Before The Architect - Articles - Crawlspace Ventilation of Moisture

Crawlspace Air Quality

BEFORE THE ARCHITECT – DREAM HOME DESIGNING BACKGROUND – UNIQUE HOME DESIGNING ARTICLES

HOME BUILDING CONSTRUCTION PROBLEMS - HOME CRAWLSPACE VENTILATION QUALITY
By Before The Architect Copyright 2003-2009 Before The Architect

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hOME BUILDING CONSTRUCTION PROBLEMS - DREAM HOME CRAWLSPACE VENTILATION

CRAWLSPACE MOISTURE

Special consideration shall be made for home foundation crawlspace ventilation of moisture in this order from more preferential to less preferential (unless your local fire inspector disapproves, whose approval shall be explicitly requested and received before home designing is done for crawlspace indoor air quality and whose disapproval or at least agita may arise from the derivative difficulties in regarding – reasonably or not – that an unvented crawlspace is a plenum)

Crawlspaces shall be regarded as interiors to conditioned space, including

	Heating and cooling supply and exhaust
	Continuous interiors, perimeter insulation to barrier moisture and thermal transfer
	Continuous crawlspace floor level insulation to barrier moisture

Failing which, then the crawlspace shall be vented, including

There shall be a continuous moisture and vapor barrier at crawlspace grade

Comment: It is this dream home designer’s experience down all the years that the primary force in poor indoor air quality in a home crawlspace is the lack of a continuous barrier to moisture and vapor.

	Each foundation face greater than 3 linear feet in length shall have a foundation crawlspace vent
	Each crawlspace vent shall be as high on the foundation as possible
	A crawlspace vent shall be within 3 linear feet of a corner

Crawlspace ventilation shall not be less than 1 square foot "net free" vent area to 150 square feet of vented surface area, regardless of the area location or physically proximate form of vapor or moisture barrier

Net free vent area shall be the area of a crawlspace vent opening adjusted by the following factors

	1/4 linear inch-1/8 linear inch screen alone or louvers alone= 1.25
	1/16 linear inches screen=2.00
	Louvers and 1/4 linear inch screen to 1/8 linear inches screen=2.25
	Louvers and 1/16 linear inch screen=3.00

All reasonable effort shall be made to cross-ventilate each crawlspace vented area

Crawlspace ventilation to establish and maintain indoor air quality - minimize crawlspace moisture - shall be not an offset or substitute for mitigations of, among others:

Poor building standards of

Moisture management

Vapor management

Thermal management

Roof covering color

Poor sealing of building envelope

Inadequate drainage for

	Runoff
	Footings
	Sanitation

Poorly graded site and other landscaping matters

. . . . . . .

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