IMC 802.7 and 802.8 focus on two field conditions that are easy to overlook: supporting the vent, and protecting its required clearance where it passes through insulation.
Plain-English Highlights
Section 802.7 requires every portion of the vent to be adequately supported for the design and weight of the materials used. For plan review, consider vent material and diameter, vertical and horizontal runs, fittings and offsets, manufacturer support spacing, roof and wall penetrations, thermal movement, and wind exposure at exterior terminations - the appliance connection should not carry the weight of the vent system, and supports must maintain alignment, slope, joint integrity, and required clearances.
Section 802.8 requires an insulation shield where a vent passes through an insulated assembly, to maintain separation between the vent and the insulation. The shield must be constructed of at least No. 26 gage sheet metal, maintain the vent manufacturer's required clearance to combustibles, extend at least 2 inches above attic insulation, and be secured against displacement.
A listed insulation shield furnished as part of the vent system must be installed according to the manufacturer's instructions - the shield prevents loose-fill, batt, or blown insulation from contacting or migrating into the vent clearance zone.
Permit Proof Chain
Vent material, diameter, and full run identified -> support type and spacing selected per the vent manufacturer's instructions -> penetration and thermal-movement conditions coordinated -> insulated-assembly crossings located -> insulation shield gage, clearance, height above insulation, and securement specified -> listed shield product data referenced where the vent system furnishes one.
Where To Show It
M-001: vent support and clearance notes. M-101: vent routing and support locations. M-501: hangers, brackets, penetrations, and insulation shield details. Roof / attic plans: vent path through insulated assemblies. Building sections: shield height above insulation. Specifications: listed support and shield requirements.
**Do** - Support the full vent path independently of the appliance connection. - Follow the vent manufacturer's support spacing and attachment requirements for the actual vent material and diameter. - Maintain the required clearance to combustibles through every insulated assembly the vent passes through. - Show the insulation shield extending at least 2 inches above attic insulation and secured against displacement.
**Do Not** - Allow the appliance collar to support the vent weight. - Let insulation contact the vent or fill the required clearance space. - Treat vent support and insulation protection as field-only details with no drawing basis. - Specify a shield gage or configuration lighter than the No. 26 gage minimum without a listed-product basis that meets or exceeds it.
Masterbuild QA Lens
Walk the vent path in section from the appliance to the termination and mark every support point and every insulated-assembly crossing. A run with no marked supports or no shield detail at an attic crossing is not field-ready, regardless of how the plan view looks.
Drawing / Submittal Check
Compare support type and spacing on the details against the vent manufacturer's installation instructions for the specified material and diameter. Confirm the insulation shield detail states gage, required clearance, height above insulation, and securement method, and matches any listed shield furnished with the vent system.
Common Review Risk
A vent runs through an attic with insulation shown on the architectural drawings, but no shield is detailed on the mechanical drawings, and the clearance to combustibles is not called out at that crossing. Separately, a long horizontal run shows no support spacing, leaving alignment and slope dependent on field judgment.
When To Escalate
Escalate any vent run without documented support spacing, any insulated-assembly crossing without a detailed shield, shield gage or clearance below the minimum without a listed-product justification, and any condition where thermal movement, wind exposure, or roof/wall penetration details are not coordinated with the vent manufacturer's instructions.
Field Tip
Review the vent path through the attic in section. Confirm the supports carry the vent, the shield protects the clearance zone, and future insulation work cannot bury the vent.