Laminate Flooring Crawl Space Considerations
Crawl space conditions are an important consideration when installing laminate flooring, engineered or solid wood floor. A crawl spaces 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 into 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 plank.
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 manufactures 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.
Crawl space earth (or thin concrete slab) should be covered 100 percent by 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
It conversation you 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 though some specialty treated papers and low permeance paint that prevents condensation of water vapor are 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
Classes 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
A 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 that is vapor semi-impermeable. A vapor retarder is a Class II vapor control layer.
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Hi Terry, great comments! I installed my laminate flooring about a year ago. Now, the subfloor is rotten. Thru research and your site, I see that I used an underlayment with a vapor barrier attached. The house is peer/beam with a crawlspace. Built in the ’60’s. When removing the damaged flooring, I found that there was a layer of felt paper between the subfloor and original hardwood flooring. Well, when I put the laminate down, I used the salesman’s advice and put a foam pad that ALSO had a vapor barrier. I know NOW that that is the wrong way. LOL. (I really mean, UGH!). My question is this. When replacing the subfloor I will be using TWO layers of 3/4 in. plywood to bring the floor up to the original height. Do I use felt between the two layers THEN a foam pad WITHOUT a vapor barrier, OR just lay the two layers of plywood down THEN use a pad with a vapor barrier before putting the laminate back down? Thanks!!! David
David
What I see as the most important point here is to make sure you have a proper vapor retarder in the crawlspace. Using something like rosin paper betweeen the two layers of plywood may help to control squeaks though it is really not a vapor barrier. Between the plywood and the laminate use foam of a type that is suggested by the laminate manufacturer for the product you are installing. The dealer should be able to tell you which foams the approve of.
Hope this helps, Terry
Hello Terry
I am installing on a wood sub floor with a 48″ crawl space with a concrete base . It has plenty of ventilation but it’s on a lagoon right next to the bay , so my question is can I use sound and thermal underlayment ?
Excellent post. I want to thank you for this informative read; I really appreciate sharing this great post. Keep up your work. Thank you so much.
Your welcome!
Hi Terry,
I am a consulting civil engineer doing a forensic inspection on a commercial building (Hospital) that has a flooring problem. Here is the issues, Contractor abated the existing tile flooring which was installed with black mastic. Both tile and mastic was asbestos based. Product was removed by professional abatement company. Flooring contractor installed laminate flooring planks that look like wood and applied manufactures recommended glue. Product is installed over a concrete floor with a non vented crawl space and there is no vapor barrier. Flooring is also cleaned by hospital crews with water, bleach and other sterilizing products. Planks were installed during summer months with temps in the 90’s. contractor didn’t acclimate product before installing. Product curling and coming loose. Used Mega glue, still happening. I think it is the non-vented crawl space . Jim
Based on the information provided, this could be one of or a combination of the following: Product, installation, specification, maintenance or site related problem. The only way we can advise you is for us to visit the site of installation and perform our investigation and onsite testing. If you would like to file an inspection request, you can do so at https://TheWeinheimerGroup.com
Terry
Hello Terry,
Lots of googling led me to this site and I am looking for some help. I am getting ready to install select surfaces laminate flooring (from sam’s club) in my family room which is above a crawl space. My crawl space has a vapor retarder over the ground in the crawlspace. There is insulation between the joists, and my subfloor is 3/4 inch plywood. I also live in PA so I have Radon remediation system constantly venting the ground under the vapor retarder to the outside.
My question is since I have a vapor retarder in my crawl space do I need to install a vapor barrier over my plywood subfloor under the laminate flooring (with foam pad). OR will it be acceptable to install the laminate flooring without the additional vapor barrier.
You will need to read the manufacturers installation instructions to make that decision. While most of the products will not require a vapor retarder over wood, there are a few that do.