There will be a gap between the interior door and the wooden floor. How much gap should be left? The intuitive thought is: the smaller, the better. But how small is small enough? Generally, the door gap can be kept within 1 cm. Of course, it can be smaller, even down to 3–5 mm. However, the recommended minimum is at least 5 mm. Why? Because wooden flooring expands, and interior doors may also swell or warp. Leaving a gap of a certain size is safer for long‑term use. A slightly larger gap can also prevent sand or grit from getting stuck, which could scratch the floor when the door opens. If you prefer a very small gap, make sure the original subfloor is level enough; otherwise, the door may close but then be impossible to open (opening it would hit the wooden floor).