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Safety Cue
Task-specific safety guidance for ordinary work hazards.
Project 16
Air-Seal and Insulate Around Ducts in Unconditioned Spaces
Complete the building-envelope air sealing and insulation around one accessible duct, boot, chase, or mechanical penetration in an unconditioned space without altering the duct system itself, while preserving duct insulation, condensate drainage, and required service access.
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, fire, or major damage is possible.
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Field Safety Cue
Practical work-area safety: lighting, footing, access, 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 instruments.
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Measurement Cue
Depth, clearance, and documentation guidance.
Job Overview
This project qualifies you to complete the building-envelope air sealing and thermal insulation around one accessible duct, boot, chase, or mechanical penetration located in an unconditioned space such as an attic, crawlspace, garage, or unconditioned basement, without performing any duct-sealing or duct-repair work covered under Book 9. The finished work product is a continuously air-sealed and insulated enclosure boundary around the assigned duct area, with the duct's own insulation preserved at full thickness, service access maintained, and condensate drainage undisturbed.
You will review the duct location and HVAC records, confirm the duct is de-energized where work could disturb it, inspect for existing duct-insulation damage or moisture, identify the enclosure boundary around the duct, seal framing and service gaps adjacent to the duct, seal boot transitions to the building air barrier, repair minor duct-insulation facing tears using HVAC-compatible methods only, install building insulation around the duct area without compressing the duct's own insulation, and inspect the finished area for gaps, thermal bypasses, and blocked access.
This project depends on prior air-sealing and cavity-inspection chapters and depends specifically on Book 9 duct-sealing and duct-insulation records, which this chapter does not repeat or redo. It feeds directly into the Chapter 19 final quality inspection and the Chapter 20 capstone, both of which verify duct-adjacent thermal control as part of the complete thermal enclosure.
Skills You Will Demonstrate
- IN-091 — Identify ducts located in unconditioned space and the enclosure boundary around them.
- IN-092 — Seal duct-adjacent framing and service gaps using compatible air-sealing materials.
- IN-093 — Protect existing duct insulation from damage and compression during building-insulation work.
- IN-094 — Seal boot connections to the building air barrier without blocking registers or dampers.
- IN-095 — Maintain service access to filters, dampers, shutoffs, cleanouts, and condensate drains.
- IN-096 — Inspect the completed duct area for thermal-bypass gaps and confirm airflow-related conditions after work.
Where This Skill Fits
Framing-joint sealing from Chapter 3, service-penetration sealing from Chapter 4, and attic bypass work from Chapter 5 all apply around ducts the same way they apply anywhere else in the enclosure. What makes duct-adjacent work distinct is the requirement to never treat the duct itself, its insulation, or its connections as part of this chapter's scope. Any duct leakage, disconnection, or insulation damage beyond a minor facing tear must be referred to Book 9.
This chapter's completed record becomes one line item in the Chapter 19 final inspection and one required task in the Chapter 20 capstone sequence, both of which confirm that enclosure work around mechanical systems did not compromise duct performance, service access, or condensate management.
Scope and Intended Use
This project covers:
- identifying the building-enclosure boundary around one accessible duct, boot, chase, or mechanical penetration
- air-sealing framing and service gaps adjacent to the duct using compatible materials
- sealing boot-to-floor, boot-to-wall, or boot-to-ceiling transitions to the building air barrier
- repairing minor tears in duct-insulation facing only, using the approved HVAC-compatible method
- installing building insulation around the duct area while preserving full duct-insulation thickness
- maintaining clearances from flues, exhaust ducts, motors, transformers, and other heat-producing equipment
- preserving service platforms, filter access, shutoffs, cleanouts, and electrical clearances
This project does not authorize the learner to:
- seal, patch, reconnect, or otherwise repair the duct system itself; that work belongs to Book 9 and to a qualified HVAC contractor
- compress, remove, or replace the duct's own insulation beyond a minor facing repair
- block register openings, dampers, balancing devices, condensate drains, or filter access
- work on energized equipment, disturbed refrigerant lines, or duct systems showing signs of significant leakage, disconnection, or contamination
Any condition that meets a stop-work criterion in Step 5 of the Work Order must halt work in that area and be referred to a qualified HVAC contractor or other appropriate professional before this chapter's work continues.
