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Safety Cue
Task-specific safety guidance for ordinary work hazards.
Chapter 11
Install Headwall and Apron Flashing
Measure, cut, form, and integrate apron or headwall flashing at a roof-to-vertical-wall transition, coordinating the flashing with underlayment, wall drainage, and adjoining shingle courses so wall and roof water discharge onto the finished roof surface rather than behind it.
Field Cue System
These cues appear at the point of work. They identify safety, code, manufacturer, and measurement issues before they become rework or hazards.
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Critical Safety Cue
Serious injury, fall, or major damage is possible.
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Field Safety Cue
Practical work-area safety: footing, weather, housekeeping, and access.
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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 materials, fastening schedules, and equipment.
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Measurement Cue
Slope, span, clearance, and reference-point guidance.
Job Overview
This chapter qualifies you to fabricate and install apron or headwall flashing at a roof-to-vertical-wall transition and to integrate it with the roof covering and wall-drainage layer in the correct shingle-lap order. The finished work product is one continuous, corrosion-compatible headwall or apron flashing assembly, dry-fitted, fastened, sealed at approved locations only, and photographed before wall finishes conceal it.
You will measure the headwall from fixed references, cut and form the flashing including end dams and corner returns, integrate the lower roof leg with underlayment and shingles in the manufacturer-controlled order, fasten only in approved locations, lap multiple sections correctly, integrate the wall leg behind the WRB, counterflashing, or cladding, and inspect the completed transition before it is covered.
This chapter builds directly on the roof-covering work established in Chapter 8 and the sidewall step-flashing method taught in Chapter 10. A headwall crosses the slope rather than running along it, so the flashing must carry water across the full width of the wall intersection in a single, continuous, laterally lapped assembly rather than as a shingle-by-shingle system.
Skills You Will Demonstrate
- RF-061 — Measure headwall flashing length, corners, and end conditions from defined references.
- RF-062 — Cut metal flashing to the approved profile using approved tools without damaging its coating.
- RF-063 — Install apron flashing in the correct relationship to the roof covering and wall drainage layer.
- RF-064 — Lap underlayment and adjoining shingle courses with the flashing in the correct shingle-lap order.
- RF-065 — Seal exposed transitions only at approved locations using compatible sealant.
- RF-066 — Inspect the completed headwall assembly for coverage, laps, fastening, and drainage direction.
Where This Skill Fits
Headwall and apron flashing depends on the deck, underlayment, and roof-covering work completed in Chapters 1, 5, and 8, and on the wall-drainage relationship taught alongside step flashing in Chapter 10. It must be integrated while the surrounding shingle courses are installed; it may not be inserted after the shingle field is complete unless an approved repair detail specifically permits it.
This chapter's flashing sequence feeds directly into later ridge, ventilation, and gutter work whenever a headwall condition is present on the Chapter 20 capstone structure, and it establishes the flashing-integration discipline used again in Chapter 12 for penetrations and in Chapter 18 for leak diagnosis.
Scope and Intended Use
This chapter covers:
- reviewing the approved headwall detail, flashing profile, wall-leg height, roof-leg width, metal type, end dams, corner transitions, underlayment relationship, counterflashing, and siding clearance
- measuring the headwall length and identifying inside corners, outside corners, step-flashing transitions, and end conditions
- cutting and forming apron flashing, end dams, corner returns, hems, and kickout transitions from an approved metal-cut and lap plan
- dry-fitting the flashing and integrating the lower roof leg with underlayment, membrane, and shingles in the manufacturer-controlled order
- fastening only in approved locations, lapping multiple sections to shed water, and integrating the wall leg behind WRB, counterflashing, cladding, or trim
- applying compatible sealant only at approved end joints, reglets, corners, or terminations
- inspecting and documenting the completed flashing before wall finishes are installed
This chapter does not authorize the learner to:
- select an unstated flashing profile, wall-leg height, roof-leg width, or metal type; these are set by the approved headwall detail and this chapter does not substitute a different design
- bridge a designed drainage opening or weep path with sealant, or use sealant as a substitute for required flashing, laps, fastening, or drainage geometry
- cut, notch, or fasten through siding, trim, or wall-cladding systems beyond the clearance and integration steps this chapter specifically authorizes
- insert headwall flashing beneath two completed shingle fields unless an approved repair detail specifically permits it; this chapter assumes integration while surrounding courses are being installed
Any headwall condition that does not match the approved detail, or any wall assembly requiring counterflashing beyond this chapter's scope, must be referred to the responsible authority before the flashing is installed.
