Start with three questions
These quick checks tell you whether this page applies to your house.
- When the fan runs, can you feel air coming out of a roof cap, wall cap or soffit vent outside?
- In the attic, does the fan's flexible duct end in the insulation or point at a vent instead of connecting to one?
- Is the plywood or plank sheathing above the bathroom darker than the rest of the roof deck?
What is going on up there
A bath fan moves warm, humid air. If it discharges into the attic, that moisture spreads into a space that in winter is nearly as cold as outdoors. It condenses on nails and on the underside of the roof sheathing, freezes on cold nights, and melts on sunny days. Over several winters the sheathing above the bathroom turns gray or black, and nail tips may show rust streaks or drip marks on the insulation.
Wheat Ridge ranches tend to have low-slope roofs with shallow attics that are hard to move around in, which is one reason ducts get left short. Kitchen range hoods and dryer vents sometimes have the same problem. Ice dams can add more water at the eaves in snowy years.
Technician with a backpack HEPA vacuum cleaning an opened wall cavity. Shown to illustrate the work described; not a job for this site or at any address named here.
How attic sheathing mold is usually handled
Fix the venting
Run insulated duct from each fan to a dedicated roof or wall termination with a damper. Do not rely on a ridge or soffit vent as the outlet.
Protect the house
Attic hatches and ceiling openings are sealed and air filtration is set up so dust from the work does not fall into living space.
Clean the sheathing
Growth is removed mechanically, often by HEPA vacuuming and sanding, wire brushing or media blasting, depending on the extent.
Assess the insulation
Insulation that is wet, matted or heavily contaminated is removed and replaced after the attic is dry.
Check attic ventilation
Confirm that soffit and roof vents are open and that air leaks from the house, such as around light fixtures and the hatch, are sealed.
Common questions
- Does attic mold make the house air unhealthy?
- Attic air does not usually flow into living space in large amounts, but ceiling leaks around fixtures and hatches can pull it in. Fixing the moisture and sealing those leaks both help.
- Does the roof need to be replaced?
- Usually not. Sheathing with surface growth is normally cleaned. Only sheathing that is delaminated or soft needs replacing, which may be done during a reroof.
General information for Wheat Ridge, not a quote or professional advice. In an emergency, call 911.