How to Replace an Interior Door: Prehung Door Replacement
Follow these steps and get perfect results.
A full day
Less than $20
IntroductionLearn how to install a prehung door. We'll show you foolproof tips and techniques to help you do a great job even if you're a beginning carpenter.
- Cordless drill
- Miter saw
- Scribing tool
- 4d finish nails
- 6d finish nails
- 8d finish nails
- Interior door and trim
Project step-by-step (17)
How to Install a Prehung Door Overview
Check the floor
Check the floor for level and the jambs for plumb. Measure the exact amount the floor is off level. The opposite jamb must be cut by this much to level the door in the opening. Hanging a door correctly is one of the most satisfying jobs in the home improvement world, but it’s often the most challenging. Unless it’s installed correctly, your door can have uneven gaps along the jamb, or it can bind or not even latch.
In this article, we’ll show you foolproof tips and techniques that’ll give you great results every time you need to know how to install a prehung interior door. All you need are simple carpentry tools and some basic home improvement skills and tools to easily master the techniques. Allow about an hour and a half for your first door, and once you get the hang of it, your next door will go in twice as fast. When learning how to install a prehung door, follow these steps:
When you buy your door, pick up a package of wood shims and 4d, 6d and 8d finish nails. Also get a straight 7-ft. 2×4 and cut another 2×4 the width of your opening (Photo 1) that are both straight as you sight down the edge. Since installing trim is part of the door installation, purchase some matching door trim and be sure you’ve got a miter saw to cut it. You’ll also need to pick up a lockset for the door even though we won’t cover the installation in this article.
Pro Tips for How to Install a Prehung Door
- An accurate level is crucial for a good installation. Check it by laying it on a flat surface. Memorize the bubble’s position. Then flip the level end for end and check the bubble. If the bubble doesn’t settle in the exact spot, find an accurate level.
- Check the length of your prehung door jambs. They may be longer than you need. You may have to trim both sides to minimize the space under the door. In most cases, the door should clear the floor by 1/2 in.
- If you’re setting your door into adjoining rooms that’ll be carpeted later, you can hold both jamb sides 3/8 in. above the floor and avoid having to trim your doors.
- Use blocks to level jamb bottoms. If you’re installing a door on an unfinished floor and need space under the jambs for carpet, just rest the jambs on temporary blocks while you’re hanging the door. Adjust the size of the blocks so the bottoms of the jambs are on a level plane. Leaves a space of anywhere from 3/8 in. to 5/8 in. under the jambs, depending on the thickness of the carpet and pad.
- Check the plug. Make sure the plug that holds the door slab in place is the type that can be removed after the door is installed. If it’s not, sometimes you can cut off the plastic strap and insert the plug back in through the doorknob hole. It’s difficult to move the door when the slab is flopping all over the place, but it’s worse to install a door that won’t open.
- It’s not always necessary to use shims on the top doorjamb—the casing will hold it in place. And on new homes and additions, walls can compress as they settle and push down on the top shims, causing the jamb to bow down. Only shim the top jamb if you’re working with a 3-ft.-wide door, and the top jamb arrives bowed from the factory.
Level the floor
Use a level to check the floor. Rest a level across the opening and level it with one or more shims. Mark the shim at the thickest point, and measure the thickness of the shim at the mark. That’s exactly how much you’ll need to cut off the jamb at the opposite side of the opening.
Trim the prehung door frame jamb with a jigsaw
Mark and cut the jamb on the high side with a jigsaw (remove any packaging strips at the bottom of the jambs). If you cut more than 1/4 in. from the jamb, you may need to trim the bottom of the door so it conforms to the floor slope.
Trim the jamb with a circular saw
You can also use a circular saw to cut down jambs when they need it. Install an 80-tooth blade to prevent tearing out the wood veneer. It’s easy to cut off the wrong jamb, so make sure you cut the jamb that rests on the high side of the floor. It’s the one on the opposite side of the opening where you marked your shim. A rafter square works great as a saw guide.
