CRC · California Residential Code

When are unvented attic assemblies permitted and what conditions apply?

An attic can be left unvented only when it is entirely inside the conditioned envelope and every rule in **§ R806.5** is followed: no Class I vapor retarder on the ceiling side, required treatment for air‑impermeable insulation in certain climate zones, special 1/4‑inch spacing for wood shingles/shakes, and meeting the insulation placement/condensation‑control options (see Table R806.5). Confirm product vapor‑retarder class and check Table R806.5 for required above‑deck R‑values before finalizing the assembly.

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Last reviewed: July 6, 2026

What the code requires — 2-4 sentences

The California Residential Code permits unvented attic and unvented enclosed rafter assemblies only when all the conditions listed in § R806.5 are met. Key conditions include that the attic be completely inside the building thermal envelope, no interior Class I vapor retarders be installed on the ceiling side, controls for condensation depending on the insulation type, and special requirements for wood shingles/shakes and certain climate zones. See § R806.5 for the full set of required items .

The single most important rule: an attic may be left unvented only when it is inside the conditioned envelope and every condition of § R806.5 is satisfied.

Requirements in detail

What “unvented attic” means (defined behavior)

  • Unvented attic (or unvented enclosed rafter assembly) refers to an attic or enclosed rafter space where the ceiling is applied directly to the underside of the roof framing and there is no cross ventilation required by the usual venting rules; such assemblies are permitted only when the conditions of § R806.5 are satisfied .

The checklist from § R806.5 (plain-English mapping)

  • The unvented attic space must be completely within the building thermal envelope (§ R806.5.1) .
  • Interior Class I vapor retarders must not be installed on the ceiling (attic floor) side of the assembly (§ R806.5.2) .
  • If wood shingles or shakes are used, provide a minimum 1/4‑inch (6.4 mm) vented airspace above the structural sheathing between shingles/shakes and underlayment (§ R806.5.3) .
  • In Climate Zones 5–8, any air‑impermeable insulation must be a Class II vapor retarder or have a Class II coating/covering in direct contact with the underside of the insulation (§ R806.5.4) .
  • Insulation must meet the layering and placement rules summarized in § R806.5.5 and its subitems (5.1, 5.2, 5.3) which depend on the air permeability of the insulation and whether rigid board insulation is installed above the structural sheathing; see § R806.5.5 and Table R806.5 for condensation-control R-values where required .

Decision table — key dimensions and values

Decision dimension Required value / action Code Reference
Location of attic relative to thermal envelope Must be completely within the building thermal envelope § R806.5.1
Interior vapor retarder on ceiling side Not permitted to be Class I on the ceiling side § R806.5.2
Wood shingles / shakes Minimum 1/4‑inch (6.4 mm) vented airspace above sheathing § R806.5.3
Climate Zones 5–8 + air‑impermeable insulation Air‑impermeable insulation must be Class II or have Class II coating in direct contact § R806.5.4
Insulation placement when air‑impermeable only Must be in direct contact with underside of structural roof sheathing § R806.5.5.1.1
Insulation when air‑permeable is used below sheathing Rigid board or sheet insulation must be installed above the structural roof sheathing per R‑values in Table R806.5 (for condensation control) § R806.5.1.2 and Table R806.5 (table values not reproduced here)

Note: Table R806.5 (referenced for condensation control R‑values and percentages) is referenced in the code text, but the exact numeric R‑value requirements in Table R806.5 were not included in the file excerpts available to me; check Table R806.5 in the CRC for the precise R‑value percentages and values required for specific climate zones and insulation assemblies .

Other related installation controls

  • Ventilation rules in other sections (e.g., the normal cross‑ventilation ratio 1/150 or 1/300 exception) apply to vented attics; unvented assemblies are a separate permitted alternative only when § R806.5 conditions are satisfied (§ R806.2, R806.1) .
  • Maintain clearance where eave/cornice vents exist: blocking/bridging must not obstruct flow and there must be a 1‑inch (25 mm) space between insulation and roof sheathing where required (§ R806.3) — this is relevant when converting or mixing venting strategies .

Exceptions & special cases

  • The CRC lists an exception allowing reduced vent area ([1/300] instead of [1/150]) for vented attics when specific conditions are met (Class I or II vapor retarder in CZ 6–8 and balanced upper/lower venting). That is a vented‑attic exception and does not by itself allow an unvented assembly unless § R806.5 is followed .
  • Where wood shingles or shakes are used on an unvented assembly, the code requires the 1/4‑inch vented airspace even though the attic is otherwise unvented (§ R806.5.3) .
  • The CRC includes a Note about climate zone mapping differences between the IECC climate zones referenced in Chapter 8 and the California Energy Code — verify which climate‑zone mapping is controlling for energy‑code vs. R806 purposes (see the R806 Note) .

If you need to treat ducts or mechanical equipment in the attic: the California Energy Code and the California Mechanical Code contain cross‑requirements (e.g., placing ducts/air handlers within conditioned space or meeting energy‑code verification). Those are outside § R806.5 but commonly affect the decision to use unvented attics — consult the Energy and Mechanical Code sections for the project specifics .

