Because a large percentage of breathable air in a residential building comes from the crawl space, it is crucial to use a vapor barrier in your encapsulation that meets crawl space code requirements. Air ventilation and moisture control are critical components of keeping a crawl space free from mold, mildew, rot, harmful gasses, insects, and pests.
What is the International Residential Code for Crawl Spaces?
The International Residential Code (IRC) is a set of international standards related to the construction of residential buildings. These guidelines are not necessarily upheld by state governments. So, it is important to know local codes when proceeding.
In the most recent edition of the IRC, published in 2021, crawl space code is defined under section R408, which outlines the code considerations for the space underneath the floor.
The unique climate of the local area often dictates the code criteria for crawl space ventilation and moisture control.
Crawl Space Code Requirements for Ventilated Spaces
It was once thought that crawl spaces needed to be ventilated to keep air moving and to keep moisture out. However, ventilation openings can often serve as an entryway for water, mold, insects and animals. IRC allows for both ventilated and unventilated crawl spaces.
Ventilated crawl spaces require a vent on each wall, with a required square foot of ventilated area for every 500 square feet of the crawl space. These requirements may change if the vents are positioned to provide cross ventilation, or if the ground is covered with a Class I vapor retarder of at least 6 mils.
For vented crawl spaces, the 2021 IRC guidelines added new specifications for under-floor vapor retarders. In certain warm and humid climate zones, IRC requires Class I and II vapor retarders to cover the air-permeable insulation between the floor joists and exposed to the grade.
Crawl Space Code Requirements for Unventilated Spaces
Unventilated crawl spaces that are part of the building’s conditioned space are required to be covered with a Class I vapor retarder, and must have some form of ventilation.
A Class I vapor retarder is a low-permeance polyethylene sheeting that prevents moisture without tearing or puncturing. The vapor retarder should cover the ground to prevent moisture and toxic gasses in the ground from damaging the structure of the building. The vapor retarder must be sealed with vapor tape at the overlapping seams, and must extend up the walls of the crawl space at least six inches.
An unvented crawl space additionally requires some type of ventilation to conditioned air. This might be accomplished by giving the crawl space access to the conditioned air inside the house through a vent in the floor.
What is the Best Vapor Retarder for My Crawl Space?
These high-quality products can be used by builders and contractors to meet IRC and local code compliance requirements.
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