Determining Attic Condensation Problems and Concerns

Clues To Determine the Extent of Condensation Problems or Concerns

• Rust on the nail points coming through the roof. The nails are in direct contact with the exterior and condensation will always form on the coldest, most dense material in the space.
• Small, blackish stains on the plywood or similar sheathing, at the nails. As water forms on the nails, some of the moisture can be absorbed into the sheathing, causing the stains.
• Water stains on the floor or deck in the attic, or in the insulation below the nail points. This is caused when enough water forms on the nails to start to drop off of the nails.
• Mold starts to form on the north side of the roof sheathing, at the lowest point in the roof system. This is the first clue that may require action. Mold is a problem and proper ventilation is the solution.
• The mold grows up the north side. When it is covering about 50% of the north side, it begins to grow up the south side. This is a serious condition and should be addressed immediately.
• If the mold continues, it will become dense and start to delaminate the plywood or OSB sheathing, or deteriorate the wood sheathing. The sheathing may become black and wet, and actually look like it is raining in the attic. This condition usually occurs only when there is 10 or more inches of insulation and someone intentionally closes or covers all of the vents in the roof system.
• If the condensation moves beyond the level outlined above, it will probably impact the roofing materials. This level will typically require replacement of the sheathing and the roofing.