Building A New Home
 To Minimize Radon and Moisture Vapor Entry

 
Thinking about building a new home?
With a little planning, and minimal expense, you can have a passive soil gas ventilation system installed in a new home as its being constructed.  By building this component into a new home you can:
  1. Minimize the entry of radon gas
  2. Prevent moisture vapor intrusion 

Radon gas increases your risk of developing lung cancer, while moisture vapor decreases the efficiency of your air conditioner in the summer months when you want to cool your home. Both of these gases can enter your home through a sump pit and cracks and joints in the floor.

Ice on an Outlet pipe Radon System 

"Soil air is laden with moisture vapor which can condense and freeze at low temperatures."

Fortunately these two problems can be minimized with the use of an inexpensive passive, soil gas ventilation system. Designed to function without power, a passive soil gas ventilation system operates by natural convection. The theory is simple: Warm air moves through the porous rock beneath the basement floor and then rises through the warm, vertical ventilation pipe.
 
How Natural Convection Works

Convection Process

Natural convection fuels the operation of the system, and there are no components that require electricity. By providing a pipe to vent soil gases below the basement floor, the area beneath the home can be depressurized and soil gas can rise through the vertical pipe without entering the home. The passive soil gas ventilation system described here will significantly improve indoor air quality and help make your home more comfortable. To view the larger images, click on the thumbnails below.

A Passive, Soil Gas Ventilation System (SGVS) consists of the following components:

1. A four inch layer of 1/4 to two inch gravel aggregate to create a permeable layer for the flow of soil gases and to create a "capillary break" from the soil moisture below the home.

Taping 6 mil plastic <-- 2. A sheet of six mil. polyethylene sheeting (or three mil. cross-laminated sheeting) laying on top of the gravel aggregate.

3. A 3 or 4 inch diameter PVC ventilationRadon Vent Pipe in an Interior Wall
pipe rising vertically from the gravel bed beneath the basement floor through the attic and out letting above the roof. -->

4. An electric junction box should be installed in the attic near the ventilation pipe to permit the installation of a radon fan if the future owner should decide to activate the system.

Attaching Membrane
 
<-- As a best management practice, seal all joints, cracks and openings around utility penetrations in the floor and walls below grade. Use an elastomeric sealant to provide an air-tight seal.
     
Drainage Pipe with Tee Fitting
 The Soil Gas Ventilation System can also be adapted to treat a crawlspace.  Soil gas is trapped beneath a sheet of 6-mil plastic (or better) membrane which is laid on the soil surface throughout the entire crawlspace. The membrane is then attached about 12" up on the side walls. -->
Important Considerations

 1. To function without a fan, the soil gas ventilation pipe Horizontal Pipe Runmust be installed vertically (plumb); even warm air will not rise when channeled through a horizontal run of pipe like this. -->  

Radon Vent Pipe in an Interior Wall 
<-- 2. The vertical, soil gas ventilation pipe must be installed within the conditioned floor area of the home; soil gas ventilation pipe installed in an exterior wall is typically too cold to function by natural convection. Most vertical ventilation pipes can be hidden within an interior wall.

Basement Floorplan
 
3. A passive soil gas ventilation system is a formal building "system" and should be shown on the construction drawings for all floors. When the passive soil gas ventilation system is shown on the set of construction blueprints almost any worker can ensure that it is installed properly in the intended location. -->
 

Roof Penetration

<--  4. The outlet of a passive soil gas ventilation system should penetrate the roof on the back-side of the home.
 
Pipe Labeling  5. Be sure to clearly label the soil gas
ventilation pipe so it doesn't get confused with other utility systems. -->
 

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