How to Install a Door

A new door in 1 day? Let our old pro teach you a few new tricks!

A seasoned pro shows you how to replace a front door, step-by-step, including measuring and ordering a new door, removing the old one and ensuring that the new one goes in perfectly square and level and is fastened securely.

By the DIY experts of The Family Handyman Magazine


One day




Over $500

Step 1: Measure the old door and order the new one

One of the biggest mistakes homeowners make is to grab a door off the home center shelf and expect it to fit right. So my first coaching task was to help Robin and Danny measure for and order the door. First we measured the width and height of the door. Then Robin carefully pried off the interior trim (Photo 1) so we could measure the rough opening, which is the width between the studs and the height from the floor to the header.

“Protecting the wall with a putty knife saved the wall paint. Neat trick!”
— Robin

Next we measured from the back of the outside trim, or brick molding, to the face of the interior wall to find the jamb width. Ordering the new door with the right jamb width ensures that the interior trim fits without the need for added jamb extensions. Finally we went back outside and measured the width from the outside of the brick molding and the height from the bottom of the sill to the top of the exterior trim. To avoid having to patch siding, it's best to order a door assembly that will fill the space. This may mean asking for special exterior trim that's wider than standard 2-in.-wide “brick molding.” If you're ordering a door and sidelight(s), you can adjust the width by substituting a different size sidelight or by adjusting the space between the door and the sidelight. The door and sidelight were assembled at the plant and arrived as a single unit. Installation of a door without a sidelight is the same.

With the door size, jamb width and dimensions of the rough and exterior opening in hand, Robin and Danny went door shopping. They discovered that the standard configuration of a 3-ft. door and sidelight was a few inches too narrow and 1/2 in. shorter than their existing door and sidelight. The salesperson recommended spending a little extra money to add a spacer between the door and the sidelight. This corrected the width problem. Robin and Danny could have ordered a custom height door and frame for several hundred dollars more, but they decided to live with the height difference and cover the gap with trim later. We decided to add a strip of plywood under the sill to raise the door slightly, so in the end the shorter height worked out perfectly.

“I was shocked at all the door options available. The choices were limitless.”
— Danny

Robin and Danny wanted a door that looked like wood, minus the maintenance hassles. They chose a Therma-Tru fiberglass door with a surprisingly realistic-looking oak wood grain. The cost of the door and sidelight unit was $1,300. Fortunately (for us, anyway!), the door assembly plant wasn't too busy and the door was delivered about 10 days later.

Step 2: Remove the old door

Robin was surprised at how easy the door and frame were to remove, especially after the interior and exterior trim were off (Photos 1 and 2). And she got to learn a new skill—operating a reciprocating saw (Photo 3). If you don't have a recip saw, you can use a hacksaw blade.

Step 3: Prep the opening

Working in older houses or where the door is exposed to the weather, I often have to repair a water damaged subfloor or otherwise rebuild the sill area before installing the new door. In this case, the subfloor was in good condition, but we noticed that the new door sill was thinner than the old one. After taking a few measurements, we decided to add a strip of plywood over the subfloor to raise the door so it would clear the entry rug (Photo 5). Robin checked to be sure the sill area was level. We could have shimmed under the plywood with strips of building paper or scrap vinyl flooring to level the floor if necessary.

Since our door was covered by an overhanging roof, we didn't need additional protection from water, but if you install a door that's exposed to the weather, be sure to add a sill pan to protect the subfloor (one brand is Jamsill Guard, and a metal drip cap over the exterior trim.

Step 4: Set the new door in place

With the old door out and the opening prepared, we were ready to install the new door and sidelight. Before we started, I explained to Robin and Danny that our goal was to set the new door frame in the opening and then adjust it with shims until the door fit perfectly. First we removed all the packing material from the new door and hoisted it into the opening to check the fit. The width was a little tight. We didn't have much wiggle room between the siding and the brick molding, but it was obvious we could make it work. So we removed the door unit and Danny applied heavy beads of polyurethane caulk to the sill and exterior sheathing (Photos 6 and 7). Danny and Robin moved the door to the opening and tilted it into place (Photo 7).

Step 5: Shim, square and fasten the frame

Now we were ready to tack it in and add shims. Shimming a door is the most critical part of the installation since it's when you tweak the frame to make the door fit perfectly and operate smoothly. I helped Robin and Danny center the top of the door frame with an equal caulk space between the siding and the trim on each side, and then tack the two top corners with 16d galvanized casing nails, letting the heads stick out so we could make adjustments later if necessary (Photo 8).

Next, Robin held a level to the hinge-side trim while Danny pried on the frame until the jamb was plumb (Photo 9). We drove another nail at the bottom of the hinge-side jamb to hold the frame plumb. With the door temporarily tacked in place, Danny and I headed around through the back door with a couple of bundles of wood shims. I gave him pointers as he wedged pairs of shims behind the hinges and along the top and far side of the frame. The goal was to create an even gap between the door and the frame (Photo 10). The key to shimming is to look at the gap between the door and the frame, and then decide how you can wedge the frame to correct any problems. We spent about 45 minutes adjusting shims before we were satisfied with the way the door fit.

“I didn't know that shimming a door was such a fussy, time-consuming job.”
— Danny

Nails through the exterior trim hold the door frame temporarily, but they don't offer enough support to keep the door square over time. For that we still needed to drive 3-in. screws through the jamb and into the wall framing (Photo 11). We drove the screws at the shim locations to hold the shims in place and avoid bending the jamb. Then Danny set the nails that we had left sticking out and added nails about 16 in. apart along the exterior trim. After Danny completed this step, he made one final check of the door's fit in case adjustments were needed before we added insulation and reinstalled the interior trim.

Step 6: Add the finishing touches

It was a relief to have the door securely installed. Robin and Danny relaxed, knowing they could lock the door for the night. I didn't have to warn Danny about the dangers of squirting too much expanding foam into the space around the door (Photo 12). He'd already learned that the hard way. With the space between the door and the frame well sealed and insulated, we moved to the outside, where we fitted a piece of trim over the door and caulked around the brick molding to seal the exterior. Now all that was left to do was install new interior trim, finish the door and install the new handle and lock.

Required Tools for this Project

Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.

  • Hammer
  • Tape measure
  • Caulk gun
  • Drill/driver, cordless
  • Countersink drill bit
  • Level, 4-ft.
  • Hearing protection
  • Pry bar
  • Putty knife
  • Reciprocating saw
  • Safety glasses

You'll also need leather gloves.

Required Materials for this Project

Avoid last-minute shopping trips by having all your materials ready ahead of time. Here's a list.

  • New door
  • Wood shims
  • Polyurethane caulk
  • Galvanized casing nails, 16d
  • Screws, 3-in.
  • Minimum expanding foam
  • Door latch and lock

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