Seal Attic Bypasses and Chase Openings

Job Overview

This project qualifies you to block and air-seal accessible attic bypasses, open chases, dropped soffits, partition tops, and heat-source transitions identified during the Chapter 1 inspection. The finished work product is a continuous attic-plane air barrier at every assigned bypass, with rigid backing installed and sealed at large openings, partition tops and penetrations sealed with compatible product, chimney and flue transitions protected with approved noncombustible blocking and clearance, and every closure photographed and mapped before loose-fill insulation covers the work.

You will review the attic air-barrier plan and ventilation layout, establish safe attic access, identify open chases and heat-source penetrations, measure and install rigid backing over large bypasses, seal partition tops and penetrations, install noncombustible blocking and clearance at chimneys and flues, build insulation dams around required clearance zones, and inspect the completed attic plane from both sides where accessible.

This project depends directly on the Chapter 1 inspection record and, where applicable, on the framing-joint and service-penetration seals completed in Chapters 3 and 4. The bypass closures completed here must be finished and inspected before Chapter 6 baffles and Chapter 10 loose-fill insulation can proceed, because loose-fill material poured over an open bypass will fall through it and fail to air-seal the assembly.

Skills You Will Demonstrate

• IN-025 — Identify attic bypasses at chases, soffits, partition tops, and penetrations.
• IN-026 — Block open chases using approved rigid air-barrier backing.
• IN-027 — Seal around chimneys and flues using approved noncombustible materials and clearances.
• IN-028 — Seal dropped soffits without trapping recessed fixtures or ducts.
• IN-029 — Seal partition tops and associated penetrations with compatible sealant.
• IN-030 — Inspect the completed attic air barrier for continuity, ventilation clearance, and heat-source protection.

Where This Skill Fits

Chapters 3 and 4 sealed framing joints and service penetrations at the wall and floor levels. This chapter completes the air barrier at the attic plane, where the largest and most consequential bypasses typically occur: open wall cavities that run straight from a wall stud bay into the attic, plumbing and duct chases, dropped soffits over cabinets, and the partition-top gap that runs the length of every interior wall.

Every bypass closure completed here must be finished, inspected, and photographed before Chapter 6 installs ventilation baffles and before Chapter 10 installs loose-fill attic insulation. Loose-fill material cannot correct an open bypass; it will simply fall through into the wall cavity below, wasting material and leaving the air leak in place. The clearances and noncombustible blocking installed here at chimneys and flues also establish the exclusion zones that Chapter 10's insulation dams must respect.

Scope and Intended Use

This project covers:

• reviewing the attic air-barrier plan, ventilation layout, fireblocking requirements, and heat-source clearances identified in the chapter project specification
• identifying open wall cavities, plumbing chases, duct shafts, dropped soffits, stair openings, partition tops, tub surrounds, and cabinet chases from safe attic access
• identifying chimney, flue, fireplace, recessed-light, fan, and other heat-producing penetrations requiring clearance
• measuring bypass openings and installing approved rigid air-barrier backing with mechanically supported edges
• sealing partition-top joints and associated wire or pipe penetrations with the approved sealant
• closing dropped-soffit openings at the attic plane without trapping recessed fixtures or ducts
• installing approved noncombustible blocking and high-temperature sealant at chimneys and flues, and building insulation dams around required clearance zones
• inspecting the completed attic air barrier from both sides where accessible and documenting all concealed closures

This project does not authorize the learner to:

• use combustible foam, caulk, wood blocking, or standard insulation within a prohibited fire-clearance zone at any chimney, flue, or heat-producing component
• seal, block, or reduce a soffit-to-ridge ventilation channel, attic intake or exhaust vent, or any required ventilation path
• disturb, sample, or work near vermiculite, suspected asbestos, active knob-and-tube wiring, or other stop-work hazardous conditions
• install loose-fill or batt attic insulation; that work belongs to Chapters 10 and 11 and may not begin until this chapter's closures are inspected

Any condition meeting a stop-work criterion in Step 5 must halt work in that area and be referred to the appropriate qualified professional before the bypass closure continues.

Prerequisites

• A completed Chapter 1 inspection record identifying every attic bypass, chase, dropped soffit, partition top, and heat-source penetration in the assigned attic, with location references
• Confirmation that any hazardous-material concerns identified in Chapter 1 have been cleared or referred to qualified remediation before this chapter's attic entry
• Confirmation that active roof leaks and wet attic framing have been corrected before bypass closures are installed
• A safe, ventilated, hazard-controlled work area established under the Chapter 2 procedure
• The chapter project specification identifying the approved rigid backing material, compatible sealant, and noncombustible blocking product for this attic

Project Specification Sheet

A. Finished Project

One continuous attic-plane air barrier across every assigned bypass: rigid backing installed and sealed at open chases and large bypasses, partition tops and their penetrations sealed with compatible product, dropped soffits closed at the attic plane, chimney and flue transitions protected with approved noncombustible blocking and required clearance, and insulation dams built around every heat-source clearance zone. The closure is limited to the bypasses, chases, and heat-source transitions identified in the Chapter 1 inspection record and the chapter project specification; it does not include ventilation-baffle installation, which is a Chapter 6 project.

B. Component Schedule

C. Material Takeoff

Obtain the rigid backing material, compatible sealant or foam, noncombustible blocking material, and high-temperature sealant identified in the chapter project specification, in the quantity needed to cover every bypass, chase, soffit, and heat-source transition recorded in the Chapter 1 inspection record for this attic, plus the waste allowance stated in the project specification. Do not substitute a different backing, sealant, or blocking product without confirming compatibility with the specified assembly and required fire clearance.

D. Fastener and Hardware Schedule

E. Reference Conventions

Attic plane: the horizontal air-barrier surface at the ceiling level of the attic, where bypasses are closed before loose-fill insulation is added. Bypass: any opening that allows air to move from a lower conditioned space into the attic without crossing a continuous air barrier. Clearance zone: the area around a heat-producing component within which insulation, foam, and combustible material are prohibited by the specified clearance distance. Insulation dam: a rigid barrier built to keep loose-fill insulation out of a clearance zone, ventilation path, or attic access area.

F. Acceptance Standards