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Safety Cue
Task-specific safety guidance for ordinary work hazards.
Project 04
Install Interior Door Casing
Establish the casing reveal, cut and fit head and side casing, fasten the assembly to jamb and framing, and inspect the completed door-trim installation for reveal consistency, joint alignment, and unimpaired door operation.
Field Cue System
These cues appear at the point of work. They identify safety, code, manufacturer, and measurement issues before they become rework, callbacks, or hazards later in the book.
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Critical Safety Cue
Serious injury, fire, or major damage is possible.
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Field Safety Cue
Practical work-area safety: lighting, cords, footing, and housekeeping.
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Code Alert
Local requirements vary. Verify permit, inspection, and jurisdictional rules.
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Manufacturer Cue
Follow product-specific instructions for tools, materials, and equipment.
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Measurement Cue
Clearance, layout, spacing, and reference-point guidance.
Job Overview
This project qualifies you to install a complete three-piece interior door-casing set: head casing and two side casings, mitered at the corners, fastened to jamb and wall framing, and held to a consistent reveal along both jamb legs and the head. The finished work product is one fully installed, permanently fastened door-casing assembly with tight, aligned miter joints and unimpaired door operation.
You will verify that the jamb is secure and operating correctly, establish the casing reveal from the Project 01 survey, measure and cut head and side casing to the required miters, dry-fit and adjust the assembly, fasten it to jamb and wall framing using the approved fastener schedule, and inspect the finished casing for reveal, plane, joint alignment, and door operation.
This project depends directly on Project 01's controlling reveal line and Project 05's prehung door jamb, and on the measuring, marking, and mitering skills developed in Project 03. The casing installed here is left with fasteners set but not yet filled or caulked; Project 18 completes that surface preparation after every trim assembly in the room is installed.
Skills You Will Demonstrate
- FC-019 — Establish the casing reveal on both jamb legs and the head from the approved controlling-line layout.
- FC-020 — Cut head casing to the required length and miter angles while preserving profile orientation.
- FC-021 — Cut side casing to the required length and miter angles, independently measured for each leg.
- FC-022 — Fasten casing to jamb and wall framing using the approved fastener pattern without damaging the profile.
- FC-023 — Align and pin miter joints at the correct reveal without distorting the assembly.
- FC-024 — Inspect door-trim fit for reveal, joint alignment, casing plane, and unimpaired door operation.
Where This Skill Fits
This project applies the Project 01 controlling reveal line to the first permanently installed trim assembly in the room and applies the measuring, marking, and mitering procedure from Project 03 to a finished, visible joint. It requires a jamb installed and adjusted under Project 05 and hardware operating correctly under Project 06 before the reveal is finalized against the door.
The casing method used here — establishing reveal, cutting to long point or short point as required by the miter, dry-fitting before permanent fastening, and pinning the miter without distorting the reveal — is reused directly in Project 07 for window casing and referenced again in Project 13 for rail returns and Project 14 for batten terminations.
Scope and Intended Use
This project covers:
- verifying that the door jamb is secure, plumb, adjusted, and operating correctly before casing is planned
- establishing and marking the approved casing reveal on both jamb legs and the head
- measuring, cutting, and test-fitting head and side casing pieces
- adjusting miters without changing the established reveal
- fastening casing to jamb and wall framing using the approved fastener pattern
- pinning or fastening miter joints using the approved method
- inspecting casing plane, reveal, joint alignment, and door operation
- correcting proud miters, open joints, bowed casing, and inconsistent reveals
- documenting jamb or wall irregularities that affected the installation
This project does not authorize the learner to:
- install or adjust the prehung door unit itself; the jamb must already be set, plumb, and operating correctly under Project 05 before this project begins
- fill, caulk, sand, or prime the finished casing; this occurs in Project 18 after every trim assembly in the room is complete
- alter fire-rated door assemblies, labeled frames, self-closing devices, or smoke seals beyond the approved listed casing detail
- conceal jamb or wall irregularities with filler, caulk, or excessive compound instead of documenting and correcting them
Any door opening with an unresolved jamb, hardware, or wall-plane defect must be corrected before casing begins on that opening.
Prerequisites
- Project 01 room survey completed with an Approved or fully corrected Conditional readiness decision, including the controlling reveal line for this opening
- Project 02 cutting and assembly station set up and passed its readiness inspection
- Project 03 measuring, marking, and mitering skills demonstrated independently
- Prehung door installed under Project 05, with hinge and strike jambs plumb, secure, and passing inspection
- Door hardware installed and adjusted under Project 06, with the door latching, swinging, and closing correctly
- Surrounding drywall inspected under Project 01 for damage or plane variation exceeding what the casing profile can follow
Project Specification Sheet
A. Finished Project
Quantity: one complete three-piece casing set per door opening, consisting of one head casing and two side casings, mitered at both upper corners, fastened to jamb and wall framing.
