CMC · California Mechanical Code
Where and how must exhaust ducts terminate?
Exhaust outlets must be located a minimum distance from property lines, building openings, and intakes depending on the air class (3 ft, 10 ft, or 30 ft). Clothes dryers have special rules (no screen, backdraft damper, rigid metal duct) and all terminations must respect outdoor‑air intake separations; see CMC §§ 502.2–502.2.4 and the dryer rules in § 504.4 for details.
Last reviewed: July 6, 2026
What the code requires — 2–4 sentences
Exhaust ducts must terminate outdoors at locations and with clearances that depend on the air class being exhausted. The general termination rules are in § 502.2 and the specific distance requirements are in § 502.2.1, § 502.2.2, § 502.2.3, and § 502.2.4 of the California Mechanical Code. Classes of air are defined elsewhere (see Section 203.0 and classification in Section 403.9) and the termination distances below are based on those classes. These requirements are stated in § 502.2 and its subsections.
The single most important rule: place the exhaust outlet so its discharged air cannot enter the building, pollute neighbors, or create a nuisance — follow the minimum horizontal and vertical separation distances required for the air class.
Requirements in detail
Key defined terms (first mention):
- Environmental air, Class 1, Class 2, Class 3, Class 4, and product-conveying are the air/class terms used by the CMC; see Section 203.0 and Section 403.9 for definitions and classification.
- Exhaust openings to the outdoors must be protected by a corrosion-resistant screen of specified mesh unless an exception applies (see § 502.1).
Summary table — decision-relevant distances
| Air class / type | Minimum distance from property line | Minimum distance from openings into the building | Minimum from exterior walls/roofs in direction of discharge | Minimum above adjoining grade or public way | Code Reference |
|---|---|---|---|---|---|
| Environmental, Class 1, Class 2 | 3 ft (914 mm) | 3 ft (914 mm) | (not specially required beyond openings) | 10 ft (3048 mm) above a public way; also separation from outdoor air intakes per § 402.4.1 | § 502.2.1 |
| Class 3 | 10 ft (3048 mm) | 10 ft (3048 mm) | 3 ft (914 mm) from exterior walls/roofs in direction of discharge | 10 ft (3048 mm) above adjoining grade; also per § 402.4.1 | § 502.2.2 |
| Class 4, product-conveying, flammable/explosive vapors/fumes/dusts | 30 ft (9144 mm) | 10 ft (3048 mm); 30 ft (9144 mm) from combustible walls/openings in direction of discharge | 6 ft (1829 mm) from exterior walls/roofs in direction of discharge; 30 ft (9144 mm) from combustible walls/openings | 10 ft (3048 mm) above adjoining grade; also per § 402.4.1 | § 502.2.3 |
| Clothes dryer exhausts (domestic) | Follow Environmental/Class1/2 distances; dryer discharges shall not terminate over a public way or where condensate/vapor creates nuisance/hazard | As above; backdraft damper required; no screen at dryer termination | See dryer construction/length limits in § 504.4, § 504.4.2, § 504.4.2.1 | Terminate to outside — must meet § 502.2.1; length limits apply | § 502.2.1 and § 504.4 (dryers) |
Notes:
- The code repeatedly adds the requirement that the termination must also respect "the minimum separation distance from ventilation system outdoor air intakes determined in accordance with § 402.4.1." That means you must check § 402.4.1 when locating an exhaust relative to intakes.
- All outdoor exhaust openings shall be covered by a corrosion‑resistant screen meeting § 502.1 sizing limits unless an exception applies (e.g., clothes dryers).
Other mandatory termination equipment/location rules
- Exhaust ducts must terminate outside the building and be equipped with backdraft dampers or motorized dampers that close when not in use, except where the exhaust fan runs continuously (see § 504.1).
- Type I hood exhaust (commercial grease hood) termination follows a separate rule — see § 510.9 (exception in § 502.2.3).
- Rooftop terminations for some systems (e.g., Type II hood systems) must be directed away from roof surfaces within 40 in (1016 mm) in addition to the § 502.2 spacing.
Exceptions & special cases
- Clothes dryers: screens at the dryer termination are prohibited and dryers must have a backdraft damper; dryer ducts must be rigid metal and have length limits (see § 504.4, § 504.4.2, § 504.4.2.1). The dryer termination still must meet the Environmental/Class 1/2 spacing in § 502.2.1 and must not terminate over a public way or an area where condensate/vapor creates a nuisance.
