DIY Guide

Installing an Interior/Exterior Door: DIY Guide

Swapping a pre-hung door is a very manageable DIY project — the main skill is getting the frame plumb and level.

DIY-Friendly

A pre-hung door replacement (frame included) is straightforward for someone comfortable with a level and a drill. Cutting a brand-new rough opening into a wall is a bigger structural step best left to a pro.

Skill Level

Intermediate

Time Required

2–4 hours per door

Physical Demands

Lifting the door unit into place, moderate

What this costs

Hiring it out	$226–$1,900 per door installed
Tool rental	Miter saw (for trim) $30–$50/day
Your time	2–4 hours per door

The figure above is an installed cost — material and labour together. We do not publish a material-only DIY figure for this project because our cost data does not separate the two here, and estimating it by assuming a labour share would be a guess rather than a source.

What moves the number

Interior versus exterior — An exterior swap adds a sill pan, flashing materials, a full tube of sealant per opening and the labour to tie into the water-resistive barrier.
Condition of the opening — A square, plumb, solid opening is a two-hour job. A rotted sill, sagging header or racked wall turns it into framing repair first.
Pre-1978 construction — Where the RRP Rule applies to your situation the work goes to a certified firm, and even where it does not, containment and clean-up add materials and time.

Run your own numbers with the cost calculator — figures last verified July 2026.

HomeGuide — Door Installation Cost (2026) — retrieved 2026-07-13
Angi — Door Installation Cost (2026) — retrieved 2026-07-13

Before you start

Replacing a pre-hung door is one of the few jobs where a beginner can match a professional result, because it comes down to one skill repeated in three directions: getting the frame plumb, level and square in an opening that is probably none of those. The door, hinges and jamb arrive already fitted to each other — your job is to hold that relationship while fastening it to a wall that has moved since it was built.

An interior pre-hung door is joinery, and the failure mode is a door that will not latch. An exterior one is a hole in the building envelope, and the failure mode is water in the wall — which is why exterior openings carry flashing requirements interior ones do not. Check two things before buying. Is this the dwelling's required egress door? Otsego County, Michigan's handout for the 2015 Michigan Residential Code requires at least one per dwelling unit: side-hinged, clear width of not less than 32 inches measured between the face of the door and the stop with the door open 90 degrees, clear height of not less than 78 inches, and openable from inside without a key — while other doors explicitly need not meet those dimensions. And how old is the house? Pulling casing off a pre-1978 opening disturbs painted surfaces, and EPA counts a removed component by its entire surface area.

Code and permits

A like-for-like door replacement in an existing opening does not normally require a building permit. Two sets of rules still apply: the residential code's dimensional requirements for the dwelling's required egress door, and — on exterior openings — its flashing and air-sealing requirements. Creating a new opening, widening an existing one or altering the header is structural work and a different conversation with your building department.

Michigan Residential Code 2015, as set out by Otsego County, Michigan § R311.4.1 — Egress Door — At least one egress door shall be provided for each dwelling unit. It must be side-hinged, provide a minimum clear width of 32 inches measured between the face of the door and the stop with the door open 90 degrees and a minimum clear height of 78 inches measured from the top of the threshold to the bottom of the stop, and be readily openable from inside without a key, special knowledge or effort. Other doors are not required to meet these dimensions.

Washington State Residential Code 2021, as set out by the City of Ellensburg § 703.4 and R703.4.1 — Flashing at exterior window and door openings — Approved corrosion-resistant flashing shall be applied shingle-fashion at exterior window and door openings to prevent water entering the wall cavity or reaching structural framing. Flashing must follow the fenestration manufacturer's instructions; where none are provided, pan flashing shall be installed at the sill, sealed or sloped to drain outward, with protection at head and sides. Self-adhered membranes comply with AAMA 711, mechanically attached flexible flashings with AAMA 712 and fluid-applied membranes with AAMA 714. Air sealing shall be installed on the interior side of the rough opening gap.

Section numbers and the figures inside them move between editions and between states — Michigan's amended code is the source for the egress figures here, Washington's for the flashing text. Your jurisdiction decides which edition applies and whether a like-for-like door swap needs a permit at all.

Stop and call a pro if…

These are hard stops, not cautions. If you hit one, the job is finished for you until a licensed trade or your building department signs off on it.

