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Exterior Doors: How (Not) to Install Them

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I have "muddled through" many home renovation projects and enjoy sharing my discoveries of how (not) to do it yourself.

The before picture.

The before picture.

DIY Exterior Door Replacement

Sometimes an exterior door is out of sight or only gives access to a seldom-used space, so you don't notice that it's rotting away. But if you let it sit too long, you risk water leaking into the surrounding area and causing rot in more than just your door.

Don't let one of your doors turn into the shredded remains of the door you see in the photo below. This door was either not meant for exterior use, or the plywood repair was inadequate.

Repairing or replacing a door doesn't have to be hard or very expensive. This project was probably 6–8 hours of work, spread over three afternoons, and it cost less than $200.

So do as I say—and not as I did.

Below are pictures of the "stuff"—a basic steel-sheathed door (pre-hung of course, it's way easier), a vinyl brick molding kit, a lockset, and some spray caulking. It's not too tough to cartop the door home, as you can see.

The door was in stock at about $115 at a prominent "big box" retailer. It pays to shop around, apparently; the other guys would have had to special-order a "left-hand outswing" door and would have charged about $75 more.

For those unfamiliar with this terminology, "left-hand" means that the knob is on the left, and "outswing" means that the door opens outward, toward you. "Outswing" was necessary since there wasn't enough clearance inside for the door to open, and "left-hand" was desirable to keep the user safely away from the edge of the deck onto which this door opens. (You'll see the layout in some of the later pictures.)

Note The terminology is not always consistent--although the foregoing reflects the discussion I had at the store (a somewhat confusing one!). This type of door is elsewhere termed a "right-hand reverse" door. (See comment by reader "D Best" below.)

This reflects the placement of the hinges, not the knob, while "reverse" refers to the "outswing"—since an outswinging door is the less common of the two possibilities. A diagram and discussion are here:

Door Swinging Wikipedia

The first step is to pry off the old brick molding—that's the trim that surrounds an exterior door. It's quite straightforward, as illustrated in the photo. If you're lucky, it may be possible to remove it in one piece and reuse it—but it's hard not to break a piece, even if you are careful. I'd already decided to replace the molding, so I didn't even try.

Use a pry bar to remove old brick molding.

Use a pry bar to remove old brick molding.

Here's the decayed framing I mentioned above. You can see a bit of the white door casing at the top of the frame; I cut it away in places to facilitate its removal. Clearly, this rot damage is a very, very bad thing.

Decayed framing.

Decayed framing.

Here, I've cut away all the decayed wood in the studs (the upright pieces.) Still to be removed is the rotted portion of the joist (the horizontal piece resting on the concrete floor.)

Cutting away the rotten joist wood was the hardest part of this repair—it's tough to saw up to the edge of the wall, but not into it, and there was very poor access to the area I needed to work on. I actually used a small chainsaw, working with elaborate caution. (I don't think I'd recommend that to you—but that is what I used).

Decayed studs cut away, removing all rotted wood.

Decayed studs cut away, removing all rotted wood.

Having removed the rotten wood, the next need is clearly to replace it with sound wood. The method I used was to "sister" pieces together. That means that in addition to the piece replacing the rotted wood, a "backing piece" which overlapped the joint between new and old wood was added for strength and stability.

That's part of the reason that the two old studs were cut away at different heights, as shown in the photo above: it created that overlap in joints, giving decent rigidity to the repair without the need of a separate sistered backing piece.

The photo below shows the sister piece atop the joist.

I thought I had a nice picture of the sister studs, but apparently not. Still, you probably get the idea.

Before you start installing your door, read the instructions.

Or perhaps I should say, "read the instructions as best as you can?" The ones that came with my door were quite generic, relating to many different models in the company's product line, and were not always as clear as I could have wished. Still, I was glad I took the time; reading them was more helpful than not.

Start by fitting the door into the rough opening to see how well—or ill!—it fits. In my case, somewhat on the "ill" side; I'd made some sort of error in the vertical measurement, and the rough opening was too big for the door I had purchased!

Possibly I was guilty of assuming that the existing door was the standard 80 inches, whereas it appears to have been roughly 82, or possibly I confused the dimensions of the door with those of the rough opening. Author Scott Grice gives the allowances for sizing the rough opening thus:

". . . 3/4 in. for the jamb, 3/4 in. for finish flooring, 3/8 in. for underlayment, and 3/4 in. for wiggle room at the top of the door, and the top of the trimmer (the bottom of the header) needs to be 82 5/8 in. above the subfloor."

(Since my door would be over the concrete, no allowance for flooring or underlayment is required, reducing the correct rough opening size to 81 1/2".)

It probably wouldn't have affected my buying decision, had I realized the discrepancy prior to buying the door—it's cheaper and faster to adjust the framing a bit than to custom order a special sized door.

