Here you will find answers to frequently asked questions about attic mold, including causes, cleaning, remediation, and ventilation.
1. Should you use bleach to kill mold?
NO. Professor Jeffrey Morrell. Department of wood science at Oregon State University has this to say:
“The ion structure of chlorine bleach may prevent it from penetrating into porous materials such as drywall and wood. Sodium hypochlorite may stay on the surface of materials, whereas mold may have mycelium growing into the materials. Thus when you spray porous surfaces with bleach, the water in the solution soaks into the material while the chemicals stay on top.”
2. Can I use circle vents in the soffit area?
NO. Even two 4’ around vents in every bay will not supply the needed nine square inches per foot of net free ventilation required by the building code.
3. Can I use an over-the-gutter vented drip edge (hicks vents)?
NO. Water from the gutter will evaporate into the vented drip edge and get drawn into the attic creating condensation on the plywood and eventual mold growth.
4. Can I vent the bathroom fan into the soffit?
NO. By definition, soffit vents are intake vents, and ridge vents are exhaust vents. Warm moist air from the bathroom exhaust will be drawn right back into the attic through the soffit vents. The fan should be vented through the roof.
5. Should I install an attic fan to cool down the attic?
MAYBE. It really depends on the CFM (cubic feet per minute) of the fan and the available air from the soffits. An attic vent fan can create a huge amount of negative air pressure. If the soffit vents are not of sufficient size to balance the amount of exhaust created by the fans, then air will be drawn (make up air) from the living space. In the summer, cooler “air-conditioned” air from the living space will get drawn into the attic actually making the house warmer.
NOTE; The same problem occurs when ridge vents are installed without soffit vents.
6. Do some ridge vents work better than others?
YES. The “shingle vent II” has side wings that create a wind up-lift much like an airplane wing. Other venting systems such as the roll vent do not provide ample airflow and should not be used to ventilate an attic.
7. What is an attic staircase cover?
A staircase cover is installed on the inside of the attic over the pull-down staircase. It prevents heat from being transferred (convection) to the attic in the winter and prevents heat from the roof (migration) downward in the summer. The stair case cover should be equal to or greater than the R-value of the attic insulation.
8. How much attic insulation do I need?
The current minimum standard for insulation in an attic is R-38. “R” stands for resistance to heat flow.
9. Can I have too much insulation in my attic?
MAYBE. Moisture can be brought into the attic in many ways. In older homes vapor barriers were not installed. Moisture can also travel through recessed light fixtures, electrical, plumbing, chimney chases, and gaps in drywall. More insulation means the likelihood of trapping water vapor will increase. If you add more insulation, you will need to add additional ventilation. Consider having the attic air sealed to reduce vapor migration into the attic space.
10. What is a soffit vent?
A soffit vent is an intake vent installed in the soffit area between the siding and the facia board. The current intake ventilation standard is a minimum of 9 sq. inches of net free ventilation per foot.
11. What is a ridge vent?
A ridge vent is an exhaust vent installed at the peak of the roof. The sheathing needs to be cut a minimum of ¾ of an inch on each side of the ridge to achieve 9 sq. inches per foot of exhaust for balanced ventilation.
12. What are soffit vent chutes and insulation dams.?
A soffit vent chute prevents the insulation from covering the soffit vents. Insulation dams prevent the spillage of blown-in insulation into the soffit area.
13. Can you combine gable and ridge vents.
MAYBE, The ridge vent may draw air from the gables, instead of the soffits. If the ridge vent is installed improperly or there is not sufficient airflow in the attic, then both ridge and gables may be used together. If the ridge and soffit vents are installed properly, gable vents should not be needed.
14. How do I calculate ventilation?
Typical ventilation requirements are based on the attic area. Divide by 300 or 150 depending on the type of construction.
For example, an attic measuring 20×50 ft=1000 sq. ft.
The minimum ventilation without a vapor barrier would be 1000 divided by 150 which would equal 6.6 sq. ft or 960 sq. inches. (1 sq. foot is 144 sq. inches)
The minimum ventilation with a vapor barrier is 1000 divided by 300 which would equal 3.3 sq. ft. or 480 sq. inches.
Half of the venting should come from the soffit and half from the ridge.
15. Should I insulate my basement ceiling?
NO. Insulation should be installed around the perimeter of the basement at the floor joist pockets to reduce air infiltration. A dirt basement should not be insulated.
1) A 700 sq. ft dirt basement can discharge 10 gallons of water a day. Even a concrete-floored basement can discharge large quantities of water through simple evaporation. The insulation will absorb the water vapor and become soggy; presenting a condition that will lead to mold growth.
2) The average ground temperature is 55 degrees. If it is below 55 degrees outside, your basement will be warmer than the living areas of the house if the floors are insulated. The correct way to insulate a basement with a concrete floor would be to insulate the floor joist pockets only and then the walls and add a zone of heat to the basement. Since the basement is already at 55 degrees, it doesn’t take a lot to heat it. That warmth will translate to the upper living space floors making the home more comfortable and energy-efficient. The added benefit is a warm, dry, mold-free basement.