contractors with specific experience related to what you are dealing with, rather than a handyman. You want to call a contractor with experience, training and the proper insurance to make sure the job is done correctly the first time.

Remediation costs will also depend on the following…severity of the problem, access, materials, equipment, labour, time and applied methodologies. For more information on this topic, check out my article called Tips for hiring a mold remediation company.

What can be done to prevent attic mold?

The simple answer is to keep the attic warm and dry. As mentioned earlier, call a mold inspector to find the moisture source. The attic will always have enough food in the form of organic debris drawn in from the outside… so deal with the moisture first.

Strategies that we believed to be effective for reducing attic mold may be changing in the near future, especially in and around Vancouver/lower mainland, with regards to the “Night Sky Radiation” issue.

Innovations to building construction have spawned many new approaches to attic design. Building science specialists, engineers and energy advisors are testing ways to reduce moisture, advance energy efficiency and improve structure. Until concrete protocols come to fruition, it is best to contact an experience attic/roofing/remediation contractor. Also, consider the following…

  • Install ample insulation to ensue the attic is warm, and around skylights as well.
  • All vent ducts should be made from the appropriate materials, (rigid metal/flexible aluminum, not plastic) properly sealed and vented to the exterior. This includes bathroom, dryer and kitchen vents.
  • The attic hatch, and all voids should be properly sealed to prevent moisture and airflow from migrating into the attic space.
  • Cathedral ceilings should have insulation installed and adequate clearance between the sheathing and insulation to encourage airflow.
  • Heat ducts should be properly insulated, especially in cooler climates.
  • Ensure that the slope is proper to prevent ice damming (cooler climates) and condensation issues on the attic deck.
  • Make certain that all soffit vents are clear to allow proper airflow. Installation of baffles (rectangular Styrofoam boards to encourage air movement from the soffit up through the attic) should be utilized to achieve this.
  • Adequate ventilation, such as ridge or roof vents should be installed to allow the air to escape.
  • Gable vents (vents along the side walls of the attic) should not compete with upper ridge or roof vents. They may need to be closed off. It would be best to speak to a roofer about this as needed.

For more information on this topic, just let me know. If you found this article interesting and informative, please pass it along…