Reference Conventions
Establish these references before recording any measurement or cutting any metal, and use them consistently across the specification sheet and inspection record.
| Term | Definition |
|---|---|
| Headwall | A vertical wall surface that meets a roof plane across its slope, requiring flashing that carries water laterally before it drops onto the roof below |
| Apron flashing | The flashing piece at the base of a headwall that laps over the roof covering and turns up against the wall |
| Roof leg | The horizontal portion of the flashing that bears on and integrates with the roof covering |
| Wall leg | The vertical portion of the flashing that turns up the wall surface and integrates behind the WRB, counterflashing, or cladding |
| End dam | A formed upturn at the end of a flashing section that prevents water from running off the side of the flashing at a termination |
| Reglet / counterflashing | A wall-mounted receiving detail or overlapping metal component that covers the top of the wall leg |
| Kickout transition | The detail that directs water from a headwall or sidewall condition away from the wall and into the gutter or roof surface below |
Headwall Flashing Record
Before beginning fabrication, record the controlling documents and location identification directly on the flashing documentation form:
Project / address: ______ Headwall detail revision: ______ Location on roof plan: ______
Date started: ____________ Installer name: ____________
Prerequisites
- Chapter 1 deck-readiness decision issued as proceed or conditional-proceed with corrections completed for the affected roof plane and wall intersection
- Chapter 2 roof-access and fall-protection system established and accepted for the work positions this chapter requires
- Roof deck, wall surface, membrane, underlayment, and adjoining roofing courses at the headwall location complete and ready for integrated flashing work
- Approved headwall detail, flashing profile, wall-leg height, roof-leg width, metal type, end-dam requirements, corner-transition details, underlayment relationship, counterflashing detail, and siding clearance obtained and confirmed current
- Compatible flashing metal, fasteners, and sealant staged and confirmed against the approved specification
Common Field Fundamentals
A headwall is different from a sidewall. A sidewall runs along the slope and is flashed piece-by-piece with step flashing integrated course by course, as taught in Chapter 10. A headwall runs across the slope, so the flashing must be a continuous run (or a run of laterally lapped sections) wide enough to carry the full width of water arriving from above the wall. Getting the roof-leg and wall-leg relationship right, and keeping every lap oriented to shed water downslope and across the run in the approved direction, is the central skill of this chapter.
Roof legIntegrates with underlayment and shingles beneath and above per the approved detail
Wall legTurns up behind WRB, counterflashing, or cladding at the required height
End damsPrevent side-running water at terminations and corners
Corner transitionsInside and outside corners formed without open gaps or reverse laps
Multi-section lapsOriented to shed water in the prevailing drainage direction
Fastener zonesApproved locations only, kept out of primary water paths
Sealant zonesApproved end joints, reglets, corners, or terminations only
Reference methodEvery measurement and lap recorded against the approved headwall detail
Roof-Leg and Wall-Leg Integration
Integrate the lower roof leg with underlayment, membrane, and shingles in the manufacturer-controlled order so water from the wall drains onto the roof covering rather than behind it. Integrate the wall leg behind WRB, counterflashing, cladding, or trim components in the same shingle-lap sequence, maintaining the required clearance between roofing and siding or trim.
RF-061 – RF-066
Flashing Fabrication / Integrated Installation
Headwall and Apron Flashing Installation
A. Finished-Work Specification
Deliverable: one continuous headwall or apron flashing assembly covering the full measured length of the wall intersection, formed with the specified end dams and corner transitions, dry-fitted, integrated with underlayment and shingles in the approved sequence, fastened only at approved locations, sealed only at approved terminations, and photographed before wall finishes conceal it.
B. Governing Documents
| Document | Confirmed Current | Notes |
|---|---|---|
| Approved headwall / apron flashing detail | ||
| Flashing manufacturer's instructions | ||
| Underlayment and roofing-system specification | ||
| Wall WRB / counterflashing / siding-system detail | ||
| Chapter 1 roofing-readiness decision | ||
| Chapter 2 roof-access and fall-protection record |
C. Acceptance Standards
| Check | Standard |
|---|---|
| Roof-leg coverage | Matches the approved roof-leg width across the full measured headwall length |
| Wall-leg height | Matches the approved wall-leg height and integrates behind WRB, counterflashing, or cladding |
| End dams | Formed at every required termination; no side-running water path at an end condition |
| Corner transitions | Formed without open gaps, reverse laps, or exposed unsupported metal |
| Multi-section laps | Meet the specified lap dimension and are oriented to shed water in the prevailing drainage direction |
| Fasteners | Located only in approved zones, out of primary water paths |
| Sealant | Present only at approved end joints, reglets, corners, or terminations; no bridging of designed drainage openings |
| WRB / cladding integration | Wall leg integrated in correct shingle-lap order with siding and trim clearance maintained |
| Documentation | Flashing material, dimensions, laps, fastening, sealant, and inspection results recorded and photographed before concealment |
D. Required Project Sequence
- Review the approved headwall detail, flashing profile, wall-leg height, roof-leg width, metal type, end dams, corner transitions, underlayment relationship, counterflashing, and siding clearance. Confirm the revision or date on each document and record the confirmation on the governing-documents table above.
