CRC · California Residential Code

Duct sizing, materials, insulation and installation rules

For homeowners: California requires HVAC ducts be sized per ACCA Manual D (or Energy Code tables for returns), built of permitted materials, sealed and tested when outside conditioned space, and insulated per Title 24 rules (typically R‑6 for residential attic ducts unless exceptions apply).

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Last reviewed: July 6, 2026

What the code requires — 2-4 sentences

The California Mechanical Code requires that all ducts and plenums used for heating, cooling, ventilation or exhaust comply with Chapter 6 (duct systems) — see § 601.0 for scope and applicability. Sizing must follow the standards in Chapter 18 or other approved methods, with a specific residential exception to use ACCA Manual D / Zr and the California Energy Code return-duct sizing tables — see § 601.2 and § 601.2.1. Materials for duct interiors must meet the combustibility and smoke/flame-spread limits in § 602.1 / § 602.2, with listed exceptions for typical residential return/outside-air ducts. (References: § 601.0, § 601.2, § 601.2.1, § 602.1, § 602.2. )

Most important rule (plain English): Design residential ducts using ACCA Manual D (or the Energy Code tables for return ducts), use permitted noncombustible or low flame/smoke materials inside ducts, insulate or locate ducts per the Energy Code, and test & seal ducts so they meet leakage and sealing limits. (See § 601.2, § 602.2, E § 502.4.1–.4.4.)

Requirements in detail

Scope — what is covered

  • § 601.0 (General): All ducts and plenums that are part of heating, cooling, ventilation, or exhaust systems must comply with Chapter 6; exhaust ducts and combustion-air ducts have related requirements in Chapters 5 and 7 respectively.

Sizing requirements (how to size ducts)

  • § 601.2 requires sizing in accordance with Chapter 18 standards or other approved methods. Residential systems have an explicit exception to use ACCA Manual D and ACCA Manual Zr (or other approved methods).
  • § 601.2.1 points designers to the California Energy Code Tables 150.0‑B and 150.0‑C as an alternative method for return-duct sizing for single- and multiple-return systems; those tables are an approved, prescriptive pathway and tie into the Energy Code field verification/testing paths.
  • The CMC Appendix E includes more specific field limits for velocities and allowable sizing practice for verification (see E § 502.4.4).

Key sizing decision values (from CMC Appendix E and Energy Code):

Parameter / limit Value Code Reference
Maximum main duct velocity 1000 ft/min (5.08 m/s) E § 502.4.4, CMC § 601.2
Maximum secondary (branch) duct velocity 600 ft/min (3.05 m/s) E § 502.4.4
Residential mandatory return sizing (prescriptive alternative) Tables 150.0‑B / 150.0‑C (Cal. Energy Code) CEC § 150.0(m) & CMC § 601.2.1

Material requirements (what you may use)

  • § 602.1 (General): Duct materials must comply with the subsequent material sections in Chapter 6.
  • § 602.2 requires that materials exposed within ducts or plenums be noncombustible or have a flame spread index ≤ 25 and smoke-developed index ≤ 50 when tested as a composite (ASTM E84 / UL 723). Certain items (including return-air / outside-air ducts serving dwelling units, some filters, evaporative media, listed plenum products, and duct insulation installed per § 605.0) are excepted. Gypsum board is explicitly not permitted for positive‑pressure ducts, and concealed spaces in healthcare settings have additional restrictions.

Material decision table:

Inside-duct material requirement Acceptable? Code Reference
Noncombustible materials Yes § 602.2
Materials tested as composite with ASTM E84 (flame ≤ 25 / smoke ≤ 50) Yes § 602.2
Gypsum board for positive-pressure ducts Not permitted § 602.1 note
Return-air / outside-air ducts serving a dwelling unit Exception (allowed) § 602.2 exceptions

Insulation and air-tightness (installation rules)

  • Thermal insulation requirements for ducts are covered both in CMC Appendix E and the California Energy Code:
    • CMC Appendix E (E § 502.4.1) states ducts shall be R‑8 and requires vapor retarders on conditioned-air supply ducts where the mean outdoor dewpoint exceeds 60°F. It also notes insulation is not required where ducts are within conditioned space.
    • The California Energy Code (Title 24) requires a minimum installed level of R‑6 for portions of supply and return ducts in single-family households, with exceptions (uninsulated ducts entirely in conditioned space; R‑4.2 allowed in certain unvented attics if conditions are met). See Section 150.0(m) for the residential mandatory features/exceptions. This is the energy‑code mandatory rule for residential buildings.
  • Sealing and leakage:
    • Joints, seams and penetrations of ducts must be made airtight with mastics, gasketing or other approved means; register penetrations must be sealed to the wall or floor assembly (E § 502.4.2).
    • For systems with ducts or air handlers outside conditioned space, a duct leakage test is required. The maximum permitted leakage is 1 cfm per 100 ft² of duct surface area at a test pressure of 0.1 inch water gauge (per SMACNA or the referenced test manual) — see E § 502.4.3 and E § 502.4.3.1.

