Pre-Hung Interior Doors Are One of the Most Misunderstood Installations

Instructions for hanging a pre-hung door when the jambs will be painted.

Pre-hung interior doors are one of the most misunderstood installations. Consequently, one of the most feared. And it doesn’t have to be this way at all.

There are a series of simple, progressive steps that you can easily follow to hang a perfect door.

And a few tools and supplies.

First of all, the Rough Framed opening needs to be neatly done, plumb and square, and about ½” to ¾” larger in width and 1” higher than the frame of the door going into the opening.

STEP 1- Check that Rough Opening!

Measure the opening to verify that you have the clearance stated above.
Try to borrow a 6’ level if you don’t have one. Also have your 2’ level on hand.
Check to see that the framing is plumb and level in every direction and side you can get the 6” level to rest on.

Here’s a hint that will make leveling easier: Using double-sided tape, affix two identical small blocks of wood to the flat edges of the level, one at each end. These blocks of wood will enable the long length of the level to span any bumps or irregularities in the surface to be leveled. This will keep the level from “rocking” on an imperfect wall or stud. And you only need to have each of those two blocks resting upon the surface to be leveled to get a good, plumb reading.

STEP 2 - Check the level across the door opening on the surface of the floor.

Using your 2’ level, lay it on the floor where the door will sit when closed.
If it is good, or very close, you’re fine.
Now place the 6’ level across the opening, but this time put it on the face of both walls to check that the walls line up straight with other. They probably do (this is almost never a problem) If they don’t, just keep that fact in mind, and we’ll deal with it later when the jamb goes in. Proceed to STEP 3 if all is level and aligned.
But...If the floor is substantially higher (1/2” or more) at the side of the opening where the door will be hinged, you are still OK, but the door bottom may have to be trimmed off across the opening to look right and seal well.

(Now, this “trimming” can potentially cause problems as the finished door is swung open. We will check for that in a moment.)

If the floor is substantially higher (1/2” or more) at the side where the door handle will latch, you will almost certainly have to do some bottom trimming.

But, before we do any trimming, we also need to check the level of the floor wherever the door will pass above the surface of the floor in its opening arc. You know how sometimes you find a door that “scrapes” in the middle of the swing somewhere? Or a door that “wedges” itself tight to the floor when fully open? Aggravating, isn’t it? Well, that was all caused by someone not checking the floor “swing” area for high spots. You’re going to check, aren’t you?

If you find any high spots, I think you already know that may mean shaving just a tad more off the bottom of the door. But it also may not. It will all depend upon just how bad that “bump” is.

If it is real bad, the door may not be able to be successfully hung until the floor problem is fixed.

If it is only a bit off, and we are putting in carpet anyway, then we can deal with this situation later. Just remember that it is a glaring sign of a poor installation to have the door “scrape” the carpet. And it will soon wear an ugly arc in the carpet surface.

Trimming the door will be discussed at the end of this article.

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STEP 3

Now we are back to looking at trimming the door to make it look nice and level across the opening when it is shut.

We will first address a door opening that is high on the hinge side.

Always determine the future height of your finished floor. This will depend upon what’s going down on the floor in that room into which the door will swing. Is it going to be vinyl, tile, wood, carpet? Is the carpet going to be extra thick or have a thick padding under it?
These things are important to know (and by “knowing”, I mean knowing fully just exactly how thick any of your floor coverings will be.) You door has to clear them... all the way through the swing arc. Yet, you do not want the door set so high that there is a gap beneath it when it is firmly closed.
Unfortunately, this “fine tuning” part is going to take some initiative and estimation on your part. Remember this: You can always cut a little more OFF. Once it’s gone, you can’t put it back on the door.

Let’s say you’ve decided the carpet you’re going to put in that room (the one into which the door will swing) is going to need about 1” of clearance for the door to swing completely clear of it, yet still look good when closed. Well, all you do is measure down that distance you decided upon (notice how I leave this decision up to you?), and mark a square line across the back of the hinge side of the jamb. Cut it off neatly with a saw. It should now be your chosen distance longer than the door.