- Confirm that the roof deck, wall surface, membrane, underlayment, and adjoining roofing courses are ready for integrated flashing work. Verify the Chapter 1 readiness decision and Chapter 5 underlayment record cover this location before proceeding.
- Measure the headwall length from defined outside references and identify inside corners, outside corners, step-flashing transitions, and end conditions. Record each measurement and feature location against the roof sketch established in Chapter 1.
- Prepare a metal cut and lap plan that minimizes joints and directs each lap away from prevailing drainage. Identify the number of sections required, the length of each section, and the lap location and direction between sections before cutting any metal.
- Cut and form the apron flashing using approved tools without damaging its coating. Use tin snips or metal shears for cutting and seaming pliers or a metal brake for forming, and remove sharp burrs from every cut edge.
- Form end dams, corner returns, hems, or kickout transitions required by the detail. Form each feature to the exact dimension specified in the approved detail; do not approximate an end dam or corner return by eye.
- Dry-fit the flashing and verify continuous wall contact, roof bearing, corner fit, and drainage direction. Confirm the dry-fit before fastening any section, and correct any section that does not achieve continuous contact.
- Integrate the lower roof leg with underlayment, membrane, and shingles in the manufacturer-controlled order. Follow the exact layering sequence specified in the roofing-system instructions rather than a generalized shingle-lap assumption.
- Position the flashing so water from the wall drains onto the roof covering rather than behind it. Verify this relationship at every section before fastening.
- Fasten only in approved locations and keep exposed fasteners out of primary water paths. Use the specified fastener type and spacing and confirm each fastener location against the approved detail before driving it.
- Install adjoining shingle courses beneath or over the roof leg as required by the approved assembly. Coordinate this step directly with the Chapter 8 field-shingle sequence at this location; do not complete the shingle field first.
- Lap multiple flashing sections by the specified amount and orient laps to shed water. Verify each lap meets the minimum dimension from the cut and lap plan established in Step 4.
- Integrate the wall leg behind WRB, counterflashing, cladding, or trim components in shingle-lap order. Confirm the wall leg is fully covered by the wall-drainage layer or approved counterflashing before trim or siding is installed.
- Maintain required clearance between roofing and siding or trim. Measure the clearance against the approved specification and record any shortfall as a deficiency.
- Use compatible sealant only at approved end joints, reglets, corners, or terminations. Confirm sealant compatibility with the flashing metal and wall-drainage materials before application.
- Do not bridge designed drainage openings or weep paths with sealant. Identify every designed opening in the wall-drainage system before applying sealant near it.
- Inspect roof-leg coverage, wall-leg height, end dams, laps, fasteners, sealant, WRB integration, and water path. Compare each item to the Acceptance Standards table above.
- Correct short flashing, reverse laps, open corners, exposed fasteners, blocked drainage, or incompatible materials. Reinspect each corrected item against the same standard used in the original finding.
- Photograph concealed transitions before wall finishes are installed. Label each photograph with its location on the roof sketch.
- Record flashing material, dimensions, laps, fastening, sealant, and inspection results. Complete the documentation form and attach it to the project record before wall finishes proceed.
Common Headwall Flashing Checks
Apply the same checks to every headwall or apron condition on the roof, regardless of length or corner count.
- Coverage check: confirm the roof leg and wall leg meet the approved dimensions across the full measured length.
- Drainage-direction check: confirm every lap and the roof-leg position direct water onto the roof covering, not behind it.
- Corner and end-dam check: confirm every corner and termination is formed to the approved dimension without an open gap or reverse lap.
- Fastener-zone check: confirm every fastener is located only in an approved zone, out of primary water paths.
- Sealant-zone check: confirm sealant appears only at approved terminations and does not bridge a designed drainage opening.
- Documentation check: confirm dimensions, laps, fastening, sealant, and photographs are complete before wall finishes conceal the work.
Complete the Headwall Flashing Inspection Record below before wall finishes are installed.
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Failure Points and Troubleshooting
Cleanup
This chapter ends with a documented, photographed flashing assembly, not a pile of metal offcuts left on the roof or ground.