Installation decision table:

Installation item Requirement / limit Code Reference
Minimum residential duct insulation (Energy Code prescriptive) R‑6 (with listed exceptions) CEC § 150.0(m)
Minimum duct insulation per CMC Appendix E R‑8 (note: CMC Appendix E) E § 502.4.1
Duct sealing (joints, seams, register penetrations) Airtight with mastics/gaskets/approved methods E § 502.4.2
Duct leakage test limit (outside conditioned space) 1 cfm / 100 ft² of duct surface at 0.1 in. w.g. E § 502.4.3.1

Exceptions & special cases

  • Residential sizing: Residential duct systems are explicitly allowed to follow ACCA Manual D or ACCA Manual Zr — the CMC gives this exception in § 601.2. For return ducts, the California Energy Code Tables 150.0‑B/C provide prescriptive return sizing as an alternative to field verification.
  • Insulation exceptions in the Energy Code:
    • Ducts entirely within conditioned space need no insulation (field-verified). (CEC § 150.0(m) / RA3.1.4.3.8 verification).
    • Ducts in unvented attics: minimum R‑4.2 allowed if attic has ≥ R‑30 at roof deck, gable ends meet wall insulation rules, and whole-building leakage ≤ 3.0 ACH50 (with verification). See Energy Code exceptions.
  • Materials exceptions (from § 602.2): Return-air and outside-air ducts serving a dwelling unit are exempted from the strict noncombustible/composite ASTM E84 requirement; listed plenum products and specific items (filters, evaporative media) are also excepted.

If a required provision or number is not present in the retrieved text you asked me to use, I have noted that plainly and have not invented additional section numbers or values.

Common mistakes

  • Relying on the wrong insulation number: CMC Appendix E references R‑8, while the California Energy Code prescriptive residential requirement is R‑6 (with exceptions). For residential mandatory features the Energy Code (Title 24) is the controlling energy-prescriptive source — don't ignore § 150.0(m).
  • Not sealing register penetrations and wall/floor duct penetrations to the assembly (required by E § 502.4.2). That error commonly causes leakage and failed field tests.
  • Oversizing or undersizing using only rough thumb rules instead of ACCA Manual D or Energy Code tables for residential systems (the CMC explicitly points to those methods in § 601.2).
  • Installing combustible interior materials (or gypsum board for positive-pressure ducts) without verifying plenum listing/approval — § 602.2 is strict about flame/smoke indexes and the gypsum prohibition.
  • Forgetting to perform the duct leakage test when required: systems with ducts/air handlers outside conditioned space must be tested to the leakage limit in E § 502.4.3.1.

Worked example — small single‑family supply system

Scenario: A 3‑ton (typical) central air conditioner with design supply 1200 cfm total. Main supply trunk carries the 1200 cfm; secondary branch to a zone carries 300 cfm.

  1. Velocity limits (E § 502.4.4): main ≤ 1000 ft/min; branch ≤ 600 ft/min.
  2. Required main duct cross-sectional area = 1200 cfm ÷ 1000 ft/min = 1.2 ft² = 173 in².
    • Circular duct diameter = sqrt(4×Area/π) = sqrt(4×1.2/π) ≈ 14.8 in → choose 15‑inch round duct.
  3. Branch duct for 300 cfm at ≤600 ft/min: area = 300 ÷ 600 = 0.5 ft² = 72 in².
    • Circular diameter ≈ 9.6 in → choose 10‑inch round duct.
  4. Insulation: If the ducts are in an unconditioned attic, apply the Energy Code prescriptive minimum R‑6 unless the dwelling meets one of the exceptions (e.g., ducts inside conditioned space or the unvented‑attic R‑4.2 pathway) — check CEC § 150.0(m). If following CMC Appendix E (project method), note the R‑8 guidance in E § 502.4.1 and reconcile with the Energy Code requirements for mandatory residential features.
  5. Leakage test: If the air handler or ducts are outside conditioned space, test the duct system. If the total duct surface area is, say, 400 ft², the maximum allowed leakage at test pressure is 400 × (1 cfm/100 ft²) = 4 cfm (E § 502.4.3.1). Seal joints/registers per E § 502.4.2, then retest as required.

