Install Fiberglass Batt Insulation in Wall Cavities

A. Finished-Project Specification

Deliverable: every assigned wall cavity filled with fiberglass batt insulation matching the approved width, thickness, thermal rating, and facing, fitted around wiring, boxes, pipes, bracing, and blocking without gaps, voids, folded corners, slumping, or damaging compression, inspected for full top, bottom, edge, and back contact, and photographed before concealment.

B. Cavity Fit Schedule

Cavity Type	Required Fit Method	Common Failure
Standard, unobstructed	Single batt cut to measured height, full edge contact on all sides	Batt cut short, leaving a gap at the top or bottom plate
Horizontal wiring	Batt split into front and back layers so cable sits between two full-thickness layers	Batt compressed against the cable instead of split around it
Electrical box	Batt notched to fit around the box without stuffing compressed material behind it	Loose fiberglass packed behind the box, creating a dense compressed mass
Pipe or brace	Batt cut around the obstruction to preserve full depth on both sides	Batt torn or crushed to force it past the obstruction
Narrow or irregular	Single accurately cut piece filling the full irregular shape	Loose scraps stuffed into the void instead of one fitted piece

C. Material Takeoff

• Batt product: width, thickness, thermal rating, and facing exactly as identified in the approved wall-insulation schedule.
• Quantity: sufficient batts to cover every assigned cavity at full width and height, plus a reasonable allowance for cutting waste around obstructions.
• Fasteners: staples only if the approved facing-attachment method specifies stapled facing tabs; otherwise none required.

D. Acceptance Standards

Check	Standard
Full contact	Every cavity shows full contact at the top plate, bottom plate, both stud edges, and the back of the cavity, with no visible gap
Compression	No batt is compressed below its manufactured thickness anywhere in the cavity, including behind boxes and obstructions
Wiring fit	Every horizontal wire has insulation both behind and in front of it, achieved by splitting the batt rather than compressing it against the cable
Box fit	Every electrical box is fitted with a notched batt and is not covered or buried in compressed insulation
Facing orientation	Facing orientation and attachment match the approved wall-insulation schedule in every cavity
Clearance	No insulation contacts a non-IC recessed light, flue, chimney, or other restricted heat-producing component
Documentation	Every completed cavity is photographed before drywall, with product, cavity count, deficiencies, and corrections recorded

E. Preparation — Review and Verification

1. Review the wall-insulation schedule, cavity dimensions, batt product, facing requirements, fire restrictions, and inspection stage. Confirm the schedule matches the wall section you are assigned before cutting any material.
2. Confirm that air sealing, rough systems, fireblocking, and required inspections are complete. Obtain sign-off or written confirmation from the responsible party for any inspection you did not personally witness.
3. Verify that cavities are dry, clean, and free of debris, pests, and hazardous materials. Exclude and refer any cavity that fails this check before proceeding to the next step.

F. Measurement and Batt Selection

1. Measure stud spacing, cavity depth, blocking, wiring, pipes, boxes, and irregular geometry. Record measurements for each cavity independently rather than assuming uniform framing across the wall.
2. Select batts matching the approved width, thickness, thermal rating, and facing. Confirm the product label against the schedule before cutting.

G. Cutting

1. Stage cutting on a clean surface using the approved insulation knife and straightedge. Keep the cutting surface free of debris that could contaminate or damage the batt facing.
2. Cut batts slightly oversize only as directed to obtain full edge contact. Do not cut batts undersize, which leaves gaps at the plates or stud edges.

H. Placement and Fitting

1. Place the batt from top to bottom without folding or forcing it. Support the batt as you position it so it does not sag or twist before reaching the bottom plate.
2. Split the batt around horizontal wiring so insulation lies behind and in front of the cable. Do not compress the batt flat against the cable; separate it into two layers with the wire between them.
3. Fit insulation around electrical boxes without stuffing large compressed masses behind them. Notch the batt to the box outline rather than packing loose material behind it.
4. Cut around pipes, bracing, and blocking to preserve full depth on both sides. Make relief cuts sized to the obstruction rather than tearing an opening larger than needed.
5. Fill narrow and irregular spaces with accurately cut pieces rather than scraps loosely packed into voids. Measure and cut a single piece for each irregular space where practical.
6. Keep facing orientation and attachment consistent with the approved vapor-control design. Verify facing direction against the schedule before placing each batt.
7. Do not staple facing in a manner that creates gaps or violates the specified installation. If stapling is required, place staples on the flange only, without pulling the facing away from the framing.

I. Clearances and Restricted Components

1. Maintain clearances around non-IC lights, flues, chimneys, heat-producing devices, and other restricted components. Verify each component's listing and required clearance before insulating near it, and stop if the listing cannot be confirmed.
2. Do not cover junction boxes or serviceable equipment. Leave every box, panel, and access point fully visible and reachable.

J. Inspection and Documentation

1. Inspect every cavity for top, bottom, edge, and back contact. Use a flashlight to check the back of each cavity, not just the visible front face.
2. Correct gaps, compression, folded corners, slumping, or wrong-facing orientation. Remove and refit any batt that fails the inspection rather than patching over a deficiency.
3. Photograph the completed wall before drywall. Capture each cavity clearly enough to verify fill quality from the photograph alone.
4. Document batt product, cavity count, deficiencies, and corrections. Record this information on the project worksheet for use in the Chapter 19 final inspection.