NWFA CI cheat sheet

NWFA Certified Inspector Body of Knowledge

• Wood flooring inspector's core job: determine whether a complaint is caused by manufacturing defect, installation error, environmental conditions, or owner maintenance - and cite the applicable NWFA/NOFMA standard for each finding.

• Moisture content (MC) of wood flooring must be within 2-4 percentage points of the equilibrium moisture content (EMC) of the job site at time of installation; document with a calibrated pin or pinless meter and record species, readings, and date.

• Equilibrium moisture content is governed by temperature and relative humidity; typical interior EMC ranges from about 6% (cold, dry winter) to 11%+ (humid summer). Inspectors must report indoor RH and temperature readings alongside MC.

• Wood is hygroscopic: it shrinks as it dries and swells as it absorbs moisture. Cupping (edges high, center low) indicates moisture gain on the top face or drying of the bottom; crowning (center high) indicates the reverse or prior cupping that was sanded flat.

• Gapping between strips in winter with closure in summer is normal seasonal movement, not a defect; permanent gaps, crush marks at edges, or gaps concentrated at perimeter indicate installation or acclimation problems.

• Subfloor flatness tolerance for wood flooring is typically 3/16 inch in 10 feet (or 1/8 inch in 6 feet); check with a 10-foot straightedge and record all high/low spots.

• Concrete subfloor moisture testing: calcium chloride test (ASTM F1869) results in pounds per 1,000 sq ft per 24 hours, or in-situ relative humidity probe (ASTM F2170). Follow the flooring manufacturer's stated limit; typical limits are 3-5 lbs or 75-80% RH.

• Inspector reports must be factual, dated, photographed, and non-adversarial: identify the condition, the probable cause, the standard violated (if any), and recommended corrective action - never assign legal liability.