Reference Conventions
Establish these references before beginning any duct-adjacent air-sealing or insulation work, and use them consistently throughout the project.
| Term | Definition |
|---|---|
| Duct-adjacent boundary | The building air-barrier and thermal boundary that passes near, around, or through a duct chase, boot, or mechanical penetration, distinct from the duct system itself |
| Boot connection | The transition where a duct or register boot passes through the floor, wall, or ceiling into the building envelope |
| Duct-insulation facing | The outer vapor-retarder or reflective layer on existing duct insulation, which may receive a minor tape repair under this chapter but may not be replaced or redesigned |
| Insulation dam | A supported barrier that prevents loose-fill or batt insulation from resting directly on and loading a flexible duct |
| Service access point | Any filter, damper, balancing device, shutoff, cleanout, or condensate drain that must remain reachable after this chapter's work is complete |
| Referral condition | Any duct leakage, disconnection, insulation damage beyond a minor facing tear, or energized-equipment hazard that must be referred to Book 9 or a qualified HVAC contractor rather than addressed in this chapter |
Duct-Area Air-Sealing and Insulation Record
Before beginning work on any duct area, record the location and coordination references directly on the project worksheet:
Structure/address: ______ Duct area location: ______ Date: ______
Book 9 duct-sealing/insulation record reviewed: ______ HVAC equipment shut down: ______ (Yes/No/Not required)
Prerequisites
- Completed Chapter 1 inspection record identifying this duct area as a deficiency or work-plan item
- Access to Book 9 duct-sealing and duct-insulation records for the assigned duct area
- Completed Chapter 3 framing-joint air sealing and Chapter 4 service-penetration sealing for the same general area, where applicable
- Confirmation that rough plumbing, electrical, and HVAC work in the area has passed required inspections
- Safe attic, crawlspace, garage, or basement access with adequate lighting
- Compatible sealant, foam, rigid backing, insulation, dam material, and HVAC-compatible repair tape staged and within their temperature and cure limits
Common Field Fundamentals
Duct-adjacent work always separates two questions: what belongs to the building enclosure, and what belongs to the duct system. Everything in this chapter answers only the first question. If a duct problem is discovered, document it and refer it; do not attempt to fix it as part of this project.
Framing/Service GapsAir-sealed using Chapter 3 and Chapter 4 compatible methods
Boot ConnectionsSealed to the building air barrier without blocking registers or dampers
Duct InsulationPreserved at full thickness; only minor facing tears repaired
Service AccessFilters, dampers, shutoffs, cleanouts, and condensate drains kept reachable
Building Envelope Versus Duct System
A duct passing through an unconditioned attic or crawlspace crosses the building's thermal and air-control boundary without being part of it. The building envelope must still be continuous around the penetration. Confusing the two systems leads to two common errors: sealing the building envelope so tightly that duct service access is buried, or attempting duct repairs that belong to a qualified HVAC contractor under Book 9.
IN-091 – IN-096
Air Sealing / Insulation / Mechanical Coordination
Duct-Area Air-Sealing and Insulation Work Order
A. Finished-Project Specification
Deliverable: one accessible duct, boot, chase, or mechanical penetration in an unconditioned space with continuous building-envelope air sealing and insulation completed around it, existing duct insulation preserved at full thickness, minor facing tears repaired only where authorized, and all filters, dampers, shutoffs, cleanouts, and condensate drains left accessible.
B. Duct-Area Component Schedule
| Component | Treatment | Material | Preparation |
|---|---|---|---|
| Framing gaps adjacent to duct | Air-seal per Chapter 3 method | Compatible caulk or approved low-expansion foam | Clean, dry substrate; rigid backing at large openings |
| Service penetrations near duct | Air-seal per Chapter 4 method | Caulk, foam, gasket, or approved firestop as required | Identify service, temperature, and fire requirement first |
| Boot-to-floor/wall/ceiling transition | Seal to building air barrier | Compatible sealant or approved foam | Do not block register, damper, or balancing device |
| Duct-insulation facing (minor tear only) | Patch tear only | HVAC-compatible repair tape | Confirm tear is minor; larger damage is a referral condition |
| Building insulation around duct | Install without compressing duct insulation | Batt or rigid insulation matching the approved schedule | Use dams or supports to prevent loose fill from loading ducts |
C. Acceptance Standards
| Check | Standard |
|---|---|
| Framing and service seals | Continuous, bonded, and free of pinholes, skips, or missed transitions adjacent to the duct |
| Boot connection | Sealed to the building air barrier with no gap greater than the product's permitted joint width and no blocked register or damper |
| Duct insulation thickness | Equal to or greater than the pre-work measurement at the same recorded locations |
| Facing repair | Limited to minor tears using HVAC-compatible tape; no repair extends to structural or connection damage |
| Building insulation fit | Full depth around the duct area with no gaps, voids, or compression against the duct |
| Service access | Filters, dampers, shutoffs, cleanouts, and condensate drains remain reachable without removing building insulation |
D. Preparation — Records and Shutdown
- Review the duct location, HVAC drawings, duct-insulation condition, air-barrier detail, equipment access, condensate, and fire-clearance requirements. Record the source document and date reviewed for each.
