Dear Pat: We are having a new room addition built and I am doing some of the work. I have to install two new interior prehung doors and replace one other. What is the proper technique to install one? — Kathy N.

Dear Kathy: Installing a prehung door seems like a relatively simple task because the door is already prehung in the frame. Actually, though, it is often done improperly even by professional builders and remodelers. In an existing house, it can be even more difficult than in the new addition because the house may have settled and the walls are not plumb to start with.

Signs of improper installation are doors that never close tightly in the frame. This is a particular problem during summer when the indoor air is more humid and the door may swell. Another problem is a door that swings shut on its own and never stays open without a doorstop under it. Even if the door does close, it may be very uneven in the doorframe, and this just looks bad.

I have seen an installation job so bad that the door swung the wrong way. Unless there is some unusual situation, interior doors should swing into the room, not out into a hall or foyer. Also, make sure the door has the hinges on the correct side. If they are on the wrong side, the opened door may block access to a wall light switch.

Once the rough wall openings are completed, measure them before ordering your prehung door. Typically, the rough wall openings should be a minimum of 2 inches larger than the door. This provides room for the jamb legs and about one-quarter of an inch of wiggle room for shims to true the door in the opening.

When the new prehung doors are delivered, make every attempt to find room to store them in the rooms where they will be installed. This allows them to acclimate to the room's air conditions. Never store them on a concrete garage floor because they will pick up moisture. If you have no other place but the garage to store them, first place a sheet of plastic film over the concrete floor.

It is important to make sure the sides of the rough opening are vertical. The hinge side is most important. If it is off more than one-eighth of an inch from floor to ceiling, the door may swing opened or closed on its own once it is hung. Also check for any protrusions (nails, screws, etc.) and cut them off.

Plumb the hinge-side trimmer stud with shims. Some people use just one tapered shim under each of the hinges. I prefer to use two tapered shims opposite one another so the surfaces are parallel. Once the shims are fixed in place, cut off any excess with a utility knife or saw.

For the door you are replacing, the flooring will already be in place, so you will know how much to cut off the bottom the jambs for it to fit. For the new addition, the finished flooring will likely not be installed yet. Use a tapered shim under the hinge-side jamb to raise it the appropriate amount for clearance over the future flooring. The final step is to tip the door and install it in place.

Send your questions to Here's How, 6906 Royalgreen Dr., Cincinnati, OH 45244 or visit www.dulley.com. To find out more about Pat Logan and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.