Common mistakes

  • Assuming “no vents” is enough: installers sometimes omit the required vapor‑control and insulation placement checks — but § R806.5 requires both the thermal‑envelope condition and specific insulation/vapor retarder conditions .
  • Putting a Class I vapor retarder (e.g., polyethylene sheet) on the ceiling side — that is explicitly prohibited for unvented assemblies (§ R806.5.2) .
  • Forgetting the wood shingle / shake airspace requirement — even if the attic is unvented, § R806.5.3 still requires the 1/4‑inch vented airspace under those roof coverings .
  • Using air‑impermeable insulation in Climate Zones 5–8 without confirming it is a Class II vapor retarder (or coated) in direct contact with the underside — a common oversight that violates § R806.5.4 .
  • Relying on generic R‑value rules without checking Table R806.5: condensation control may require specific above‑deck rigid insulation amounts when air‑permeable insulation is used under the sheathing; Table R806.5 contains those values (table not reproduced here) .

Worked example — concrete scenario

Scenario: Single‑family house in Climate Zone 6 (California), owner wants unvented attic above the conditioned living space. Proposed assembly uses closed‑cell spray foam directly beneath the roof sheathing and no soffit/ridge vents.

Apply the code checklist:

  1. Thermal envelope: The spray‑foam sealed roof/ceiling assembly will place the attic inside the conditioned envelope — satisfies § R806.5.1 .
  2. Interior vapor retarder: Do not install a Class I vapor retarder on the ceiling side (no polyethylene sheeting on attic floor) — required by § R806.5.2 .
  3. Climate zone control for air‑impermeable insulation: In CZ 6, spray foam is air‑impermeable; the code requires that any air‑impermeable insulation be a Class II vapor retarder or have a Class II coating/covering in direct contact with the underside of the insulation (§ R806.5.4). Verify the specific spray‑foam product labeling or use an additional coating/covering if needed to meet Class II performance .
  4. Insulation placement rules: Because only air‑impermeable insulation is being used and it will be in direct contact with the underside of structural roof sheathing, the assembly meets § R806.5.1.1 / 5.1.1 requirement into which § R806.5 divides options .
  5. Wood shingles/shakes: If the roof covering were wood shingles or shakes, the installer would also have to provide a 1/4‑inch vented airspace above sheathing — check § R806.5.3 (not applicable if using asphalt shingles or tile) .

Conclusion for this scenario: The unvented attic is permitted if product documentation shows the spray foam meets Class II vapor‑retarder requirements for CZ 6 (or you provide the required coating), there is no Class I vapor retarder on the ceiling side, and the attic is sealed within the thermal envelope — consistent with § R806.5 .

Related provisions — quick reference

  • § R806.1 — Ventilation required for enclosed attics and rafter spaces (vented assemblies) .
  • § R806.2 — Minimum vent area rules (1/150 and the 1/300 exception) — relevant when choosing vented vs unvented approaches .
  • § R806.3 — Vent and insulation clearance (1‑inch clearance where applicable) .
  • R806 Note — Climate zone mapping note that explains IECC vs California Energy Code climate zone differences for this section; verify the climate zone basis you are using .
  • California Energy Code cross references (attic insulation placement and duct/air‑handler location) — see Title 24, Part 6 and the CRC cross‑references for energy‑related requirements .

If you want, I can:

  • Pull Table R806.5 and interpret the exact R‑value percentages for each climate zone (requires retrieving that table from the CRC), or
  • Review a specific assembly (manufacturer datasheets, climate zone and roofing type) and produce a compliance checklist tied to the exact subitems of § R806.5.

Code references

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

  • CRC § 6.4 High relevance — show source text

    The balance of the required ventilation provided shall be located in the bottom one-third of the attic space. Where the location of wall or roof framing members conflicts with the installation of upper ventilators, installation more than 3 feet (914 mm) below the ridge or highest point of the space shall be permitted.

    R806.3 Vent and insulation clearance. Where eave or cornice vents are installed, blocking, bridging and insulation shall not block the free flow of air. Not less than a 1-inch (25 mm) space shall be provided between the insulation and the roof sheathing and at the location of the vent.

    R806.4 Installation and weather protection. Ventilators shall be installed in accordance with manufacturer’s instructions. Installation of ventilators in roof systems shall be in accordance with the requirements of Section R903. Installation of ventilators in wall systems shall be in accordance with the requirements of Section R703.1.

    R806.5 Unvented attic and unvented enclosed rafter assemblies. Unvented attics and unvented enclosed roof framing assemblies created by ceilings that are applied directly to the underside of the roof framing members and structural roof sheathing applied directly to the top of the roof framing members/rafters, shall be permitted where all the following conditions are met:

    1. The unvented attic space is completely within the building thermal envelope.
    2. Interior Class I vapor retarders are not installed on the ceiling side (attic floor) of the unvented attic assembly or on the ceiling side of the unvented enclosed roof framing assembly.
    3. Where wood shingles or shakes are used, a minimum [1] / 4 -inch (6.4 mm) vented airspace separates the shingles or shakes and the roofing underlayment above the structural sheathing.
    4. In Climate Zones 5, 6, 7 and 8, any air-impermeable insulation shall be a Class II vapor retarder, or shall have a Class II vapor retarder coating or covering in direct contact with the underside of the insulation.
    5. Insulation shall comply with Item 5.3 and either Item 5.1 or 5.2: 5.1. Item 5.1.1, 5.1.2, 5.1.3 or 5.1.4 shall be met, depending on the air permeability of the insulation directly under the structural roof sheathing. 5.1.1. Where only air-impermeable insulation is provided, it shall be applied in direct contact with the underside of the structural roof sheathing. 5.1.2. Where air-permeable insulation is installed directly below the structural sheathing, rigid board or sheet insulation shall be installed directly above the structural roof sheathing in accordance with the R-values in Table R806.5 for condensation control.

