One-Hour Corridor Assembly Fails Inspection
A one-hour fire-rated corridor is being drywalled with one layer of 5/8 in. Type X on each side of 3-5/8 in. 20-gauge steel studs at 24 in. on center. Mineral wool fills the stud cavity. The framing inspection passed. The drywall installer placed boards vertically, aligned joints on opposite sides, and used 1-1/4 in. screws at 12 in. on center in the field and at the perimeter. The bottom board sits 3/4 in. above the floor. One electrical box for a fire-alarm device was cut through the board without a putty pad, and the joints were finished with lightweight ready-mixed compound. The inspector cites the assembly for missing perimeter fasteners at the top track and for the box penetration. The general contractor says the assembly is listed and the board is Type X, so it should pass.
1. Which field conditions matter to the fire rating, and why does the general contractor's reasoning miss the point?
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A listed assembly is a system, not just a board type. Type X board alone does not make the corridor rated if the fastening, joint treatment, penetration protection, and stud configuration do not match the listing. Aligned joints on opposite sides can create a continuous path for heat and smoke and may not match the listed staggered-joint condition. Missing perimeter fasteners at the top track can allow the board to pull away and expose the cavity under fire conditions. The electrical box cut through the board without a putty pad is a direct breach: the box must be protected with an approved firestop method, such as a putty pad listed for the assembly. The 3/4 in. floor gap may be acceptable only if the listing and firestop details allow it; it should not be ignored. Lightweight ready-mixed compound may be acceptable for finishing, but the joint system must follow the listed design. The contractor is treating a system requirement as a material substitution.
2. What corrections would you make before requesting re-inspection?
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First, verify the specific listed assembly and compare every field condition to it. Add the missing perimeter fasteners at the top track using the specified screw type and spacing, and check that screws are not overdriven. Protect the electrical box with a listed putty pad or other approved firestop method, and seal the annular space as required. If the listing requires staggered joints on opposite sides, one side may need to be rehung or the joints reinforced per the listing; surface taping alone does not correct alignment. Address the floor gap with the listed firestop detail if required. Confirm that the mineral wool is continuous and not compressed away from the board. Replace any damaged board and re-finish joints with the specified compound. Then document the corrections with photos and the listing reference before calling for inspection.
3. How would you handle the schedule pressure if the fix requires removing one side of the corridor?
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I would separate life-safety from schedule. A one-hour corridor is an egress component; if the assembly does not match the listing, the building may not be safe to occupy. I would notify the general contractor in writing that the alignment issue cannot be resolved by patching if the listing requires staggered joints, and provide the shortest compliant sequence: protect the corridor, remove the minimum number of boards on one side, add the required fasteners and firestop, and rehang. If the inspector will accept an alternative listed assembly with aligned joints, I would submit that documentation before doing any work. I would not let the crew conceal the defect behind paint. The schedule discussion should include the inspection window and the owner's safety, not just the drywall crew's hours.