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Roof Structure

Water Leakage

Problem: Rotting of roof structural members and roof sheathing materials.

Cause: Excessive moisture in the attic space.

Wood begins to rot when it reaches a moisture content of 20% or greater and where the ambient temperature is higher than 66°F (22°C). Moisture carried into the attic space can be absorbed by structural members and roof sheathing, creating the conditions necessary for decay. Moisture is carried into the attic space by humid indoor air leaking from the interior of the house as shown in Figure 22.

Air Leaks That Allow Moisture Into Attic

Figure 22 - Air Leaks That Allow Moisture Into Attic

Solutions: Control air leaks to attic space from house.

  • Reduce the amount of humid indoor air entering the attic by setting up an effective air barrier system between the interior heated space and the attic space. The air barrier system can be made up of polyethylene, solid framing members, sealants, gaskets, wood panels, drywall and other products. The system must be continuous.
  • Properly seal penetrations through air barriers, such as at partitions, electrical boxes, and plumbing pipes, by using flexible material to ensure air tightness.

Additional information on air leakage protection in your home

Additional information on roofs and roofing