    5.1.3. Where both air-impermeable and air-permeable insulation are provided, the air-impermeable insulation shall be applied in direct contact with the underside of the structural roof sheathing in

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    ROOF-CEILING CONSTRUCTION

    accordance with Item 5.1.1 and shall be in accordance with the R-values in Table R806.5 for condensation control. The air-permeable insulation shall be installed directly under the air-impermeable insulation.

  • CRC § 1.1 High relevance — show source text

    Openings in roof framing members shall conform to the requirements of Section R802.7. Required ventilation openings shall open directly to the outside air and shall be protected to prevent the entry of birds, rodents, snakes and other similar creatures.

    R806.1.1 Vents in the Wildland Urban Interface (WUI). Where provided, ventilation openings for enclosed attics, gable ends, ridge ends, under eaves and cornices, enclosed eave soffit spaces, enclosed rafter spaces formed where ceilings are applied directly to the underside of roof rafters, underfloor ventilation, foundations and crawl spaces, or any other opening intended to permit ventilation, either in a horizontal or vertical plane, shall be in accordance with Part 7, California Wildland-Urban Interface Code to resist building ignition from the intrusion of burning embers and flame through the ventilation openings. R806.2 Minimum vent area. The minimum net free ventilating area shall be [1] / 150 of the area of the vented space. Exception: The minimum net free ventilation area shall be [1] / 300 of the vented space provided both of the following conditions are met:

    1. In Climate Zones 6, 7 and 8, a Class I or II vapor retarder is installed on the warm-in-winter side of the ceiling.
    2. Not less than 40 percent and not more than 50 percent of the required ventilating area is provided by ventilators located in the upper portion of the attic or rafter space. Upper ventilators shall be located not more than 3 feet (914 mm) below the ridge or highest point of the space, measured vertically. The balance of the required ventilation provided shall be located in the bottom one-third of the attic space. Where the location of wall or roof framing members conflicts with the installation of upper ventilators, installation more than 3 feet (914 mm) below the ridge or highest point of the space shall be permitted.

    R806.3 Vent and insulation clearance. Where eave or cornice vents are installed, blocking, bridging and insulation shall not block the free flow of air. Not less than a 1-inch (25 mm) space shall be provided between the insulation and the roof sheathing and at the location of the vent.

    R806.4 Installation and weather protection. Ventilators shall be installed in accordance with manufacturer’s instructions. Installation of ventilators in roof systems shall be in accordance with the requirements of Section R903. Installation of ventilators in wall systems shall be in accordance with the requirements of Section R703.1.

    R806.5 Unvented attic and unvented enclosed rafter assemblies. Unvented attics and unvented enclosed roof framing assemblies created by ceilings that are applied directly to the underside of the roof framing members and structural roof sheathing applied directly to the top of the roof framing members/rafters, shall be permitted where all the following conditions are met:

    1. The unvented attic space is completely within the building thermal envelope.
    2. Interior Class I vapor retarders are not installed on the ceiling side (attic floor) of the unvented attic assembly or on the ceiling side of the unvented enclosed roof framing assembly.
    3. Where wood shingles or shakes are used, a minimum [1] / 4 -inch (6.4 mm) vented airspace separates the shingles or shakes and the roofing underlayment above the structural sheathing.
  • CRC § 1202.2.2 High relevance — show source text

    1202.2.2 Openings into attic. Exterior openings into the attic space of any building intended for human occupancy shall be protected to prevent the entry of birds, squirrels, rodents, snakes and other similar creatures. Openings for ventilation having a least dimension of not less than [1] / 16 inch (1.6 mm) and not more than [1] / 4 inch (6.4 mm) shall be permitted. Openings for ventilation having a least dimension larger than [1] / 4 inch (6.4 mm) shall be provided with corrosion-resistant wire cloth screening, hardware cloth, perforated vinyl or similar material with openings having a least dimension of not less than [1] / 16 inch (1.6 mm) and not more than [1] / 4 inch (6.4 mm). Where combustion air is obtained from an attic area, it shall be in accordance with Chapter 7 of the California Mechanical Code .

    1202.3 Unvented attic and unvented enclosed rafter assemblies. Unvented attics and unvented enclosed roof framing assemblies created by ceilings applied directly to the underside of the roof framing members/rafters and the structural roof sheathing at the top of the roof framing members shall be permitted where all of the following conditions are met:

    1. The unvented attic space is completely within the building thermal envelope.
    2. No interior Class I vapor retarders are installed on the ceiling side (attic floor) of the unvented attic assembly or on the ceiling side of the unvented enclosed roof framing assembly.
    3. Where wood shingles or shakes are used, not less than a [1] / 4 -inch (6.4 mm) vented airspace separates the shingles or shakes and the roofing underlayment above the structural sheathing.
    4. In Climate Zones 5, 6, 7 and 8, any air-impermeable insulation shall be a Class II vapor retarder or shall have a Class II vapor retarder coating or covering in direct contact with the underside of the insulation.
    5. Insulation shall comply with either Item 5.1 or 5.2, and additionally Item 5.3.

