Home Carpentry – Part 1: Installing New Doors : Interior & Exterior, Done Right
A practical guide from Mike Sansing of Your Handyman Pros
A new door can change how a room feels, improve privacy, update your home’s style, and help keep Utah weather where it belongs: outside. But door installation is more than hanging a slab and turning a screwdriver. The opening needs to be measured correctly, the frame must be square and plumb, and the hardware and seals all need to work together.
In this first article of our four-part Home Carpentry: The Ultimate DIY Guide for Utah Homeowners series, we’ll cover the basics of installing both interior and exterior doors.
Pre-Hung vs. Slab Doors: Which Should You Choose?
The first decision is whether you need a pre-hung door or a slab door.
What Is a Pre-Hung Door?
A pre-hung door comes as a complete assembly. The door is already attached to a frame with hinges, and exterior units often include a threshold and weatherstripping.
Choose a pre-hung door when:
You are creating a new doorway.
The existing jamb is damaged, warped, or out of square.
You are replacing an exterior door.
You want a simpler installation with factory-installed hinges.
The existing frame does not match the new door style or size.
Pre-hung doors are usually the better choice for exterior installations because the frame, threshold, and weather seals are designed to work together.
What Is a Slab Door?
A slab is only the door panel. It does not include a frame, hinges, or pre-installed hardware.
A slab door can be a good option when:
The existing frame is in good condition.
The opening is square and properly sized.
You want to replace only the door’s appearance.
You are comfortable mortising hinges and fitting the latch.
The new slab matches the existing door’s height, width, thickness, and swing.
A slab replacement can save materials, but it is not always the easier project. Even a small difference in hinge or latch placement can cause binding, gaps, or a door that refuses to close correctly.
How to Measure a Door Opening
Accurate measurements prevent one of the most frustrating home repair problems: buying a door that does not fit.
For a replacement door, measure the existing opening in several places:
Measure the width between the jambs at the top, middle, and bottom.
Measure the height from the finished floor to the top of the jamb.
Measure the jamb depth, or the thickness of the wall that the new frame must cover.
Measure the door slab if you are replacing only the panel.
Check the swing direction before ordering.
Use the smallest width measurement. If the opening is 30 inches at the top, 29 ⅞ inches in the middle, and 29 ¾ inches at the bottom, the smallest measurement is the one that matters.
For a new rough opening, the framed opening must be larger than the complete door unit to allow room for shims and adjustments. Exact requirements vary by manufacturer, so always check the installation instructions. As a general rule, installers leave clearance around the unit rather than trying to force a tight fit.
Also check the opening for:
Matching diagonal measurements from corner to corner.
Twisted or bowed framing.
A level subfloor or sill.
Proper finished-floor height.
Enough clearance for the door to swing freely.
A rough opening that is not square can often be corrected, but it should be addressed before the door is permanently fastened.
Hanging a Pre-Hung Interior Door
Interior doors do not need exterior flashing or sill pans, but they still require careful shimming.
Start by placing the pre-hung unit into the rough opening. Center it as needed and make sure the door is positioned for the correct finished wall surface.
1. Plumb the Hinge Jamb
The hinge-side jamb is the starting point. Use a level to make it perfectly vertical, or plumb. Temporarily secure it near the top, but do not fully tighten every fastener yet.
2. Shim Behind Each Hinge
Place shims between the jamb and the framing directly behind each hinge location. This keeps the jamb from flexing when the hinge screws are tightened.
Use pairs of shims where possible so the frame stays supported without being pushed out of alignment.
3. Check the Reveal
The reveal is the gap between the door slab and the jamb. Adjust the frame until the gap is consistent along the top and both sides. A common target is approximately ⅛ inch, although the manufacturer’s instructions should take priority.
4. Secure the Latch Side
Shim the strike-side jamb near the top, middle, and bottom. Check that the door closes without rubbing and that the latch enters the strike plate cleanly.
Do not rush this step. A door that looks centered but has an uneven reveal may bind later as the house moves slightly with seasonal changes.
5. Install Casing and Finish
Once the door opens, closes, and latches correctly, permanently fasten the frame. Then install casing, fill nail holes, caulk the trim, and paint or stain as appropriate.
