How do I cut the bottom off a door?

The usual reason is a new floor. The job itself is not difficult, but three things catch people out: the door is not always parallel to the floor, so measuring at one point gives a wrong line; the veneer on the faces chips badly unless it is scored first; and hollow-core doors have far less material to remove than they look like they do.

Safety

Step by step

1. Work out how much you actually need to remove.Close the door onto the new floor level and find where it binds. Allow a small clearance — enough to clear carpet or a threshold strip without leaving a draughty gap.
2. Check what the door is made of before committing.A solid timber door has material to spare. A hollow-core door has a narrow solid rail at the bottom, and cutting past it opens the void. GuideHQ has a separate guide on that limit.
3. Mark the line with the door hung, not on the bench.Floors are rarely level and doors are rarely square to them. Mark the clearance at several points along the bottom while the door is in place, then join those marks. The line may not be parallel to the existing edge, and that is correct.
4. Take the door off and support it properly.Wedge it, take the hinge screws out, and lay it across trestles or a bench so the offcut is supported and cannot break away.
5. Score along the line on both faces.A sharp knife against a straightedge, cutting through the veneer or the paint film. This is what stops the face splintering as the saw exits, and it makes the difference between a clean edge and a ragged one.
6. Cut a millimetre or two outside the line.Leave a little material to remove by hand. Cutting exactly to the line gives you no way to correct a wandering cut.
7. Plane down to the line and ease the arrises.Work in from both ends towards the middle so the ends do not break out. Then run the plane lightly along the sharp corners to take the edge off.
8. Seal the cut edge before rehanging.A bare bottom edge absorbs moisture and is the reason many doors swell later. Prime or seal it, particularly on a bathroom or external door.
9. Rehang and check the clearance through the whole swing.Doors can clear at the closed position and catch halfway across the room, especially over a threshold strip or an uneven floor.

Common mistakes

• Measuring the gap at one point only. — If the floor slopes, the door will still catch at the other end. Mark at several points and join them.
• Cutting without scoring the face first. — The veneer chips out along the cut, and on a painted door the paint tears back in flakes. Neither can be repaired invisibly.
• Leaving the cut edge bare. — It is the edge closest to spills, mopping and damp air, and unsealed timber takes up moisture and swells.

Questions people ask