Related provisions

  • § 601.0 — Duct systems general scope (CMC Chapter 6).
  • § 601.2 — Sizing requirements; residential exception to ACCA Manual D/Zr.
  • § 601.2.1 — California Energy Code return duct sizing reference (Tables 150.0‑B / 150.0‑C).
  • § 602.1 — Materials general (CMC Chapter 6 material compliance).
  • § 602.2 — Combustibility / flame & smoke limits inside ducts/plenums and exceptions.
  • E § 502.4.1 — Duct insulation (R values guidance) and vapor retarder requirement.
  • E § 502.4.2 — Duct sealing / register penetration sealing.
  • E § 502.4.3 / E § 502.4.3.1 — Duct leakage testing and permitted leakage.
  • E § 502.4.4 — Duct sizing velocity limits (1000 ft/min main, 600 ft/min branch).
  • California Energy Code § 150.0(m) and related tables — residential duct insulation and prescriptive return duct sizing rules.

Code references

Grounded in the retrieved California Residential Code — click a citation to read the verbatim passage:

  • CRC § 1.5. High relevance — show source text

    For openings less than or equal to 6 feet in
    height that have both a head track and a sill track, the spans are permitted to be multiplied by a factor of 1.5.
    d. Minimum Grade 33 ksi steel shall be used for 33 mil and 43 mil thicknesses. Minimum Grade 50 ksi steel shall be used for 54 and 68 mil thicknesses.|For SI: 1 mil = 0.0254 mm, 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 mile per hour = 0.447 m/s, 1 ksi = 1,000 psi = 6.895 MPa.
    a. Deflection limit:L/240.
    b. Head and sill track spans are based on components and cladding wind pressures and 48-inch tributary span.
    c. For openings less than 4 feet in height that have both a head track and sill track, the spans are permitted to be multiplied by 1.75. For openings less than or equal to 6 feet in
    height that have both a head track and a sill track, the spans are permitted to be multiplied by a factor of 1.5.
    d. Minimum Grade 33 ksi steel shall be used for 33 mil and 43 mil thicknesses. Minimum Grade 50 ksi steel shall be used for 54 and 68 mil thicknesses.|For SI: 1 mil = 0.0254 mm, 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 mile per hour = 0.447 m/s, 1 ksi = 1,000 psi = 6.895 MPa.
    a. Deflection limit:L/240.
    b. Head and sill track spans are based on components and cladding wind pressures and 48-inch tributary span.
    c. For openings less than 4 feet in height that have both a head track and sill track, the spans are permitted to be multiplied by 1.75. For openings less than or equal to 6 feet in
    height that have both a head track and a sill track, the spans are permitted to be multiplied by a factor of 1.5.
    d. Minimum Grade 33 ksi steel shall be used for 33 mil and 43 mil thicknesses. Minimum Grade 50 ksi steel shall be used for 54 and 68 mil thicknesses.|For SI: 1 mil = 0.0254 mm, 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 mile per hour = 0.447 m/s, 1 ksi = 1,000 psi = 6.895 MPa.
    a. Deflection limit:L/240.
    b. Head and sill track spans are based on components and cladding wind pressures and 48-inch tributary span.
    c. For openings less than 4 feet in height that have both a head track and sill track, the spans are permitted to be multiplied by 1.75. For openings less than or equal to 6 feet in
    height that have both a head track and a sill track, the spans are permitted to be multiplied by a factor of 1.5.
    d. Minimum Grade 33 ksi steel shall be used for 33 mil and 43 mil thicknesses.

  • CRC § 403.4.7 High relevance — show source text

    Smoke exhaust 910 Smoke removal, high-rise buildings 403.4.7 Smokeproof enclosure 909.20.3, 909.20.5, 1023.12 Spray rooms and spaces 416.2.2, 416.3 Stages 410.2.5, 410.2.7 Under-floor ventilation 202.4 Vents, Penetration Protection 714 Vermiculite, Fire Resistant 721 Vertical Opening Protection Atriums 404.6

    Duct penetrations 717.1 Elevators 713.14, 3007.6.1, 3008.6.1 Exceptions 1019, 1023.2 Group I-3 408.5 High-rise 403.2.1.2, 403.2.2, 403.5.1 Live/work units 508.5.6 Open parking garages 406.5.9 Permitted vertical openings 712 Shaft enclosure 713, 1019, 1023.2 Vestibules, Exit Discharge 1028.2 Vinyl Expanded 803.7, 803.8 Rigid 1404.15 Violations 114 Voice Alarm (see Alarms, Voice) Walkway 402.4.3.1, 3104 During construction 3306 Encroachment, public right-of-way 3202.3.4

    Fire resistance Table 601

    Live load Table 1607.1 Materials per construction type Chapter 6 Opening protection 716, 717, 1026.2 Wall, Exterior 705, 1401 Bearing Chapter 6

    California Energy Code and International Energy Conservation Code Climate Zones 1404.3.3 Combustible wall covering 1405 Coverings 1404 Drawings 107.2.4 Exterior insulation and finish systems (EIFS) 1407 Exterior structural members 704.9

