Exterior Door Installation Guide

Complete guide covering pre-hung vs slab doors, rough opening sizing, threshold leveling, shimming, and lockset installation

Pre-hung vs Slab Door Selection

Choosing the Right Door Type

Pre-hung doors include the jamb, hinges, and door already assembled, making installation faster and easier. Slab doors are just the door itself, requiring you to mortise hinges and bore for the lockset.

Recommendation: For exterior doors, always use pre-hung units with properly weatherstripped jambs for best results.

Door Type Comparison

Feature	Pre-hung Door	Slab Door
Installation Time	2-4 hours	4-6 hours
Skill Level Required	Intermediate	Advanced
Cost	$300-1500	$150-800 (door only)
Weather Stripping	Pre-installed and fitted	Must install separately
Hinge Installation	Pre-mortised and attached	Must mortise and install
Best Use Case	New construction, replacements	Existing jamb in good condition

Pre-hung Door Advantages

Faster installation: Jamb, hinges, and bore already complete
Guaranteed fit: Door fits jamb perfectly from factory
Weather tight: Weatherstripping pre-installed and sealed
Better seal: Factory-cut reveals ensure consistent gaps
Energy efficient: Proper sealing reduces air infiltration

Slab Door Use Cases

Replace damaged door: When jamb is sound and true
Historic restoration: Matching existing jamb profile
Custom sizing: Non-standard door sizes
Budget constraints: Lower upfront cost
Special applications: Custom wood species or design

Rough Opening Sizing

Critical Rough Opening Formula

The rough opening must be sized correctly to allow for shimming and adjustment while providing adequate support for the door unit.

Standard Formula: RO Width = Door Width + 2 inches | RO Height = Door Height + 1 inch

Standard Rough Opening Sizes

Door Size	Rough Opening Width	Rough Opening Height	Purpose
30" × 80" (2/6)	32"	81"	Single entry door
32" × 80" (2/8)	34"	81"	Standard entry door
36" × 80" (3/0)	38"	81"	Main entry, ADA compliant
60" × 80" (5/0 Double)	62"	81"	French doors, double entry
72" × 80" (6/0 Double)	74"	81"	Patio doors, wide entry

Rough Opening Requirements

Level threshold: Must be perfectly level (within 1/16")
Plumb jack studs: Sides must be perfectly vertical
Square corners: Check diagonal measurements (equal within 1/8")
Proper header: Sized for load bearing requirements

Header Sizing Guidelines

30-36" door: Double 2x6 or 2x8 (load-bearing)
60" double door: Double 2x10 minimum
72" patio door: Double 2x12 or LVL beam
Non-load bearing: Can use single 2x4 flat

Threshold Leveling & Sill Pan Flashing

Critical Threshold Requirements

The threshold is the most critical component for preventing water intrusion. It must be perfectly level side-to-side and properly flashed underneath.

Rule: Threshold must be level within 1/16 inch and installed over sill pan flashing for waterproofing.

Sill Pan Flashing Installation

1.Install back dam: Place foam or wood strip at back edge
2.Apply membrane: Flexible flashing from back dam to 1" past exterior
3.Create end dams: Fold corners up sides at least 6-8 inches
4.Slope outward: Sill should slope 3-5 degrees toward exterior
5.Seal seams: Use flashing tape on all seams and corners

Leveling the Threshold

Use long level: 4-6 foot level across full width
Shim underneath: Use composite shims for solid support
Check both directions: Level side-to-side, slight slope front-to-back
Tolerance: Within 1/16" over full width (critical!)
Test closure: Door should close smoothly without binding

Waterproofing Best Practices

• Install sill pan flashing before setting door (first line of defense)
• Back dam prevents water from running under threshold into house
• End dams at corners prevent water from leaking at sides of threshold
• Membrane should extend up jambs 6-8 inches minimum
• Integrate with building wrap/WRB using proper sequencing
• Test with water before finishing - pour water on threshold, check for leaks

Shimming Techniques & Locations

Critical Shimming Locations

Proper shimming is essential for door operation and longevity. Shims must be placed at specific structural points to prevent jamb bowing and ensure smooth door swing.

