Post on 11-Oct-2020
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Building Science 2008 Joseph Lstiburek – Rain Control 1
Building Science Joseph Lstiburek – Rain Control 2
Rain Control Layer Air Control Layer Vapor Control Layer Thermal Control Layer
Building Science
Rain Control
presented by www.buildingscience.com
Rain
• Rain is the largest source of moisture • We need better control for better insulation
and airtightness • Rain penetration control
– Site and massing – Surface features – Enclosure wall strategy
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Controlling Rain Penetration
• Deflection – reduce water on building – redirect water away – slope surfaces, use flashing
• Drainage / Exclusion / Storage – enclosure design – provide drainage, or storage or barrier
• Drying – allow any remaining water to dry
Deflection
! Surface & site features are also important
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Don’t concentrate water!
Categorization
• Elements and joints can be different
John Straube
Mass/Storage/Reservoir Walls
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Categorization
• Elements and joints can be different
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Claddings that leak
• Brick • Stucco • Wood, vinyl, fiber cement • Adhered veneer • EIFS • Metal panels, metal roofs • Shakes, shingles
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Drainage
• Must have continuous drainage plane
• Drainage plane must be: 1. Water tolerant 2. Capillary inactive (water
repellent / non-wicking)
• Small gap required • As small as 1 mm
• Flashing is very important • Weep holes
Terms: sheathing membrane, building paper, housewrap, Stupid terms: weather resistant barrier (WRB)
Requirements Drained Walls
• Drainage plane • Water repellent, continuous
• Drainage gap – 1/16” is enough!
• Flashing – Waterproof to direct water outward
• Weep holes – Above grade
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Drainage Plane Lapped Housewrap, paper
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Drained Walls
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Laps are the most reliable
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Liquid applied = continuous
Drained gap behind brick
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Laps are the most reliable
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Beware: These are vapor barriers!!!
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Ventilation helps drying. Not always needed.
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Drainage Gaps
• Gap avoids hydrostatic pressure – drains away water
– Requires only small gap, e.g. 1/16”
• Reduces time of wetness on housewrap sheathing membrane
• May allow ventilation drying if >1/8”-1/2”
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Weep holes
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JJAC Test house 2001
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Stucco sticks to paper/housewraps
• leaks
42 Water drained astonishingly well between sheets of building paper
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• Vinyl drains well with no strapping
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Drained gap behind wood
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Water can build up here -- we need a waterproof barrier
Note standing water
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Continuity at Corners Base Flashing
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New materials
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E.g. StoCorp Diverter Flashing
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Saddle flashing
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Building Science University of Waterloo
Rain
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Exterior sealant is temporary, aesthetic, water shedding layer
Leaky windows
• Moisture sensitive substrates are a problem
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Door Sills
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Door sill
1932
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Old EIFS
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Substrate + moisture = problem
• Moisture sensitive substrates are a problem
EIFS & Rain Control: Recent lessons on how to fail
Kitchener, ON Grand Rapids, MI
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EIFS
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Building Science
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Conclusions
• Drainage is the key, cladding leaks • All penetrations need to be drained! • Beware flashing, it needs to waterproof • Understand older systems are different
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