How to Install a Pre-hung Door

Back in the 1800s each and every door was handmade by a carpenter to fit a particular doorframe. While this generally led to people having quality doors, it wasn’t very efficient. The amount of time it took to make one door hampered the construction industry and kept poorer people from being able to buy the quality doors they needed for their homes. In many cases, poor-quality homemade doors were used instead.

All of this changed when factory made pre-hung doors started to be manufactured in quantity. Pre-hung doors had several advantages over others, including that they are consistent in size. This allows carpenters to rough-in door frames, knowing that the doors they buy will fit in those frames. It also greatly reduces the cost of the doors, as well as the amount of labor required to install the doors themselves.

A large part of the time advantage that comes with pre-hung doors is that there is no question about the spacing of door hinges and locksets, as those are already cut into the door and frame at the factory. Since the factory does this with a template, the locations are extremely consistent, eliminating problems with doors binding or hinges squeaking due to strain on the hinges.

Just for clarity, in case you’re not familiar with pre-hung doors; what they are, are doors which are already installed into a door frame. Installing them actually consists of installing the frame into the rough door opening. Almost all doors are installed this way, so it is well worth knowing how.

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Pre-hung doors, Reuse Warehouse

Preparing the Door Opening for the Door

In most cases, you will be hanging doors into door openings which were created when the home was framed. If you are building the home yourself or doing a remodeling project which will require creating door openings, the 2”x 4” framed opening should be 1-1/2” larger than the door in both directions, to make room for the frame. So, a 36” wide door (standard size interior door) would need a door opening of 37-1/2” x 81-1/2”.

Walls with doorways in them are typically built with the footer going across the doorway, so that when the wall is stood in place, the bottom of the door frame is aligned properly. If the footer has not been cut out of the door frame, you will need to cut it (usually done with a sawzall, although an oscillating tool works as well) flush with the studs on either side of the door frame.

If you are cutting a doorway into an existing wall, this gets a bit more complicated, as you need to create the rough frame as well. This consists of double 2”x 4” studs on both sides and above the door. So, to install the rough frame, you’ll actually have to cut the existing studs back farther than the size needed for the door frame and then patch the drywall back in.

Doors are normally installed before flooring is. But if you have existing flooring and are cutting a doorway into an existing wall, you will not have matching flooring in the door opening itself. If you do not have matching flooring available to install there, you can solve the problem by installing a wood threshold.

How to Hang the Pre-Hung Door

Very little preparation needs to be done to the pre-hung door, before it is installed. But there are two things that you will need to do. The first is to remove the thin strip of wood that is nailed across the bottom of the door frame, holding the two sides of the frame spaced apart. The second is to remove the two double-headed nails that have been driven thought the door frame into the latch side of the door.

Please note that once you remove these items, the door frame will tend to be a bit wobbly. To reduce the risk of damaging the door frame, I would recommend waiting until you are ready to install the door, before removing the wood strip and then partially place the door into the opening, before removing the two double-headed nails.

You will notice that the door does not come all the way down to the bottom of the frame. This is done intentionally, so as to ensure that the door will clear whatever floor covering you are going to install.

Place the door and its frame into its opening, centering it so that there is the same amount of space on both sides. This should be roughly 1/8”, although it can vary, depending on how accurately the door frame was cut. Use at least two sets of door shims on either side of the door frame, to hold it in place, tapping the shims into place from opposite sides.

The door shims I am referring to are wood wedges about ¼” thick at the thick end and about eight inches long. They are used in pairs, inserting one from each side of the wall, so that they overlap between the door frame and the stud. Using them in pairs in this manner ensures that the door frame does not get twisted when nailed to the studs.

The edges of the door frame should be flush with the surface of the drywall on both sides, if the wall was built according to standard construction techniques.

You’ll want to nail the hinge side of the frame first, but before attaching the door frame to the studs, check it with a four foot level to ensure that is plumb in both directions. If the framing isn’t exactly plumb, you may need to adjust your shims to make up for it. Then, use finishing nails to attach the door frame to the stud, nailing it through the shims.

With the hinge side of the door frame attached, close the door and check the gap between the door and frame all around. If the gap above the door is uneven, it could indicate unevenness in the floor. That can be compensated for by cutting a small amount off the bottom of the frame on the latch side of the frame or by raising it up slightly off the floor. If you have to raise it slightly, slide a pair of door shims under the frame to support it.

The top of the door frame doesn’t actually have to be shimmed and attached, although some carpenters do so. If you choose to do so, it should be done in the same manner as the hinge side of the frame, nailing through a pair of shims.

The last side of the frame to be attached is the latch side. Once again, you want to check the gap between the door and frame, ensuring that it is consistent. Please note that you will need to adjust the positioning of the bottom of the frame to match the gap at the top, not vice-versa. A minimum of 1/8” of gap is required, to allow space for the striker plate.

As with the hinge side, you need to use door shims and nail through the shims with finishing nails to secure the door frame to the wall framing. Before nailing, check that the edges of the door frame are flush with the surface of the drywall on both sides.

Please note that you do not need to use a level on this side of the door frame, as the spacing is more critical than having the frame plumb. If you installed the hinge side of the frame plumb and kept the gap consistent, then this side should be plumb as well.

Finishing Off the Installation

There will be excess material from the door shims sticking out of both sides of the wall. To eliminate this, simply score both sides of the shims with a utility knife and then bend them to break them off. It should break fairly cleanly. If necessary, tap any protrusions sticking up with a hammer to flatten them.

To finish the pre-hung door installation, trim out the door frame with architectural “door casing” molding. There are two basic designs for this installation, even though there are several different styles of door casing. The simpler is to use just the casing, mitering the top corners at 45 degrees. In this case the door casing should be cut off at 90 degrees at the floor and should sit flush with the floor.

The second way of installing the molding is to use corner blocks at the four corners, cutting the door casing at 90 degrees so that it fits flush up against the edges of the corner blocks. In this case, the corner blocks are installed first and then the molding is cut to fit.

One final note, baseboard is normally installed after the door casing, so that it buts up into the casing or the corner blocks. If you are doing a remodeling job, you may have to remove the baseboard to install your pre-hung door and then reinstall it afterwards.

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