Required: Shim every 12 inches on all jambs, plus at each hinge location and at strike plate

Shim Placement Requirements

Location	Shim Requirement	Purpose	Fastening
Hinge side jamb	Behind each hinge (3 locations)	Support hinge stress, prevent sag	3" screw through hinge
Strike side jamb	Behind strike plate location	Prevent jamb flex when closing	3" screw at strike
Intermediate jambs	Every 12" max on both sides	Prevent jamb bow, maintain plumb	2-1/2" to 3" screws
Top corners	Both corners of head jamb	Support head, prevent sag	3" screws
Head jamb center	Center of head on wide doors	Prevent head deflection	3" screw

Shimming Best Practices

Use composite shims (won't rot or compress like wood)
Insert shims in pairs from opposite directions for stability
Shim snug but don't overtighten (shouldn't bow jamb)
Drive screws through shims into solid framing
Check door operation after each shim adjustment
Score and snap shims flush before insulating

Common Shimming Mistakes

Missing shims at hinges (causes door sag over time)
No shim at strike plate (jamb flexes, latch fails)
Over-shimming (bows jamb in, door binds)
Spacing shims too far apart (allows jamb flex)
Using single shims instead of pairs (unstable)
Not checking reveal consistency after shimming

Weather Stripping Types

Kerf-In Weather Stripping

Thin fin inserted in kerf cut

• Best for: Side and head jambs
• Installation: Slides into 1/16" saw kerf
• Material: Vinyl or silicone fin
• Pros: Invisible, effective seal
• Cons: Requires kerf cut in jamb
• Replacement: Pull out, slide new fin in

Compression Weather Stripping

Foam or bulb seal (most common)

• Best for: All jambs, easy retrofit
• Installation: Nail or adhesive backing
• Material: EPDM foam, vinyl bulb
• Pros: Easy install, adjustable
• Cons: Visible, wears over time
• Lifespan: 5-10 years depending on use

Adhesive-Backed Stripping

Foam tape with adhesive

• Best for: Quick repairs, temporary
• Installation: Peel and stick
• Material: Open or closed cell foam
• Pros: Fast, no tools needed
• Cons: Adhesive fails, short lifespan
• Lifespan: 1-3 years typical

Door Sweep & Bottom Seal Options

U-shaped bottom seal: Wraps under door, best seal but may interfere with threshold
Door sweep (exterior): Screws to outside face, adjustable height, protects from weather
Door shoe: Replaces bottom edge, integrated drip cap and seal
Automatic door bottom: Spring-loaded, drops when door closes (expensive but effective)
Threshold gasket: Built into threshold, door compresses it when closed
Combo units: Threshold with integrated sweep provides best performance

Lockset Installation Specifications

Standard Boring Specifications

Most modern exterior locksets follow standard boring dimensions. Pre-hung doors come pre-bored, but slab doors require precise drilling.

Standard: 2-1/8" face hole, 1" edge hole (latch), backset 2-3/8" or 2-3/4" from door edge

Lockset Boring Dimensions

Measurement	Standard Size	Alternative	Notes
Face bore diameter	2-1/8"	2-3/8" (some locks)	Through door face for cylinder
Edge bore diameter	1" (7/8" min)	1-1/8" for deadbolt	Into door edge for latch
Backset distance	2-3/8"	2-3/4"	From door edge to center of bore
Height from floor	36" to center	34-38" acceptable	Comfortable operating height
Deadbolt height	6-12" above knob	40-48" from floor	Above lockset, comfortable reach

Strike Plate Mortise

Mortise depth: Flush with jamb surface (1/8" deep typical)
Latch hole: Bore 1" deep into jamb for latch clearance
Alignment: Must align perfectly with latch bolt
Fastening: Use 3" screws into framing behind jamb
Security: Use strike plate with metal box for deadbolt

Door Swing Clearance

Top reveal: 1/8" gap between door and head jamb
Side reveals: 1/8" on hinge side, 1/8" on latch side
Bottom clearance: 1/2" to 3/4" above threshold
Seasonal adjustment: Wood doors swell in humidity
Operation test: Smooth close without binding or gaps

Step-by-Step Installation Process

Verify Rough Opening & Prepare

•Measure rough opening: should be door width + 2 inches, height + 1 inch
•Check RO is level (threshold within 1/16 inch), plumb, and square
•Inspect framing: header, jack studs, and sill plate must be solid
•Remove any protruding nails, staples, or debris from opening
•Test fit door unit in opening to verify proper fit before flashing

Install Sill Pan Flashing

•Place back dam (foam rod or wood) at back edge of sill
•Apply flexible flashing membrane from back dam to 1 inch past exterior edge
•Extend membrane up both sides of opening 6-8 inches minimum
•Fold corners up at 45 degrees to create watertight end dams
•Roll all edges with J-roller for good adhesion and seal
•Ensure sill slopes 3-5 degrees toward exterior for drainage