You are removing casing or jamb from a pre-1978 opening and the disturbed painted area will exceed 6 square feet

Removing a painted component counts its entire surface area as disturbed, so a casing set clears the minor-repair threshold on its own. Past that point the dust is the hazard, and dry-scraping it in an occupied room is how lead gets into a house's carpet and stays there.

Who to call
A certified renovator — or, if you are proceeding in your own home, follow lead-safe work practices: contain, work wet, no heat guns, clean up thoroughly.

EPA Lead Renovation, Repair and Painting Rule, 40 CFR Part 745 Subpart E § 40 CFR 745.83 — minor repair and maintenance activities — Minor repair and maintenance covers activities disrupting 6 square feet or less of painted surface per room for interior work and 20 square feet or less for exterior work. Where components are removed, the entire surface area removed is the amount of painted surface disturbed, and jobs in the same room within the same 30 days are treated as one job.

The door is the dwelling's required egress door and the replacement will not give 32 inches clear width and 78 inches clear height

The required egress door is the code's guaranteed way out of the dwelling. A narrower replacement is a compliance failure that stays invisible until an inspection or a sale.

Who to call
Your building department, before you buy the unit — widening the opening is structural work with a header, and a permitted job in most jurisdictions.

Michigan Residential Code 2015, as set out by Otsego County, Michigan § R311.4.1 — Egress Door — The egress door must be side-hinged with a minimum clear width of 32 inches measured between the face of the door and the stop with the door open 90 degrees, a minimum clear height of 78 inches from the top of the threshold to the bottom of the stop, and must be openable from inside without a key, special knowledge or effort.

Safety Warnings

• Get a second person to help lift and hold exterior doors while shimming — they're heavy and awkward alone
• Drive the hinge pins and take the slab off before prying the old jamb
• In a pre-1978 home, never dry-sand, dry-scrape or use a heat gun or torch on painted trim; work wet, contain the area and clean up thoroughly
• Wear eye protection when cutting fasteners between an old jamb and the framing

Choosing your materials

Option	Best for	Trade-off
Interior pre-hung, hollow core	Bedrooms and closets, where weight and cost matter more than sound.	Little sound isolation, and a hollow slab takes hardware badly. Masonite specifies #8 finishing nails for hollow-core units — lighter fastening than a solid-core door needs.
Interior pre-hung, solid core	Bathrooms and home offices, where noise matters.	Heavy enough that hanging it alone is awkward, and Masonite calls for #8 2½-inch finish screws rather than nails. On an under-fastened jamb it will sag.
Exterior pre-hung with integral sill and brickmould	Almost every exterior replacement — sill, weatherstrip and threshold arrive tuned to the door.	It brings the whole envelope with it — sealant, sill pan, flashing and head protection all have to be right.

Tools & Materials

Tools

Level (4 ft)Buy
ShimsBuy
Drill/driverYou likely own
Pry barYou likely own
Miter saw (for trim)Rent — $30–$50/day

Materials

Pre-hung door unit (confirm handing, jamb depth and clear dimensions)
Shims and trim/casing
Elastomeric or polyurethane sealant — at least one full tube per exterior sill
Sill pan and flashing complying with AAMA 711, 712 or 714 (exterior doors)
Low-expansion insulating material for the rough-opening gap
#8 x 2-1/2 inch exterior-grade screws; #8 or #6 finish nails for interior trim

