NWFA CWFI cheat sheet

Moisture content is measured with a pin or pinless meter; readings must be corrected for species and temperature, and a minimum of 20 readings per 1,000 sq ft is standard practice for establishing an average.

Equilibrium moisture content (EMC) is the moisture level wood reaches when exposed to a given relative humidity and temperature; typical interior EMC ranges from 6% to 9% in conditioned North American homes.

Wood flooring expands as moisture content rises and shrinks as it falls; movement occurs predominantly across the width of the board, with lengthwise movement being negligible.

A moisture-related gap or cupping complaint requires comparing the flooring moisture content to the subfloor moisture content and to the EMC of the occupied space; a difference of more than roughly 2-4 percentage points between flooring and subfloor warrants investigation.

Cupping (edges high, center low) indicates a moisture gradient with higher moisture at the bottom of the board; crowning (center high, edges low) indicates higher moisture at the top surface, often from a prior cupping that was sanded before drying.

Gapping between boards in heating season is commonly a normal response to low interior relative humidity; sustained interior RH below roughly 30% during heating is a recognized cause of seasonal shrinkage gaps.

Acceptance of a finished floor is judged under normal lighting from a standing position, not by raking light or close inspection; natural variation in grain and color is a characteristic of wood, not a defect.

Site-related causes of finish failure include inadequate acclimation, subfloor moisture, HVAC not operating, and improper environmental conditions; these are distinct from product manufacturing defects.

Inspection reports should document instrument type and calibration, number and location of readings, environmental conditions at inspection, and the moisture content of flooring, subfloor, and any framing members.

Acclimation is required before installation; flooring, subfloor, and building must reach moisture equilibrium, and the flooring moisture content should be within a few percentage points of the subfloor's expected in-service moisture content.

Concrete subfloor moisture is evaluated with an ASTM F1869 calcium chloride test (limit commonly 3 lb per 1,000 sq ft per 24 hours) or ASTM F2170 in-situ relative humidity test (limit commonly 75% RH), unless the manufacturer specifies otherwise.

Wood subfloor moisture content should generally be no more than about 12% and within 2-4 percentage points of the flooring, depending on the product and regional conditions.

Subfloor flatness tolerance is typically 3/16 inch in 10 feet (or 1/8 inch in 6 feet) for most wood flooring; excessive variation must be corrected before installation.

Expansion space is required at all perimeter walls and fixed vertical obstructions; the amount depends on flooring width, span, and expected seasonal moisture change, and is specified by the manufacturer.

Installation methods include nail/staple, glue-down, and floating; the method and any required underlayment are dictated by the product and the substrate, and deviation from manufacturer instructions can void warranties.

Sand and finish sequence: rough sand with coarse grit, progress through finer grits, screen between coats, apply finish per manufacturer's spread rate, and allow proper dry time between coats.

Job-site conditions at installation and finishing generally require interior temperature between roughly 60 and 80 degrees Fahrenheit and relative humidity between roughly 30% and 50%, maintained before, during, and after installation.

Inspection should reference the applicable NWFA guideline and the manufacturer's written instructions; where they conflict, the more restrictive requirement typically governs the installation.