The most critical step of any door installation is making sure the bottom of each doorjamb is at the proper height. If you’re installing a door on a finished floor and the floor isn’t level, you’ll have to cut a little off the bottom of one of the jambs. If the floor slopes slightly and the jamb isn’t trimmed to compensate, your latch won’t line up. You must check the floor with an accurate level as shown in Photos 1 and 2.
Check Your Rough Opening Carefully and Prepare the Door Before Starting
Nail on stops
Nail temporary cleats to the wall opposite the door opening to act as stops for the door frame. To ensure the jambs are centered in the wall, shim them away from the drywall slightly with a stack of three note cards as shown.
Set the door in the opening
Push the door and frame into the opening. Open the door and shim the bottom edge of the open door to keep the frame tight against the stops on the other side.
Check the rough opening
Make sure your door is going to fit into the opening. Measure the height of the opening, and then measure the width at both the top and the bottom. Next, check each side with a level. The sides don’t have to be perfectly plumb (they rarely are), but they do have to be close enough to allow adequate room for your door.
If your rough opening is 1/2 in. bigger than your door but the sides of the opening are each 1/2 in. out of plumb, that opening is not big enough to hang your door properly. Finally, check to see if the walls are plumb.
Shim and nail below the bottom hinge
Shim the bottom of the door frame about 4 in. up from the floor on the hinge side, making sure the hinge side is exactly plumb, and then nail it. Tape your level to a straight 2×4 as shown. Next, shim the center area of the jamb to straighten it and then nail it. Check the whole length with your straightedge.
Lock the strike-side jamb in place
Tack a 4-in. 1×2 to the front edge of the jamb with a 4d finish nail. Set up an even 3/16-in. gap between the door and the strike-side jamb. Then screw the block to the studs to hold the jamb in this position.
Nail near the strike plate
Shim and nail the strike side near the strike plate and then near the floor.
Break away the shims
Score the shims several times with a sharp blade and then snap them off to make way for the trim.
Attach the trim
Nail the trim to the door frame with No. 4 finish nails. Nail the trim to the framing with No. 6 finish nails.
In this article, we’ll focus on installing standard prehung doors. These have a door jamb that’s 4-9/16 in. wide and are made to fit into a 2×4 wall that’s 4-1/2 in. thick. This gives just enough of a fudge factor to have the jamb a bit proud of the wall surface on each side and to make up for any irregularities in the trimmer studs of the walls. Most openings will be about 82 in. high for standard doors, so that’s what we’ll focus on. If your wall is thicker or your opening is shorter, you’ll have other concerns we won’t cover here.
Before you order your door, check the width of your opening. It should be 2 to 2-1/2 in. wider than the door. This extra space gives you room to fit the jambs and the shims into the opening to hang the door. If your rough opening is 32 in., get a 30-in. prehung door. Also check the vertical sides of the rough opening to make sure they’re reasonably plumb. Openings that have a trimmer stud out of plumb more than 3/8 in. from top to bottom will make it nearly impossible to install the door. It would be somewhat like trying to put a rectangle into a parallelogram. Small variations from plumb are quite common, however. Checking both sides and getting familiar with any problems with the opening will give you an idea of how much and where to shim the jambs later.
Most installation problems occur because the floor isn’t level under the doorway. If the floor slopes slightly and the jamb isn’t trimmed to compensate, your latch won’t line up. You must check the floor with an accurate level as shown in Photo 1.
For complete directions, just follow our step-by-step photos and instructions.
How Do You Fit the Jamb to Floors of Different Heights?
Cut a 1-ft. long strip of 1/4-in. plywood the same width as your door jamb. Drop it to the high side of the floor, tack it in place, set your scribe and mark the contour of the floor onto the plywood. Remove the plywood, cut the shape with a jigsaw and transfer the shape to the bottom of the jamb. Cut along your mark with a jigsaw. Do this for each side of the door. If your transition is more than 1/2 in., you may need to trim the bottom of the door as well.