Hinges and Hardware Matter
Door hardware is both functional and decorative. Before installation, confirm that the hinges, latch, strike plate, and handle are compatible.
For interior doors:
Match the hinge size and finish.
Confirm the door’s swing direction.
Use screws long enough to secure the hinges properly.
Make sure the latch bevel faces the correct direction.
Check that the strike plate is aligned with the latch.
If you are installing a slab door, hinge locations must match the existing jamb precisely. You may need to mortise the hinge recesses with a router or chisel. The latch bore and edge bore must also be drilled at the correct height and backset.
That is where a seemingly simple door replacement can turn into detailed finish carpentry.
Exterior Doors: Prepare for Utah Weather
Exterior doors in the Salt Lake Valley must handle freezing temperatures, snow, wind, summer heat, and repeated freeze-thaw cycles. A door can look beautiful and still perform poorly if the sill and frame are not sealed correctly.
Use a Sill Pan and Flashing
A sill pan helps direct water away from the subfloor if moisture gets past the threshold. Depending on the installation, the pan may be a manufactured product or a properly formed flashing system.
The rough opening should also be flashed according to the door manufacturer’s instructions. Pay attention to the sill, jambs, and head of the opening. Water often finds the smallest unsealed joint.
Seal the Frame
After the door is positioned and adjusted:
Apply compatible sealant under or around the sill as directed.
Use low-expansion foam between the frame and rough opening.
Caulk exterior trim with a quality paintable exterior sealant.
Seal gaps around the frame without blocking drainage paths.
Confirm that brickmould and exterior casing sit tight against the surrounding surface.
Low-expansion foam is important because standard expanding foam can bow the jamb and prevent the door from operating correctly.
Adjust the Threshold and Weatherstripping
The weatherstripping should make even contact around the closed door without requiring excessive force. If the door is difficult to close, the seal may be too tight or the frame may be out of alignment.
An adjustable threshold should support a snug seal at the bottom. One simple check is the paper test: place a sheet of paper over the threshold, close the door, and pull. The paper should resist slightly. If it slides out easily, the threshold may need adjustment. If it tears, the seal may be too tight.
Correct adjustment helps reduce drafts, protects the entry, and improves comfort during Utah’s cold winters and hot summers.
Common Door Installation Mistakes
Here are several problems we see repeatedly:
Measuring only once.
Ordering based on the door slab size instead of the complete unit.
Forgetting jamb depth.
Failing to check the finished-floor height.
Installing the latch-side jamb before the hinge side is plumb.
Driving fasteners without shims behind the hinges.
Using too much expanding foam.
Skipping flashing or sill protection on an exterior door.
Caulking over areas that need to drain.
Installing the handle or lock at the wrong height.
Ignoring an uneven reveal.
Assuming a door will “settle into place” after installation.
A door should operate properly before trim is installed. Casing can hide a gap, but it cannot correct a crooked frame.
When Should You Call a Licensed Professional?
A careful homeowner may be able to replace a standard interior door, especially when the opening is already square and the new unit is the same size. Exterior doors, structural changes, water damage, and unusual openings deserve more caution.
Call a professional if:
The rough opening needs to be resized.
The wall may be load-bearing.
The frame shows rot, water damage, or structural movement.
The exterior threshold is not level.
You are changing an entry door’s size or location.
The door will not stay square after shimming.
You need related electrical, plumbing, or HVAC work moved.
You want the installation sealed and finished under one project plan.
At Your Handyman Pros, we help homeowners with door installation, trim carpentry, repairs, and larger remodeling projects throughout the Salt Lake Valley, including Sandy, Herriman, Riverton, Magna, West Valley City, Bountiful, and nearby Utah communities. I’m Mike Sansing, a licensed and insured B100 General Contractor, Lic. 12888335-5501. My wife, Kristy, and I manage projects with a focus on dependable workmanship and clear communication.
If you are planning a door replacement, request an estimate from Your Handyman Pros. You can also visit our Pro Tips & Projects page for more practical home repair and remodeling advice.
A new door should close smoothly, seal tightly, and look like it belongs in your home. When the measurements, shims, hardware, and weatherproofing are handled correctly, the result is more than a cosmetic update: it is a durable home improvement you can enjoy every day.
Next in the series: baseboards, door casing, and moulding: the details that make a room look finished.
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