- Coordinate with Book 9 duct-sealing and insulation records. Confirm the duct itself has already been sealed and insulated under Book 9 procedures before beginning this chapter's building-envelope work.
- Shut down HVAC equipment when work could disturb ducts, wiring, or controls. Record the shutdown time and the person who authorized it, or record that shutdown was not required and state why.
E. Inspection and Stop-Work Decision
- Inspect for damaged duct insulation, condensation, disconnected ducts, leakage, pests, mold, and hazardous materials. Record the condition of the duct insulation and boot connection before any work begins.
- Stop work for wet insulation, refrigerant-line damage, energized equipment, severe contamination, or inaccessible mechanical defects. Record the condition as a referral, identify the qualified HVAC contractor or other professional required, and do not proceed with this chapter's work in that area until the referral is resolved.
F. Air Sealing Around the Duct Area
- Identify the enclosure boundary around the duct or chase. Mark where the building air barrier and thermal boundary pass the duct so the seal is complete rather than a partial patch.
- Seal framing and service gaps adjacent to the duct using compatible materials. Apply the Chapter 3 and Chapter 4 methods appropriate to each gap's size and service type.
- Seal boot-to-floor, boot-to-wall, or boot-to-ceiling transitions to the building air barrier. Apply a continuous bead or bond around the full perimeter of the transition.
- Do not block register openings, dampers, duct access, balancing devices, or condensate drains. Verify each remains fully operable after the seal cures.
G. Duct-Insulation Protection and Repair
- Repair minor tears in duct insulation facing only with the approved HVAC-compatible method. Confirm the tear is minor before proceeding; refer larger damage instead of attempting a repair.
- Do not compress duct insulation with new building insulation. Maintain a visible gap or supported separation between the building insulation and the duct's own insulation layer where the design requires it.
H. Building Insulation Installation
- Install insulation around the duct area while preserving the full duct-insulation thickness. Cut and fit building insulation to the surrounding framing, not against the duct's insulated surface.
- Use dams or supports to prevent loose fill from loading flexible ducts. Install dams before any loose-fill insulation is placed nearby.
- Maintain clearances around flues, exhaust ducts, motors, transformers, and heat-producing equipment. Confirm no insulation or sealant enters a prohibited clearance zone near the duct area.
- Preserve service platforms, filter access, shutoffs, cleanouts, and electrical clearances. Confirm each remains reachable without disturbing the completed insulation.
I. Inspection, Restoration, and Documentation
- Inspect for gaps, thermal bypasses, crushed duct insulation, buried access, and blocked ventilation. Correct any deficiency before concealing the area.
- Restore equipment and observe the area for condensation, movement, or airflow-related disturbance. Confirm the HVAC system operates normally after restoration.
- Document the air-sealing and insulation treatment and any HVAC repairs referred to Book 9. Record materials used, locations sealed, duct-insulation thickness before and after, and any referral made.
Common Inspection Quality Check
Review the completed duct-area work using the same checks regardless of which portion of the boundary was sealed.
- Boundary check: confirm the building air barrier is continuous around the duct, boot, or chase with no unsealed gap remaining.
- Duct-insulation check: confirm duct-insulation thickness at the recorded locations equals or exceeds the pre-work measurement.
- Access check: confirm filters, dampers, shutoffs, cleanouts, and condensate drains remain reachable.
- Clearance check: confirm no insulation or sealant entered a prohibited heat-source clearance zone.
- Referral check: confirm any duct defect beyond a minor facing tear was documented and referred rather than repaired in this chapter.
- Restoration check: confirm HVAC equipment was restored and observed for normal operation after the work.
Complete the Inspection Checklist below before concealing the duct area or beginning Chapter 17.
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Failure Points and Troubleshooting
Cleanup
This project ends with a sealed, insulated, and fully accessible duct area, not with excess foam, loose insulation, or unrestored equipment.
- Remove excess cured foam, sealant, and insulation debris from around the duct area
- Confirm all tools, sealant tubes, and foam cans are removed from the attic, crawlspace, or basement
- Confirm HVAC equipment has been restored to its normal operating condition
- Match every photograph to its corresponding worksheet entry and location reference
- File the completed duct-area record, including any Book 9 referral, with the project records
Field Terms
- Duct-Adjacent Boundary
- The building air-barrier and thermal boundary near a duct chase, boot, or mechanical penetration, distinct from the duct system itself.