- Continuous‑running exhaust fans may waive the backdraft damper requirement per § 504.1 exceptions.
- Type I hood exhaust is handled under § 510.9 (i.e., different rooftop/stack termination requirements).
Common mistakes
- Assuming the same clearance applies to all exhausts — different air classes have different distances (3 ft vs. 10 ft vs. 30 ft). Always identify the air class first. § 502.2 and subsections.
- Forgetting to check separation from outdoor air intakes per § 402.4.1 (the intake clearance can be stricter than the property‑line or opening clearance). § 502.2 references § 402.4.1.
- Installing a screen at the dryer exhaust termination (screens are not allowed at dryer terminations) or installing a damper/device that obstructs dryer flow—both violate § 504.4.
- Using decorative caps, hoods, or dampers that reduce airflow or collect lint (for dryers) — the code requires smooth, rigid, properly sized ducts and prohibits certain attachments that impede airflow for clothes dryers. § 504.4 and related text.
- Assuming rooftop spacing is only horizontal — the code often requires vertical clearances too (e.g., 10 ft above public way or adjoining grade). See § 502.2.1–§ 502.2.3.
Worked example — concrete scenario
Scenario: You are locating an exhaust stack for a paint shop that is classified as Class 3 air. The proposed stack outlet is at the roof edge, 8 feet horizontally from the adjacent property line and 6 feet above the adjoining grade; there is an operable window 12 feet away horizontally.
Apply the code:
- For Class 3, the exhaust must be not less than 10 ft (3048 mm) from a property line (see § 502.2.2). Proposed: 8 ft → does NOT comply.
- It must be 10 ft from openings into the building. Proposed window is 12 ft away → this is OK (meets 10 ft requirement).
- It must be 10 ft above adjoining grade. Proposed: 6 ft above grade → does NOT comply.
Remedy options:
- Move the outlet horizontally to be ≥ 10 ft from the property line; OR
- Extend a vertical stack so the outlet is ≥ 10 ft above adjoining grade (e.g., add at least 4 ft of vertical termination above current outlet), provided this does not create other code conflicts (like exceeding rooftop height limits or creating a new intake issue); AND
- Verify separation from any outdoor air intakes per § 402.4.1 (this could impose a larger required distance).
Related provisions
- § 502.1 — Exhaust opening protection (screen size & exceptions).
- § 502.2 — General termination requirement and reference to subsections.
- § 502.2.1, § 502.2.2, § 502.2.3, § 502.2.4 — Specific separation distances by air class (the controlling subsections used above).
- § 402.4.1 — Minimum separation distance from ventilation system outdoor air intakes (referred by § 502.2.*).
- § 504.1 — Backdraft protection and requirement that exhaust ducts terminate outside the building.
- § 504.4, § 504.4.2, § 504.4.2.1 — Clothes dryer termination, duct construction, and length limits.
- § 510.9 — Type I hood exhaust termination (exception referenced in § 502.2.3).
Code references
Grounded in the retrieved California Mechanical Code — click a citation to read the verbatim passage:
CMC § 502.2 High relevance — show source text
Exception: Clothes dryers.
502.2 Termination of Exhaust Ducts. Exhaust ducts shall terminate in accordance with Section 502.2.1 through Section 502.2.4. Classes of air shall be as defined in Section
203.0 and classified in Section 403.9.
502.2.1 Environmental, Class 1, and Class 2 Air Ducts. Environmental, Class 1, and Class 2 air duct exhaust shall terminate not less than 3 feet (914 mm) from a property line, 10 feet (3048 mm) above a public way, 3 feet (914 mm) from openings into the building and the minimum separation distance from ventilation system outdoor air intakes determined in accordance with Section 402.4.1. The discharge of dryer exhaust ducts shall not terminate over a public way or over an area where condensate or vapor could create a nuisance or hazard.
502.2.2 Class 3 Air Ducts. Class 3 air duct exhaust shall terminate not less than 10 feet (3048 mm) from a property line, 3 feet (914 mm) from exterior walls or roofs that are in the direction of the exhaust discharge, 10 feet (3048 mm) from openings into the building, 10 feet (3048 mm) above adjoining grade, and the minimum separation distance from ventilation system outdoor air intakes determined in accordance with Section 402.4.1.
