Exterior Door Installation: How To Install A Prehung Door

This article is the last of a three part series on staining, finishing and installing an unfinished, pre-hung wood door. The first article, "How To Stain and Finish A Wood Door" covers choosing the right door for your application, unpacking it and staining it in preparation for replacing an old door. In the second article, I covered the removal of an old door and getting the doorway ready for a new door. Things like threshold preparation, squaring up the opening and what to look for once your old door is removed are all covered. In this last of the 3 article series, I'll walk you through the actual installation of the new door and finishing up.

door gap between door jamb and bricks

Before Installing Your Pre-hung Door 

So now you have your fresh finished wood door and you've put a nice finish on it and you're ready to install it. You need to make sure your completed door is back together with all the hardware and the door jamb it came with, put back together the same way you got it when it arrived.

When the door and jamb are together as a single unit, it will be much easier to square up your finished entryway and ensure that your new door will open and close properly. It's important to put any shims, plugs, and spacers back in where they were when you bought the door to ensure structural integrity during the new installation.

You may need an extra set of hands to help you set the new door in place because a fully assembled door can be pretty heavy.

So you have a finished pre-hung door and it's all back together with the hinges on and everything is lined up and in place. Once it's together the way it was when you bought it, you're ready to go..

On my project, I painted the door jamb at the same time I applied the finish on the door, while everything was apart. Even though I had to do a lot of touching up after the installation, it was a lot easier to achieve a nice final job than to try and paint the entire jamb after installation. When you do as much as possible to the new door before removing the old door, the installation is faster and easier. No one wants an opening in their home any longer than necessary!

sill, sub-sill and jamb of a prehung exterior door.

Preparing the Rough Opening for Your New Door

In preparing the rough opening, you need to secure a sub-sill or threshold "base" for your new door. I used a 2" x 10" and cut it carefully to fit into the opening of this doorway. This piece needs to be as close to level as possible.

Use a level to check it before gluing it in. Shims may be necessary to get it right. On mine, I used door shims on the right-hand side of the threshold and glued it into place using liquid nails. I used LOTS of construction glue! Perhaps half of a caulking gun sized tube. Liquid nails will dry hard eventually and create a nice base for the threshold.

Setting the Door and Casing into Place

Place the pre-hung door centered within the opening and check it on each side for plumb. Once you're happy with the placement, you can begin to slide shims in between the jamb and the studs. Do not force a shim in deeper than just slightly more than right after it touches both sides of the gap. During this step, you'll discover the importance of a level sub-sill.

The best places to shim on the opening side of the door are above and below the knob and deadbolt, about a foot off the ground and about a foot from the top of the jamb. On the hinge side of the door, shim just above and below the hinges - this will give it the most strength.

screws next to hinges will support your pre-hung door best

Securing the Door

You can use a nail gun and 2-1/2" trim nails to hold it in place, but you'll need to use some 3" (or longer) screws to drive through the jamb into the surrounding studs. Amazon has a nice selection of nail guns if you're looking for a new one. You can click here to check them out.

Counter-sink the screws, but do not over tighten them! Over-tightening will warp the frame and become bowed. Door trim that surrounds the finished installation adds strength on top of any screws you use and it will be solid once you're finished.

Shims can be broken off or cut off where they stick out. I insulated the gap between the pre-hung door and the studs somewhat loosely but made sure there were no voids anywhere before I put up the trim.

At the bottom of the threshold where the 2X10 met the concrete, I "caulked" the gap with liquid nails. (Yes, it will last for years and years!).

careful painting and clean caulk will add a nice finsih to your door installation

Trimming and Finishing the New Door

On the "indoors" side of my door, matching trim was used to cover the gap between the jamb and the interior walls. Brick molding that came with the new door covered the exterior gaps. You can see in the pictures where I drilled tap holes for my screws. After everything is screwed in and solid, you'll need to fill the holes and touch up paint after everything dries.

Then, I caulked everything nice and neat and installed the striker plate, knob, and deadbolt after removing the packing pieces that came attached to the prehung door from the manufacturer.

You may need to adjust the threshold and the sweep if your door has minor adjustments that need to be made, but my door did not. Everything fit really well.

Door is secured in place but no trim has been added yet

The door is installed but still needs trim and touch ups.

Completed installation of the prehung door with paint and trim

Complete new door.

Pro Tips For A Superior Pre-hung Door Installation

  • You can use a piece of paper to test the space between the sweep and the threshold. Close the door with a piece of paper under it. Pull out the paper. If there is no friction, the sweep is too high. If the paper tears, the sweep is too low.
  • Take your time and do a good job. A pre-hung entry door is a great investment and improvement in your home. Do it right. It isn't difficult with the right tools and some ingenuity.
  • Hire someone who really knows how to hang a pre-hung door the right way if you don't feel confident you can do it. It'll take you about 2-3 hours to do a good job, so plan accordingly on a nice day.
  • This was a great project. The unstained door ran just under $400.00 and after staining and finishing it, it looks and feels high end. Finding the right paint match for the trim helps a lot too.

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