Blog by Beebe Cline

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How to Install a Door

Installing a door used to be a very challenging project, attempted by only the most talented carpenters. The pre-hung door has leveled the playing field. The door slab is already mounted on hinges, the jamb is cut and sized, the casing is installed and in most cases the doorknob hole has already been drilled. Essentially, somebody else has already done a good bit of the door installation for you. If you follow these steps, a homeowner who's good with a level and hammer (or even better, a nail gun) can install a new door in less time than you'd think.

Time: Around 2 hours for someone who hasn't done this before
Skill level: Moderate
Cost: A pre-hung hollow core door costs about $65 at a big-box store.
Of course, you'll need a pre-hung door from the lumberyard. Big-box stores sell all the standard sizes.
  • Nail gun: Once you use a nail gun, you will never want to use a hammer again. You will also need a compressor and a hose.
  • Wooden shims: These wedge-shaped slivers of wood are very handy to keep in your tool box. For this project, they will keep the door from expanding and contracting.
  • Channel lock pliers: I prefer these over standard pliers. We will use these to remove staples.
  • Casing/trim nails or gun nails
  • Hammer: If you don't know what this is, please do not attempt this DIY.
  • Tape measure: See above.
  • Carpenter's pencil: Note that it's flat to prevent it from rolling away. This is a noble idea, but you will still lose it one day.
  • Safety goggles
  • 4-foot level: I prefer this over a 2-footer or the pocket "torpedo" level. The longer the level, the more accurate it will be. It also works great for a straight edge.
Doors come in standard sizes, usually measured in inches: 24, 28, 30 and so on. Many lumberyards label them by both feet and inches.

The standard rough opening height is 83 inches from the subfloor to the top of the opening.

The rough or framed opening should be two inches wider than the door slab. This allows for the jambs (the wood on either side of the door), plus wiggle room to get the door level and plumb. In this case, the rough opening measures 20 inches, so we'll use a small, 18-inch door.

Note: Doors come in right-hand (RH) and left-hand (LH) models. The easiest way to determine which door you need is to face the door on the hinge side. If you would normally reach out with your right hand to open it, you have a right-hand door. If you would reach with your left hand, you have a left-hand door.
Use your hammer to gently knock off these blocks. You can also twist these off with your hands or use the claw of the hammer. Remove any remaining staples with pliers.
Pull out the nails between the jambs that are holding the door together for transport. I've mistakenly nailed up a door with this nail still in place. Doing this won't make you feel very good about yourself, to say the least.

You'll also want to remove the staples that hold the front and back jamb together.
Pull the rear section away from the front section of the door.

I love this. Whoever invented the pre-hung door is a true genius in my book.
Place the door on blocks. This particular home will have a tile floor, so we have the door on 3/4-inch blocks. For a hardwood floor, also use a 3/4-inch block (or be nice and put in the door after your hardwood guy installs the floor). For carpet, use a 3/8-inch or 1/2-inch block. If you have really thin carpet, you may want to go lower. For a vinyl floor, just place the door on the subfloor.
Hold the door in the opening.

Ideally you want the doorknob on the same side as a light switch, so that when you open the door it's easy to turn on the lights. It's also nice to have a door open into a wall, so it can rest against the wall when it's open. Try coordinating your door in one of these ways. The side with the hinges showing will be the front side.
Hold a level against the hinges to make sure the door is plumb (level in the vertical position).
Measure the distance from the door to the closest wall at the top and bottom of the door. In my opinion, it is more important that these distances are equal than to have the door completely plumb. Your eye will compare how the door looks in relation to the wall.

If the wall itself is really out of plumb, I try to split the difference between the door being plumb and matching the distance off the wall at the top and bottom.
The gap between the jamb and the door must be consistent across the top. The same goes for the gap down the side.

Contractor's tip: You can cheat this gap by slightly altering the height of either side of the door. Lift one side higher off the blocks on the floor or remove a block and cheat the door down a bit. You can also push the top of the door assembly to the left and right to adjust the gap. Note: You will take the door out of plumb by doing this, so please check after altering the door to make sure it is close to plumb. Like all things in life, this only works in moderation.
I like to stick my finger through the space for the door knob and make sure the door lines up with the hole drilled in the jamb. This way you're sure the doorknob striker lines up with the strike plate.
Shoot or hammer a nail into the top hinged side of the door casing. Work your way down the door, equally spacing about four or five nails. I start at about the height of the top hinge and stop around the bottom hinge.

Check the following before nailing:

The door is plumb.
2. The distance from door casing to the nearest wall is consistent.
3. The door has a consistent gap at the top and down the doorknob side.
4. Check that the doorknob hole and the hole in the jamb line up.
I like to use the nail gun to put the nails close to the outside of the casing. In this case, there is a line grooved into the casing about 3/4-inch from the outside. It provides a nice target for the gun and accepts putty well, which will conceal the nail holes later. These nails are very important because they are the main anchors holding the door in place. If you do not hit the solid framing lumber in the wall, the door will not stay in place. The closer you get to the inside of the casing, the more likely you will miss the framing lumber.

If you have not shot a nail gun before, you will not be able to "feel" that you missed the lumber. Take a second to peek around the back side of the door to confirm you have not missed. If you see your nails, move closer to the outside of the casing. You can also pull on the side you just shot to make sure it is anchored.
After nailing the hinge side, shoot about five nails down the opposite side. Continue to check the consistency of the gap down this side.
Get ready to set the rear jamb into place.
Now you'll want to add shims to the door to fill any gaps. You can fill larger gaps by placing shims on top of each other in opposite directions — fat end to skinny end — and sliding them toward each other until the gap is filled.

Install the shims near the top and bottom on each side of the doorway. First, put the shims on the hinge side. The shims will fit between the jamb and the 2-by-4 framing. I like to place one set of shims just under the top hinge, and the other just above the bottom hinge. These will keep the door from expanding and contracting, and make the door system feel more solid when shutting the door.

Here, Mark Simon, lead carpenter on this project, used two full shims and slid the opposing ends together until they formed a tight fit. Install the shims just until they fit snugly in the jamb — do not force them in, or they may push the jamb outward.
Contractor's tip: I like to cut shims into 3.5-inch pieces, stack a few together and push them into the jamb. Then I'll shoot a nail through the jamb and the shims to hold them in place.
Slide the rear part of the jamb back into the slots.

Note: This door is made for 2-by-4-foot framing. If you are working in a basement, you may need to buy a door made for a 2-by-6 framed wall.
Nail in the jamb the same way you did on the other side of the door.
We will now lock the rear and front jambs together. There's a tongue and groove between the two jambs to keep them together. You'll need to secure that with a nail to make the door assembly into one unit and keep it stable when the door opens and closes.

Squeeze the jambs together with one hand and shoot a nail through the middle section. This can be a pretty tricky shot. If you are too close to the edge, it can split the jamb; if you are too far from the edge, you may not catch the rear jamb. I would recommend starting in the middle and working your way over until you feel it catch.

Be careful doing this with a nail gun, and keep your hand a safe distance from the gun. Yes, I learned this the hard way.
The finished product: An 18-inch, right-hand, single-bore, hollow-core, masonite, three-panel door with 356 casing.