- Boot Connection
- The transition where a duct or register boot passes through the floor, wall, or ceiling into the building envelope.
- Duct-Insulation Facing
- The outer vapor-retarder or reflective layer on existing duct insulation.
- Insulation Dam
- A supported barrier preventing loose-fill or batt insulation from loading a flexible duct.
- Service Access Point
- A filter, damper, balancing device, shutoff, cleanout, or condensate drain that must remain reachable.
- Referral Condition
- Any duct-system defect beyond a minor facing tear that must be referred to Book 9 or a qualified HVAC contractor.
- Thermal Bypass
- A path allowing air, and the heat it carries, to move around or through insulation without crossing a continuous air barrier.
- Condensate Drain
- The pipe or path carrying condensation away from HVAC equipment; must remain clear and reachable.
Skill Check
- Why must duct-system repairs be referred to Book 9 rather than performed as part of this chapter, even when the defect is discovered during this project?
- What is the difference between the building envelope's air barrier and the duct system, and why does confusing the two lead to errors in this project?
- Name three service access points that must remain reachable after this chapter's work, and explain why burying one of them is a failure.
- Why must duct-insulation thickness be measured both before and after installing building insulation nearby?
- Under what condition may a duct-insulation facing tear be repaired in this chapter, and what method is required?
- Why is an insulation dam required before loose-fill insulation is placed near a flexible duct?
- What conditions require HVAC equipment to be shut down before this chapter's work begins?
- List three stop-work conditions specific to duct-adjacent work and state the required response for each.
- Why must the finished work be observed for condensation, movement, or airflow disturbance after equipment is restored?
- How does this chapter's completed record feed into the Chapter 19 final inspection and the Chapter 20 capstone?
Competency Rubric
| Competency | Independent Pass Standard | Not Demonstrated | With Assistance | Independently |
|---|---|---|---|---|
| IN-091 | Identifies ducts in unconditioned space and correctly marks the building enclosure boundary around them | |||
| IN-092 | Seals duct-adjacent framing and service gaps continuously using compatible materials | |||
| IN-093 | Preserves full duct-insulation thickness and repairs only minor facing tears using the approved method | |||
| IN-094 | Seals boot connections to the building air barrier without blocking registers or dampers | |||
| IN-095 | Maintains reachable access to filters, dampers, shutoffs, cleanouts, and condensate drains | |||
| IN-096 | Inspects the completed duct area for gaps, thermal bypasses, and blocked access, and confirms normal airflow after restoration |
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 — Duct-Area Worksheet
| Item | Condition Before | Treatment Applied | Condition After | Photo Ref. | Referral (if any) |
|---|---|---|---|---|---|
| Framing gaps | |||||
| Service penetrations | |||||
| Boot connection | |||||
| Duct insulation/facing | |||||
| Building insulation | |||||
| Service access points |
HVAC equipment restored and observed: ______ (Yes/No) Book 9 referral filed: ______ (Yes/No/Not applicable)
Inspection declared complete: ______ (Pass/Fail) Date: ____________ Inspector name: ____________
Performance Check
With the duct-area work complete, review the worksheet against the Acceptance Standards table and confirm the building air barrier is continuous around the duct, boot, and service penetrations, duct-insulation thickness equals or exceeds the pre-work measurement, any facing repair was limited to a minor tear, no register, damper, or condensate drain was blocked, all service access points remain reachable, and HVAC equipment was restored and observed for normal operation. If any item is incomplete, return to the relevant portion of the duct area and complete it before concealing the work or beginning Chapter 17.
Project Closeout
You have completed the sixteenth project in the insulation and air-sealing sequence: air-sealing and insulating around ducts in unconditioned spaces. This project required you to identify ducts in unconditioned space and their enclosure boundary (IN-091), seal duct-adjacent framing and service gaps (IN-092), protect existing duct insulation from damage and compression (IN-093), seal boot connections to the building air barrier (IN-094), maintain service access to filters, dampers, shutoffs, cleanouts, and condensate drains (IN-095), and inspect the completed duct area for thermal-bypass gaps and airflow-related conditions (IN-096).
You now have a documented, continuously sealed and insulated duct-area boundary with duct insulation, drainage, ventilation, and service access preserved. That record carries directly into the next project: building and installing an insulated attic hatch or access cover that maintains the same standard of continuous air sealing and preserved access.
File your completed duct-area worksheet, before-and-after photographs, thickness measurements, and any Book 9 referral with the project records. You will reference this exact documentation at the Chapter 19 final quality inspection and again during the Chapter 20 capstone.