SpecTopics: Air Sealing at Roof-to-Wall Joints
When the requirement for a continuous air barrier was added to the 2012 IBC/IECC, many architects and specifiers continued to utilize the roof membrane as the air seal which ties into the wall air barriers, without adding a roof deck-level air barrier.
The use of a roof deck-level air and vapor barrier is recommended for certain building types, like natatoriums and food processing facilities. It is also recommended in climate zones where hygrothermal analysis determines that the interior moisture drive doesn't allow a long enough drying cycle for the roof assembly.
In cold climates when there is no deck-level air barrier, the winter vapor drive allows warm, moist air from the interior of the building to rise and infiltrate the roof assembly. During the summer, the vapor drive is reversed and pushes the accumulated moisture into the building, where it is taken out by the HVAC system. If the "drying period" of the summer is longer than the "wetting period" of the winter, then the roof assembly is considered "self-drying".
This concept has been used successfully for decades. However, issues can begin when air leakage at roof and wall gaps or around penetrations starts to introduce large amounts of indoor air. Indoor air may contain a higher volume of moisture, meaning more moisture accumulation for the roof assembly to overcome during the drying period.
When a deck-level air barrier is not specified, make sure the specifications and details show sealing of all penetrations through the roof assembly, such as pipes, conduits, and steel supports, at the deck level.
An additional area of concern is roof-to-wall connections with tilt-up construction. The gap between the roof and wall at deck level must be air sealed to prevent indoor air from infiltrating and causing damage to the roof assembly. Damage can be caused not just by interior moisture gain, but by air building pressures. Tilt-up construction is used heavily with warehouse construction, and with the number of loading dock doors in these types of buildings, interior pressures can fluctuate and act as a bellows on unsealed edges.
To learn more about air leakage and construction-generated moisture, review Spec Supplement SS-01 here.
You can review our installation guide for roof deck-level air and vapor barrier products here.
Contact Craig Tyler with questions.
The use of a roof deck-level air and vapor barrier is recommended for certain building types, like natatoriums and food processing facilities. It is also recommended in climate zones where hygrothermal analysis determines that the interior moisture drive doesn't allow a long enough drying cycle for the roof assembly.
In cold climates when there is no deck-level air barrier, the winter vapor drive allows warm, moist air from the interior of the building to rise and infiltrate the roof assembly. During the summer, the vapor drive is reversed and pushes the accumulated moisture into the building, where it is taken out by the HVAC system. If the "drying period" of the summer is longer than the "wetting period" of the winter, then the roof assembly is considered "self-drying".
This concept has been used successfully for decades. However, issues can begin when air leakage at roof and wall gaps or around penetrations starts to introduce large amounts of indoor air. Indoor air may contain a higher volume of moisture, meaning more moisture accumulation for the roof assembly to overcome during the drying period.
When a deck-level air barrier is not specified, make sure the specifications and details show sealing of all penetrations through the roof assembly, such as pipes, conduits, and steel supports, at the deck level.
An additional area of concern is roof-to-wall connections with tilt-up construction. The gap between the roof and wall at deck level must be air sealed to prevent indoor air from infiltrating and causing damage to the roof assembly. Damage can be caused not just by interior moisture gain, but by air building pressures. Tilt-up construction is used heavily with warehouse construction, and with the number of loading dock doors in these types of buildings, interior pressures can fluctuate and act as a bellows on unsealed edges.
To learn more about air leakage and construction-generated moisture, review Spec Supplement SS-01 here.
You can review our installation guide for roof deck-level air and vapor barrier products here.
Contact Craig Tyler with questions.
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