Log in to view the full article
The Problem
I was called to inspect the wood flooring in a home in the low country of South Carolina. The plank floors were showing signs of cupping. When I did the inspection in May, the floors had been installed for approximately four weeks.
The Procedure
Because of high ebb tides and storm surges from hurricanes, houses built in the flood plains near the ocean must be built on piers. This particular house was built 15 feet high and was located in the flood plain of the Ashley River on an island near Charleston, S.C. It was a model home in a new development. The wood flooring—solid 5-inch-wide hickory plank—was installed in the entire first floor, stairs, and the landing at the top of the stairs.
The first shipment of wood flooring had been refused and returned to the mill. Within three to four days after the replacement wood arrived in the retailer's warehouse, the general contractor demanded the wood be installed, and the retailer complied. The wood was taken to the house, and installation started the next day. I was told that no moisture readings were taken.
The Cause
When I arrived, the temperature inside the house was 87 degrees Fahrenheit and the relative humidity was nearly 60 percent. The HVAC system was not turned on.
I did many random moisture tests with a pin meter. The results averaged 10.2 percent moisture content (MC). I did several moisture tests of the double layer of plywood. The results averaged 12.5 percent. In this area of the coastal region, 12 to 13 percent MC readings are normal.
I also measured a 20-board run. Each of the planks had swollen 1 / 64 to 1 / 32 of an inch. The average MC for each board was almost the same as the random MC test (10.2 percent).
By this point, the analysis of the case seemed simple—the wood was not acclimated—but, there was even more. I did tests for the nailing pattern/schedule and found that the schedule was irregular. The fasteners ranged from a few inches to more than 12 inches in many locations. For plank flooring this wide, the recommended distance is 8 inches. In addition, the interior environment was not being maintained to NOFMA and NWFA standards.
The choice of wood also was a consideration. Plank flooring has a natural tendency to cup slightly due to its width and grain orientation. However, this is a hickory, which has a tangential dimensional change coefficient (or shrinkage/swell ratio) of 0.00411. That ranks it as one of the more volatile common wood flooring species in terms of shrinkage and swelling. This ratio can be used to predict how much the floor may shrink or swell with loss or gain of moisture. To calculate this, you simply multiply the width (5-inch) by the shrinkage/swell ratio for the tangential cut (for hickory, 0.00411), which in this case equals 0.02055 for each percentage of MC gained or lost. Multiplied over the entire width of the room, this becomes significant movement.
It is because of these factors that wood flooring must be properly acclimated to the site. Wood is typically dried to a MC between 6 and 9 percent.
The MC of the subfloor, remember, was 12.5 percent. The wood cupped because of too great a MC differential between the plank flooring and the subfloor.
How to Fix the Floor
While many cupped wood floors can be saved after the MC stabilizes by sanding and refinishing, this one, because of the incorrect nailing pattern and/or lack of fasteners, could not be saved. It required removal of the existing floors and installation of new flooring.
In the Future
Who was at fault? The GC who demanded installation before it acclimated? The retailer for agreeing? The installer for doing it? In my opinion, there was enough blame for everyone!
Many wood flooring contractors get into similar trouble because of pressure from builders or homeowners to install the flooring before it has acclimated. They feel that if they insist on the recommended job-site conditions (building closed in with all windows and doors installed, HVAC system running for at least 48 hours, job site at "normal living conditions," all wet trades such as drywalling and painting completed), they'll lose business. When they ignore these requirements, they do generate more business—for inspectors such as myself. And, in unfortunate circumstances such as this one, they usually must assume the full financial responsibility for the failed floor.
It isn't always easy, but don't take chances with your customers' floors. Acclimate the flooring, take MC readings of the subfloor and wood flooring, and document those readings. Make sure they're within the correct range before you install the flooring.