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Laminate flooring is strong, durable and extremely forgiving, but it still has limitations and is not necessarily suitable for every home. Laminate features an organic core and, just like other materials in the home that fall in this class, it will and expand and contract as it reacts to changes in moisture content.

Before beginning any job it is important to evaluate the job site to ensure it is suitable for a laminate flooring installation. I like to begin the evaluation outside. My biggest concern is rain water management. Whether the home is on a slab, a crawl space or over a basement, it is critical to keep as much water as possible away from the foundation. If the soil becomes saturated with water, it can penetrate the foundation walls or rise through the ground surface into the foundation or crawl space.

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The first place I look for water management is by looking up. 0.62 gallons of water are collected per square foot of roof per inch of precipitation For example, a 1,000-square-foot roof will collect 620 gallons of water for every inch of rain that falls on it. Properly installed, clean, working gutters, with down spouts and spill guards, will direct this water away from the foundation (Photo 1).

The next place I look is the landscaping. On new construction, the final grade should be completed. On all homes the soil should be sloped away from the structure. A rule of thumb is ½” per foot for at least 6 feet. Look for things like raised flower beds, heavy shrubbery close to the foundation walls, and cracked or broken driveways. Is the driveway slopped away from the house?

Lawn sprinklers should be directed away from the foundation walls. Look for discoloration, mold or mildew on the foundation walls (Photo 2).

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Crawl spaces

Wooden subfloors constructed over a crawl space MUST have adequate ventilation. Crawl space should be a minimum of 18” from the ground to the bottom of the joist. 18” of clearance beneath duct work is also desirable (Photo 3). The ground should be covered 100% by a vapor retarder of black polyethylene (minimum 6 mil). The seams should overlap at least 8 inches; and the film run up the wall at least 6 inches. In cases where a thin concrete slab is covering the ground a vapor retarder should still be installed. The crawl should have perimeter venting equal to 1.5% of crawl space square footage. In other words, 1,000 sq ft of space would have 15 sq. ft. of venting. You are looking for good cross ventilation with no dead air space. In some areas of the country a closed crawl space is preferred. To function properly a supply and return air should be included in the space. Always follow local building codes. You have to actually look in. Is there standing water?

Excess moisture in the crawl space can penetrate subfloors through a process known as diffusion - the transport of water molecules through a surface due to a difference in vapor pressure – and have an adverse affect on the flooring.

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Concrete slabs

All concrete slabs must be tested for moisture. Unless you have a crystal ball there is no way to tell if the slab is properly constructed with a vapor retarder separating the concrete from the soil. Also, converted garages and rooms that were not originally intended to receive finished flooring will not have a vapor retarder beneath the slab.

The maximum acceptable moisture measurements for concrete subfloors must not exceed the manufacturer’s recommendation. Some manufacturers accept meter readings (Photo 4) and some require a Calcium Chloride test (Photo 5).  Be sure to record the measurements for future reference.  New concrete must cure for at least 60 days and then be tested.  Cover all concrete slabs, regardless of grade level or age with a non-recycled resin 6-mil polyethylene film as a vapor retarder.

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Basement floors and walls should be dry. Look for signs of mold or mildew. Check items lying on the floor. Sometimes just opening the basement door you’ll be greeted by that musty smell.

 Is an HVAC in place and working? The ventilation system should be operating for at least 2 weeks prior to installation. It is best to install the floor in an environment that’s as close to normal living conditions as possible, 60° to 85° F and 35% to 75% RH. Record the temperature and relative humidity. Hygrometers are inexpensive and invaluable. Again, record your test results.

Check for floor flatness. Typically a measurement of 3/16” in 10 ft. is required although each manufacturer’s numbers may vary a little. Always check the instructions for the floor you are installing.

Flatness can be check with a straight edge, laser level, or string line. I usually just click 3 laminate planks together and use them as a straight edge (Photo 6).

Measure and record the subfloor moisture content. Own a moisture meter and know how to use it.

Check in several locations and average the results. Numbers may vary by geographic region, but in most areas of the U.S. you’re looking for less than 12% MC.


Always document all of your observations and test. Digital cameras are wonderful. Most everyone has one in their phone. Take notes and pictures; temperature and RH; subfloor, wood or OSB; Joist direction and spacing; dimensional lumber or TGI. Some things may not seem very important, but it only takes a second to look and it’s good to get in the habit of writing everything down.  Good notes are very valuable when a problem pops up.