Step-by-Step

1
Settle the lead-paint question before anything is pried
30 minutes of checking
If the house predates 1978, removing casing and jamb disturbs painted surfaces — decide how you will work before you start.
EPA states the Renovation, Repair and Painting Rule generally does not apply to homeowners working on their own pre-1978 home, but does apply if they rent out part of it, operate childcare there, or buy, renovate and sell homes for profit. Scale matters too: EPA's interpretation of “minor repair and maintenance activities” under 40 CFR 745.83 covers work disrupting 6 square feet or less of painted surface per room, and states that where components are removed the entire surface area removed is the amount disturbed. A casing set clears that easily. In practice: contain the room, work wet, no dry sanding or heat guns, clean up properly.
Check your workYou know the build year, whether the rule reaches you, and containment is up before the first piece of casing moves.
⚠ Therma-Tru's instructions say the same from the other direction: take proper precautions if lead paint is suspected, which it notes was commonly used before 1979.
Door Installation Cost Calculator
Estimate interior and exterior door installation costs including hardware and labor
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2
Measure, remove the old unit, and check the opening
2 hours · Pry bar, Level (4 ft), Shims
Measure the outside frame, pull the old door and jamb, then confirm the opening is the right size, square, plumb and solid.
Measure before you buy. Therma-Tru's first instruction is to check the width and height of the outside frame — explicitly not the brickmould — and verify the rough opening is large enough; on the required egress door, check clear dimensions rather than nominal size. Masonite's interior guidance is a gap of 7/8 inch or more above the finished flooring.
Take the slab off first by driving the hinge pins up and out — a door still hanging on a jamb you are prying is a heavy pendulum. Score the caulk and paint line before prying, then cut the fasteners between jamb and stud. With the frame out, check the sill of an exterior opening for softness.
Then run Therma-Tru's checklist literally: correct size, square, framing and walls plumb, sub floor level and solid. Check corners with a framing square, confirm with diagonals, and check plumb with a 6-foot level on both sides in both directions. Add the string test — strings stretched diagonally across the opening from outside should gently touch in the centre, and if they do not, the opening is out of plumb by twice that distance. The instructions repeat “fix any problems now” after each check, and add that doing so may require a licensed contractor.
Check your workDiagonals match, both sides read plumb both ways, the strings just kiss in the middle, and the framing is sound and dry.
3
Set the unit, then shim and fasten the frame
1–2 hours · Level (4 ft), Shims, Drill/driver
Place it in the opening, shim at the hinge side first, and check plumb with a level before securing.
On an exterior door the sealant goes down first: three 1/4-inch beads of elastomeric or polyurethane sealant run the full width of the opening on the sub floor, using at least an entire tube. Over a sill pan the pan is dry-fitted and sealed to the sub floor first — and you specifically do not caulk the bottom of the sill when a pan is used, because the pan has to drain.
Tilt the unit in and hold it with #8 x 2-1/2 or 3-inch exterior-grade screws partially driven through the centre pre-drilled holes in both jambs; do not fasten through the brickmould. Then plumb the hinge jamb and only the hinge jamb — both manufacturers agree on that order. Shim above the screw at every hinge, re-check with a 6-foot level, drive those screws home, and only then shim the latch side to align evenly with the wall. By design the hinge side sits closer to the jamb than the lock side.
Check your workThe door swings freely and stays where you leave it, the latch engages without lifting the door, and no daylight shows along the weatherstrip.
⚠ Skipping shims behind the strike plate is the most common cause of a door that won't latch properly.
4
Flash and seal an exterior opening
1–2 hours
Integrate the door head and sides with the wall's water-resistive barrier, and air-seal the rough-opening gap from inside.
Under the residential code as set out in the City of Ellensburg's flashing bulletin for the 2021 Washington State Residential Code, approved corrosion-resistant flashing must be applied shingle-fashion at exterior door openings, extending to the exterior wall finish or to a water-resistive barrier for drainage. It must follow the fenestration manufacturer's instructions, and where none are provided, pan flashing shall be installed at the sill, sealed or sloped to drain outward, with protection at head and sides — self-adhered membranes to AAMA 711, mechanically attached flexible flashings to AAMA 712, fluid-applied to AAMA 714. And the line most DIY installs miss: air sealing on the interior side of the rough opening gap.
Check your workHead flashing laps over the door and under the water-resistive barrier, nothing sheds water inward, and the rough-opening gap is air-sealed from inside.
⚠ Sealant is not flashing. A bead of caulk around the outside of the brickmould traps the water that gets past it.
5
Install trim/casing and finish
1–2 hours · Miter saw (for trim), Drill/driver
Nail trim around the frame, caulk gaps, and fill nail holes.
Masonite's casing spec is #6 finishing nails at roughly 16 inches apart; set the casing to a consistent reveal off the jamb edge. On an adjustable exterior sill, close the door on a dollar bill and pull — there should be tension at each screw position; if the bill tears the sill is too high, and no tension means it is too low. Finally, all bare wood including the frame must be primed and painted or stained and top-coated before exposure, and an outswing door must have all six edges finished.
Check your workThe reveal is consistent all the way round, the dollar-bill test gives light tension at every screw position, and no bare wood is exposed — including the bottom edge.