- Remove metal offcuts, sharp trim scraps, and packaging from the roof surface and the ground below
- Store leftover flashing metal for reuse in later authorized flashing work
- Remove excess sealant from exposed roofing and wall surfaces before it cures
- Compile the flashing documentation form and photographs into the project record
- Confirm the wall finish contractor or crew has the photographs and documentation before covering the wall leg
Field Terms
- Headwall
- A vertical wall surface that meets a roof plane across its slope.
- Apron Flashing
- The flashing piece at the base of a headwall that laps over the roof covering and turns up against the wall.
- Roof Leg
- The horizontal portion of the flashing that bears on and integrates with the roof covering.
- Wall Leg
- The vertical portion of the flashing that turns up the wall surface and integrates behind the WRB, counterflashing, or cladding.
- End Dam
- A formed upturn at the end of a flashing section that prevents side-running water at a termination.
- Reglet / Counterflashing
- A wall-mounted receiving detail or overlapping metal component that covers the top of the wall leg.
- Kickout Transition
- The detail that directs water from a headwall or sidewall condition away from the wall and into the gutter or roof surface below.
- Weep Path
- A designed opening in a wall-drainage system that must remain open and unsealed.
Skill Check
- Why must headwall flashing be integrated while surrounding shingle courses are installed rather than after the shingle field is complete?
- What is the difference between the roof leg and the wall leg of an apron flashing assembly, and what must each integrate with?
- Why is a metal cut and lap plan prepared before any flashing metal is cut?
- What condition must an end dam satisfy at a flashing termination?
- Why is sealant not an acceptable substitute for required flashing, laps, fastening, or drainage geometry?
- What must be verified before applying sealant near a wall-drainage opening?
- Where are fasteners permitted on the roof leg, and why must they avoid primary water paths?
- What must be confirmed about the wall leg before siding or trim is installed?
- Why must the completed flashing be photographed before wall finishes conceal it?
- What are the two possible outcomes when a corner transition does not dry-fit cleanly, and which one is authorized under this chapter?
Competency Rubric
| Competency | Independent Pass Standard | Not Demonstrated | With Assistance | Independently |
|---|---|---|---|---|
| RF-061 | Measures headwall length, corners, and end conditions from defined references and records them accurately | |||
| RF-062 | Cuts and forms metal flashing to the approved profile using approved tools without damaging the coating | |||
| RF-063 | Installs apron flashing in the correct relationship to the roof covering and wall-drainage layer | |||
| RF-064 | Laps underlayment and adjoining shingle courses with the flashing in the correct shingle-lap order | |||
| RF-065 | Applies compatible sealant only at approved locations without bridging designed drainage openings | |||
| RF-066 | Inspects and documents the completed headwall assembly for coverage, laps, fastening, and drainage direction |
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 — Headwall Flashing Inspection Record
| Item | Condition Found | Correction Required | Corrected (Y/N) | Reinspection Result |
|---|---|---|---|---|
| Roof-leg coverage | ||||
| Wall-leg height | ||||
| End dams | ||||
| Corner transitions | ||||
| Multi-section laps | ||||
| Fastener locations | ||||
| Sealant locations | ||||
| WRB / counterflashing integration | ||||
| Siding / trim clearance |
Flashing acceptance decision: ______ (Accepted / Corrections Required / Refer to Responsible Authority) Date: ____________ Inspector name: ____________
Performance Check
With the headwall flashing complete, review the Headwall Flashing Inspection Record against the Acceptance Standards table and confirm the roof-leg and wall-leg dimensions match the approved detail, every corner and end dam is formed without a gap or reverse lap, every fastener is located in an approved zone, sealant appears only at approved terminations without bridging a designed drainage opening, and the wall leg is fully integrated behind the WRB or counterflashing. Photograph the completed assembly and record dimensions, laps, fastening, and sealant locations before wall finishes are installed.
Chapter Closeout
You have completed the headwall and apron flashing chapter: measuring, fabricating, and integrating a continuous flashing assembly at a roof-to-wall transition. This chapter required you to measure headwall flashing from defined references (RF-061), cut and form metal flashing to the approved profile (RF-062), install apron flashing in the correct relationship to the roof covering and wall drainage layer (RF-063), lap underlayment and shingles with the flashing in the correct order (RF-064), seal exposed transitions only at approved locations (RF-065), and inspect the completed assembly for coverage, laps, fastening, and drainage direction (RF-066).
You now have a continuous, documented headwall flashing assembly integrated with the surrounding roof covering and wall-drainage layer. That record carries directly into the next chapter: flashing a plumbing vent or other roof penetration using the same integration discipline established here.
Store the completed flashing documentation and photographs with the project record. Chapter 18 references this record if a leak is later diagnosed near this wall intersection.