Remodeling projects often require cutting the bottom of an interior door. Installation of new floor covering often raises the height of the floor, causing the door bottom to bind against it and preventing proper operation. To solve the problem, remove the door from its hinges and cut the bottom shorter–but keep in mind, there’s a right way and wrong way to do this.
How Much Clearance Floor is Required?
For basic function of the door to swing open and closed, its bottom should clear all obstructions (floor registers, etc.) by at least 1/8 inch. Now, depending on the circumstances of the room in question, you might want more clearance to allow better return airflow throughout the house.
For example, we recently trimmed the door of a kitchen pantry which had no air-conditioning duct, so we kept the floor clearance to 1/8 inch because the homeowner preferred the look of a smaller gap, and the door had no issue with airflow. However, a bedroom with HVAC registers is usually separated from the air return by the door, in which case a very tight gap beneath the door may restrict the system’s airflow. A common symptom of this is a door that resists opening or that slams shut when the HVAC system activates, due to an air-pressure imbalance. In this case, a 5/8-in. gap beneath the bedroom door is considered standard. For floors with high-pile carpets, a larger gap might be necessary, and for venting the humid air of bathrooms, some pro remodelers recommend as much as 7/8-in. door-to-floor clearance.
How to Shorten a Door
Use a strip of plywood, cardboard or a ruler as a gauge to mark the cut height. Place the gauge along the painter’s tape and use it to mark a line along the width of the door.
Remove the hinge pins (always starting at the bottom and working upward), then remove the door, place on sawhorses and clamp it securely. It’s smart to first blanket the sawhorses to protect the door finish. Apply extra tape along the door bottom to protect the door finish from the saw base.
Use a square to mark the cut-line completely around all sides of the door.
Use a sharp utility knife and straight edge to repeatedly score the cut-line around all edges of the door. This is an important step because it prevents the wood veneer from chipping out when the saw teeth exit the door.
Equip a circular saw with a thin-kerf blade. For the straight cut, align a saw guide* along the razor-scored cut-line, with the blade kerf aligned with the waste side of the cut.
Set the saw’s cutting depth so only the tip of three teeth extend beyond the thickness of the door.
Carefully make the cut while holding onto the waste piece so it doesn’t fall away and chip out the wood as you complete the cut.
If necessary, touch up the cut with sandpaper–but if you follow these steps carefully, you’ll probably find no sanding necessary. Re-hang the door, and the job is done.
Side Note 1: Make a Saw Guide
If you don’t have a saw guide like the one shown in the photos, you can custom-make one to fit your saw, as I demonstrated at Extreme How-To several years ago.
Side Note 2: Matt’s Video on How to Shorten a Door
I made this video for ‘Extreme How-To’ a few years ago. Enjoy!