502.2.3 Product Conveying, Flammable, and Class 4 Air Ducts. Ducts conveying Class 4 air or explosive or flammable vapors, fumes, or dusts shall terminate not less than 30 feet (9144 mm) from a property line, 10 feet (3048 mm) from openings into the building, 6 feet (1829 mm) from exterior walls or roofs that are in the direction of the exhaust discharge, 30 feet (9144 mm) from combustible walls or openings into the building that are in the direction of the exhaust discharge, 10 feet (3048 mm) above adjoining grade, and the minimum separation distance from ventilation system outdoor air intakes determined in accordance with Section 402.4.1.
Exception: Type I Hood exhaust termination shall be in accordance with Section 510.9.
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tem in accordance with Section 505.7.3 do not require design as Class 1 product-conveying ducts.
Exceptions:
(1) Ductless range hoods where installed in accordance with the manufacturer’s installation instructions.
(2) Condensing clothes dryers where installed in accordance with the manufacturer’s installation instructions.
504.1.1 Backdraft Protection. Exhaust ducts shall terminate outside the building and shall be equipped with backdraft dampers or with motorized dampers that automatically shut where the systems or spaces served are not in use. [OSHPD 1, 1R, 2, 4 & 5] Exception: Back- draft dampers are not required when the exhaust fan must operate continuously.
Exception: Where the exhaust duct does not discharge into a common exhaust plenum and one of the following:
(1) The exhaust fan runs continuously.
CMC § 504.0 High relevance — show source text
Equipment used to exhaust explosive or flammable vapors, fumes, or dusts shall bear an identification plate stating the ventilation rate for which the system was designed.
Fans located in systems conveying corrosives shall be of materials that are resistant to the corrosive or shall be coated
with corrosion-resistant materials.
504.0 Environmental Air Ducts.
504.1 General. Where not specified in this chapter, exhaust ducts shall be constructed and installed in accordance with
Chapter 6 and shall be airtight as approved by the Authority Having Jurisdiction. Environmental air ducts that have an alternate function as a part of an approved smoke control sys
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501.0 General.
501.1 Applicability. This chapter includes requirements for environmental air ducts, product-conveying systems, and commercial hoods and kitchen ventilation. Part I addresses environmental air ducts and product conveying systems. Part II addresses commercial hoods and kitchen ventilation.
502.0 Termination.
502.1 Exhaust Opening Protection. Exhaust openings terminating to the outdoors shall be covered with a corrosionresistant screen having not less than [1] ⁄ 4 of an inch (6.4 mm) openings, and shall have not more than [1] ⁄ 2 of an inch (12.7 mm) openings.
Exception: Clothes dryers.
502.2 Termination of Exhaust Ducts. Exhaust ducts shall terminate in accordance with Section 502.2.1 through Section 502.2.4. Classes of air shall be as defined in Section
203.0 and classified in Section 403.9.
502.2.1 Environmental, Class 1, and Class 2 Air Ducts. Environmental, Class 1, and Class 2 air duct exhaust shall terminate not less than 3 feet (914 mm) from a property line, 10 feet (3048 mm) above a public way, 3 feet (914 mm) from openings into the building and the minimum separation distance from ventilation system outdoor air intakes determined in accordance with Section 402.4.1. The discharge of dryer exhaust ducts shall not terminate over a public way or over an area where condensate or vapor could create a nuisance or hazard.
502.2.2 Class 3 Air Ducts. Class 3 air duct exhaust shall terminate not less than 10 feet (3048 mm) from a property line, 3 feet (914 mm) from exterior walls or roofs that are in the direction of the exhaust discharge, 10 feet (3048 mm) from openings into the building, 10 feet (3048 mm) above adjoining grade, and the minimum separation distance from ventilation system outdoor air intakes determined in accordance with Section 402.4.1.
CMC § 504.4 High relevance — show source text
(6) Range hoods shall discharge to the outdoors through a single wall duct and shall not terminate in an attic or crawl space.