    Fire district D102.2.6, D102.1 Fire-resistance ratings 703, 705.5, Table 705.5, 706.5.1, 707.4, 1402.4 Flashing, veneered walls 1404.11.1, 1404.4

    Foam plastic insulation 2603.4.1.4, 2603.5 Glazing, rated 715.8 Joints 705.10, 714 Light-transmitting plastic panels 2607 Materials 705.4, 1403.1, 1405 Metal composite material (MCM) 1406 Nonbearing Chapter 6 Opening protection 705.11, 705.9, 716.2.5.4

    Parapets 705.12 Performance requirements 1402 Projections 705.2 Structural stability 705.7 Vapor retarders 1404.3 Veneer (see Veneer) Weather resistance 1402.2, 1404.2, 1406.6, 1407.4 Weather-resistant barriers 1404.2 Wall, Fire (see Fire Walls) Wall, Foundation (see Foundations) Wall, Interior Finishes 803, 1210.2 Opening protection 716, 717 Wall, Interior Nonbearing (See Partitions) Wall, Masonry 202 Wood Contact 2304.12.1.3,

  • CRC § 2.9 High relevance — show source text

    Fire district D102.2.9 Height modifications 503.1.4, 504.3 Impact resistance 1504.7 Insulation 1508 Lightning protection systems 1511.7.6 Materials 1506 Mechanical equipment screen 1511.6 Parapet walls 1503.2, 1503.3 Penthouses 713.12.1, 1511.2 Photovoltaic panels and modules 1511.10, 1511.10.1 Radiant barrier 1510

    Tanks 1511.3 Towers, spires, domes and cupolas 1511.5, 3108 Weather protection 1503 Wind resistance 1504.1, 1504.3, 1504.4, 1609.6 Roof Construction Construction walkways 3306.7 Coverings (see Roof Coverings) 1609.6.2 Draftstopping 718.4 Fire resistance Table 601 Fireblocking 718.2 Live loads 1607.14, Table 1607.1,

    3111.1.2

    Materials Chapter 6 Penetration of fire-resistant assemblies

    714 Protection from adjacent construction 3307.1

    Rain loads 1611

    Roof deck 1609.6.1 Signs, roof mounted H110 Slope, minimum Chapter 15

    Snow load 1608 Solar systems, rooftop-mounted 3111.1, 3111.3.2 Trusses 2206.1.3, 2303.4, 2308.11.12 Ventilation 1202.2

    Wood (see Roof Construction, Wood) Roof Construction, Wood 602.4, 602.5 Anchorage to walls 1604.8.2 Attic access 1209.2 Ceiling joists 2308.11.1 Diaphragms 2305.1, 2306.2 Fastening requirements 2304.10 Fire-retardant-treated Table 601,

    603.1

    Framing 2304.11.4, 2308.11 Rafters 2306.1.1, 2308.11.2 Sheathing 2304.8.2, 2308.11.9 Trusses 2303.4, 2308.11.12 Ventilation, attic 1202.2 Wind uplift 2308.11.4 Roof Coverings 1507 Asphalt shingles 1507.2, 1609.2.1 Built up 1507.10 Clay tile 1507.3, 1513 Concrete tile 1507.3, 1513 Fire district D102.2.4

  • CRC § 5A-3 High relevance — show source text

    METHOD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5A-3

    501A General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5A-3

    502A Additions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5A-4

    503A Alterations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5A-5

    504A Reserved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5A-7

    505A Reserved. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5A-7

    506A Change of Occupancy. . . . . . . . . . . . . . . . . . . . . . . . . . . .5A-7

    CHAPTER 6 CLASSIFICATION OF WORK . . . . . . . . . . . . . . . 6-3

    601 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

    602 Alteration—Level 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

    603 Alteration—Level 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

    604 Alteration—Level 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

    605 Change of Occupancy. . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

    606 Additions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

    607 Historic Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

    CHAPTER 7 ALTERATIONS—LEVEL 1 . . . . . . . . . . . . . . . . . .7-3

    701 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3

    702 Building Elements and Materials . . . . . . . . . . . . . . . . . 7-3

  • CRC § 140.8 High relevance — show source text

    C. An energy management control system (EMCS) or other controls that provides the specified lighting control functionality and complies with all requirements applicable to the specified controls may be used to meet these requirements. 4. Internally illuminated address signs. Internally illuminated address signs shall either: A. Comply with Section 140.8; or B. Consume no more than 5 watts of power. 5. Residential garages for eight or more vehicles. Lighting for residential parking garages for eight or more vehicles shall comply with the applicable requirements for nonresidential garages in Sections 110.9, 130.0, 130.1, 130.4, 140.6 and 141.0.

    (l) Reserved.

    (m) Air-distribution and ventilation system ducts, plenums and fans.