How much higher was the hinge side of the door opening than the latch side? Say 3/8”? Let’s use that measurement only as an example. (Remember, this is just an example to work with here; your numbers may be somewhat different.)

Hook your tape over the top of the hinge side jamb piece. That’s the outside top of the whole frame. Pull down to where you cut it off. It should read somewhere around 81 ¾” to 83”.

Now measure the other jamb from the outside top, and mark it 3/8” (our “example” measurement) longer than the hinge side. Now cut this one off too.... but cut it on the “wrong” side of the line so that you will end up a saw blade shorter than you intended for it to be. The reason for this will be explained later. You just want to be sure the latch side of the jamb is about 1/8” shorter than necessary for possible adjustments at installation.

Congratulations. You now have this door frame ready to install.

Trimming the door will be discussed at the end of this article.

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We will now address a door opening that is high on the latch side.

Always determine the future height of your finished floor. This will depend upon what’s going down on the floor in that room into which the door will swing. Is it going to be vinyl, tile, wood, carpet? Is the carpet going to be extra thick or have a thick padding under it?
These things are important to know (and by “knowing”, I mean knowing fully just exactly how thick any of your floor coverings will be.) You door has to clear them... all the way through the swing arc. Yet, you do not want the door set so high that there is a gap beneath it when it is firmly closed.
Unfortunately, this “fine tuning” part is going to take some initiative and estimation on your part. Remember this: You can always cut a little more OFF. Once it’s gone, you can’t put it back on the door.

Now it changes.

How much higher was the latch side of the door opening than the hinge side? Say 3/8”? Let’s use that measurement only as an example. (Remember, this is just an example to work with here; your numbers may be somewhat different.)

Hook your tape over the top of the hinge side jamb piece. That’s the outside top of the whole frame. Pull down to where you cut it off. It should read somewhere around 81 ¾” to 82”.

Now measure the other jamb from the outside top, and mark it 3/8” (our “example” measurement) shorter than the hinge side. Now cut this one off too..... but cut it on the “wrong” side of the line so that you will end up a saw blade shorter than you intended for it to be. The reason for this will be explained later. You just want to be sure the latch side of the jamb is about 1/8” shorter than necessary for possible adjustments at installation.

Congratulations. You now have this door frame ready to install.

Trimming the door will be discussed at the end of this article.

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Finally, we address a door opening that is pretty much level all the way across.

Always determine the future height of your finished floor. This will depend upon what’s going down on the floor in that room into which the door will swing. Is it going to be vinyl, tile, wood, carpet? Is the carpet going to be extra thick or have a thick padding under it?
These things are important to know (and by “knowing”, I mean knowing fully just exactly how thick any of your floor coverings will be.) You door has to clear them... all the way through the swing arc. Yet, you do not want the door set so high that there is a gap beneath it when it is firmly closed.
Unfortunately, this “fine tuning” part is going to take some initiative and estimation on your part. Remember this: You can always cut a little more OFF. Once it’s gone, you can’t put it back on the door.

Hook your tape over the top of the hinge side jamb piece. That’s the outside top of the whole frame. Pull down to where you cut it off. It should read somewhere around 81 ¾” to 82”. (To this point, this was the same as for both the doors above.)

Now it changes.

Now measure the other jamb from the outside top, and mark it exactly the same as the hinge side. Now cut this one off too..... but cut it on the “wrong” side of the line so that you will end up a saw blade shorter than you intended for it to be. The reason for this will be explained later. You just want to be sure the latch side of the jamb is about 1/8” shorter than necessary for possible adjustments at installation.

Congratulations. You now have this door frame ready to install.

Trimming the door will be discussed at the end of this article.

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STEP 4

Ready for the install.

Under all the bottoms of all your jambs that will sit on concrete, I want you to put either a piece of thin metal, or a small strip of roofing paper. Under no circumstances, anywhere in any construction, is any “untreated” wood to make direct contact with concrete or block walls. Installing your door jambs directly on a wood floor is no problem.

