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Installing and replacing doors

This section explains the how-to steps for taking out old doors and installing new ones. When buying new doors, most people get prehung units with the door already square & plumb with the jambs.

Installing a prehung door is usually easier, but not always possible. We'll take you through the steps of installing a door and jambs separately along with the hardware details.

Hanging a door can be a frustrating process the first time or two. Taking time to check for plumb/square/level throughout the project will prevent frustration and achieve good results.


Removing an existing door

  1. Take the door off the hinges or tracks.
  2. Remove the door casing (trim) on both sides.
  3. With a reciprocating saw or mini-hacksaw, cut through nails holding the jambs.
  4. If the door has a threshold plate, pry or cut it loose.

Framing a rough opening

On exterior and load-bearing walls you'll be removing a few existing wall studs that support the house. Therefore, the door's rough opening framing must take over the load.

In most cases, 2x4 or 2x6 lumber is used for side framing and two 2x10s (or larger) lumber makes up the header. Mark the outline of the doorway— 6" wider and 3" higher to accommodate framing. Make sure to remove any baseboard in the way.

Saw or chisel away the existing wallboard/plaster. Cut the existing wall studs in the new opening where the top of the framing header will be, or remove them completely if the header reaches the wall's top plate.

Remove the soleplate at the threshold. A reciprocating saw or hand saw is handy for this job. Cut two 2x4s (or 2x6) king studs to run the full length of the wall, or use an existing wall stud if possible.

Scab on trimmer studs to the king studs to support the header. Cut and fit the header on the trimmer studs and toenail the header to the king studs.


Installing door jambs

If you're putting in a prehung door, fitting the door into the jambs is already done for you. You just need to shim the jambs correctly into the frame. Whether you're installing each jamb separately, or installing a pre-hung door, getting the jambs in place is done basically the same way.

Shim the side jambs plumb/square with the opening and tack them in place. Test fit the header jamb and when it's square secure the side jambs.

NOTE: Place shims behind hinge and strike plate areas for secure fastening—especially exterior or locking doors.

Check for squareness again, shim if needed, and nail the header jamb in place.


Fitting the door

These are the extra steps needed if you don't have a prehung door. Compare the squareness of the jamb frame to the door. If it's not square or you're putting on an old door, it may be necessary to trim the door to fit.

TIP: Consider installing the door knob if it isn't already. It can help you control the door while test fitting and handling. (For more on that, check out our Door Knob Tips.)

When the door and the jamb frame are square to each other, adjust the gaps between the door and jambs—usually 1/16" at top, 1/8" on the knob side and up to 1/4" on the bottom. If installing carpet later, include that in bottom clearance.

Fit the door, block it with shims and check the gaps—plane the door if needed. When the door fits correctly, you're ready to mark the hinges.


Hanging a hinged door

Most doors have three hinges. A heavy or extra secure door may require more hinges. In this instance, we'll install the hinges to the jamb before fastening the hinges to the door. But some people screw them to the door first.

Mark and mortise the jamb hinges—usually 7" from the top of the upper hinge to the top of the door, and 11" from the bottom of the lower hinge to the bottom of the door. Center the middle hinge.

Locate the hinges to stick out slightly from the jamb so they won't "pinch" when opening/closing.Fasten the hinges to the jamb. Then fit the door and trace around the door hinge pieces (hinge leaf). Mortise out the door and fasten the hinges.

TIP: Don't completely tighten the screws to allow the hinges some "play" while getting the hinge pins in.

Tap the door pins in and test the door. If it opens/closes freely, you're ready to put on the door stop and latch hardware.


Shimming hinges

A newly hung door may bind or sag a bit, due to a jamb being out of plumb. Or accidentally making the hinge mortise too deep creates an uneven gap along the latch side of the door.

Both of these problems may easily be corrected by shimming a hinge or two with a cut piece of cardboard, thin flooring scrap, or in some cases a shim cut out to fit behind of the hinge.

Close the door and check the gaps. If the door sticks at the top hinge, shim the top hinge and snug the bottom hinge, and vise versa for a door sticking at the bottom hinge.

If the door sticks at the top knob-side corner, tighten the top hinge and shim the bottom hinge, and vise versa for a door sticking at the bottom knob-side corner.

Remove the hinge across from the gap you wish to close. Place the shim in the mortise and reattach the hinge over it. Note how much the door gap changed and shim other hinges accordingly if necessary. However, shimming out too thick will often make the shim visible.


Door knob tips

Do not try to install a door knob without an appropriately-sized hole saw. Go buy one—and a good quality chisel for mortising.

Most knobs and latch kits have instructions and a handy template to use, so we won't discuss actual installation here. In most cases, the knob and latch are located 3' from the bottom of the door.

With the knob on, locate the strike plate location by transposing the knob location measurements. A less conventional method is to "color" the knob latch point with pencil lead, turn the knob to retract the latch, position the door shut, and release the knob to mark the edge of the strike plate on the side jamb.

  Trimming your door to size
  Buying a new door

When selecting a new door, you will need to make a careful note of the overall size of the opening into which it is to fit. As you will no doubt find, door openings are rarely square or perfectly upright. The new door will need to be trimmed to suit.

Doors come in standard sizes, so you will need to choose one which suits, making allowance for trimming. Most doors can be trimmed to fit. Be sure to check the thickness of the door as this will also need to suit your frame.


Preparing the new door

Many new doors come with the stiles untrimmed. These ‘horns’ as they are called should be cut off square. Lay the door on your workbench and use a carpenter's try square to mark the cut line. Hold the handle section against the edge of the door and line the blade up with the bottom/top of the door. Mark the line and trim with a reasonably fine-toothed saw.

You should hold the saw so that it cuts cleanly along the line, but also pay attention to the angle of the blade in relation to the face of the door so that the bottom/top edge is also square.



Measure the width of the opening at the top and bottom but deduct 4mm, to allow 2mm clearance at both sides. Transfer these measurements to the door. If the door is only a little wider than the opening, measure from one edge and mark the cut line. If, however, it is a good deal larger, measure and mark the cut lines so that an equal amount will be trimmed from both sides. This is essential when fitting paneled or framed doors to ensure they appear symmetrical.

Now, measure the height and transfer the measurements in a similar fashion, allowing 2mm for clearance at the top and 6mm clearance for the floor. The latter may well need to be more if the floor is carpeted or uneven. If in doubt, take off the minimum. It’s always possible to take off more, but a little difficult to add more on!



Use a vice on your workbench to steady the door. Pack both sides with cardboard to prevent damage to the door. Trim to the marked lines using a sharp plane. The trick is to hold the plane firmly in contact with the surface, square with the edge, and run it along smoothly. Work your way gradually down to the trim line over the entire length. Avoid trimming a short section at a time as this will lead to an undulating surface.

When trimming the top and bottom, you must only work from the outer edge, in. If you plane towards the outer edge, the end of the stiles will split.

Where more than 6mm or so needs to be trimmed from the door, it makes sense to use a saw to cut the majority of the excess before finally planing down to the trim line.

Offer the door up to the opening and check the fit. If necessary, mark any additional trimming and plane as before. To help with this process, use a couple of small cheese shaped wooden wedges to hold the door off the floor by the appropriate amount. At this stage, any minor adjustments can be made from one edge rather than both without noticeably upsetting the symmetry.