504.4 Clothes Dryers. A clothes dryer exhaust duct shall not be connected to a vent connector, gas vent, chimney, and shall not terminate into a crawl space, attic, or other concealed space. Exhaust ducts shall not be assembled with screws or other fastening means that extend into the duct and that are capable of catching lint, and that reduce the efficiency of the exhaust system. Exhaust ducts shall be constructed of rigid metallic material. Transition ducts used to connect the dryer to the exhaust duct shall be listed and labeled in accordance
with UL 2158A, or installed in accordance with the clothes dryer manufacturer’s installation instructions. Clothes dryer exhaust ducts shall terminate to the outside of the building in accordance with Section 502.2.1 and shall be equipped with a backdraft damper. Screens shall not be installed at the duct termination. Devices, such as fire or smoke dampers that will obstruct the flow of the exhaust shall not be used. Where joining of ducts, the male end shall be inserted in the direction of airflow.
504.4.1 Provisions for Makeup Air. Makeup air shall be provided in accordance with the following:
(1) Makeup air shall be provided for Type 1 clothes dryers in accordance with the manufacturer’s installa tion instructions. [NFPA 54:10.4.4.1] Where a closet is designed for the installation of a clothes dryer, an opening of not less than 100 square inches (0.065 m [2] ) for makeup air shall be provided in the door or by other approved means.
(2) Provision for makeup air shall be provided for Type 2 clothes dryers, with a minimum free area of 1 square inch (0.0006 m [2] ) for each 1000 British thermal units per hour (Btu/h) (0.293 kW) total input rating of the dryer(s) installed. [NFPA 54:10.4.4.2]
504.4.2 Domestic Clothes Dryers. Where a compartment or space for a Type 1 clothes dryer is provided, not less than a 4 inch diameter (102 mm) exhaust duct of approved material shall be installed in accordance with Section 504.0.
Type 1 clothes dryer exhaust ducts shall be of rigid metal and shall have smooth interior surfaces. The diam eter shall be not less than 4 inches nominal (100 mm), and the thickness shall be not less than 0.016 of an inch
(0.406 mm).
504.4.2.1 Length Limitation. Unless otherwise permitted or required by the dryer manufacturer’s instructions and approved by the Authority Having Jurisdiction, domestic dryer moisture exhaust ducts
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shall not exceed a total combined horizontal and ver tical length of 14 feet (4267 mm), including two 90 degree (1.57 rad) elbows. A length of 2 feet (610 mm) shall be deducted for each 90 degree (1.57 rad) elbow in excess of two.
CMC § 519.1 High relevance — show source text
519.1 Where Required. Type II hoods shall be installed above equipment and dishwashers that generate steam, heat, or products of combustion, and where grease or smoke is not present.
Exceptions:
(1) Dishwashing machines connected to a Type II duct system and exhausted directly to the outdoors.
(2) Dishwashing machines with a self-contained condensing system listed in accordance with UL 921 and installed in a space where the HVAC system has been engineered to accommodate the latent and sensible heat load emitted from such appliances as approved by the Authority Having Jurisdiction. Such equipment shall be provided with an interlocking device to prevent opening of the appliance prior to completion of its cycle. 519.2 Construction of Type II Hoods. Type II hoods constructed of steel shall be not less than 0.024 of an inch (0.61 mm) (No. 24 gauge). Hoods constructed of copper shall be of copper sheets weighing not less than 0.17 ounces per square inch (oz/in [2] ) (7.47 kg/m [2] ). Joints and seams shall be substantially tight. Solder shall not be used except for sealing a joint or seam. 519.3 Type II Hood Exhaust System Net Airflow. The net airflow for Type II hoods shall be in accordance with Section 508.5.1.5 for light-duty cooking appliances. The net airflow for Type II hoods serving dishwashing appliances shall comply with Section 519.3.1.
519.3.1 Dishwashing Appliances. The net airflow for Type II hoods used for dishwashing equipment shall be not less than 200 cubic feet per minute (0.094 m [3] /s) per linear foot (m) of hood length.
519.4 Type II Exhaust Duct Systems. Ducts and plenums serving Type II hoods shall be constructed of rigid metallic materials in accordance with Chapter 6. Duct bracing and supports shall comply with Chapter 6. Ducts subject to positive pressure shall be adequately sealed.
519.5 Termination of Type II Hood Exhaust System. The exhaust system shall terminate in accordance with Section 502.2.2. Rooftop terminations shall be directed away
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from roof surfaces within 40 inches (1016 mm). The discharge outlet of moisture conveying exhaust ducts, such as dishwasher exhaust ducts, shall not terminate over a public way or over an area where condensate or vapor could create a nuisance or hazard.
