SMD’s are the most effective system for homes built on crawlspaces.
As of January 1, 2014
New Residential Construction requires:
In buildings with crawlspace foundations, the required components of a passive SMD must be installed during construction. (See Section 3 of this presentation).
This allows for the conversion to an active system via installation of a fan by a licensed professional.
32 ILAC 422.150(h)(9)
Soil Gas Retarder / Vapor Barrier
A soil gas retarder membrane must be installed in basement or crawlspace areas without a concrete floor.
Crawlspace depressurization without the use of a soil gas retarder membrane should only be used when the crawlspace is inaccessible.
Note: The use of an HRV in a crawlspace does not exempt the mitigation contractor from installing a soil gas retarder.
The soil in crawlspaces must be covered with a continuous layer of minimum 6-mil polyethylene soil gas retarder.
The ground cover must be lapped a minimum of 12 inches at joints and must extend to all foundation walls enclosing the crawlspace area.
Any seams in soil gas retarder membranes must be overlapped at least 12 inches and sealed in a permanent air tight manner using compatible glues.
The membrane must also be sealed around interior piers and to the inside of exterior walls with furring strips and compatible glues.
32 ILAC 422.150(h)(9)
Example of a Non-Compliant Crawlspace
This 1800 sf crawlspace had a small 150 sf area that was inaccessible. The soil gas retarder was omitted and an HRV installed in lieu of a sub-membrane depressurization system and mitigation fan.
This application is not only high maintenance and expensive for the homeowner, HRVs are typically not capable of reducing radon levels more than a pico curie or two. Waste of time and money.
Example Of Correct Installation of Vapor Barrier
Seams overlapped properly
Vapor barrier is brought 12″ up the wall and sealed with compatible glue and furring strips