Set Door Unit in Opening

•Remove shipping braces but leave door secured in frame
•With helper, lift door unit and tip into opening from exterior
•Center door in opening with equal gaps on sides (about 1 inch each)
•Push exterior brick mold tight against sheathing
•Tack top corners with one nail each (temporary hold only)
•Check that door is roughly plumb and level before proceeding

Level & Shim Threshold

•Place 4-6 foot level across threshold, check side-to-side level
•Insert shim pairs under threshold until perfectly level (within 1/16 inch)
•Shim at both ends and center, approximately every 12 inches
•Verify level doesn't change when pressing down on threshold
•Open and close door to verify smooth operation (no binding)
•Once level, secure threshold area with screws through threshold into subfloor

Plumb & Shim Side Jambs

•Check hinge jamb with 6-foot level, adjust until perfectly plumb
•Place shim pairs behind each of three hinge locations
•Check strike jamb for plumb, shim behind strike plate location
•Add intermediate shims every 12 inches on both jambs
•Measure diagonal corners (must be equal within 1/8 inch for square)
•Open and close door repeatedly, checking for smooth operation and even gap

Secure Jambs & Check Reveals

•Drive 3-inch screws through hinge-side jamb at each hinge location (through shims)
•Install 3-inch screw through strike-side jamb at strike plate location
•Add 2-1/2 to 3-inch screws through shims every 12 inches on both jambs
•Check reveals: should be consistent 1/8 inch gap all around door
•Verify door closes smoothly, latches properly, and seals against weather stripping
•Adjust shims if needed and re-test before proceeding

Install Side & Head Flashing

•Apply flashing tape to jack studs from sill pan up past header
•Overlap sill pan flashing by 3-4 inches at bottom
•Install head flashing tape across top, overlapping side flashing by 2-3 inches
•Ensure proper shingle effect (upper layers over lower layers)
•Integrate with building wrap/housewrap above and to sides
•Seal around any protruding brick mold or casing

Insulate Gaps with Low-Expansion Foam

•Remove temporary shipping brackets from door (if present)
•Spray water into gaps between jambs and framing (improves foam adhesion)
•Apply low-expansion foam, filling gaps 50-75% full
•Foam between and around shims, not directly on top of shims
•Allow 1-2 hours for foam to cure fully
•Trim excess foam flush with jambs using utility knife
•Test door operation again after foam cures

Exterior Finishing & Caulking

•Nail brick mold to framing with 8d galvanized finish nails every 12 inches
•If no brick mold, install exterior trim or integrate with siding system
•Apply quality exterior caulk between trim and siding/sheathing
•Do NOT caulk bottom of brick mold (allows water drainage)
•Caulk top and sides completely for weathertight seal
•Tool caulk smooth for professional appearance

Install Interior Trim & Hardware

•Install interior door casing maintaining 1/4 inch reveal on jambs
•Miter corners at 45 degrees for clean appearance
•Nail casing to jack studs and header (not to door jamb)
•Install lockset if not pre-installed (follow manufacturer instructions)
•Install deadbolt 6-12 inches above lockset for security
•Test all hardware operation: knob, deadbolt, and door closure
•Caulk between casing and wall, fill nail holes with putty
•Final check: door swings freely, latches securely, seals weathertight

Best Practices & Common Mistakes

DO:

Install sill pan flashing before setting door (critical for waterproofing)
Verify threshold is perfectly level within 1/16 inch before securing
Shim at all critical locations: hinges, strike plate, every 12 inches
Use 3-inch screws through jambs into framing for structural attachment
Test door operation multiple times before insulating with foam
Use only low-expansion foam to avoid bowing jambs
Check reveals are consistent (1/8 inch) on all sides when closed
Allow drainage at bottom - don't caulk bottom of brick mold

DON'T:

Skip sill pan flashing (leads to rot and water damage over time)
Set door on unlevel threshold (causes door to swing open or closed)
Forget back dam on sill (water runs under threshold into house)
Use regular expanding foam (will bow jambs and void warranty)
Over-shim or over-tighten screws (distorts jamb, binds door)
Miss shimming at strike plate (latch won't engage properly)
Rely on caulk alone for weatherproofing (use proper flashing)
Caulk bottom of door trim (blocks weep holes, traps water)