Still, good luck isn't guaranteed, and you should exercise the care that I somehow failed to. (You can clearly see the gap between the original rough opening and the top of the door in the closeup photo.)

Well, easier to fill in space than to enlarge it. I just added a piece to the top of the rough opening to adapt opening to the door.

That done, the door could be "shimmed" in place. "Shims" are wedges, used to adjust and secure doors and windows in place prior to nailing or screwing them to the framing. You can buy packages of them cheaply anywhere building supplies are sold.

The whole point is to ensure that the door or window is really and truly plumb and level. ("Plumb" means exactly vertical; "level" means exactly horizontal—in BOTH horizontal dimensions!) If this is neglected, you are putting your installation at risk of not operating properly—your door may not latch properly, may not close, or may tend to swing open annoyingly.

Use your level liberally, and recheck as much as you need to to be certain! I did.

Unfortunately, I was so intent upon this laudable and necessary goal that I forgot something else.

One of the best parts of the installation instructions I got was the bit about how to shim the door correctly. Basically, it had you start at the bottom, then do the top corners, then work from the bottom up, checking and rechecking as you went.

The first thing it said was the center the door in the opening. I didn't.

You see, the opening was a bit on the large side, and I was a bit short of shims and didn't want to run out for more. Since I had already found that the stud at the right side of the doorway was beautifully plumb, I decided to shim hard against that stud instead. What I didn't realize was that that would complicate caulking and the installation of the brick molding when the time came to accomplish those steps of the process.

So do as I say, and not as I did. . .

Door installed.

Door installed.

Here's the door, installed and the gaps around the frame caulked. You can see the ragged edge created by the spray caulking on the left, and contrast it with the nice clean line at the right. Note, too, the gap filled at the top.

Well, the "uncentered approach" wasn't the best way to do things, but it wasn't too, too terribly bad, either.


The next thing was the installation of the lockset. Pre-hung doors come with the appropriate pockets already routed into them, and into the casing, so installation is pretty easy—just a matter of checking that latch and strikeplate line up OK, and screwing the hardware in place. Everything you need is included, barring tools of course.

You can probably figure it out on your own, but it may be a bit easier securing the knobs before the latch or vice versa, so check the instructions for the recommended sequence.

Checking fit on new brick molding.

Checking fit on new brick molding.

Once your door is latching correctly, you are ready for the brick molding. Here, you can see that I need to trim the siding a bit. That's one of the consequences of my failure to center the door in the opening.

One of the other consequences is that I had to be a bit more careful in placing the nails I used to fasten the brick molding; the nails had to go into the wood, not caulk, after all!

By the way, a simple mitre box is invaluable in trimming the brick molding to size, especially if you need to trim the header (top piece) or if you are cutting molding from stock pieces since in either of those cases you are going to have to make a 45-degree cut. (If you can use a kit "as-is" you may be able to skip this cut—but apparently, kits are all made for a 36-inch door, so I had to cut the header to fit my 32-inch door correctly.)

Brick molding installed.

Brick molding installed.

Okay, so installing the brick molding took a little extra trimming and will still take a little extra caulking. Still, it looks pretty good, doesn't it?

Well, except for that bit at the top, where the old siding doesn't even come close to meeting the brick molding.

New siding is indicated. You can see the sequence below.

The photos pretty much speak for themselves, I think—the only slightly tricky bit was nudging the new siding into place under the piece above; the fit was just a bit tight. I used a piece of scrap wood, carefully tapped with a hammer, to ease the new piece of siding into its spot without damaging anything.

With that done, it was straightforward to caulk and seal around the edges of the door. I began with the spray filler/sealer. Be careful with this product, as there are a couple of variants of this stuff, and it's important to use the version intended for use with doors and windows—the other type expands more (and more forcefully!) and can bend frames, causing windows and doors to jam.

But it's very useful material. Once that base layer cured, I added a layer of latex sealer to give a better surface for painting. Truth to tell, if you look closely it's not that great a surface even now. A sandable product could have been used to allow a really good finish.

But as I said, this door is relatively little-seen anyway, so it didn't seem worth the time.

A couple of "finishing" photos—the first shows a coat of primer/sealer applied to the brick molding and wall. (I plan to paint the door at a later date, too--once the color is negotiated successfully!)

The second is the "after" picture, showing that even a duffer l like me can get a reasonable result in the end, despite the odd detour, error and workaround. And I'm hoping that, as a result of reading this Hub, you'll be spared one or two of those!

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.


Doc Snow (author) from Camden, South Carolina on August 19, 2017:

Thanks, Juliet. It may take a while for my next "how-to," as we are quite literally in a different place. However, there is definitely construction in our future, and I suspect I *will* be writing about it!