519.6 Makeup Air. Makeup air shall be provided in accordance with Section 511.3.
519.7 Independent Exhaust Duct System. Single or combined Type II exhaust systems shall be independent of all other exhaust systems.
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CALIFORNIA MECHANICAL CODE – MATRIX ADOPTION TABLE
CHAPTER 6 – DUCT SYSTEMS
CMC § 519.4 High relevance — show source text
519.4 Type II Exhaust Duct Systems. Ducts and plenums serving Type II hoods shall be constructed of rigid metallic materials in accordance with Chapter 6. Duct bracing and supports shall comply with Chapter 6. Ducts subject to positive pressure shall be adequately sealed.
519.5 Termination of Type II Hood Exhaust System. The exhaust system shall terminate in accordance with Section 502.2.2. Rooftop terminations shall be directed away
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from roof surfaces within 40 inches (1016 mm). The discharge outlet of moisture conveying exhaust ducts, such as dishwasher exhaust ducts, shall not terminate over a public way or over an area where condensate or vapor could create a nuisance or hazard.
519.6 Makeup Air. Makeup air shall be provided in accordance with Section 511.3.
519.7 Independent Exhaust Duct System. Single or combined Type II exhaust systems shall be independent of all other exhaust systems.
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CALIFORNIA MECHANICAL CODE – MATRIX ADOPTION TABLE
CHAPTER 6 – DUCT SYSTEMS
(Matrix Adoption Tables are non-regulatory, intended only as an aid to the code user. See Chapter 1 for state agency authority and building applications.)
Adopting Agency BSC BSC-
CGSFM HCD Col6 Col7 DSA Col9 Col10 OSHPD Col12 Col13 Col14 Col15 Col16 Col17 BSCC DPH AGR DWR CEC CA SL SLC Adopting Agency BSC BSC-
CGSFM 1 2 1-AC AC ** SS** ** SS/CC** 1 1R 2 3 4 5 6 6 6 6 6 6 6 6 6 Adopt Entire Chapter X X X Adopt Entire Chapter as
amended (amended sections
listed below)X X X X X X X X X Adopt only those sections
that are listed belowX Chapter/Section _601.2. CMC § 1.1. High relevance — show source text
(1) The fan for overhead range hoods and downdraft exhaust equipment not integral with the cooking appliance shall comply with UL 507.
(2) Overhead range hoods and downdraft exhaust equipment with integral fans shall comply with UL 507.
(3) Domestic cooking appliances with integral downdraft exhaust equipment shall comply with UL 858 or CSA/ANSI Z21.1/CSA 1.1.
(4) Microwave ovens with integral exhaust for installation over the cooking surface shall comply with UL 923.
(5) All domestic kitchen exhaust ducts used in conjunction with domestic range or cooktop hoods shall be constructed of metal and shall have smooth interior surfaces, fastened and sealed with duct mastic or metal tapes that meet the requirements of UL 181A.
Exception: Ducts for domestic kitchen downdraft grillrange ventilation installed under a concrete slab floor shall be permitted to be of approved Schedule 40 PVC provided the following conditions are met:
(1) The under-floor trench in which the duct is installed shall be completely backfilled with sand or gravel.
(2) Not more than 1 inch (25.4 mm) of 6 inch diameter (150 mm) PVC coupling shall be permitted to protrude above the concrete floor surface.
(3) PVC pipe joints shall be solvent cemented to provide an air and greasetight duct.
(4) The duct shall terminate above grade outside the building and shall be equipped with a backdraft damper.
(6) Range hoods shall discharge to the outdoors through a single wall duct and shall not terminate in an attic or crawl space.
504.4 Clothes Dryers. A clothes dryer exhaust duct shall not be connected to a vent connector, gas vent, chimney, and shall not terminate into a crawl space, attic, or other concealed space. Exhaust ducts shall not be assembled with screws or other fastening means that extend into the duct and that are capable of catching lint, and that reduce the efficiency of the exhaust system. Exhaust ducts shall be constructed of rigid metallic material. Transition ducts used to connect the dryer to the exhaust duct shall be listed and labeled in accordance
with UL 2158A, or installed in accordance with the clothes dryer manufacturer’s installation instructions. Clothes dryer exhaust ducts shall terminate to the outside of the building in accordance with Section 502.2.1 and shall be equipped with a backdraft damper. Screens shall not be installed at the duct termination. Devices, such as fire or smoke dampers that will obstruct the flow of the exhaust shall not be used. Where joining of ducts, the male end shall be inserted in the direction of airflow.