Common mistakes

Plumbing the latch jamb first, or fastening both jambs at once

Why it happens
The latch side is where the gap is visible, so it is the side your eye wants to fix.

The fix
Set and fasten the hinge jamb plumb first — both manufacturers do it in that order — then align the latch jamb to the hanging door. If a door is already fastened out of square, back the latch-side screws off rather than planing the slab.

Relying on a bead of exterior caulk instead of flashing

Why it happens
Caulk is visible and quick; flashing is hidden and looks like extra work on a door that is already in.

The fix
Flash the head and sides shingle-fashion into the water-resistive barrier and pan-flash the sill where the manufacturer supplies no detail. If a door is already installed without flashing, pull the exterior trim and flash it — do not add more sealant.

After the job: care and maintenance

First month
Re-check the latch and reveal after the frame has settled and the house has been through a temperature swing.
Twice a year
Close the door on a dollar bill at each sill screw position and check for tension, adjusting the sill as needed.

FAQ

Can I install a door myself?

Yes — replacing a pre-hung door in an existing opening is a manageable DIY project. The key skill is getting the frame plumb and level, which determines whether the door will swing and latch properly. What separates a good result from a frustrating one is preparation: both manufacturers cited here spend most of their instructions on the opening rather than on the door.

Do I need a permit to replace a door?

For a like-for-like swap into an existing opening, usually not. What changes the answer is touching the opening itself — cutting a new one, widening one or altering the header is structural work and normally a permitted job. Either way, the code's requirements for the required egress door and for flashing at exterior openings still apply.

Does lead paint really matter for a door swap?

In a pre-1978 house, yes. EPA states the RRP Rule generally does not apply to homeowners working on their own home, but it does apply if you rent out part of it, operate childcare there, or renovate and sell homes for profit. The scale test is informative either way: the minor repair threshold is 6 square feet of disturbed painted surface per room, and where a component is removed the entire surface area removed counts. A casing set clears that on its own.

How do I know if my rough opening is square enough?

Compare the diagonals, check the corners with a framing square, and check both sides for plumb with a 6-foot level in both directions. Then run Therma-Tru's string test: strings stretched diagonally across the opening from outside should gently touch in the centre, and if they do not, the opening is out of plumb by twice that distance. If any check fails by more than a shim's worth, fix the framing first.

Why won't my new door latch?

Almost always because there is nothing solid behind the strike plate, or because the frame was fastened out of plumb. Shim behind the strike as well as every hinge, and check that you plumbed and fastened the hinge jamb first, then aligned the latch jamb to the hanging door. Before chasing an uneven gap: by design the hinge side sits closer to the jamb than the lock side.

Sources

Every figure, clearance and code section on this page traces to one of these. Manufacturer instructions govern their own product and override anything general said here.

Therma-Tru. Installation Instructions for Pre-Hung Fiberglass Entry & Patio Door Systems — accessed September 3, 2026.Opening checks and the string test, sub-floor sealant beads, sill pan sequence, screw spec, the dollar-bill threshold test.
Masonite. How To Install Interior Doors — accessed September 3, 2026.Shimming behind each hinge, fastener choice for hollow versus solid core, casing nails, clearance under the door.
City of Ellensburg, Washington — Community Development Department. Residential Bulletin BB-17: Exterior Flashing Requirements (2021 Washington State Residential Code) — accessed September 3, 2026.Flashing at exterior door openings, AAMA 711/712/714, the pan-flashing default, interior-side air sealing.
Otsego County, Michigan — Building Department. Residential Building Code Handout for Landings, Stairways, Handrails & Guards (2015 Michigan Residential Code) — accessed September 3, 2026.The egress door requirement — side-hinged, 32-inch clear width at 90 degrees, 78-inch clear height.
U.S. Environmental Protection Agency. Renovation, Repair and Painting Program — accessed September 3, 2026.That the RRP Rule covers pre-1978 homes, and when it reaches a homeowner doing the work themselves.
U.S. Environmental Protection Agency. How will EPA interpret the term “minor repair and maintenance activities”? (40 CFR 745.83) — accessed September 3, 2026.The 6 sq ft interior / 20 sq ft exterior thresholds and the removed-component rule.

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