    1. CMC compliance.

    A. All air-distribution system ducts and plenums, including but not limited to, mechanical closets and air-handler boxes, shall meet the requirements of the CMC Sections 601.0, 602.0, 603.0, 604.0, 605.0 and ANSI/SMACNA-006-2006 HVAC Duct Construction Standards Metal and Flexible, 3rd Edition, incorporated herein by reference.

    2025 CALIFORNIA ENERGY CODE 163

    on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

    SINGLE-FAMILY RESIDENTIAL BUILDINGS— MANDATORY FEATURES AND DEVICES

    B. Portions of supply-air and return-air ducts and plenums of a space heating or cooling system shall be insulated in accordance with either Subsection i or ii below:

    i. Ducts shall have a minimum installed level of R-6.0, or Exception 1 to Section 150.0(m)1Bi: Portions of the duct system located in conditioned space below the ceiling separating the occupiable space from the attic are not required to be insulated if all of the following conditions are met:

    a. The noninsulated portion of the duct system is located entirely inside the building’s thermal envelope as confirmed by visual inspection. b. At all locations where noninsulated portions of the duct system penetrate into unconditioned space, the penetration shall be draft stopped compliant with CFC Sections 703.1 and 704.1 and air-sealed to the construction materials that are penetrated, using materials compliant with CMC Section E502.4.2 to prevent air infiltration into the cavity. All connections in unconditioned space are insulated to a minimum of R-6.0 as confirmed by visual inspection. Exception 2 to Section 150.0(m)1Bi : Ducts located in an unvented attic shall have a minimum insulation value of R-4.2, verified by visual inspection where:

    a. The attic has at least R-30 insulation between the roof rafters in contact with the roof deck.

    b. The gable ends meet the wall insulation requirements of Section 150.1(c)1B. c. The dwelling unit achieves a whole building leakage rate of 3.0 ACH50 or less, as confirmed by field verification and diagnostic testing in accordance with Reference Residential Appendix RA3.8. ii. Ducts do not require insulation when the duct system is located entirely within conditioned space, as confirmed through field verification and diagnostic testing in accordance with the requirements of Reference Residential Appendix RA3.1.4.3.8. For dwelling units with attics, the duct system shall be located below the ceiling separating the occupiable space from the attic.

  • CRC § 6-3 High relevance — show source text

    601 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

    602 Alteration—Level 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

    603 Alteration—Level 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

    604 Alteration—Level 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

    605 Change of Occupancy. . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

    606 Additions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

    607 Historic Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

    CHAPTER 7 ALTERATIONS—LEVEL 1 . . . . . . . . . . . . . . . . . .7-3

    701 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3

    702 Building Elements and Materials . . . . . . . . . . . . . . . . . 7-3

    703 Fire Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-4

    704 Means of Egress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-4

    705 Reroofing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-4

    706 Structural. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-5

    707 Reserved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6

    708 Energy Conservation. . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6

    CHAPTER 8 ALTERATIONS—LEVEL 2 . . . . . . . . . . . . . . . . . .8-3

    801 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-3

    802 Building Elements and Materials . . . . . . . . . . . . . . . . . 8-3

  • CRC § 1616.2.2.1 High relevance — show source text

    Demolition 3303 Design Flood 1612 Design Strength Column splice 1616.2.2.1 Conformance to standards 1706.1

    New materials 1706.2 Designated Seismic System 1704.3.2, 1704.4, 1704.5 Seismic certification 1705.14.3

    Special inspection 1705.13.4 Detached Single-family Dwelling 202 Detectable Warning 202 Diaphragms 202 Analysis 1604.4 Ceilings 2508.6

    Penetrations 714

    Permit application 105.1 Relocation 107.2.8

    Retention 107.5

    Review 107.3

    Roof assemblies 1503

    Roof live load 1603.1.2

    Roof rain load data 1603.1.9

    Roof snow load 1603.1.3

    Seismic 1603.1.5, 1705.14.2, 1705.14.3 Site plan 107.2.6 Special loads 1603.1.8 Temporary structures 3103.2 Wind data 1603.1.4 Construction Types 202, Chapter 6 Aircraft-related occupancies 412.2.1, Table 412.3.6, 412.5.2 Classification 602 Combustible material in Type I and Type II construction 603, 805 Covered and open mall buildings 402.4.1 Fire district D102.2.3

    Fire resistance Table 601, Table 705.5 High-rise 403.2 Type I Table 601, 602.2, 603 Type II Table 601, 602.2, 603 Type III Table 601, 602.3 Type IV Table 601, 602.4 Type V Table 601, 602.5 Underground buildings 405.2 Continuity Head-Of-Wall System 202 Continuous Insulation (ci) 202 Contractor’s Responsibilities 901.5, 1704.4 Control Area 414.2, 707.3.8 Construction 414.2.1

