A focused pre-closure inspection of rectangular duct flange gaskets to confirm continuous gasket placement, corner continuity, compression allowance, and the specified material before the joint is closed.
- Verify continuous gasket around the full perimeter
- Check tight, clean corner continuity per detail
- Confirm visible, uniform compression allowance
- Match gasket material, size, and profile to the approved submittal
The checklist
Review approved submittal and drawings
- Open the latest approved submittal and joint detail for this duct; note specified gasket material, thickness, width, profile, orientation, and placement.
Verify packaging label matches submittal
- Compare manufacturer, material type, thickness, width, and profile on the gasket label to the approved submittal. If a shelf-life or use-by date is printed, verify it has not passed.
Inspect gasket stock/installed segments for damage
- Check the gasket roll or cut lengths for kinks, cracks, permanent compression set, or surface tears before final placement.
Measure gasket thickness at three points
- Use a caliper to measure uncompressed thickness at the start, middle, and end of a side; compare readings to the submittal.
Inspect flange faces are clean and dry
- Confirm both mating flanges are free of dust, oil, sealant residue, and debris that could affect sealing.
Check flange land flatness and condition
- Place a straightedge along each side; confirm no visible rocking, dents, raised burrs, or damage on the sealing land.
Confirm gasket profile and orientation
- Verify the installed gasket profile (e.g., flat, bulb, hollow) and its orientation match the approved detail.
Confirm continuous gasket around perimeter
- Trace the gasket along all four sides; verify no breaks, missing sections, or cuts from corner to corner.
Verify gasket is centered on flange land
- Check edge distance along each side; the gasket does not overhang the duct opening or the outer edge of the flange.
Inspect corner continuity and fit
- At all corners, verify mitered or butt joints meet tightly per detail, with no visible gaps, overlaps, or twists.
Check for stretching, buckling, or ripples
- Look along each side for signs of stretched, thinned, buckled, or rippled gasket that could affect sealing.
Verify attachment method matches submittal
- Confirm adhesive-backed gaskets show uniform bond lines or, if non-adhesive, that specified clips/adhesive are present as detailed.
Spot-check adhesion at three locations
- Attempt to lift the gasket edge by hand at the start, middle, and end of a side; the gasket remains bonded without peeling or blisters.
Ensure holes and corner hardware are clear
- Verify the gasket does not obstruct bolt/cleat slots or corner pieces; trim only if allowed by the submittal.
Inspect for contaminants on gasket surface
- Remove metal shavings, tape, plastic film, dust, or moisture on the gasket before closure.
Confirm visible compression allowance
- Verify the gasket projects above the flange land uniformly on all sides and that no doubled or stacked layers are present.
Temporarily clamp one side to check squeeze
- Apply a short cleat or clamp on one edge and snug it; confirm a continuous compression imprint appears along that edge. Remove the clamp and verify no tearing or permanent deformation of the gasket.
Verify adhesive/sealant working time (if used)
- If adhesive or sealant is used, confirm application and assembly are within the product label's open/working time; do not proceed if time has been exceeded.
Record inspection details
- Log material ID, batch/lot (if shown), thickness measurements, observations, and any corrective actions; attach photo references of each side and corners.
Obtain pre-closure sign-off
- Get inspector and installer sign-off confirming gasket placement, corners, compression allowance, attachment method, and material match the approved submittal.
Preview the printable checklist
Preview page one below. Open the image or download the PDF for all pages.
At a glance
- Open the latest approved submittal and joint detail.
- Verify packaging label, material, size, profile, and any shelf-life date.
- Inspect gasket condition and measure uncompressed thickness at multiple points.
- Confirm clean, flat flange faces and clear hardware openings.
- Ensure continuous, centered placement with tight, untwisted corners.
- Verify attachment method, adhesion, and uniform compression allowance.
- Trial-clamp to confirm squeeze and avoid over-compression.
- Record findings and obtain pre-closure sign-off.
How to perform a rectangular duct flange gasket pre-closure inspection
- Review the latest approved submittal and joint detail; note the required material, thickness, width, profile, orientation, and placement.
- Verify the packaging label matches the submittal for manufacturer, material, size, and profile; check any shelf-life date.
- Inspect gasket stock or installed segments for damage and measure uncompressed thickness at three points; compare to the submittal.
- Prepare both flanges: clean and dry surfaces, check land flatness with a straightedge, and keep holes and corner hardware clear.
- Confirm the specified profile and orientation; place a continuous, centered gasket around all four sides with tight, clean corners.
- Look for stretching, buckling, or ripples and remove any contaminants on the gasket surface.
- Verify attachment method and adhesion, confirm visible compression allowance, and temporarily clamp one edge to check squeeze; keep within adhesive/sealant working time if used.
- Record inspection details with photos and obtain pre-closure sign-off from the installer and inspector.
Start with the approved detail
Use the latest approved submittal and joint detail as the single source of truth for the gasket’s material, size, profile, orientation, and placement.
- Open the current approved submittal and joint detail for the duct section.
- Note specified material, thickness, width, profile, orientation, and placement.
- Verify the packaging label matches the submittal; check any shelf-life or use-by date.
Assess gasket condition and dimensions
A sound, dimensionally correct gasket is essential for an even seal and reliable compression.
- Inspect roll or cut lengths for kinks, cracks, compression set, or surface tears.
- Measure uncompressed thickness with a caliper at the start, middle, and end; compare to the submittal.
- Confirm the profile and orientation match the approved detail before final placement.
Prepare the flange surfaces
Clean, flat flange lands help the gasket seat uniformly and prevent leaks.
- Ensure both mating flanges are clean and dry, free of dust, oil, sealant residue, and debris.
- Use a straightedge to check the sealing land for flatness; no rocking, dents, burrs, or damage.
- Keep bolt/cleat slots and corner hardware locations clear of obstruction.
Place for continuity and alignment
Correct placement ensures the gasket seals the full perimeter without gaps or overhangs.
- Run a continuous gasket along all four sides with no breaks from corner to corner.
- Center the gasket on the flange land; avoid overhanging the duct opening or outer edge.
- Fit corners per detail with tight mitered or butt joints, free of gaps, overlaps, or twists.
- Check for stretching, buckling, or ripples; remove any contaminants on the gasket surface.
Attachment and compression allowance
Proper attachment and visible, uniform projection support consistent squeeze when the joint is closed.
- Use the specified attachment method; verify clips/adhesive or adhesive-backed bonds as detailed.
- Spot-check adhesion at multiple locations; the gasket should not peel or blister.
- Confirm a uniform projection above the flange land on all sides; no doubled or stacked layers.
- Apply a temporary clamp or short cleat to confirm a continuous compression imprint, then remove and check for damage.
- If adhesive or sealant is used, stay within the product’s open/working time.
Close-out and documentation
Clear records enable traceability and confirm readiness to close the joint.
- Log material ID, batch/lot (if shown), thickness readings, observations, and corrective actions.
- Attach photos showing each side and all corners.
- Obtain installer and inspector sign-off before joint closure.
