Engineered hardwood flooring is designed to minimize gaps due to expansion and contraction of the wood. But to answer a common question: Yes, it can still have gaps. Gapping in engineered hardwood can be due to many factors, including (but not limited to) the material's manufacturing, changes in humidity, and the type and quality of the installation.
How Engineered Flooring is Different
Wood expands and contracts with changes in humidity. It swells in high humidity and shrinks in low humidity. The amount of expansion and contraction largely depends on the orientation of the wood grain. Wood moves most across the grain rather than with the grain. Traditional hardwood flooring boards (and the top layer of engineered floors) are cut parallel to the grain. As a result, the boards tend to get wider and narrower (across the grain) more than they get longer and shorter (with the grain).
Engineered flooring essentially consists of a hardwood top layer laminated to a plywood core, or base. Plywood is assembled in layers using a technique called cross-graining. The grain of each layer is perpendicular to the grain of the layers above and below. As one layer wants to expand or contract side to side, the neighboring layers want to move front to back. Thus, the layers work against one another, with the result of minimal overall expansion and contraction. This is why engineered flooring is sometimes called "dimensionally stable."
Gapping Due to Humidity
A more accurate description for engineered flooring might be "relatively dimensionally stable." The plywood core of engineered flooring helps reduce gapping due to natural expansion and contraction, but it doesn't always eliminate it. And that explains one common cause of gapping in engineered flooring. It's also why installers should acclimate the flooring before installing it (discussed below).
One of the common solutions suggested for this problem is to carefully "condition" your home year-round to maintain ideal humidity levels. The idea is to run an air conditioner to lower humidity in summer and run a humidifier to raise it in winter. Unfortunately, this wasteful and environmentally irresponsible approach is the only possible remedy. Otherwise, you simply have to live with this natural drawback of wood.
Gaps Related to Installation
Engineered hardwood flooring can be nailed down, glued down, or "floated" (not nailed or glued to the subfloor). In all cases, the floorboards must be fitted tightly together during the initial installation. If not, and there are gaps between boards, the gaps are there for good, although they may shrink slightly during periods of high humidity.
Glue-down floors present some special challenges that can vex inexperienced installers. If the boards aren't fit together properly before the adhesive begins to set, any resulting gaps can be hard to correct. Even if the installer comes back and closes the gaps, the adhesive has a "memory" that can pull the boards back to their original position, opening up the gaps again. For this and other reasons, glue-down installation is best left to experienced installers.
A floating floor, the natural choice of most DIYers, involves click-together flooring that is simply laid over a foam pad underlayment. The best way to prevent gapping with this installation is to cut the boards the right size and to click them together properly, making sure there is no gapping with each board before moving to the next one.
With all types of installation, flooring manufacturers unanimously recommend acclimating the flooring for several days by laying out the material in the room where it will be installed. This allows the wood to adjust to the ambient humidity and temperature in the room before the flooring is installed. If an installer fails to acclimate the material, there's a potential for greater wood movement after the boards are installed.
Gaps Due to Material Flaws
The engineered construction of engineered flooring helps minimize the effect of natural flaws in wood, but it's still wood, and wood has some flaws. It's impossible to machine flooring with 100 percent accuracy in every board. As a result, some boards won't fit together perfectly. If a gap shows up when you're installing the flooring, try to find a board that fits better. Otherwise, if the gap is left in the floor, the only solution is to replace the board or to fill the gap with a color-matched wood filler.