Attic mold usually starts at the rear of the house.
- The front of your house faces the street and the back faces the woods. Because of the location of your driveway and street, there probably aren’t as many trees in the front. Less trees equal less shade.
- The kitchen and baths are usually located at the rear of the house. This means your high moisture areas are located under the shadier, cooler section of the house.
- The pull down staircase is usually in the hall, right outside the bathroom and right down the hall from the kitchen. Any excess moisture from these areas will naturally be drawn into the attic around gaps in the cover. This upwards movement of air is called convection. In the summer when the attic is hotter, the downward movement of air is called migration.
- If you have an attic staircase, it should have a cover equal to or greater than the R-Value of the insulation.
When the sun comes up and starts to heat up the attic, the sunny warmer side pushes accumulated moisture in the attic to the cooler shadier side. Mold needs water to grow. If the plywood stays damp enough for long enough mold growth will begin. If you have a good attic ventilation system, that excess moisture will be drawn out of the attic. If you have a poor ventilation system water will condense on the roofing nails and eventually drip down on to your insulation.
If you combine mold spores, an edible surface (your attic plywood) and water you will grow mold. If left unchecked the mold spores will spread to the gable ends and eventually to the front section of the attic.
Here is a list of the common conditions leading to attic mold:
1) Cooking and showers.
2) Gas appliances.
3) Excess humidity from clothes dryers.
4) Fish tanks and plants.
5) Wet basements including open sump pump pits, dirt basements and foundation cracks.
6) Efflorescence caused by water infiltration into the basement usually due to improper yard grading.
7) Inadequate ventilation in the attic due to:
A) Blocked, missing or undersized soffit vents.
B) Blocked, missing or undersized ridge vent.
C) Blocked, missing or damaged soffit vent chutes.
8) Leaking ductwork due to improperly installed HVAC systems.
9) The bathroom fan venting into the attic or soffit.
10) The kitchen stove exhaust fan venting into the attic.
11) Improperly installed insulation including missing vapor barriers.
12) Ice dams.
13) Missing or undersized attic staircase cover.
14) Open chasses around pluming, light fixtures or chimney.
15) A lack of solar drying (trees and shrubs.)
16) Roofing, vent pipe flashings, skylights and chimney flashing leaks.
17) Plumbing and heating system leaks.