Case Review: Attic Mold
The photo in the thumbnail of this bulletin is of a pice of plywood roof sheathing as seen from the attic. The sheathing was brand new and installed just over a year ago. So what went wrong and why does it now look like a petri dish in a lab?
Assuming that the roof was properly installed, which this was, more on that later. Condensation, air leakage and lack of ventilation created a perfect combination that allowed mold to thrive in the attic of this home. Unknown to the owners, there were hidden (behind trim) gaps along the majority of the exterior walls of their home. These gaps permitted air travel from the living space into the attic and allowed for warm air to enter into the cool attic. Once in the tight space of the attic, the warm air clashed with the cool surfaces of the sheathing and caused condensation and increased moisture while also heating the environment. Ventilation could have at least helped reduce the amount of warm air staying stagnant in the environment but the small gable vents were insufficient in this case.
So, how do you know that this air leakage theory was what happened and not just a leaking/improperly installed roof?
Mold growth was fairly limited to the same areas where the large gaps were found inside rather than wide spread throughout the attic.
Once those gaps were fixed and air leakage was effectively stopped then the attic began to dry out and condensation build up stopped.
What to do about the improper ventilation? Retrospectively adding venting points can be costly and if not installed properly can cause a point of failure when it comes to waterproofing a roof. For this house a “smart” fan was installed, it has a built in thermostat and hygrometer to measure both temperature and humidity. It also connects to the owner’s phone so that attic conditions can be monitored closely.
Unfortunately we aren’t done yet. We have removed the conditions that mold needs for growth. However, even if we get conditions so perfect that the mold can no longer grow, “dead” mold can still be an allergen. In most cases, this attic would be a perfect candidate for dry ice blasting but at it’s peak, this attic only has 24” of vertical space. So now what? Book answer, new roof and sheathing, only a year and a half after the first one was installed. Obviously a major cost, and during January in North Idaho, a rough option all around. So what we will be doing since seeing improvement with the changes so far, is using our registered fungicide to hit every square inch of this attic and monitoring this situation closely in the coming weeks/months.
Mold air tests performed prior to the work talked about in this bulletin showed a relatively safe living environment. With no major amounts of spores being found in the living space of this home. Additional air testing and monitoring will be a part of the plan moving forward for this home.