Laminate Flooring Crawlspace Considerations For a Long-Lasting Floor
Installing laminate flooring over a crawlspace, the conditions are an important consideration when installing laminate, engineered, or solid wood flooring. A crawl space must have a proper vapor retarder ground cover spread over the soil. A crawl space must also have proper cross ventilation and no dead air spaces. Without the appropriate vapor barrier and cross ventilation, crawl space moisture will attack the underside of a subfloor and enter the laminate flooring core. Excessive crawl space moisture may result in cupping, bulging, or swelling of the planks or blistering at the surface of the planks.
For the crawl space and other site-related standards, laminate manufacturers will often refer to NWFA guidelines. The National Wood Flooring Association. These guidelines are excellent for both wood and laminate floors. A manufacturer’s own guidelines always take precedence over industry guidelines.
Regarding Crawl Space, NWFA guidelines state:
Crawl space should be a minimum of 18” (457mm) from ground to underside of joists.
100% of the earth in a crawl space, (or thin concrete slab) should be covered. A vapor retarder of black polyethylene (minimum 6 mil) or any recommended puncture-resistant membrane, such as Class C, meeting ASTM D-1745. See figure 1-1.
Figure 1-1
Crawl Space Conditions
a. Where a proper ground covering is in place and when venting is required by local building codes, the crawl space should have perimeter venting equal to a minimum of 1.5 square feet per 100 square feet of crawl space square footage, unless local building codes differ from this specification. Note: Local-building codes may differ. Follow local building codes.
b. For crawl spaces without ventilation openings, vapor retarder joints must overlap a minimum of 6 inches and be sealed or taped. The vapor retarder should also extend at least 6 inches up the stem wall and be attached and sealed to the stem wall. Continuously operated mechanical exhaust and perimeter wall insulation or conditioned air supply and insulation must be provided.
What’s the Difference Between a Vapor Retarder and Vapor Barrier
In conversation, as well as much of the industry literature, you will encounter the term “Vapor Barrier”. The most recent standards for these products now use the term “Vapor Retarder”. While the best products available may be close to that of a barrier, all have a permeance rating, and all will pass a measurable amount of moisture vapor. Even the term vapor barrier is somewhat misleading as it will not totally prevent the transmission of water vapor. A vapor barrier is actually a vapor-resistant membrane, and therefore the change to the term “vapor retarder.”
For our purpose, a vapor retarder is a specially thin plastic sheeting; however, some specialty-treated papers and low-permeance paint are also available for other purposes.
The vapor retarder must have a vapor permeance (the rate that moisture can pass through materials) of not more than 1.0 perm. The test procedure for classifying vapor retarders is ASTM E-96 Test Method A – the desiccant or dry cup method.
Vapor Permeance
Class Test procedure for determining vapor permeance class is ASTM E-96 Test Method A-the desiccant or dry cup method.
- § Class I: Materials that have a permeance of 0.1 perm or less. (Note: this is the definition of a “vapor barrier”.)
- § Class II: Materials that have a permeance of 1.0 perm or less and greater than 0.1 perm. (Note: This is the definition of a “vapor retarder”.)
Vapor Retarder
Vapor retarder is a material that has a permeance of 1.0 perm or less and greater than 0.1 perm. A Vapor retarder is a material is vapor semi-impermeable. A vapor retarder is a Class II vapor control layer.
FAQ’s
How do vapor permeance ratings classify vapor retarders and barriers?
Materials with a permeance of 0.1 perm or less are classified as Class I vapor barriers, which are nearly impermeable. Materials with a permeance between 0.1 and 1.0 perm are classified as Class II vapor retarders, which are vapor semi-impermeable and suitable for controlling moisture in crawl spaces.
What is the difference between a vapor retarder and a vapor barrier?
The term ‘vapor barrier’ is commonly used, but industry standards now prefer ‘vapor retarder’ because these materials pass some moisture vapor through them. A vapor retarder typically has a permeance rating of 1.0 perm or less, meaning it resists moisture transmission but does not completely prevent humidity from passing through.
What is the proper way to install a vapor retarder in a crawl space?
The vapor retarder should cover all exposed earth in the crawl space or slab, with joints overlapping by at least 6 inches and sealed or taped. It should extend at least 6 inches up the stem wall and be securely attached and sealed to it. Proper ventilation or mechanical exhaust systems should also be in place to maintain dry conditions.
What standards should be followed for crawl space conditions according to NWFA guidelines?
According to NWFA guidelines, the crawl space should have a minimum height of 18 inches from ground to the underside of the joists. Additionally, 100% of the earth or thin concrete slab in the crawl space should be covered with a vapor retarder, such as black polyethylene of at least 6 mil thickness or another recommended puncture-resistant membrane, ensuring proper moisture control.
What are the key considerations for installing laminate flooring over a crawlspace?
When installing laminate flooring over a crawlspace, it is crucial to ensure that the crawl space has a proper vapor retarder ground cover spread over the soil, adequate cross ventilation, and no dead air spaces. These conditions prevent moisture from attacking the underside of the subfloor, which could cause damage such as cupping, swelling, or blistering of the planks.
