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Letter to the editor

Door hanging not a newbie's job

Experience helps when working with a prehung door.

By Tim Carter, Special to the Times
Published February 23, 2008

Q: How hard is it to install a prehung interior door? Is this job as easy as the salesman made it out to be? What can you share so that I might have a fighting chance as I wrestle with this door?

A: Installing a prehung door is not a job I would entrust to a rookie carpenter. The job is fraught with all sorts of little challenges that are solved with tricks that come with lots of experience.

First, let's define a prehung door. An assembled prehung door unit is a factory-built package with frame (jamb), applied door stop, hinges, beveling, bore, and backset, all completed, assembled, and ready to be installed as a single unit. Visit www.prehungdoors.info for a good walk-through of all these terms and pieces.

I am going to assume you purchased the right size prehung door and that it is handed correctly. "Handed" refers to whether the door opens on the left or the right.

Prehung doors often come from the factory with the jambs a little long. This is done on purpose so you can install the door in places where there will be carpet and not have to cut off the bottom of the new door. The goal is to have about a half-inch of airspace between the bottom of the door and the top of the carpet or any finished flooring material. The doorjambs don't have to touch the subfloor in carpeted situations, but they must be in contact with hardwood flooring, ceramic tile, cork or other finished floors that are typically smooth.

Before the door is installed, make sure the top and bottom edges of the door are painted. Lay the box flat on the floor and open it to see if this was done at the factory. It is important to have the top and bottom of doors sealed to prevent warping.

Prehung doors typically come from the factory with a 1/8-inch gap between the edges of the door and the door jamb. The doors are almost always perfectly square, so the challenge is to square up the jamb within the rough opening so the gap between the door and the jamb stays consistent. The biggest challenge is cutting the lengths of the jambs correctly so the gap at the top of the door is correct. If one leg of the jamb is too long, you will end up with the door rubbing against the top jamb or a gap between the door and the jamb just above the doorknob.

Doorjambs must be installed plumb. Use a 4-foot level to see how plumb the rough opening is on the hinge-side of the door. Use wood shims with the level and tack the shims against the jamb until the level is perfectly plumb. It is best to install shims at the same height as the door hinges.

Put the prehung door into position, slide it up against the shims, and see how things look. You know you are in great shape if the gaps along the hinge side of the door and the top of the door are the consistent 1/8 inch. Don't worry for now about the gap along side the doorknob side of the door. This is the least important jamb.

Use 10-penny finish nails to attach the hinge jamb of the door to the rough jamb. Carefully nail through the jamb and into the shims. Do not drive the nails completely into place. Leave at least 1/2 inch of the nails exposed in case you need to make adjustments to the length of the door jambs or you have to move the jambs slightly in and out so the door fits perfectly. Once all adjustments are made, all shims are in place and the door fits well, then you can drive the nails home, recessing the nail heads with a nail-setting tool.

To add a professional touch to your installation once it's complete, temporarily remove the top hinge from just the doorjamb. Doors are heavy, and over time the weight of the door can actually pull the jamb away from the finish nails. This will cause the door to rub and not fit well.

Drive a 3-inch-long screw through the jamb into the rough jamb at this upper hinge. Now the door should stay put for many years. Predrill the hole so you do not split the jamb. Create a countersink hole so the head of the screw does not touch the back side of the hinge once the hinge is reinstalled.

Some carpenters just remove one of the regular short hinge screws and replace it with a longer one that will penetrate into the rough jamb. This method will also work.

When shimming the jambs, place the shims at roughly 2-foot intervals, and always nail through the jamb at a location where you have installed shims.

Tim Carter is a licensed contractor. To view previous columns or tap into his archive of information and sources of building materials, visit Ask the Builder at www.askthebuilder.com. You can write to Tim Carter at P.O. Box 36352, Cincinnati, OH 45236-0352.

[Last modified February 22, 2008, 16:45:47]