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Exterior Door Installation: Preparing The Doorway For A New Door

By Phil Vandermeer / October 11, 2011

Here’s my second article in a sort of “exterior door installation” series. You can see my article on “How To Stain And Finish A Wood Door” for pictures and description of the work I did on the bare door of this project before preparing the doorway.

Removing The Old Door And Trim

Before you begin removing an old door, you should have everything you need for the new door installation ready to go including the new door, and you need to be sure all the new door dimensions will work in the rough opening. Manufactured doors come in standard widths of 30″, 32″ and 36″… 80″ high and 1-3/4″ door thickness is typical. The jamb width is usually 4-9/16″ or 5-9/16″. Other sizes than typical ones I just stated are also available. but the point here is to make sure you do not have to stop in the middle of a project to go get needed materials.

Remove the old exterior door, the interior trim, the exterior trim and the threshold. Take mental note of the placement of shims that supported the old casing. If there’s insulation, remove that as well.

old exterior door laying in the grass

Here’s the old door after removal. It’s in worse shape than it probably appears.

There should be insulation filling the gaps if there’s not any, so be sure you have some for the new door installation. A hammer and crowbar are what I use for removing old casings. Once the existing door is removed, the rough opening needs to be cleaned well.

The Key To A Successful New Door Installation

The real key to a successful door installation is the preparation of the bottom of the existing opening. If your rough opening threshold is bowed, crooked or bumpy, you’ll need to straighten it up and get it as square as possible to plumb. That just means it needs to be nice and flat and level to the ground or structure it’s going into and be very solid. If the integrity of the existing threshold is at all in question, replace it.

There are several methods used for truing up the bottom of the rough opening. If the existing base of the opening is concrete, you could add concrete to it to level it out, but it is likely that the overlay of concrete will crack and crumble.

Preparing the threshold for new exterior door installation

Photo taken immediately after removing the old threshold.

Probably sooner rather than later too. I have heard of shimming and filling with expanding foam, but I can’t see that as particularly trustworthy. I have never tested the method myself, so I cannot say for sure.

Mostly, I’ve been lucky enough to have only installed doors in nearly square doorways. A good concrete leveler seems to be the right answer to this dilemma, but it is impractical to use in a doorway since it needs to be poured. Perhaps some shoring may work with a good leveler. This handyman hasn’t tried it.

I Love Liquid Nails

What I have done is run some shims under the threshold until I get it level, then remove the threshold. I use liquid nails generously (possibly over half a tube of the “general construction” glue – the light brown stuff) along the path of the threshold then re-install it over the shims. The liquid nails takes about 48 hours to dry, but once it dries, it is very hard, waterproof and holds everything together. Liquid Nails is a staple in my door installation tool kit.

New threshold in place for new door installation

2X10 base cut to fit. Shimmed slightly to level and liquid nailed!

At one property, I put in a threshold and had to remove it three years later after the owner decided to replace the entire door. I used my Liquid Nails trick to install the threshold, and boy, it took a lot of time and serious effort to remove that piece of wood! It is my preferred method and it works for years and years.

Clean Everything Now – Before Door Installation

Once the base of the doorway is clean and level, you should also clean all the way around the rough opening and make sure the exposed studs are clean and solid. Check everything with a square and level so you can get a good idea where your shims will need to go. You don’t need to take a memory course or anything like that :-), but getting a strong sense of how the old door went in will help you out later on. There should not be any nails sticking out anywhere.

Sure-fire Trick For Duplication

Take a picture if you want to make your new door installation even easier. No. Seriously. Take pictures of both sides of the door after you remove all the outside trim, and before you remove the jamb. Take an overall picture and a picture of each side. Don’t rely on your memory to know where the shims were used or if the old door was exactly centered in the opening or not. You never know why the last door installation was done the way it was. Pictures can often solve new problems that come up with your new door.

Wrap up

With the old door removal complete, the base of the threshold in, and everything cleaned up, you should be ready to install your new door.

What you'll see after old door and trim is removed

The old casing needed a lot of shimming, including this piece of 2X4, which I removed.

I didn’t really write about painting the jamb, but you can see part of it in one of the posted photos. I chose a satin exterior latex enamel that complimented the natural colors of the wood door and painted it during the same period I stained and finished the door.

I cover door installation and offer some useful door installation tips in my article “How To Hang A Prehung Door” if you want to check that out. That article covers the last part of this project and you can see the final results, too.

This is not a particularly difficult job to complete, and some basic care to ensure everything is correct from the start will form the foundation of a superb new door installation project. Do you have some door installation questions? Maybe you’d like to share what things came up for you when you did a door installation? Please comment below!



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