504.4.1 Provisions for Makeup Air. Makeup air shall be provided in accordance with the following:
(1) Makeup air shall be provided for Type 1 clothes dryers in accordance with the manufacturer’s installa tion instructions. [NFPA 54:10.4.4.1] Where a closet is designed for the installation of a clothes dryer, an opening of not less than 100 square inches (0.065 m [2] ) for makeup air shall be provided in the door or by other approved means.
CMC § 304.8 Medium relevance — show source text
80
90|19
17
15
15|26
25
23
22|53
49
45
44|60
57
52
50|107
99
94
90|126
117
109
102|207
191
178
169|241
222
208
197|359
330
307
286|502
466
438
414|805
745
696
656|961
890
833
787|1710
1590
1490
1400|1900
1760
1650
1550| |100
150
200
250
300|14
11
9
8
8|20
15
14
12
11|41
31
28
25
23|47
36
33
30
26|85
66
60
53
50|98
75
69
61
57|159
123
112
99
90|186
143
129
117
107|270
217
183
163
147|393
324
283
254
234|621
506
438
390
357|746
611
531
476
434|1330
1090
948
850
777|1480
1210
1050
934
854|For SI units: 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 inch water column = 0.249 kPa
Notes: 1 Table includes losses for four 90 degree (1.57 rad) bends and two end fittings. Tubing runs with larger numbers of bends, fittings, or both shall be increased
by an equivalent length of tubing to the following equation: L = 1.3 n, where L is additional length (ft) of tubing and n is the number of additional fittings,
bends, or both. 2 Table entries are rounded to 3 significant digits. 3 EHD = Equivalent Hydraulic Diameter, which is a measure of the relative hydraulic efficiency between different tubing sizes. The greater the value of EHD,
the greater the gas capacity of the tubing.
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CMC § 101.2.2 Medium relevance — show source text
CFC—25: California Fire Code
101.2.2, 101.4.2, 301.3.1, 302.2, 307.1, 308.1, 802.2.1, 802.2.3, 803.2.3, 803.4.1.1, 803.4.1.2, 803.4.1.3, 803.4.1.4, 803.4.1.5, 803.4.1.6, Table 804.5.1.1(1), 904.1.5, 1011.6.1.1, 1303.1.2, 1305.2.8.1, 1305.2.14, 1305.2.14.1, 1401.2, 1501.1, 1501.5, 1502.1, 1502.1.1, 1502.2, 1502.3, 1504.1, 1507.1, 1507.2
CMC—25: California Mechanical Code
302.2, 702.7, 807.1, 902.1.1, 1008.1, 1305.2.7.1, 1305.2.8, 1305.2.8.1
CPC—25: California Plumbing Code
302.2, 408.1, 702.7, 1009.1, 1009.2, 1009.3, 1009.5, 1302.1.6, 1503.1
16-4 2025 CALIFORNIA EXISTING BUILDING CODE
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
REFERENCED STANDARDS
CRC—25: California Residential Code
101.2, 101.4.1, 104.3.1, 109.3.3, 109.3.10, 302.2, 307.1, 308.1, 401.3, 402.1, 405.2.6, 502.2, 502.3, 502.4, 503.2, 503.3, 503.11, 505.2, 505.3, 507.3, 701.3, 702.4, 702.5, 706.2, 708.1, 805.2, 806.4, 809.1, 906.2, 907.1, 1011.2.1, 1103.1, 1103.2, 1103.3, 1104.1, 1201.4, 1302.1.2, 1302.1.3, 1302.1.3, 1303.1.3, 1401.2, 1402.1, 1402.2, 1402.2.1, 1402.3, 1402.4, 1402.5, 1402.6