The key to a good door installation is mainly the correct installation of only one piece of wood, the hinge jamb. This simply means three things, straight, plumb (in all directions), and secure. Once you accomplish this, the rest of the door installation just naturally falls into place.

There are several ways carpenters go about this, but I will be telling you about only one. The one I think is the best. This is not to say someone else might not have a better way...... but they aren’t writing this.

This is the typicallayout for the average interior door. As you can see, this one has three hinges. Many only have two hinges. So when I write about placing nails or screws at the hinge locations, I will be referencing this drawing. You will have to adjust your thinking to allow for where the hinges fall on your own particular doors.

The first thing we are going to do is fit the studs on the hinge side with three sets of two opposing (pointing towards each other) wedges Called “shims”) at each hinge location.

In the case of the door shown here, measure down from the bottom of the Rough Header piece about 8- ½”, and make a mark. This should put you about in the center of where the top hinge will fall.

Then do the same thing for the center hinge, again shooting for a dimension that will hit the middle of the hinge location. In this case, about 38”. (You don’t have to be all that accurate with these measurements.)

Now finish off with a location for the bottom hinge at about 67”.

What we are going to do is place a set of two wedges pretty much covering each of those marks. The reason we chose to place the wedges at these hinge locations is because it is at the hinge points that the door’s weight is concentrated. So it is there we want to fasten the jamb to the stud for the best support. Fastening only at the hinge locations also helps keep from deflecting the jamb piece, and keeps the wood straighter.

Starting at the top mark, cover the mark with a wedge held horizontally, (That’s parallel with the floor), placed flat against the stud. Now overlap that wedge with a second one, right on top of it, pointing in the opposite direction. Try to keep these wedges spaced about equally, left and right. Drive a tiny nail solidly through the two wedges to hold them in that overlapped position on the stud.

Before we go any farther, we need to take a measurement. Measure across the door opening from the face of those two wedges to the stud on the other side of the opening. It will probably be around 34” if you are installing a “two-eight” door. (That’s a 32” door... Called a “two-eight” because 32” is “two” feet and “eight” inches.) The measurement we just took is bigger because we usually allow two extra inches over nominal door size when building the Rough Opening so that the whole frame will fit in there.

Now, let’s check to see that the frame, indeed, WILL fit that opening with the wedges installed. Is the frame, measured across the top outside, smaller than the measurement you just took? It should be about ¼” to ½” smaller. If it is, good.... we can continue. If it is not, then pull the nail, and spread those wedges apart some to open up some space across the opening... Re-nail the wedges, and recheck the measurement process.

If you have verified that we can get our frame in the Rough Opening (with the wedges installed) and we still have a little slack to play with for adjustments, we can go on to setting the middle set of wedges.

Here, a 4’ level is helpful. But you can also use the 6’ level with the wooden blocks removed (Or just use the reverse side of the 6’ level so the blocks don’t interfere.)

As you may have already noticed, sliding the two wedges back and forth on top of one another creates a thicker or thinner area that they occupy. Slide them both toward each other, and they make a fatter section. Slide them apart, and the section gets thinner and thinner.

You are going to slide these next two wedges either together or apart till a level spanning the previously installed top wedges and these new wedges reads “plumb”.When you have a perfect bubble on the level, put another tiny nail in this second set of wedges.

Now go on down and do this same sliding technique from the center wedges you just installed to the bottom set (at the bottom hinge mark).

When you are done, the surfaces of all three sets of wedges will make a straight, plumb line from top to bottom. Check it with the 6’ level. The three sets of wedges are now almost ready to have the door jamb installed on them. I say “almost” because most pre-set doors come with one set of the casing molding (one side) already installed on the jamb. Some even come with both sides installed. (Both sides is not cool, so we need to take at least one side off.) And we need to deal with the ends of the wedges sticking out past the wall before we can get the door in place.