#1.) Attic mold is almost always caused by condensation, not roof leaks.
The first thing people assume when they see mold in their attic is typically ‘my roof must have a leak’. While it happens occasionally the vast majority of attic mold growth in Washington is caused by condensation. This occurs when warm, damp air from your home migrates up through the ceiling and hits the cool surface of the roof sheathing. The cold surface rapidly cools the air which in turns elevates the relative humidity. This humidity now has nowhere to go, and condenses out on the roof sheathing. Over a period of time, this condensation creates conditions conducive to mold growth.
Roof leaks also don’t typically cause a lot of mold because they are identified much sooner. A significant roof leak will allow water to drip through to the ceiling and create a drip mark on the sheetrock. Because of this, most roof leaks are fixed before major mold growth can occur.
One of the easiest ways to determine if mold in the attic is caused by condensation is to simply assess the overall extent. Roof leaks will typically cause mold growth in a limited area, directly surrounding the moisture intrusion. Condensation based mold growth will often cover large areas, and in many cases, the entire attic.
Condensation based mold growth is caused by a number of common factors:
- Disconnected bathroom or kitchen exhaust fans. This one is pretty self explanatory. Pumping large quantities of warm, humid air into a cold attic isn’t a good idea. Thankfully, this is usually a quick fix.
- Blocked soffit venting. Often insulation contractors fail to install baffles near the soffit vents and subsequently cover up the vents with blown-in insulation.
#2.) Most ridge vents are worthless
This is perhaps one of the most frustrating developments in roof construction. Years ago people began designing alternatives to the classic turtle shaped RVO roof vents. The motivation was two-fold: reduce the visibility of attic venting and provide consistent ventilation throughout the entire ridge area. Ridge vents certainly succeeded in the first goal. No question they are the more attractive option.
However, ridge vents have dramatically failed at the second goal. The primary issue lies in the internal baffling that is designed to prevent rain, bugs and other critters from entering the attic. However, the manufacturers got a bit overzealous in their baffling and drastically limited the net free area (actual air flow) of the ridge vent. Even worse, the baffles open at a 90 degree angle to the roof, eliminating the suction that helps draw air from the attic. Perhaps most egregious, at least one well known manufacturer glues filter fabric on the underside of their ridge vent. This filter inevitably becomes clogged with pollen and dust, rendering the entire ridge vent useless.
Externally baffled ridge vents overcome this issue in 2 critical ways. First, these newer vents dramatically increasing the size of the air flow ports. While slightly more visible from below, they provide significantly more air flow throughout the attic. Second, externally baffled ridge vents are oriented more in line with the roof line, improving suction.
#3.) Insulation does not need to be removed in a moldy attic.
I won’t win any insulation contractor friends over with this one. But the truth is simply hard to get around. In 90%+ of attic mold situations, replacing the insulation accomplishes very little. Consider this: Mold growth only occurs in environments with excessive moisture. In an attic, the excessive moisture occurs on the underside of the roof sheathing, due to condensation. The only way the insulation can become wet is by a roof look or in a very small percentage of cases, condensation can be severe enough to cause water to drip back down onto the insulation. Therefore, in the vast majority of attic mold scenarios, the insulation is completely unaffected by the attic mold growth.
Problems arise when inspectors or contractors see a layer of dust on the top of the insulation and confuse it with active mold growth. This is understandable, but it unfortunately leads to many customers paying an extra $2-4,000 for unnecessary insulation replacement.