Configuration: mitered head-and-side casing following the reveal, profile, and finish grade set by the approved trim schedule and finish specification for the room.
Intended use: permanent interior trim concealing the gap between the door jamb and the surrounding wall opening while preserving door operation.
Main limitations: this project does not correct jamb, hardware, or wall-plane defects; those are corrected under Projects 01, 05, and 06 before casing is measured.
B. Component Schedule
| Component | Quantity | Material | Finished Size | Preparation |
|---|---|---|---|---|
| Head casing | 1 per opening | Profile and grade per trim schedule | Length and miter angles per marked reveal; see Section G, Step 2 | Both ends mitered per the marked reveal; profile orientation preserved |
| Side casing (hinge side) | 1 per opening | Profile and grade per trim schedule | Length and top miter per marked reveal; bottom end per finish specification | Top end mitered; bottom end square or profiled as specified |
| Side casing (strike side) | 1 per opening | Profile and grade per trim schedule | Length and top miter per marked reveal; bottom end per finish specification | Top end mitered; bottom end square or profiled as specified |
The trim schedule and finish specification identified in Project 01 control profile, dimensions, and finish grade. Do not substitute a different profile or dimension without a documented revision to those controlling documents.
C. Material Takeoff
- Stock type: casing profile identified in the approved trim schedule, paint-grade or stain-grade as specified for the room.
- Purchase quantity: sufficient length for one head piece and two side pieces per opening, plus the waste allowance stated in the trim schedule for miter cutting and test-fit correction.
- Fasteners and adhesive: quantity and type per the Fastener and Hardware Schedule in Section D.
- Do not calculate quantities beyond what the trim schedule and preliminary cut list from Project 01 already establish for this opening.
D. Fastener and Hardware Schedule
| Joint | Fastener | Installation Direction | Pilot/Clearance | Final Seating Condition |
|---|---|---|---|---|
| Head casing to jamb | Finish fastener per fastener schedule | Through casing into jamb, near the inner edge | Per fastener schedule; pilot-drilled where stain-grade or prone to splitting | Head set flush to slightly below surface without crushing the profile |
| Head and side casing to wall framing | Finish fastener per fastener schedule | Through casing into stud or approved backing at the outer edge | Per fastener schedule | Head set flush to slightly below surface without crushing the profile |
| Miter joint | Pin fastener or approved joint method per fastener schedule | Through the joint face as specified | Per fastener schedule | Joint faces held flush and tight, reveal preserved |
The fastener size, spacing, and drive type are set by the approved fastener and hardware schedule referenced in the trim schedule for this room. Adhesive at the miter joint or along the jamb leg is applied only where that schedule specifies it.
E. Reference Conventions
| Term | Definition |
|---|---|
| Reveal line | The marked line on the jamb face, set back from the jamb edge, that the inside edge of the casing follows |
| Long point | The longer corner of a mitered end, used as the measuring reference for miter cuts |
| Short point | The shorter corner of a mitered end |
| Reference face | The finished front face of the casing profile, kept consistent through marking and cutting |
| Head casing | The horizontal casing piece across the top of the door opening |
| Side casing | The vertical casing piece along the hinge or strike jamb leg |
F. Acceptance Standards
| Check | Standard |
|---|---|
| Reveal consistency | Reveal matches the marked reveal line along both jamb legs and the head within the tolerance stated in the finish specification |
| Miter closure | Both head-to-side miter joints closed with no visible gap at the face under normal room light |
| Casing plane | No proud miter corner or twisted piece detectable with a straightedge across the joint |
| Fastening | Fastener pattern matches the approved fastener schedule; all heads set without crushing the profile |
| Door operation | Door swings, latches, and closes without contacting the casing at any point in its travel |
| Corrective action | Open joints, bowed casing, or inconsistent reveal corrected by recutting or replacement rather than filler; jamb or wall irregularities documented |
Field Fundamentals
Door casing conceals the gap between the jamb and the rough opening, but it does not correct jamb or wall defects. The reveal marked on the jamb face is the single controlling reference for every measurement in this project: head length, side-casing length, and miter position are all taken from that line, not from the wall opening or the jamb edge itself. Establishing the reveal accurately, on all three jamb faces, before any casing is cut is the largest single factor in avoiding mismatched joints.