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    INTERIOR ENVIRONMENT

    5.1. Item 5.1.1, 5.1.2, 5.1.3 or 5.1.4 shall be met, depending on the air permeability of the insulation directly under the structural roof sheathing. 5.1.1. Where only air-impermeable insulation is provided, it shall be applied in direct contact with the underside of the structural roof sheathing. 5.1.2. Where air-permeable insulation is provided inside the building thermal envelope, it shall be installed in accordance with Item 5.1.1. In addition to the air-permeable insulation installed directly below the structural sheathing, rigid board or sheet insulation shall be installed directly above the structural roof sheathing in accordance with the R -value percentages in Table 1202.3 for condensation control. 5.1.3. Where both air-impermeable and air-permeable insulation are provided, the air-impermeable insulation shall be applied in direct contact with the underside of the structural roof sheathing in accordance with Item 5.1.1 and shall be in accordance with the R -value percentages in Table 1202.3 for condensation control.

  • CRC § 3.8 High relevance — show source text

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    ROOF-CEILING CONSTRUCTION

    R804.3.8 Roof tie-down. Roof assemblies shall be connected to walls below in accordance with Table R804.3. A continuous load path shall be provided to transfer uplift loads to the foundation.

    SECTION R805—CEILING FINISHES

    R805.1 Ceiling installation. Ceilings shall be installed in accordance with the requirements for interior wall finishes as provided in Sections R702.1 through R702.6.

    SECTION R806—ROOF VENTILATION

    Note: The IECC climate zones used by this section differ from those used by the California Energy Code to determine applicability of energy efficiency measures. Comparison of IECC and California Energy Code climate zones is shown in Table R702.7.3.

    R806.1 Ventilation required. Enclosed attics and enclosed rafter spaces formed where ceilings are applied directly to the underside of roof rafters shall have cross ventilation for each separate space by ventilating openings protected against the entrance of rain or snow. Ventilation openings shall have a least dimension of [1] / 16 inch (1.6 mm) minimum and [1] / 4 inch (6.4 mm) maximum. Ventilation openings having a least dimension larger than [1] / 4 inch (6.4 mm) shall be provided with corrosion-resistant wire cloth screening, hardware cloth, perforated vinyl or similar material with openings having a least dimension of [1] / 16 inch (1.6 mm) minimum and [1] / 4 inch (6.4 mm) maximum. Openings in roof framing members shall conform to the requirements of Section R802.7. Required ventilation openings shall open directly to the outside air and shall be protected to prevent the entry of birds, rodents, snakes and other similar creatures.

    R806.1.1 Vents in the Wildland Urban Interface (WUI). Where provided, ventilation openings for enclosed attics, gable ends, ridge ends, under eaves and cornices, enclosed eave soffit spaces, enclosed rafter spaces formed where ceilings are applied directly to the underside of roof rafters, underfloor ventilation, foundations and crawl spaces, or any other opening intended to permit ventilation, either in a horizontal or vertical plane, shall be in accordance with Part 7, California Wildland-Urban Interface Code to resist building ignition from the intrusion of burning embers and flame through the ventilation openings. R806.2 Minimum vent area. The minimum net free ventilating area shall be [1] / 150 of the area of the vented space. Exception: The minimum net free ventilation area shall be [1] / 300 of the vented space provided both of the following conditions are met:

    1. In Climate Zones 6, 7 and 8, a Class I or II vapor retarder is installed on the warm-in-winter side of the ceiling.
    2. Not less than 40 percent and not more than 50 percent of the required ventilating area is provided by ventilators located in the upper portion of the attic or rafter space. Upper ventilators shall be located not more than 3 feet (914 mm) below the ridge or highest point of the space, measured vertically. The balance of the required ventilation provided shall be located in the bottom one-third of the attic space.
  • CRC § 1202.1 High relevance — show source text

    SECTION 1202—VENTILATION

    1202.1 General. Buildings shall be provided with natural ventilation in accordance with Section 1202.5, or mechanical ventilation in accordance with the California Mechanical Code .

    Dwelling units complying with the air leakage requirements of the California Energy Code or ASHRAE 90.1 shall be ventilated by mechanical means in accordance with Section 403 of the California Mechanical Code . Ambulatory care facilities and Group I-2 occupancies shall be ventilated by mechanical means in accordance with Section 407 of the California Mechanical Code .

    1202.2 Roof ventilation. Roof assemblies shall be ventilated in accordance with this section or shall comply with Section 1202.3.

    1202.2.1 Ventilated attics and rafter spaces. Enclosed attics and enclosed rafter spaces formed where ceilings are applied directly to the underside of roof framing members shall have cross ventilation for each separate space by ventilation openings protected against the entrance of rain and snow. Blocking and bridging shall be arranged so as not to interfere with the movement of air. An airspace of not less than 1 inch (25 mm) shall be provided between the insulation and the roof sheathing. The net free ventilating area shall be not less than [1] / 150 of the area of the space ventilated. Ventilators shall be installed in accordance with manufacturer’s installation instructions.

