Classy Flooring ATL installs hardwood floors across metro Atlanta and North Georgia, including glue-down floors over concrete slabs prepared with moisture testing and a moisture barrier. Hardwood floors can be installed in a basement, and we recommend engineered hardwood that its manufacturer approves for below-grade use, installed over a moisture barrier on a slab tested for moisture.
A basement slab sits below ground level, and NWFA has installers plan for hidden moisture from the earth around it; wood takes on moisture and swells. NWFA’s guidelines draw the line by flooring type: engineered flooring can, in general, be installed above, on or below grade, and solid hardwood stays on or above grade unless its manufacturer approves it below grade.
Is it a good idea to put hardwood floors in a basement?
It is when three things are in place: water problems fixed at the source, a slab tested for moisture, and a moisture barrier over the concrete. NWFA treats a floor as below grade when any part of the subfloor sits 3 inches or more below ground level.
A slab that feels damp, or water that shows after rain, has a cause to find first. When groundwater stands above the bottom of the slab, it puts the slab under pressure from below. NWFA calls this hydrostatic pressure and points to drainage or waterproofing around the foundation to prevent it; that is a drainage or waterproofing specialist’s work. WAKOL limits its PU 280 moisture barrier to slabs free of hydrostatic pressure, and every known moisture condition is resolved before any wood floor is installed. With the cause fixed, we specify the floor from the slab’s moisture readings.
We test every slab for moisture, whatever its age, as NWFA’s guidelines call for on every job. NWFA recommends a Class I vapor retarder over every slab on or below grade, and calls for waiting or a Class I retarder when a slab tests above 80% relative humidity with in-slab probes (ASTM F2170) or above 3 pounds per 1,000 square feet in 24 hours with a calcium chloride test (ASTM F1869). Under a glue-down, NWFA has the adhesive manufacturer set the moisture limits and the moisture control, and the retarder has to be compatible with the adhesive. On our slab glue-downs we apply two coats of WAKOL PU 280, which WAKOL rates to 98% relative humidity; above that, WAKOL evaluates the slab first. At Chateau Elan in Braselton, RH probes read 55–65% in the slab before the two coats were applied and the 7-inch engineered white oak was glued with WAKOL MS 260. Our post on hardwood over concrete covers the full slab sequence.
What type of hardwood flooring is best for a basement?
Engineered hardwood that its manufacturer approves for below-grade installation. For engineered floors, NWFA points to the manufacturer’s own instructions for moisture, acclimation, installation and care, and following them keeps the warranty. They also set the installation method. On a slab, we glue the floor down, with the moisture barrier under the adhesive. Nail-assisted glue-down, which we use over plywood, needs a wood subfloor to hold the nails; another route NWFA describes is a wood subfloor anchored to the slab, with the vapor retarder between the concrete and the wood subfloor.
Engineered hardwood comes prefinished at the factory, or unfinished, to be sanded and finished on site. A site-finished basement floor can be stained to match the floors upstairs; our color matching page covers how we match floors.
Then check the wear layer, the top layer of hardwood. NWFA’s sanding guidelines generally stop at 3/32 inch, about 2.4 mm, so the wear layer decides whether the floor can be sanded and refinished later. In a whole-house refinishing in Atlanta, the basement was 350 square feet of prefinished engineered hardwood; we measured its wear layer at 4 mm on a leftover box before sanding, then sanded through the factory finish and micro-bevels and refinished it with the rest of the house.
Is engineered hardwood flooring waterproof?
No. Engineered hardwood has a real wood surface, and wood swells when it takes on water. When the underside of a board takes on more moisture than the top, the board cups. The fix starts with finding and stopping the moisture source; the floor is evaluated again once it has dried back into balance with the room.
Day to day, wipe spills right away and damp mop once a week with a mop that is barely wet; on a factory-finished floor, use the cleaner the flooring manufacturer names. NWFA also recommends a dehumidifier in humid months, and 30–50% relative humidity at 60–80°F when the manufacturer gives no range of its own.
Can mold grow under hardwood?
Yes, when the wood or the subfloor stays wet. NWFA notes that mold can grow once wood is above 15% moisture content, while reaching that number doesn’t mean damage will happen. Fulton, DeKalb, Cobb and Gwinnett are in the warm-humid zone on NWFA’s climate map, and for hot, humid climates and the humid season, NWFA sets 13% as the most a wood subfloor should read.
Under a finished floor, moisture shows as cupping and as meter readings in the floor and subfloor above those numbers. Plywood that stays wet swells and delaminates, and it is replaced when the damage shows; our subfloor preparation page covers how we decide. Removing mold is work for a remediation specialist; the flooring work follows once the subfloor reads dry.
Planning a hardwood floor in a basement
Classy Flooring ATL is led by Claudiu Toma, an NWFA Certified Installer, NWFA Certified Sand & Finisher and NWFA Certified Sales Advisor, who completed NWFA Precision Patterns: Parquet Flooring and NWFA Precision Patterns: Medallions. Every project is carried out by our in-house crew.
Our engineered hardwood installation page shows the engineered floors we install. Planning hardwood floors for a basement in metro Atlanta or North Georgia? Tell us about your basement through our contact form, or call (770) 401-3659; we typically reply within one business day.