    Fire-resistance rating 414.2.4 Maximum allowed quantities 414.2.2 Number 414.2.3 Conventional Light-frame Construction 2302.1, 2308 Additional seismic requirements 2308 Braced wall lines 2308.10 Design of elements 2308.8 Floor joists 2308.8.2 Foundation plates or sills 2308.7 Girders 2308.8.1 Roof and ceiling framing 2308.11 Wall framing 2308.9 Conveying System S3004 Cornices

    Definition 202 Draftstopping 718.2.6 Live load Table 1607.1

    Masonry 2104.1.2 Projection 705.2, 705.2.3.1 Public right-of-way encroachments 3202.3.2, 3202.3.3 Correctional Treatment Centers

    [OSHPD 4] 1227 Application 1227.2 Ceiling heights 1227.8 Corridors 1227.5

  • CRC § 3-3 High relevance — show source text

    301 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-3

    302 Wildland-Urban Interface Area Designations . . . . . .3-3

    CHAPTER 4 WILDLAND-URBAN INTERFACE AREA

    REQUIREMENTS . . . . . . . . . . . . . . . . . . . . . . 4-3

    401 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-3

    402 Applicability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-3

    403 Access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-3

    404 Water Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-7

    CHAPTER 5 SPECIAL BUILDING CONSTRUCTION

    REGULATIONS . . . . . . . . . . . . . . . . . . . . . . . . 5-3

    501 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-3

    502 Reserved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-3

    503 Ignition-Resistant Construction and Material. . . . . .5-3

    504 Ignition-Resistant Construction. . . . . . . . . . . . . . . . . .5-4

    505 Reserved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-9

    506 Reserved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-9

    507 Replacement or Repair of Roof Coverings. . . . . . . . .5-9

    CHAPTER 6 FIRE PROTECTION REQUIREMENTS. . . . . . .6-3

    601 General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

    602 Fire Protection Plans . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

    603 Vegetation Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4

    604 Maintenance of Defensible Space . . . . . . . . . . . . . . . 6-5

  • CRC § 310.13 High relevance — show source text

    ante rooms.

    310.13 [SFM] For applications listed in Section 1.11.0 regu- lated by the Office of the State Fire Marshal, plastic piping shall not be exposed as a portion of the interior room finish in a build- ing or structure if the piping has a flame-spread rating exceed- ing 75 when tested in accordance with ASTM E84, “Test for Surface Burning Characteristics of Building Materials.” 310.14 Services/Systems and Utilities. [OSHPD 1, 2, 4 & 5] Refer to Sections 1224.4.1, 1225.2.1 and 1228.4.1.1, Cal- ifornia Building Code. 310.15 Telephone and Data Equipment Rooms.

    [OSHPD 1, 4 & 5] Where telecommunications service entrance rooms, technology equipment centers, or technology distribution rooms are provided in accordance with Section 1224.5 of the California Building Code, plumbing equipment and fixtures that are not directly related to the support of the room shall not be installed in or pass through the room.

    311.0 Independent Systems. 311.1 General. The drainage system of each new building and new work installed in an existing building shall be separate and independent from that of any other building, and, where available, every building shall have an independent connection with a public or private sewer.

    Exception: Where one building stands in the rear of another building on an interior lot, and no public or private sewer is available or can be constructed to the rear building through an adjoining court, yard, or driveway, the building drain from the front building shall be permitted to be extended to the rear building.

    Note: Accessory dwelling units are not required to have inde- pendent service utility (drainage) connections provided they meet the specific requirements in Government Code Section 65852.2.

    312.0 Protection of Piping, Tubing, Materials, and Structures.

    312.1 General. Piping passing under or through walls shall be protected from breakage. Piping passing through or under cinders or other corrosive materials shall be protected from external corrosion in an approved manner. Approved provisions shall be made for expansion of hot water piping. Voids around piping passing through concrete floors on the ground shall be sealed.

    312.2 Installation. Piping in connection with a plumbing system shall be so installed that piping or connections will not be subject to undue strains or stresses, and provisions shall be made for expansion, contraction, and structural settlement. No plumbing piping shall be directly embedded in concrete or masonry. No structural member shall be seriously weakened or impaired by cutting, notching, or otherwise, as defined in the California Building Code or California Residential Code . 312.3 Building Sewer and Drainage Piping. No building sewer or other drainage piping or part thereof, constructed of materials other than those approved for use under or within a building, shall be installed under or within 2 feet (610 mm) of a building or structure, or less than 1 foot (305 mm) below the surface of the ground. 312.4 Corrosion, Erosion, and Mechanical Damage. Piping subject to corrosion, erosion, or mechanical damage shall be protected in an approved manner. **312.5 Protectively Coated Pipe.

