Exposed double-wall spiral
Acoustic exposed system
Before you start
- Confirm double-wall construction, inner liner type, insulation thickness, joint system, weight, support detail, perforation or acoustic requirements, and outer finish standard.
- Inspect the inner liner, insulation, outer shell, couplings, and protective ends.
- Keep open sections dry and free of metal chips, dust, and damaged insulation.
- Verify the inner connection can be inspected before the outer shell is closed.
Tools and materials
Double-wall spiral duct, approved inner and outer coupling components, insulation repair materials, heavy clean bands or saddles, soft slings, clean gloves, inspection light, approved fasteners and sealant, and surface-protection materials.
Lay it out
- Lay out joint access, supports, seam orientation, and fitting sequence for the heavier assembly.
- Keep support points broad and clear of the joint.
- Plan the inner and outer connection sequence before lifting.
Set and support it
- Use supports rated for the double-wall weight.
- Handle with soft slings so the outer finish and inner liner are not crushed.
- Support both sections before closing either wall of the joint.
Make the connection
- 1
Inspect and clean the inner and outer mating ends.
- 2
Align and complete the inner liner or inner coupling first.
- 3
Verify the inner joint with a light before it is hidden.
- 4
Restore the specified insulation or acoustic material continuously.
- 5
Bring the outer shells together without disturbing the inner connection.
- 6
Complete and seal the outer coupling.
- 7
Load the supports and inspect the visible finish.
Check the install
- The inner and outer joints are both complete.
- No insulation or acoustic gap remains.
- The inner liner is not folded, separated, or obstructing airflow.
- The outer shell remains clean, round, and undamaged.
- Supports match the heavier assembly.
Common mistakes
- Closing the outer shell before inspecting the inner connection.
- Leaving an insulation gap at the joint.
- Using supports sized for single-wall duct.
- Letting fasteners or metal chips remain between the walls.
Stop and ask
Stop if the inner liner cannot be inspected, insulation is wet or missing, the inner and outer profiles do not match, or the support is not rated for the assembly.