    Exception: The net free cross-ventilation area shall be permitted to be reduced to [1] / 300 provided both of the following conditions are met:

    1. In Climate Zones 6, 7 and 8, a Class I or II vapor retarder is installed on the warm-in-winter side of the ceiling.
    2. At least 40 percent and not more than 50 percent of the required venting area is provided by ventilators located in the upper portion of the attic or rafter space. Upper ventilators shall be located not more than 3 feet (914 mm) below the ridge or highest point of the space, measured vertically, with the balance of the ventilation provided by eave or cornice vents. Where the location of wall or roof framing members conflicts with the installation of upper ventilators, installation more than 3 feet (914 mm) below the ridge or highest point of the space shall be permitted.

    1202.2.2 Openings into attic. Exterior openings into the attic space of any building intended for human occupancy shall be protected to prevent the entry of birds, squirrels, rodents, snakes and other similar creatures. Openings for ventilation having a least dimension of not less than [1] / 16 inch (1.6 mm) and not more than [1] / 4 inch (6.4 mm) shall be permitted. Openings for ventilation having a least dimension larger than [1] / 4 inch (6.4 mm) shall be provided with corrosion-resistant wire cloth screening, hardware cloth, perforated vinyl or similar material with openings having a least dimension of not less than [1] / 16 inch (1.6 mm) and not more than [1] / 4 inch (6.4 mm). Where combustion air is obtained from an attic area, it shall be in accordance with Chapter 7 of the California Mechanical Code .

    1202.3 Unvented attic and unvented enclosed rafter assemblies. Unvented attics and unvented enclosed roof framing assemblies created by ceilings applied directly to the underside of the roof framing members/rafters and the structural roof sheathing at the top of the roof framing members shall be permitted where all of the following conditions are met: 1.

  • CRC § 150.2 High relevance — show source text

    Exception 5 to Section 150.2(b)1Biib: Tapered insulation with thermal resistance less than prescribed at the drains and other low points may be used provided that the thickness of insulation is increased at the high points of the roof so that the average thermal resistance equals or exceeds the required value. J. Ceiling. Vented attics shall meet the following: i. In Climate Zones 1 through 4, 6, and 8 through 16 insulation shall be installed to achieve a weighted U -factor of 0.020 or insulation installed at the ceiling level shall result in an insulated thermal resistance of R-49 or greater for the insulation alone; and Exception to Section 150.2(b)1Ji: In Climate Zones 1, 3 and 6, dwelling units with at least R-19 existing insulation installed at the ceiling level. ii. In Climate Zones 2, 4, and 8 through 16, air seal all accessible areas of the ceiling plane between the attic and the conditioned space in accordance with Section 110.7; and Exception 1 to Section 150.2(b)1Jii: Dwelling units with at least R-19 existing insulation installed at the ceiling level. Exception 2 to Section 150.2(b)1Jii: Dwelling units with atmospherically vented space-heating or water-heating combustion appliances located inside the pressure boundary of the dwelling unit. iii. In Climate Zones 1 through 4 and 8 through 16, recessed downlight luminaires in the ceiling shall be covered with insulation to the same depth as the rest of the ceiling. Luminaires not rated for insulation contact must be replaced or retrofitted with a fireproof cover that allows for insulation to be installed directly over the cover; and Exception 1 to Section 150.2(b)1Jiii: In Climate Zones 1 through 4 and 8 through 10, dwelling units with at least R-19 existing insulation installed at the ceiling level. iv. Attic ventilation shall comply with the California Residential Code, Title 24, Part 2.5, Section R806. Exception 1 to Section 150.2(b)1J: Dwelling units with at least R-38 existing insulation installed at the ceiling level. Exception 2 to Section 150.2(b)1J: Dwelling units where the alteration would directly cause the disturbance of asbestos.

    Exception 3 to Section 150.2(b)1J: Dwelling units with knob and tube wiring located in the vented attic.

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    SINGLE-FAMILY RESIDENTIAL BUILDINGS—ADDITIONS AND ALTERATIONS TO EXISTING RESIDENTIAL BUILDINGS

    Exception 4 to Section 150.2(b)1J: Where the accessible space in the attic is not large enough to accommodate the required R -value, the entire accessible space shall be filled with insulation provided such installation does not violate Section 806.3 of Title 24, Part 2.5. Exception 5 to Section 150.2(b)1J: Where the attic space above the altered dwelling unit is shared with other dwelling units and the requirements of Section 150.2(b)1J are not triggered for the other dwelling units. K. Lighting. The altered lighting system shall meet the lighting requirements of Section 150.0(k).

  • CRC § 2.5 High relevance — show source text

    iv. Attic ventilation shall comply with the California Residential Code, Title 24, Part 2.5, Section R806. Exception 1 to Section 150.2(b)1J: Dwelling units with at least R-38 existing insulation installed at the ceiling level. Exception 2 to Section 150.2(b)1J: Dwelling units where the alteration would directly cause the disturbance of asbestos.

    Exception 3 to Section 150.2(b)1J: Dwelling units with knob and tube wiring located in the vented attic.

