If you are planning to make substantial changes to the flooring material in a room, then the chances are pretty good that you are going to have to shorten your doors. Makes sense right? If the level of the floor comes up because you added a heavy shag carpet, hardwood flooring or even a thick tile surface, then the bottom of the door is going to have to be raised as well. It may seem like a simple matter of taking the door off the hinges and cutting the bottom off. While in theory this is true, if you do not take some specific steps and do it correctly, you will substantially weaken the structure of the door and it may fall apart after minimal use.
There are two scenarios for shortening a door. The first is the easiest. It involves a solid door. Chances are, even if you have solid wood doors, they are still veneered. This means that when you cut the bottom of the door you will most likely see some kind of composite wood or particleboard. If this is the case, then you must paint or varnish the newly exposed wood. The bottom of the door acts just like a sponge and will soak up moisture and swell. If the door swells then you have several problems. First, it will warp and won't fit squarely in the door frame. Second, if it swells enough, if might not close at all. To prevent this from happening make sure that you seal all freshly cut wood. Two coats would be ideal to keep moisture from being absorbed into the door.
The second scenario for shortening a door is a little bit more complicated. This scenario involves a door that is hollow. These hollow doors are very common because they are relatively inexpensive. Since they are hollow, some care needs to be taken when attempting to shorten them.
First, you must understand how the doors are built. Each side of the hollow door is glued to a wooden frame. Sometimes this frame is made out of a product called MDF, which stands for medium density fiberboard. The boards that make up the frame are about 1 1/8" thick. This means, if you cut more than 1 1/8" off the bottom of the door, then you have cut the bottom frame of the door completely off. There will be an exposed opening at the bottom of the door which will not only ruin the structural integrity of the door, but will also allow moisture to circulate inside the door panels and cause them to warp.
In order to prevent this problem, you must salvage the bottom piece of the door frame (also called the bottom rail). Once you have made your cut, do not throw away the scrap. Using a utility knife, you should be able to separate the rail from the door panel that is glued to it. After you have freed the rail from the old panel, coat both sides with a heavy-duty wood glue and slide it back into the opening that was created when you cut the bottom of the door off. Use clamps to add light pressure until the glue dries. Now your door bottom is sealed and ready to be hung back in the frame.
A few words concerning Paneled Doors:
If you are planning on shortening a door with panels, then you need to make sure that you don't actually cut into the panel when you cut off the needed amount. Remember, the panel that is in the door has a tongue on it that extends about 1" further than the edge that you can see. If you make a mistake and cut into this part of the panel, then the door is ruined. The panel will just fall right out. The same principle is true for glass doors. Some decorative doors are made up of a wooden frame that has stained or leaded glass in it. Just like the paneled doors, you can't cut to close to the edge of the frame, or the door will be ruined. There must be enough frame left to contribute some structural strength for the door. Keep in mind that glass doors are very heavy, and they usually require a greater amount structural integrity than their wooden counterparts.
The final piece of information to keep in mind is to measure carefully. Always remember that it is easier to cut more off your door than it is to add it back on. Actually, it's impossible to add it back on so make sure you don't cut off too much or the door will be headed for the dumpster.
If you do come to the realization that your door cannot be cut down any further, whether because of panels or because it's already been cut down too much, then it is possible to order a reasonably priced custom sized door. Your local home improvement retailer should have suppliers who will manufacture a custom door for you at exactly the size that you need. While it may be a little more than the doors that you see on the sales floor, you may be surprised at how affordable they are. Though you can do this job on your own, ordering a new one may be the only answer in certain circumstances.
Brian Simkins is a freelance writer living in Chicago. He enjoys using his 14 years of home improvement experience to educate and equip new home owners.