RevealMarked on both jamb legs and the head from the Project 01 controlling line
Head CasingCut to the marked reveal with correct left and right miters
Side CasingMeasured independently per leg and mitered to match the head
FasteningSet to jamb and framing per the approved fastener schedule
Reveal, Miter, and Reference Face
Mark the reveal with a combination square held against the jamb edge, scribing a light pencil line the reveal distance in from the edge on both jamb legs and the head. Measure and cut with the casing's reference face up and the profile orientation consistent on every piece; a piece cut with the profile reversed will not match its mate at the miter even if the angle and length are correct.
FC-019 – FC-024
Installation Qualification
Interior Door Casing Installation
A. Jamb and Opening Verification
- Verify the door jamb is secure, plumb, adjusted, and operating correctly. Confirm the Project 05 and Project 06 inspection records for this opening show a passed status before proceeding.
- Confirm finished floor and jamb projection. Check the jamb reveal at the floor against the finished-floor reference recorded in Project 01.
- Inspect surrounding drywall for damage or excessive plane variation. Use a straightedge across the drywall adjacent to the jamb; if variation exceeds what the casing profile can follow, stop and refer the condition per Section E below before continuing.
B. Reveal Layout
- Establish and mark the approved casing reveal on both jamb legs and the head. Use the combination square to scribe the reveal line the distance set by the finish specification, transferred from the Project 01 controlling reveal line.
C. Head Casing
- Measure the head casing between the required long points. Take the measurement between the outside corners of the reveal marks on the two jamb legs.
- Cut the head casing with the correct left and right miters. Cut with the reference face up and the profile orientation consistent with the component schedule.
- Dry-fit the head and check reveal and joint position. Hold the head casing to its reveal marks and confirm both miter faces align with where the side casings will meet it.
D. Side Casing
- Measure each side casing independently. Measure from the head reveal mark to the floor or baseboard reference on each leg separately.
- Cut side-casing miters and square or profiled bottom ends as specified. Cut the top miter to match the head casing angle and the bottom end per the finish specification.
- Test-fit all three pieces together. Assemble the head and both side casings against the jamb without fastening and check both miter joints for closure.
- Adjust miters without changing the reveal. Use the block plane or sanding block for minor correction; recut any piece with an error the tolerance in Section F cannot absorb.
E. Fastening
- Apply adhesive only where specified. Follow the fastener and hardware schedule and any identified manufacturer instructions for the adhesive product.
- Position the head casing and secure it with initial fasteners. Hold the head to its reveal marks and drive the first fasteners per the fastener schedule, leaving room to adjust before final fastening.
- Install side casings while holding the reveal. Position each side casing to its reveal marks and confirm miter closure against the head before driving initial fasteners.
- Pin or fasten miter joints using the approved method. Drive the miter-joint fastener per the fastener schedule while holding the joint faces flush.
- Fasten the casing to jamb and wall framing with the specified fastener pattern. Complete the full fastener schedule from Section D at both the jamb leg and the wall-framing edge.
- Keep fasteners away from fragile profile edges. Follow the edge-distance guidance in the fastener schedule to avoid splitting the profile.
F. Inspection and Correction
- Check casing plane, reveal, joint alignment, and door operation. Apply the Acceptance Standards table in Section F of the Project Specification Sheet to every joint and reveal line.
- Correct proud miters, open joints, bowed casing, and inconsistent reveals. Recut or replace pieces that fail the acceptance standard; do not conceal the defect with filler.
- Set fasteners and prepare the casing for Chapter 18. Set all fastener heads below the surface without crushing the profile; do not fill or caulk at this stage.
- Document any jamb or wall irregularities that affected the installation. Record the condition, its location, and how it was accommodated or referred for correction.
Common Cutting Inspection
Apply the following checks to every casing piece before it is permanently fastened.
- Reference check: confirm every measurement was taken from the marked reveal line, not from the jamb edge or the rough opening.
- Orientation check: confirm the reference face and profile orientation are consistent across all three pieces before cutting.
- Miter accuracy check: confirm each miter angle against the combination square before the piece leaves the saw station.
- Independent-length check: confirm each side casing was measured on its own leg and not assumed equal to the other side.
- Dry-fit check: confirm all three pieces were test-fitted together before any piece was permanently fastened.
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Failure Points and Troubleshooting
Cleanup
- Remove offcuts and waste casing stock and sort reusable lengths per Project 02 staging procedures
- Return the finish nailer, nail set, block plane, and squares to their storage locations in working condition
- Vacuum or sweep saw and assembly areas of dust and small fasteners
- Store any documented jamb or wall irregularity notes with the room file established in Project 01
- Confirm the door operates freely through its full swing before leaving the opening in service
Field Terms
- Reveal
- The set-back distance between the casing's inside edge and the jamb edge, marked before any casing is cut.