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    SINGLE-FAMILY RESIDENTIAL BUILDINGS—ADDITIONS AND ALTERATIONS TO EXISTING RESIDENTIAL BUILDINGS

    Exception 4 to Section 150.2(b)1J: Where the accessible space in the attic is not large enough to accommodate the required R -value, the entire accessible space shall be filled with insulation provided such installation does not violate Section 806.3 of Title 24, Part 2.5. Exception 5 to Section 150.2(b)1J: Where the attic space above the altered dwelling unit is shared with other dwelling units and the requirements of Section 150.2(b)1J are not triggered for the other dwelling units. K. Lighting. The altered lighting system shall meet the lighting requirements of Section 150.0(k). The altered luminaires shall meet the luminaire efficacy requirements of Section 150.0(k). Where existing screw-base sockets are present in ceiling-recessed luminaires, removal of these sockets is not required provided that new JA8-compliant trim kits or lamps designed for use with recessed downlights or luminaires are installed. L. Mechanical ventilation for indoor air quality—entirely new or complete replacement ventilation systems. Entirely new or complete replacement ventilation systems shall comply with all applicable requirements in Section 150.0(o). An entirely new or complete replacement ventilation system includes a new ventilation fan component and an entirely new duct system. An entirely new or complete replacement duct system is constructed of at least 75 percent new duct material, and up to 25 percent may consist of reused parts from the dwelling unit's existing duct system, including but not limited to registers, grilles, boots, air filtration devices and duct material, if the reused parts are accessible and can be sealed to prevent leakage. M. Mechanical ventilation for indoor air quality—altered ventilation systems. Altered ventilation system components or newly installed ventilation equipment serving the alteration shall comply with Section 150.0(o) as applicable subject to the requirements specified in Subsections i and ii below. i. Whole-dwelling unit mechanical ventilation. a. Whole-dwelling unit airflow. If the whole-dwelling ventilation fan is altered or replaced, then one of the following Subsections 1 or 2 shall be used for compliance as applicable.

    1. Dwellings that were required by a previous building permit to comply with the whole-dwelling unit airflow requirements in Section 150.0(o) shall meet or exceed the whole-dwelling unit mechanical ventilation airflow specified in Section 150.0(o)1C, 150.0(o)1E or 150.0(o)1F as confirmed through field verification and diagnostic testing in accordance with the applicable procedures specified in Reference Residential Appendix RA3.7.
  • CRC § 0.098. Medium relevance — show source text

    For vented attics, the mandatory insulation shall be installed at the ceiling level; for unvented attics, the mandatory insulation shall be placed at either ceiling or roof level; B. Attic access doors shall have permanently attached insulation using adhesive or mechanical fasteners. The attic access shall be gasketed to prevent air leakage; and C. When loose-fill insulation is installed, the minimum installed weight per square foot shall conform with the insulation manufacturer's installed design weight per square foot at the manufacturer's labeled R- value. 2. Nonattic roof. Roofs without attic spaces shall meet the applicable requirements of A through C below: A. Metal building—The area-weighted average U- factor of the roof assembly shall not exceed 0.098. B. Wood framed and others—The area-weighted average U- factor of the roof assembly shall not exceed 0.075. C. Insulation placement—When insulation is installed at the roof, fixed vents or openings to the outdoors or to unconditioned spaces shall not be installed. When the space between the ceiling and the roof is either directly or indirectly conditioned space, it shall not be considered an attic for the purposes of complying with CBC attic ventilation requirements. Exception to Section 160.1(a)2C: Vents that do not penetrate the roof deck and are instead designed for wind resistance for roof membranes are not within the scope of Section 160.1(a)2C. 3. Insulation shall be installed in direct contact with a roof or ceiling that is sealed to limit infiltration and exfiltration as specified in Section 110.7, including but not limited to placing insulation either above or below the roof deck or on top of a drywall ceiling.

    (b) Wall insulation. Opaque portions of above grade walls separating conditioned spaces from unconditioned spaces or ambient air shall meet the following applicable requirements:

    1. Metal building—The area-weighted average U- factor of the wall assembly shall not exceed 0.113.

    2. Metal framed—The area-weighted average U- factor of the wall assembly shall not exceed 0.151.

    3. Wood framed and others—

    A. Nominal 2x4 inch framing shall have an area-weighted average U- factor of the wall assembly not exceeding 0.095. B. Nominal 2x6 inch framing shall have an area-weighted average U- factor of the wall assembly not exceeding 0.069. C. Other wall assemblies shall have an area-weighted average U- factor of the wall assembly not exceeding 0.102. 4. Light mass walls—A 6 inch or greater hollow core concrete masonry unit shall have a U- factor not to exceed 0.440. 5. Heavy mass walls—An 8 inch or greater hollow core concrete masonry unit shall have a U- factor not to exceed 0.690. 6. Spandrel panels and curtain wall—The area-weighted average U- factor of the spandrel panels and curtain wall assembly shall not exceed 0.280.

