Engineered Hardwood Flooring

Solid hardwood is usually nailed into a wood subfloor, and it takes on moisture from whatever it sits on. Over a slab it picks up moisture from below and cups. Engineered's cross-laid core resists that movement, and it doesn't have to be nailed. It can float on an underlay or be glued down, so a concrete slab is no longer a problem as long as it's dry and flat. That depends on a real plywood core. Some boards put a wood veneer over a fibreboard core instead. They look identical in the box, but if water reaches them they react more like laminate.

On a slab, something has to stop ground moisture reaching the wood. That can be a plastic sheet under the underlay, an underlay with the barrier built in, or, for a glued floor, an adhesive rated as a moisture barrier. Concrete on or below the ground passes moisture up from the soil, and without the barrier the boards take it in.

Flatness matters more than people expect. For floating and glued floors, most makers set a limit of about 1/8 inch in 6 feet or 3/16 inch in 10 feet; nailed floors are allowed a little more. A floating board over a hump rocks and creaks. A glued board over a low spot never beds properly into the adhesive, and that patch sounds hollow when you walk on it. If a slab is outside the limit, the high spots are ground down and the low spots filled with levelling compound before the floor goes in.

In-floor heating is where engineered really pays off, but each product has to be approved for it. The usual rules are these. The heat is turned down before installation and brought back up gradually over several days afterwards. The floor surface is kept below the manufacturer's limit, which is often around 27°C. Nails and staples are avoided wherever heating tubes or wires run in or just under the subfloor. Area rugs also trap heat, so think twice before putting a large rug on a heated floor.

Engineered is more stable than solid, but it's still wood, and it arrives at the moisture level of the warehouse it came from. Before installation, the boxes should sit in the rooms where they'll go, with the house at normal living conditions: heat on, windows in, and drywall and paint dry. How long depends on the product. Some manufacturers want the boxes opened for a few days. Others want them kept sealed until installation. Follow the instruction sheet, because the manufacturer's warranty is written around it.

Moisture readings come before the first board goes down. Over a plywood subfloor, the boards and the subfloor should read within a few points of each other, and the product's instructions give the limit. A concrete slab is tested differently, against a separate limit the manufacturer sets for concrete. If either is out, waiting is cheaper than the alternative. A floor fastened down before it has adjusted to the house is the one that opens gaps in February.

Once the floor is in, the house matters too. Most manufacturers ask you to keep indoor humidity roughly between 35 and 55 per cent. Air in the Lower Mainland is damp most of the year, but a heated house in January can be very dry inside, and dry air opens thin gaps between boards. Some gapping that closes again in spring is normal for wood. Running a humidifier in winter keeps the gaps small.

And it isn't waterproof. A spill you wipe up is fine. Standing water, a slow dishwasher leak or a pet bowl that overflows every day will stain the wood and swell the edges of the core. For full bathrooms and laundry rooms, luxury vinyl plank or vinyl tile is the better choice, and the same goes for any basement slab that has ever been damp. We'll tell you so.