A "subslab soil exhaust system" is a dedicated vent pipe/duct that pulls soil gases from beneath a slab (from a subslab aggregate layer, collection mat, or suction point) and discharges them above the roof so those gases don't build up under or inside the building. In practice, you'll see it on radon mitigation systems and other vapor-intrusion / soil-gas venting designs.
Plain English: Plain-English Highlights
511.1 general: If you provide a subslab soil exhaust system, the duct must comply with IMC 511.
511.2 materials: Use UL 181 listed Class 0 air-duct material OR IPC-approved sanitary DWV/vent materials (cast iron, galvanized steel, copper/copper-alloy Type DWV or heavier, or plastic piping).
511.3 slope: Do not trap the duct. Provide minimum slope 1/8 in per 12 in (1%) so it can drain and not hold condensate.
511.4 termination: Extend through the roof. Terminate at least 6 in above the roof AND at least 10 ft from operable openings or outside air intakes.
511.5 identification: Permanently label the duct at each floor level (tag, stencil, or approved marking).
On Plans: Why it matters
Common misses: duct run gets "accidentally trapped," roof termination is too close to an OA intake or operable window, and no labeling - so the system gets cut, capped, or tied into the wrong thing during future work.
Code Path: Where to show it
M-001: "IMC 511 SUBSLAB SOIL EXHAUST" general note (materials, 1% slope/no traps, roof termination clearances, labeling each floor).
Plans/sections: Show routing with slope arrows and call out "NO TRAPS."
Roof plan: Dimension the termination to nearby operable openings and OA intakes.
Check: Do
Coordinate the roof termination early to stay 10 ft clear of intakes/openings.
Add a simple "IMC 511 TAG REQUIRED EACH FLOOR" callout near the riser.
Review Risk: Don't
Don't add low points or offsets that create a trap.
Don't terminate near intakes/openings and assume it will "pass later."
Field Tip: Field tip
Call it out clearly as "SUBSLAB SOIL EXHAUST (SSES)" on the riser and roof plan. If it's labeled like plumbing vent or generic exhaust, it's more likely to be misrouted or capped during a remodel.
Comment "IMC511" if you want a paste-ready M-001 note + roof termination checklist.
Masterbuild QA Lens
Exhaust systems need a source-to-discharge story. Identify what is being captured, how it is captured, how it is routed, where it terminates, and what interlocks or separations protect the building.
Drawing / Submittal Check
Verify source classification, hood or pickup point, duct material, route, cleanouts or access, fan selection, discharge location, make-up air, controls, and required coordination with fire protection or alarms.
Common Review Risk
The expensive miss is treating all exhaust the same. Grease, dryer, dust, hazardous, smoke control, battery, and specialty exhaust systems carry different proof requirements.
When To Escalate
Escalate when exhaust involves grease, hazardous materials, combustible dust, battery charging, smoke control, rated shafts, energy recovery, or any discharge that can re-enter the building.
Special Exhaust Coordination
For specialty exhaust, start with the contaminant and source. Then confirm capture method, duct material, routing, discharge, separation, controls, and whether another consultant or AHJ review is required.
Duct System Coordination
For duct and plenum items, check material limits, insulation continuity, vapor control, access, listed products, and whether the surrounding space changes the requirement.