    1. Demising walls—The opaque portions of framed demising walls shall meet the requirements of Item A or B below: A. Wood framed walls shall be insulated to meet a U- factor not greater than 0.099. B. Metal framed walls shall be insulated to meet a U- factor not greater than 0.151.
    2. Bay or bow window roofs and floors shall be insulated to meet the wall insulation requirements of Table 170.2-A.
  • CRC § 10-8 Medium relevance — show source text

    000|10-8|12-6|9-8|10-0|9-0|8-2|7-7|6-4|6-2| |24|2-#4
    1-#6|60,000|12-11|15-2|11-9|12-2|11-0|9-11|9-3|7-8|7-6| |24|2-#5|40,000|15-2|17-9|13-9|14-3|12-10|11-7|10-10|9-0|8-9| |24|2-#5|60,000|18-4|21-6|16-7|17-3|15-6|14-0|13-1|10-4|10-0| |24|2-#6|40,000|18-0|21-1|16-4|16-11|14-10|12-9|11-8|9-2|8-11| |24|2-#6|60,000|21-7|25-4|19-2|20-4|17-2|14-9|13-4|10-4|10-0| |24|Center distance_A_k, l|Center distance_A_k, l|4-6|6-2|3-8|4-0|3-3|2-8|2-3|1-7|1-6| |For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 pound per square inch = 6.895 kPa, 1 pound per square foot = 0.0479 kPa, Grade 40 = 280 MPa, Grade 60 = 420 MPa.
    a. See Table R608.3 for tolerances permitted from nominal thickness.
    b. Table values are based on concrete with a minimum specified compressive strength of 2,500 psi. See Note j.
    c. Table values are based on uniform loading. See Section R608.8.2 for lintels supporting concentrated loads.
    d. Deflection criterion is_L_/240, where_L_ is the clear span of the lintel in inches, or1/2 inch, whichever is less.
    e. Linear interpolation is permitted between ground snow loads and between lintel depths.
    f. DR indicates design required.
    g. Lintel depth,D, is permitted to include the available height of wall located directly above the lintel, provided that the increased lintel depth spans the entire length of the
    lintel.
    h. Stirrups shall be fabricated from reinforcing bars with the same yield strength as that used for the main longitudinal reinforcement.
    i. Allowable clear span without stirrups applicable to all lintels of the same depth,D. Top and bottom reinforcement for lintels without stirrups shall be not less than the least
    amount of reinforcement required for a lintel of the same depth and loading condition with stirrups. All other spans require stirrups spaced at not more than_d_/2.
    j. Where concrete with a minimum specified compressive strength of 3,000 psi is used, clear spans for lintels without stirrups shall be permitted to be multiplied by 1.05.

  • CRC § 0.9 Medium relevance — show source text

    003)|Tension-controlled_3_|0.9|(e)|0.9|(f)| |1. For sections classified as transition, it shall be permitted to useφ corresponding to compression-controlled sections.
    2. ε_t_
    * is the greater of net tensile strain calculated for Pn = 0.1Agfc′_ and (ε_ty + 0.003).
    3. For sections with factored axial compression force Pu ≥ 0.1Agfc′,φ shall be calculated using equation (c) or (d) for sections classified as transition, as applicable.|1. For sections classified as transition, it shall be permitted to useφ corresponding to compression-controlled sections.
    2. ε_t_
    * is the greater of net tensile strain calculated for Pn = 0.1Agfc′_ and (ε_ty + 0.003).
    3. For sections with factored axial compression force Pu ≥ 0.1Agfc′,φ shall be calculated using equation (c) or (d) for sections classified as transition, as applicable.|1. For sections classified as transition, it shall be permitted to useφ corresponding to compression-controlled sections.
    2. ε_t_
    * is the greater of net tensile strain calculated for Pn = 0.1Agfc′_ and (ε_ty + 0.003).
    3. For sections with factored axial compression force Pu ≥ 0.1Agfc′,φ shall be calculated using equation (c) or (d) for sections classified as transition, as applicable.|1. For sections classified as transition, it shall be permitted to useφ corresponding to compression-controlled sections.
    2. ε_t_
    * is the greater of net tensile strain calculated for Pn = 0.1Agfc′_ and (ε_ty + 0.003).
    3. For sections with factored axial compression force Pu ≥ 0.1Agfc′,φ shall be calculated using equation (c) or (d) for sections classified as transition, as applicable.|1. For sections classified as transition, it shall be permitted to useφ corresponding to compression-controlled sections.
    2. ε_t_
    * is the greater of net tensile strain calculated for Pn = 0.1Agfc′_ and (ε_ty + 0.003).
    3. For sections with factored axial compression force Pu ≥ 0.1Agfc′,φ shall be calculated using equation (c) or (d) for sections classified as transition, as applicable.|1. For sections classified as transition, it shall be permitted to useφ corresponding to compression-controlled sections.
    2. ε_t_
    * is the greater of net tensile strain calculated for Pn = 0.1Agfc′_ and (ε_ty + 0.003).
    3. For sections with factored axial compression force Pu ≥ 0.1Agfc′,φ shall be calculated using equation (c) or (d) for sections classified as transition, as applicable.|

    1909A.1.12 ACI 318, Section 24.2.1. Add Section 24.2.1.1 to ACI 318 as follows:

  • CRC § 6-106 Medium relevance — show source text

    R607 Glass Unit Masonry . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-106

    R608 Exterior Concrete Wall Construction. . . . . . . . . . . . 6-107

    R609 Exterior Windows and Doors. . . . . . . . . . . . . . . . . . . 6-172

    R610 Structural Insulated Panel Wall Construction . . . 6-175

    CHAPTER 7 WALL COVERING. . . . . . . . . . . . . . . . . . . . . . . . 7-3

    R701 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3

    R702 Interior Covering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3

    R703 Exterior Wall Covering . . . . . . . . . . . . . . . . . . . . . . . . . 7-10

    R704 Exterior Soffits and Fascias. . . . . . . . . . . . . . . . . . . . . 7-32

    R705 BIPV Systems for Exterior Wall Coverings and Fenestration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-35