  • CRC § 0.42 High relevance — show source text

    Spacing of fasteners not included in this table shall be based on Table R602.3(2).
    f. For wood structural panel roof sheathing attached to gable end roof framing and to intermediate supports within 48 inches of roof edges and ridges, nails shall be spaced at 4
    inches on center where the ultimate design wind speed is greater than 130 mph in Exposure B or greater than 110 mph in Exposure C. Fastener spacing applies where roof
    framing specific gravity is 0.42 or larger. Where roof framing specific gravity is greater than or equal to 0.35 but less than 0.42 in accordance with AWC NDS, fastening of roof
    sheathing shall be with RSRS-03 (21/2″ × 0.131″ × 0.281″ head) nails.
    g. Gypsum sheathing shall conform to ASTM C1396 and shall be installed in accordance with ASTM C1280 or GA 253 . Fiberboard sheathing shall conform to ASTM C208.
    h. Spacing of fasteners on floor sheathing panel edges applies to panel edges supported by framing members and required blocking and at floor perimeters only. Spacing of fasteners
    on roof sheathing panel edges applies to panel edges supported by framing members and required blocking. Blocking of roof or floor sheathing panel edges perpendicular to the
    framing members need not be provided except as required by other provisions of this code. Floor perimeter shall be supported by framing members or solid blocking.
    i. Where a rafter is fastened to an adjacent parallel ceiling joist in accordance with this schedule, provide two toe nails on one side of the rafter and toe nails from the ceiling joist
    to top plate in accordance with this schedule. The toe nail on the opposite side of the rafter shall not be required.|For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 mile per hour = 0.447 m/s; 1 ksi = 6.895 MPa.
    a. Nails are smooth-common, box or deformed shanks except where otherwise stated. Nails used for framing and sheathing connections are carbon steel and shall have mini-
    mum average bending yield strengths as shown: 80 ksi for shank diameter of 0.192 inch (20d common nail), 90 ksi for shank diameters larger than 0.142 inch but not larger than
    0.177 inch, and 100 ksi for shank diameters of 0.142 inch or less. Connections using nails and staples of other materials, such as stainless steel, shall be designed by accepted
    engineering practice or approved under Section R104.2.2.
    b. RSRS-01 is a Roof Sheathing Ring Shank nail meeting the specifications in ASTM F1667.
    c. Nails shall be spaced at not more than 6 inches on center at all supports where spans are 48 inches or greater.
    d. Four-foot by 8-foot or 4-foot by 9-foot panels shall be applied vertically.
    e. Spacing of fasteners not included in this table shall be based on Table R602.3(2).
    f. For wood structural panel roof sheathing attached to gable end roof framing and to intermediate supports within 48 inches of roof edges and ridges, nails shall be spaced at 4
    inches on center where the ultimate design wind speed is greater than 130 mph in Exposure B or greater than 110 mph in Exposure C. Fastener spacing applies where roof
    framing specific gravity is 0.42 or larger.

  • CRC § 605.1.3 High relevance — show source text

    E 605.1.3 Dwelling Unit Ventilation. A mechanical exhaust system, supply system, or combination thereof shall be designed and provided with the capacity to deliver outdoor air ventilation to the whole dwelling unit at a continuous rate not less than that specified in Section E 605.1.3.1 through Section E 605.1.3.5. [ASHRAE 62.2:4.1]

    E 605.1.3.1 Total Ventilation Rate. The total required ventilation rate ( Qtot ) shall be as specified in Table E 605.1.3.1 or, alternatively, calculated using Equation E 605.1.3.1.

    (Equation E 605.1.3.1) Qtot = 0.03 Afloor + 7.5( Nbr + 1)

    Where:

    Qtot = total required ventilation rate, CFM Afloor = dwelling unit floor area, ft [2] Nbr = number of bedrooms (not to be less than one)

    For SI units: 1 cubic foot per minute = 0.00047 m [3] /s, 1 cubic foot

    per minute = 0.4719 L/s

    Exceptions: Dwelling-unit mechanical ventilation systems shall not be required where the Authority Having Jurisdiction determines that window operation is a locally permissible method of providing ventilation and provided one or more of the following conditions is met:

    (1) The building has no mechanical cooling and is in zone 1 or 2 of the climate zone map.

    (2) The building is thermally conditioned for human occupancy for less than 876 hours per year. [ASHRAE 62.2:4.1.1] E 605.1.3.2 Effective Annual Average Infiltra- tion Rate ( Qinf ) Using a Single-Point Enve- lope Leakage Test. Effective Annual Average

    Infiltration Rate ( Qinf ) shall be calculated using a single-point test at 0.007 psi (50 Pa). The Effective Annual Average Infiltration Rate ( Qinf ) shall be calculated using Equation 605.1.3.2:

    (Equation E 605.1.3.2) Qinf = 0.052 × Q 50 × wsf × ( H/Hr ) [z]

    Where: Qinf = estimated infiltration rate, CFM (L/s). Q50 = leakage rate at 0.007 psi (50 Pa) depressurization or pressurization, CFM (L/s). wsf = weather and shielding factor from ASHRAE 62.2.