ICC 300—2023: ICC Standard on Bleachers, Folding and Telescopic Seating and Grandstands
301.1.1, 401.1.1, 1401.1.1
ICC A117.1—2017: Accessible and Usable Buildings and Facilities
CMC § 5303.16.1 Medium relevance — show source text
1, 5303.16.1, 5303.16.2, 5306.1, 5306.2, 5306.2.1, 5306.2.2, 5307.4.6, 5503.1.2, 5503.5.2, 5504.2.1.2, 5504.2.2.2, 5505.4.1, 5604.2, Table 5604.5.2(3), 5605.5, 5701.3, 5704.2.7.7, 5704.2.8.1, 5704.2.8.2, 5704.2.9.3, 5704.2.9.4, 5704.3.3.5, 5704.3.7.1, 5704.3.8, 5705.3.4, 5705.3.5.3, 5705.3.7.1, 5705.3.7.2, 5705.3.7.3, 5705.3.7.4, 5705.3.7.5.1, 5706.2.3, 5706.4.1, 5803.1.1, 5806.4.3, 5808.1, 5808.3, 5808.3.2, 5906.2.2, 5906.2.3, 5906.4.2, 6003.1.4.2, 6005.3.1, 6109.11.2, 6204.1.2, 6306.4, 6404.1.4, 6604.1
CEBC—25: California Existing Building Code
102.3, 1011.5.2, 1103.1, 1104.18, 1105.5.2
CMC—25: California Mechanical Code
201.3, 308.3, 605.1, 605.2.1.1, 605.2.1.2, 605.2.1.3, 605.2.1.4, 605.2.1.5, 605.3, 605.4, 605.4.2.3, 605.4.2.5, 605.5.2, 605.7, 606.1, 606.2, 608.1, 608.3, 608.4, 608.5, 608.8, 608.9.1, 608.10, 608.17, 610.1.1, 903.2.11.4, 904.14, 907.3.1, 909.1, 909.10.2, 909.13.1, 910.4.7, 915.6.1, 1006.2.2.3, 1011.16, 1020.6.1, 1207.4.7, 1207.6.1, 1207.6.1.2.2, 1207.11.8, 2104.2.1, 2105.3, 2301.1, 2301.6, 2309.3.1.2, 2311.3.1, 2311.4.3, 2311.8.2, 2311.
CMC § 90.1 Medium relevance — show source text
[ASHRAE 90.1: TABLE 6.4.3.4.3]
Col1 OUTDOOR AIR INTAKE (CFM/ft2) Col3 EXHAUST/RELIEF (CFM/ft2) Col5 CLIMATE ZONE NONMOTORIZED1 MOTORIZED NONMOTORIZED3 MOTORIZED 0, 1, 2 0, 1, 2 0, 1, 2 0, 1, 2 0, 1, 2 Any height 20 4 20 4 3 3 3 3 3 Any height 20 10 20 10 4, 5B, 5C 4, 5B, 5C 4, 5B, 5C 4, 5B, 5C 4, 5B, 5C Fewer than three stories 204 10 20 10 Three or more stories 204 10 204 10 5A, 6, 7, 8 5A, 6, 7, 8 5A, 6, 7, 8 5A, 6, 7, 8 5A, 6, 7, 8 Fewer than three stories 204 4 20 4 Three or more stories 204 4 204 4 For SI units: 1 square foot = 0.0929 m [2], 1 cubic foot per minute = 0.00047 m [3] /s, 1 cubic foot per minute = 0.4719 L/s, 1 cubic foot per minute per square foot = 5.08 [(L/s)/m [2] ], 1 inch water gauge = 0.249 kPa
Notes:
1 When tested in accordance with AMCA 500D.
2 Dampers smaller than 12 inches (305 mm) in height, width, or diameter need not be tested but shall be of the same design and construction as the smallest tested damper meeting the listed leakage rate requirement.
3 Nonmotorized dampers smaller than 24 inches (610 mm) in height, width, or diameter shall be permitted to have a leakage rate of 40 CFM/ft 2 [0.203 (m 3 /s)/m 2 ].
4 Where permitted by Section E 503.4.6.4.1, exception 2.
2025 CALIFORNIA MECHANICAL CODE 425
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APPENDIX E
(2) Systems serving zones where humidity levels are required to be maintained with precision of not more than ±5 percent relative humidity to comply with applicable codes or accreditation standards or as approved by the Authority Having Jurisdiction.
