Five Simple Steps to Installing a Prehung Door

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finished-prehung_doorLive from Los Angeles, California; it’s the Doors! Jim Morrison may be long dead but the doors are here to stay. No matter where you walk around your home’s interior, there’s probably an interior door to enclose an interior space. Closets, bathrooms and bedrooms almost exclusively use a 2-3 hinged style prehung door to keep areas secure when you’re doing the stuff you don’t want other people to see (or smell) you do. Installing a prehung door is a snap, so whether you want to replace your old doors or you’re starting from scratch with a new home or room addition, you can use these five simple steps to get your door hung right—without the job looking like Mr. Magoo did the work.

1. Measuring the Door

This is a confusing task—but only if you don’t know the secret trick. Measure the door opening at the top, center and bottom. It should be an even measurement like 30”, 32”, 34” etc. If it’s not, you might want to consider making the opening smaller to make a more common prehung door fit snug. Now take your doors rough opening measurement and subtract two inches. That new measurement is the size of the prehung door you need to buy. Big secret, huh? That’s why us contractors make the big bucks.

2. Choosing the Correct Swing

You also need to know which way the door will swing open; left or right handed. This can be a little confusing, but use this trick to figure it out. Stand with your back to the inswing of the door. If the door opens all the way to the left then it’s a left hand swing door, if it opens all the way to the right, it’s a-you guessed it, right hand swing door.

3. Prepping the Door

Prehung doors usually come with some sort of useless cardboard box covering that is designed to protect the door from nothing and to annoy the installer to their wits end. Remove the covering carefully and expose the door. In most cases, the door is held in place by staples along the inside of the two pieces of door trim. It can also be held closed with a plastic door latch inside of the door handle and striker cutout. You’re going to need a pair of pliers and a bible so you can get the staples out and pray they don’t break when you do it. The factory guys who put these staples in are stoners and should be drug tested immediately.

4. Separating the Door

Where the split in a split jamb door hides

It’s not called a split jamb door for nothing. Prehung (or split jamb) doors come apart so that each side of the trim sandwiches the drywall between the two, leaving a seamless installation, ready to go with minimal effort. Pull the door apart while it’s lying flat on the ground and set the trim portion aside. Pick up the door and the jamb section carefully and walk it into the area you are ready to install it, ensuring the hinges are on the correct side before you put it in place.

5. Installing the Door

finish-nails_bottom-hinge_side_FirstUsing a level and check the 2×4 stud opening for plumb. You may need to make adjustments to the 2×4 by adding wood shims to get the stud plumb for the door frame. Set the hinge side of the split door frame flush and tight to the subfloor, carpet, tile or other flooring material. Stick a finish nail in the bottom of the jamb’s trim. Now you can level the frame. Insert finish nails every 12 inches or so from the bottom of the trim to the top, ensuring the door is plumb as you insert each nail.

Next, close the door and adjust the opposite side of the trim so that the reveal (the gap between the door and the frame) remains consistent all the way around the jamb, and then nail the trim into place through the drywall and into the 2×4 stud.

Finish the job by slipping in the other split jamb trim piece onto the opposite side of the door opening. Close the door and adjust the trim so that the reveal remains the same around the opening before you nail it in place. Once complete (and, assuming it’s your own home) go ahead and do something secret and enjoy the beautiful privacy your new door provides!

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About Eric

Since Eric built his first skateboard ramp in his parents driveway; he’s breathed, slept and eaten DIY construction. As a second generation master carpenter who runs two Florida-based construction firms, Eric’s had the chance to work on everything from Mcmansions to your local mall to the cat lady’s bathroom. So when it comes to dealing with construction s@#t; he’s the man—literally. There isn’t a tool or construction material that Eric hasn’t used and abused, and if there is; it’s rocking in a dark corner nervously waiting for him to show up for work.

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9 thoughts on “Five Simple Steps to Installing a Prehung Door”

  1. Eric, are we not going to recommend shimming/fastening the jamb for long term durability? You must have seen trim separate from a jamb over time, making a (sometimes very tricky) repair needed; one that is more than likely beyond the ability of the average homeowner. Also, if your floor is not level and the hinge side is on the low side, you cannot adjust the frame to get an even margin/reveal across the top; you need to raise the hinge side. Check this before that first nail. I would also center the frame in the rough opening. (and i have never hung a door with it open…) i think you assume a level of common sense higher than i have witnessed in beginners; most might try to take the door out and hang the frame separately!
    My neighbors are not DIYers; their favorite tools are a ballpoint and a checkbook.
    best regards, billw

    • Thanks Bill, those are some great points!

      Shims on interior doors: sometimes I use them, sometimes I don’t. I only use them on pre-hung interior doors when the rough door opening is too big or out of plumb. To keep the door from separating, I always caulk the seams. It looks nicer when it’s painted and it keeps the doors together for good. Nailing into the inside trim on the door jamb and through the shims can make cheap finger jointed jambs split and crack way too easy. That’s why I only face nail the door trim and stay off of the jamb itself.

      The floor being out of level is another great point. That’s why I always put one nail into the bottom of the hinge side first and quick-check the reveal. If the doors reveal is too far out of whack for me to adjust it as is, I’ll jack up the hinge side of the trim with a shim before I start putting nails in.

      And yes, don’t hang the door while it’s open, center the pre-hung door in the rough opening and check to be sure the reveal is correct before you start banging a bunch of nails into the trim.

      Another point I just thought of was to check the swing of the door once it’s been nailed on the hinge side too. Sometimes the wall is out of plumb (not the opening itself) and it makes the door close or open by itself. If this is the case, put some shims behind the door trim to level the door to prevent ghost openers.

      • Eric, great point/fix on the ghost openers!
        I’m just a DIY and part time fixit guy for friends and neighbors; i have seen SO many split jambs where the trim separates from one side of the jamb and the jamb collapses into the slot. The hinge side of the jamb can be braced and nailed without much effort. The other side though… very difficult to renail without taking the whole half jamb off and just impossible without an air nailer. I usually have to use a screw into that jamb to hold it tight to the trim enough to air nail/staple. I’ll definitely try your caulk trick!! I’m also wondering if a pin nailer would be strong enough to stabilize that joint. Do you think if i shot a pin(23 gauge) every 8-12 inches it would hold that joint?
        regards, bill

        • Hi Bill, I thought I’d chime in here since I’ve been playing around with pin nailers a bit lately. I personally would not recommend them for the application being covered here. They’re great for small decorative wood trim, but their holding power is pretty minimal relative to other fasteners. Hope that helps and happy door hanging!

    • I would say yes to that Todd. But just to be safe, it’s always a good idea to get the specs on your new door from the supplier and ensure the rough opening is going to work for your French door.


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