Do you feel smell of a mold entering your house under damp weather conditions, usually in summer? Do you see evidence of water stains or mold on the sheathing, rafters or trusses in your attic? Is your attic insulation packed down or stained by water or ice? If the answer is yes to any or all of these questions, you got excessive moisture in your attic.

In the same series of articles:

Why ventilate your attic?
How to Control Moisture in Attics
Attic Moisture and Your Climate
How to Fix a Water Stain on a Ceiling
How to Prevent Icicles and Ice Dams on Roofs
Why and how to install an attic vent
How to Prevent Icicles and Ice Dams on Roofs
How to replace faulty roof shingles

What can be the root cause?

  • Water leak from the roof
  • Air leaks in the ceiling of the rooms below the attic or attic hatch improperly sealed
  • Attic not adequately ventilated

What to do?

Water leak from the roof

Find moisture sources and repair roof leaks. Here are some places to look for water leaks:

  • above staircases
  • around chimneys through the attic
  • around plumbing stacks or plumbing walls
  • any light fixtures from the ceiling below
  • around electric wiring
  • around ducting for fans or heating systems
  • where additions meet an older section of the house
  • along perimeter walls
  • above lowered ceilings
  • where the side of a cathedral ceiling meets an open attic
  • at split level discontinuities
  • along partition walls
  • above pocket doors

Air leaks in the ceiling of the rooms below the attic or attic hatch improperly sealed

Here is how to look for air leaks:

  • Searching the attic at night for lights from below
  • Scanning batt insulation for dirty areas which have been filtering the air from below
  • Simply look for holes – sometimes the holes are so big that you can see into the house below
  • Do a blower test by pressurizing the house with a big fan to amplify the leakage

Once you found the air leaks, seal them. Air-seal the ceiling using polyethylene sheeting, sealed over octagonal boxes for lights, caulk holes for wires through sheeting or wall top plates and weather strip attic hatches.

Also, check if you have any pot lights on your top floor. Safety regulations prevent sealing of many types of pot lights and as a result hot air gets into your attic through them. Choose sealed pot lights or avoid them on the top floor of your house.

Do you have your heating or air conditioning ducts or equipment in the attic? These can be the major source of air leakage and heat loss in the attic. Make sure you properly seal all the ducts and equipment.

Attic not adequately ventilated

Ventilate the attic as per building code in your area. Do not increase ventilation above recommended values as it has been found that over-ventilating could in fact increase the moisture in attics. For more information on this topic read Attic Moisture Control In Your Climate. If you need additional attic ventilation, here is how to install an attic vent.

In the same series of articles:

Why ventilate your attic?
How to Control Moisture in Attics
Attic Moisture and Your Climate
How to Fix a Water Stain on a Ceiling
How to Prevent Icicles and Ice Dams on Roofs
Why and how to install an attic vent
How to Prevent Icicles and Ice Dams on Roofs
How to replace faulty roof shingles

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