[ASHRAE 90.1:6.4.3.6.2]
CMC § 25.4 Medium relevance — show source text
2
5
10
15
20
30|176
168
204
253
299
345
442|1292
971
953
923
894
866
809|704
613
602
583
562
543
502|220
209
257
313
363
415
521|1724
1273
1252
1217
1183
1150
1086|948
811
795
765
736
708
649|295
280
347
418
481
544
674|2223
1615
1591
1551
1512
1473
1399|1189
1007
991
963
934
906
848|428
401
496
589
668
741
892|3432
2426
2396
2347
2299
2251
2159|1818
1509
1490
1455
1421
1387
1318| |100|0
2
5
10
15
20
30
50|166
158
194
238
281
325
418
617|1404
1152
1134
1104
1075
1046
988
866|765
698
688
672
656
639
NA
NA|207
196
240
293
342
391
491
711|1900
1532
1511
1477
1443
1410
1343
1205|1033
933
921
902
884
864
824
NA|273
259
322
389
447
507
631
895|2479
1970
1945
1905
1865
1825
1747
1591|1300
1168
1153
1133
1110
1087
1041
NA|395
371
460
547
618
690
834
1138|3912
3021
2990
2938
2888
2838
2739
2547|2042
1817
1796
1763
1730
1696
1627
1489|For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m [2]
- NA: Not applicable.
176 2025 CALIFORNIA MECHANICAL CODE
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CHIMNEYS AND VENTS
|TABLE 803.1.2(3) MASONRY CHIMNEY [NFPA 54: TABLE 13.
CMC § 1220.4.2 Medium relevance — show source text
8|1220.4.2 – 1220.4.6| |1221.7|1221.6| |1308.2 – 1308.4.1|1308.3 – 1308.5.1| |Table 1308.3.1|Table 1308.4.1| |1308.4.2|1308.5.2| |1308.4.2.2 – 1308.6.4|1308.5.2.1 – 1308.7.3| |Table 1308.4.6.2|Table 1308.5.6.2| |1308.6.5 – 1308.13.1|1308.7.7 – 1308.14.1| |1312.1.2 – 1312.1.3|1312.1.1 – 1312.1.2| |Chapter 17|Appendix F| |Chapter 18|Chapter 17| |D 103.2|D 103.1| |E 503.5.6.7|E 503.5.6.6| |E 503.5.7.2 – E 503.5.7.6|E 503.5.7.1 – E 503.5.7.5| |Table E 503.5.7.2|Table E 503.5.7.1| |Table E 503.5.7.6|Table E 503.5.7.5| |Table E 503.5.10.1.2(1)|Table E 503.5.10(1)| |Table E 503.5.10.1.2(2)|Table E 503.5.10(2)| |E 503.5.10.1.2|E 503.5.10| |E 503.5.10.2 – E 503.5.10.2.2|E 503.5.10.1 – E 503.5.10.1.2| |E 503.5.12.1|E 503.5.12| |E 503.5.12.2|E 503.5.12.1| |E 503.6.5.4|E 503.6.5.4.1|
xxii 2025 CALIFORNIA MECHANICAL CODE
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Frequently asked questions
What is the closest an exhaust can be to my neighbor's property line?
That depends on the air class. For Environmental/Class 1/2 it's 3 ft (914 mm); for Class 3 it's 10 ft (3048 mm); for Class 4/product‑conveying/flammable it's 30 ft (9144 mm). See § 502.2.1, § 502.2.2, § 502.2.3.
Do dryer vents need screens or backdraft dampers?
Dryer exhausts must have a backdraft damper and must not have a screen at the termination; dryer ducts must be rigid metal and terminate outdoors per § 504.4 and § 502.2.1.
What if my exhaust is near a building outdoor air intake?
You must comply with the required separation distance from outdoor air intakes as determined in § 402.4.1; § 502.2 subsections explicitly require that distance be met in addition to the listed minima.
Can I put an exhaust termination over a public sidewalk?
Environmental/Class 1/2 dryer discharges shall not terminate over a public way or where condensate/vapor could create a nuisance or hazard; rooftop or stack terminations must also meet the vertical clearances (e.g., 10 ft above a public way where required). Check § 502.2.1 and dryer rules in § 504.4.
Are screens required at all exhaust outlets?
Exhaust openings terminating outdoors must be covered with a corrosion‑resistant screen of specified mesh per § 502.1, except where the code makes an explicit exception (for example, clothes dryers).
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