    H = vertical distance between the lowest and highest above-grade points within the pressure boundary, ft (m). Hr = reference height, 8.2 ft (2.5 m). z = 0.4 for the purpose of calculating the Effective Annual Average Infiltration Rate.

    For SI units: 1 foot = 0.3048 m, 1 cubic foot per minute =

    0.4719 L/s

  • CRC § 320.1.2 High relevance — show source text

    Humidifiers shall be_ located within air handling systems or ductwork to avoid moisture accumulation in downstream components, including filters and insulation. 320.1.2 Heating systems shall be designed based on the “Heating DB 99.6%” column of the Climatic Design Data in ASHRAE Handbook-Fundamentals. The systems shall be thermostatically controlled with appropriate zoning to achieve the above conditions. 320.1.3 Cooling systems shall be designed based on the 0.4% columns of the four Annual Design Conditions titled Cooling, Evaporation, Dehumidification, and Enthalpy shown by the Climate Design Data in ASHRAE Handbook-Fundamentals. The systems shall be thermo- statically controlled with appropriate zoning to achieve the above conditions.

    320.2 Requirements for Skilled Nursing, Intermedi- ate Care Facilities and Basic Services Provided in Correctional Treatment Centers. [OSHPD 2 & 4]

    320.2.1 Systems shall accommodate the provisions of Sections 320.1.2 through 320.1.3.

    320.2.2 Where air conditioning is provided, the system shall be thermostatically controlled in one or more zones. 320.3 Requirements for Outpatient Facilities and Licensed Clinics. [OSHPD 3]

    320.3.1 The system shall be designed to provide the tem- perature and humidities for sensitive areas for rooms shown in Table 4-A.

    320.4 Telephone and Technology Equipment Centers.

    [OSHPD 1 & 4] Where telecommunications service entrance rooms, technology equipment centers, or technology distribu- tion rooms are provided in accordance with Section 1224.5 of the California Building Code, the following requirements shall apply: 320.4.1 Power for HVAC systems serving the room(s) shall be supplied by the Equipment Branch pursuant to the California Electrical Code. Where redundant systems are provided, only one shall be required to be supplied by the Equipment Branch. 320.4.2 Mechanical equipment or fixtures that are not directly related to the support of the room shall not be installed in or pass through the room. Exception: Unrelated ductwork may be installed and shall be not less than 10 feet (3048 mm) above the finished floor. 320.4.3 HVAC systems shall be provided to maintain environmental conditions recommended in ASHRAE’s Thermal Guidelines for Data Processing Environment and the requirements of the specific equipment installed. 320.4.4 Technology equipment centers shall have redun- dant cooling systems each of sufficient capacity to pro- vide required cooling during periods of breakdown or maintenance of either system. One system shall be non- hydronic and on essential power. 320.5 Psychiatric Services. [OSHPD 1, 1R, 2, 4 & 5] For projects associated with provision of psychiatric services in acute psychiatric hospitals, general acute-care hospitals, and special treatment program service units in skilled nursing facilities, psychiatric, seclusion, and holding-patient rooms shall be designed with security diffusers, grilles, and registers.

Frequently asked questions

What is the single most important thing to do for residential ducts?

Design the ducts using ACCA Manual D (or the California Energy Code return‑duct tables for prescriptive return sizing), seal all joints and register penetrations, insulate per the Energy Code, and perform required leakage testing if ducts/air handler are outside conditioned space. § 601.2, E § 502.4.2–.4.3.1.

Which R‑value should I use — R‑6 or R‑8?

For single‑family residential prescriptive compliance, the California Energy Code requires R‑6 except where specific exceptions apply (e.g., ducts in conditioned space or unvented attic provisions). CMC Appendix E suggests R‑8 as a design guidance in that appendix; reconcile project requirements by following the Energy Code mandatory provisions for residential compliance. CEC § 150.0(m), E § 502.4.1.

Are return ducts inside a dwelling held to the same material tests as plenums?

There is a specific exception: return‑air and outside‑air ducts serving a dwelling unit are excepted from the strict composite ASTM E84/UL 723 requirement in § 602.2. Always confirm other local/jurisdictional requirements.

When do I have to perform a duct leakage test?

If the ductwork or air handler is located outside the conditioned space, perform the duct leakage test per E § 502.4.3.1; maximum permitted leakage is 1 cfm per 100 ft² of duct surface area at 0.1 in. w.g.

Can I use gypsum board inside ducts?

No — gypsum board is not permitted for positive‑pressure ducts (see § 602.1 note). Other interior materials must meet the flame/smoke limits or be specifically listed for plenums.

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California Residential Code