Set the door in place
Attach temporary to the jamb
To hold the doorjamb flush with the drywall before permanently fastening it, attach temporary blocks to both sides of the jamb. Use scrap lumber to make five 4-in. to 5-in. blocks, and attach each with 2-in. 18-gauge brads. Nail three blocks on the latch side and two on the hinge side (the door slab keeps the middle of the hinge side rigid). Keep the blocks away from the hinges so they won’t interfere with shimming. The casing will cover up the nail holes when the blocks are removed.
Nail the blocks to the wall
Set the door in the center of the opening. Make sure you have a consistent gap between the door slab and all three sides of the jamb. If the bottoms of the jambs were properly cut beforehand, the gaps will be consistent, the top jamb will be level and the sides will be plumb.
Double-check the hinge side for plumb before nailing the blocks to the wall with a couple of 2-in., 15-gauge finish nails. Nail the hinge side first, and then recheck the gap around the door slab before fastening the blocks on the latch side. The blocks will allow enough wiggle room for fine-tuning before the jamb is shimmed and nailed to the framing.
This is where things get serious. Nobody pays much attention to doors that work the way they should. They open—they close. But doors that were improperly installed can bind, swing open by themselves or rattle in the breeze when they’re closed. Follow these steps for a perfect door installation job.
Secure the door in place
Shim and nail the top corner
Center the frame in the opening. Slip a shim in from each side of the jamb (make sure the frame is pushed against the cleats) and nail the top sides of the door frame into the trimmer studs. The jamb should be perpendicular to your temporary cleats. Be careful not to twist the jamb as you nail it.
Check gap at stops
Before installing any shims, remove the plug that holds the door slab in place, and make sure the door opens and closes properly. The door should come in contact with the door stop evenly the whole length of the stop. If one side of the door hits the stop first, you’ll have to adjust the jambs by moving either the top side or the bottom side of the jamb in or out, depending on which part of the door hits first.
Shim behind hinges
Remove the center screw from all three hinges, and slide shims behind the empty screw hole, starting with the top hinge. Fill the whole gap evenly between the jamb and the framing or you’ll pull the door out of alignment when you drive in the screw.
If the framing on the rough opening seems to be twisted one way or the other, position your shims so the jamb stays perpendicular to the wall. Once the shims are in place, make sure the jambs are still flush with the drywall (if your walls are plumb).
Recheck the gap between the slab and the jambs. Recheck the gap between the door slab and the door stop. If this gap is more than 3/8 in., it’s best to split this adjustment between the hinge-side and the latch-side jambs; adjust the jamb so it’s only halfway corrected. And finally, nail the shims into place using three 2-in., 15-gauge nails.
Install longer screws in each hinge
Replace one factory screw in each hinge with a longer screw. Drive the screw in very slowly the last few turns, and pay close attention to the jamb. You don’t want to suck the jamb in and throw off the alignment of the door. Check all the gaps, and open and close the door after you install each screw.
Make sure the screws penetrate the framing a minimum of 1 in. The gap between the framing and this doorjamb was about 1/2 in., so we installed 2-1/2-in. screws. Don’t use drywall screws—they’re brittle and won’t hold up to years of abuse. Buy construction screws instead, and try to find one that’s close to the same color as your hinges.
Secure the latch side
Insert and secure shims 4 in. down from the top of the door and 4 in. up from the floor. Nail the shims the same way that you did on the hinge side.
We have repaired doors that were slammed shut so violently from the wind that the jamb on the latch side was knocked several inches out of place. To prevent this problem, install a long construction screw behind the latch plate. Predrill and countersink a hole in the corner of the latch plate space so it won’t interfere with the latch plate screws. Don’t use longer screws in the latch plate holes because they’re too close to the edge and can split the framing lumber.
When the door is in position, nail it into place. Follow these steps for foolproof installation.