Installing a door that already comes mounted in its frame may seem easy at first glance. You put the frame in the wall, screw it in, and you’re done. But in reality, there are a few pitfalls that can quickly turn this task into a headache.

Depending on the situation, it’s always better to learn from others’ mistakes than to experience them yourself. That’s exactly the goal of this guide. With a few good habits, you’ll save time and avoid unnecessary frustration.

Here are the 5 most common mistakes—and how to avoid them.

1. Not Checking the Frame for Level and Plumb

A door needs to be perfectly straight to function properly. Too often, people install the frame “by eye” or by relying on existing walls, which aren’t always straight. The result? The door starts rubbing or won’t close correctly.

Tip: Use a level before you start. Take the time to check plumb and squareness. A few minutes spent here can save you a lot of frustration later.

2. Forcing the Door Instead of Adjusting the Frame

When a door doesn’t close properly, many people’s reflex is to push harder, force it a little, or even shave it down. In reality, the problem usually isn’t the door—it’s the frame.

Tip: Use wooden shims to adjust the frame until the door opens and closes freely without resistance. The frame should adapt, not the door.

3. Forgetting to Leave Clearance Around the Door

Doors expand and contract with the seasons. Humidity and temperature changes cause wood to swell or shrink—even modern doors. If you install the door too tightly, it may jam with the first shift in climate.

For MDF doors, which are more stable, they don’t warp as much as natural wood. But they can still swell slightly in very humid conditions or when exposed to moisture (like in a poorly ventilated bathroom).

Tip: Leaving a 2–3 mm (about 1/8 inch) gap around the door is good practice, even with MDF doors—not because they “work” like wood, but to:

  • Prevent rubbing if the frame shifts slightly
  • Account for manufacturing tolerances
  • Compensate for small movements in the house over time

4. Screwing Too Quickly Without Shims

Some people fix the frame directly with screws, assuming it will hold fine. But without shims, the frame can warp and the door may end up crooked.

Tip: Place wooden shims at key points—near the hinges, latch, and middle of the frame. These will keep the pre-hung frame straight during installation and ensure the door operates properly.

5. Ignoring the Finished Floor

A classic mistake: installing the door without considering the flooring that will be laid afterward. The result? Once hardwood, tile, or vinyl is installed, the door rubs and has to be trimmed down.

Tip: Plan for the thickness of your finished floor before installing the door. Adjust the height so the door maintains proper clearance once the flooring is in place.

Conclusion

To sum it up: installing an interior door isn’t complicated, but it does require precision and patience. Check your levels, use shims, leave clearance, and plan ahead for the finished floor. These small details will make all the difference, ensuring your doors open and close perfectly for years to come.