- Head Casing
- The horizontal casing piece installed across the top of a door or window opening.
- Side Casing
- The vertical casing piece installed along a jamb leg.
- Long Point
- The longer corner of a mitered end, used as the standard measuring reference for miter cuts.
- Short Point
- The shorter corner of a mitered end.
- Reference Face
- The finished front face of a trim profile, kept consistent through marking, cutting, and installation.
- Dry-Fit
- Temporarily assembling trim pieces without permanent fasteners to check fit before installation.
- Pinning
- Driving a small-diameter fastener through a joint face to hold it flush and closed.
- Edge Distance
- The minimum distance from a profile edge at which a fastener may be driven without splitting the material.
- Proud Fastener
- A fastener head that sits above the trim surface instead of flush or slightly below it.
Skill Check
- Why is the reveal marked from the Project 01 controlling-line layout rather than measured directly from the jamb edge at the time of casing?
- Why must each side-casing leg be measured independently rather than cut to a single assumed length?
- What must be verified about a door jamb before casing measurement begins on that opening?
- Why is the assembly dry-fitted off the wall before any piece is permanently fastened?
- What is the correction for a miter joint with a visible gap at the face, and what must be reinspected afterward?
- What must the learner do if surrounding drywall plane variation exceeds what the casing profile can follow?
- Why are fasteners kept away from fragile profile edges, and where is the required edge distance defined?
- What must be checked about door operation after casing is fastened, and what is the corrective action if the door contacts the casing?
- Why is filler not an acceptable correction for a bowed casing piece or a major open joint?
- What condition must be documented, and where, when a jamb or wall irregularity affects the installation?
Competency Rubric
| Competency | Independent Pass Standard | Not Demonstrated | With Assistance | Independently |
|---|---|---|---|---|
| FC-019 | Establishes and marks the casing reveal on both jamb legs and the head from the approved controlling-line layout | |||
| FC-020 | Cuts head casing to the correct length and miter angles with profile orientation preserved | |||
| FC-021 | Measures and cuts each side casing independently to the correct length and miter angle | |||
| FC-022 | Fastens casing to jamb and wall framing using the approved fastener pattern without damaging the profile | |||
| FC-023 | Aligns and pins miter joints at the correct reveal without distorting the assembly | |||
| FC-024 | Inspects the finished casing for reveal, joint alignment, casing plane, and unimpaired door operation, and corrects defects found |
Mark one column per competency. Only Demonstrated Independently awards the competency; Demonstrated with Assistance authorizes additional supervised practice but does not complete the requirement.
Inspection Checklist — Door Casing Readiness Worksheet
| Item | Inspected (Y/N) | Defect Found (Y/N) | Corrected (Y/N) | Reinspected (Y/N) | Correction |
|---|---|---|---|---|---|
| Jamb operation verified | |||||
| Reveal marked on both legs and head | |||||
| Head casing miters | |||||
| Side casing miters (hinge side) | |||||
| Side casing miters (strike side) | |||||
| Dry-fit and joint closure | |||||
| Fastener pattern and edge distance | |||||
| Casing plane and reveal consistency | |||||
| Door operation through full swing |
Total open deficiencies: ____________ Total closed deficiencies: ____________
Jamb or wall irregularities documented: ______ Date: ____________ Inspector name: ____________
Performance Check
With the casing installed, review the assembly against the Acceptance Standards table and confirm the reveal is consistent along both jamb legs and the head, both miter joints are closed with no visible gap under normal room light, no proud corner or twisted piece is detectable with a straightedge, the fastener pattern matches the approved schedule with all heads set without crushing the profile, and the door swings, latches, and closes without contacting the casing at any point in its travel. Complete the Readiness Worksheet and document any jamb or wall irregularities before beginning Project 05 on the next opening or proceeding to Project 07.
Project Closeout
You have completed the fourth project in the interior finish carpentry sequence: installing interior door casing. This project required you to establish the casing reveal on both jamb legs and the head from the approved controlling-line layout (FC-019), cut head casing to the correct length and miter angles (FC-020), cut and independently measure side casing (FC-021), fasten casing to jamb and wall framing using the approved fastener pattern (FC-022), align and pin miter joints without distorting the reveal (FC-023), and inspect the finished assembly for reveal, joint alignment, plane, and door operation (FC-024).
You now have a permanently installed door-casing assembly with fasteners set and ready for surface preparation. That assembly remains unfilled and uncaulked until Project 18, after every trim assembly in the room is complete.
Store the reveal measurements and any documented jamb or wall irregularities with the room file established in Project 01. You will reference this record again in Project 18 and in the Chapter 20 capstone.