08:49AM | 09/01/05
Member Since: 08/25/05
6 lifetime posts
I may have asked this before but need to understand. The home I am speaking of is in the NorthWest section of Alabama.

How much of the "crawl space"/with dirt floor, be covered by vapor barrier? Should the "vapor barrier" cover the outer foundation walls? Should the "vapor barrier" be secured at sill/cement foundation and wood connection?

I do have vent holes in foundation for proper ventilation, they are now covered with styrofoam to keep out moisture but I am removing these foam blocks and installing "mosquito netting/ to keep out critters and insects. I am also installing new access doors w/same netting. I know that home has to "breath" so I do not want to block all vents with foam unless necessary. Is this correct process or does someone have expert advice on what is proper procedure?


05:30AM | 09/02/05
Member Since: 01/28/03
693 lifetime posts
Vapor Barrier is required by code on the entire dirt floor surface.

Joints must be taped or sealed and sealed at the wall or sill.

Vapor Barrier should extend up walls.

Whether the fundation needs to be vented depends upon whether or not the crawlspace is condition and how it is insulated.

If there is a vapor barrier on the floor AND the crawlspace is conditoned with heat or air conditioning or opens to another part of the house or basement that is, you do not need ventilation.

If the crawlspace is mechanically vented you do not need outside ventilation.

If the crawlspace vents to another inside portion of the house, it does not need to be ventilated.

If the crawlspace has vapor barrier on floors and walls, has perimeter walls insulated and ceilings left uninsulated, there is no need for ventilation.

Otherwise you need about 1 square ft of ventilation per every sq ft of floorspace.


10:26AM | 09/02/05
Member Since: 06/23/04
161 lifetime posts
Homebild may have left out a number. The International Building Code requires a NET ventilation opening of 1 square foot for every 150 square feet of crawl space area. The word NET means that the actual FREE area after deducting for the wire (if screened) or other solid parts (if a grille) of the vent covering.

Some screen suppliers will provide the net or free area in percent (i.e. "75% free area"). As an example, the framed opening of a vent 12 inches by 16 inches provides a gross area of 192 square inches (1.33 sq ft) but must be reduced to 75% of that area to obtain the actual free area. Thus 192 sq. in. x .75 yields 144 square inches (1.0 sq ft) of opening. The denser the screen you install, the less free area you are providing for ventilation. Standard 18 x 14 x .009 insect screen provides 74% free area and 4 mesh hardware cloth provides 85% free area.



10:38AM | 09/02/05
Member Since: 08/25/05
6 lifetime posts
A Big Help....Thanks
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