Building Science

Crawlspaces, Slabs, Flooring

John Straube, Ph.D., P.Eng

presented by www.buildingscience.com Building Science 2008 Slabs and Flooring No.2

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Crawlspaces, Slabs and Flooring

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Crawlspace “vent”

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Tarboro, North Carolina

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Vented

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Conditioned

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Crawlspaces, Slabs and Flooring

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Crawlspaces

•  Problem #1: Deal with liquid rain water •  Don’t drain the site into the crawlspace •  Drain the crawlspace

– To drain if below grade – To exterior if above

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Crawlspaces

•  Problem #2: Ventilation w/ outside humid air –  Solution: Don’t

•  Ventilation with hot humid summer air –  condenses on cool soil –  condenses on cool floor

•  Soil evaporation into space

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Building Science 2008 Slabs and Flooring No.20 -10.0 -5.0 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0

Temperature (°C)

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100% RH75% RH50% RH25% RH

Psych Chart: Air Vapour Content vs Temperature

Saturation

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Temperature

Air

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-10 ºC 14 º F

0 ºC 32 º F

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20 ºC 68 º F

30 ºC 86 º F

40 ºC 104º F

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Crawlspace Solutions

•  Build like a basement – Do put sealed poly on the floor to:

•  Stop soil moisture diffusing up •  Seal poly to control soil gas/radon

– Don’t ventilate with outdoor air •  Stop bringing in water vapor

– Do ventilate with indoor! •  Condition the space to remove incidental vapor

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Crawlspace

•  Act as short basements •  Unvented •  But Conditioned!

–  Must have conditioned air to/from space

–  Air movement from conditioned space via fans, HVAC

•  Airtight and vapor tight floor covering

•  Floor drain?

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Conditioned crawlspace

If remaining mold, smell, or radon: depressurize!

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Vented

•  Need to vent some times

•  Poly on soil •  Wall upside down •  Flood drains •  Animal control

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Penetrations!

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