    CHAPTER 8 ROOF-CEILING CONSTRUCTION. . . . . . . . . . . 8-3

    R801 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-3

    R802 Wood Roof Framing . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-3

    R803 Roof Sheathing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-30

    R804 Cold-Formed Steel Roof Framing . . . . . . . . . . . . . . . 8-31

    R805 Ceiling Finishes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-44

    R806 Roof Ventilation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-44

    R807 Attic Access. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-46

    CHAPTER 9 ROOF ASSEMBLIES . . . . . . . . . . . . . . . . . . . . . .9-3

    R901 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-3

    R902 Fire Classification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-3

  • CRC § 2025 Medium relevance — show source text

    Chapter 6 also regulates exterior windows and doors installed in walls. This chapter contains criteria for the performance of exterior windows and doors and includes provisions for testing and labeling, garage doors, windborne debris protection and anchorage details.

    Chapter 7 Wall Covering.

    Chapter 7 contains provisions for the design and construction of interior and exterior wall coverings. This chapter establishes the various types of materials, materials standards and methods of application permitted for use as interior coverings, including interior plaster, gypsum board, ceramic tile, wood veneer paneling, hardboard paneling, wood shakes and wood shingles. Chapter 7 also contains requirements for the use of vapor retarders for moisture control in walls.

    2025 CALIFORNIA RESIDENTIAL CODE xv

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

    Exterior wall coverings provide the weather-resistant exterior envelope that protects the building’s interior from the elements. Chapter 7 provides the requirements for wind resistance and water-resistive barrier for exterior wall coverings. This chapter prescribes the exterior wall coverings as well as the water-resistive barrier required beneath the exterior materials. Exterior wall coverings regulated by this section include aluminum, stone and masonry veneer, wood, hardboard, particleboard, wood structural panel siding, wood shakes and shingles, exterior plaster, steel, vinyl, fiber cement and exterior insulation finish systems.

    Chapter 8 Roof-Ceiling Construction.

    Chapter 8 regulates the design and construction of roof-ceiling systems. This chapter contains two roof-ceiling framing systems: wood framing and cold-formed steel framing. Allowable span tables are provided to simplify the selection of rafter and ceiling joist size for wood roof framing and cold-formed steel framing. Chapter 8 also provides requirements for the application of ceiling finishes, the proper ventilation of concealed spaces in roofs (e.g., enclosed attics and rafter spaces), unvented attic assemblies and attic access.

    Chapter 9 Roof Assemblies.

    Chapter 9 regulates the design and construction of roof assemblies. A roof assembly includes the roof deck, vapor retarder, substrate or thermal barrier, insulation, vapor retarder and roof covering. This chapter provides the requirement for wind resistance of roof coverings.

    The types of roof covering materials and installation regulated by Chapter 9 are: asphalt shingles, clay and concrete tile, metal roof shingles, mineral-surfaced roll roofing, slate and slate-type shingles, wood shakes and shingles, built-up roofs, metal roof panels, modified bitumen roofing, thermoset and thermoplastic single-ply roofing, sprayed polyurethane foam roofing, liquid applied coatings and photovoltaic shingles. Chapter 9 also provides requirements for roof drainage, flashing, above deck thermal insulation, rooftop-mounted photovoltaic systems and recovering or replacing an existing roof covering.

    Chapter 10 Chimneys and Fireplaces.

    Chapter 10 contains requirements for the safe construction of masonry chimneys and fireplaces and establishes the standards for the use and installation of factory-built chimneys, fireplaces and masonry heaters. Chimneys and fireplaces constructed of masonry rely on prescriptive requirements for the details of their construction; the factory-built type relies on the listing and labeling method of approval. Chapter 10 provides the requirements for seismic reinforcing and anchorage of masonry fireplaces and chimneys.

    Chapter 11 [RE] Energy Efficiency.

    Chapter 11 is not adopted in California. See California Energy Code, Title 24, Part 6.

    Chapter 12 Mechanical Administration.

Frequently asked questions

Can I put vapor barrier (poly) on the ceiling if I make the attic unvented?

No. § R806.5.2 explicitly prohibits installing interior Class I vapor retarders on the ceiling side of an unvented attic assembly .

Do I still need any venting with an unvented attic?

Not for the purpose of attic cross‑ventilation; however, specific roof coverings like wood shingles/shakes still require a 1/4‑inch vented airspace above sheathing per § R806.5.3. And other systems (combustion/venting) may still need outside air per other codes .

What if I use air‑permeable insulation under the sheathing?

If you use air‑permeable insulation directly under sheathing, you must install rigid board or sheet insulation above the structural roof sheathing per the R‑values/percentages in Table R806.5 for condensation control, as described in § R806.5.1.2 .

Where are the exact R‑value amounts I must use above the sheathing?

The code references Table R806.5 for the required R‑values (percentages) for condensation control. Those numeric values were not included in the excerpt I reviewed; consult Table R806.5 in the CRC to get the precise required values for your climate zone and assembly .

Does the energy code affect the decision to use an unvented attic?

Yes. The California Energy Code controls insulation placement, duct/air handler location, and minimum thermal performance — these interact with the decision to use an unvented attic. See Title 24 Part 6 cross‑requirements for specifics .

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California Residential Code