CRC · California Residential Code
Joists, girders and allowable span rules for wood floors
Homeowners: The CRC requires using the code’s joist and girder span tables (not guesswork) and following minimum bearing, blocking and lateral‑restraint rules. Check the correct table for your use (30 psf for sleeping/attics, 40 psf for living areas), confirm species/grade/spacing and provide the specified bearing and blocking; engineered members must follow manufacturer guidance.
Last reviewed: July 6, 2026
What the code requires — plain English
The California Residential Code requires that wood floor framing members (joists, girders, headers) meet minimum materials/identification rules and use the CRC allowable-span tables to determine maximum spans. Key framing details — bearing, blocking/bridging and lateral restraint — are mandatory and tied to the prescriptive tables. See § R502 and § R502.1 for scope and lumber identification requirements.
Use the CRC-prescribed joist/girder span tables (or approved engineered design) and follow the minimum bearing and blocking rules — do not exceed the tabulated spans in § R502.3 and § R502.5.
Requirements in detail
Scope and material ID
- Wood and wood-based products used as load‑supporting members must conform to this section; sawn lumber must be grade‑marked (or have an accepted certificate) per § R502.1.
- Engineered products (I‑joists, glulam, SCL, CLT) must be manufactured and identified per their referenced standards (see § R502.1.2–R502.1.6).
How allowable spans are set
- Maximum spans for floor joists are given in the CRC prescriptive tables: Tables R502.3.1(1) (sleeping/attic loads) and R502.3.1(2) (living area loads). Use the table that matches the design live/dead load and joist spacing; otherwise, use an engineered design or the AWC STJR. § R502.3.
- Allowable girder and header spans for dimension lumber are limited by referencing the wall header/girder tables (see § R502.5, which points to Tables R602.7(1)–(3)**).
Bearing, blocking & lateral restraint
- Minimum end bearing: 1 1/2 inches on wood/metal, 3 inches on masonry/concrete, or support by approved joist hangers. Alternative bearing by ribbon strip / nailed connection permitted. § R502.6.
- Joists framing from opposite sides over a bearing shall lap not less than 3 inches and be nailed with three 10d face nails, or be spliced with equivalent strength. § R502.6.1.
- Joists framing into a wood girder must be supported by approved anchors or ledger strips not less than nominal 2" × 2". § R502.6.2.
- Joists must be laterally supported at ends by full‑depth solid blocking nominal 2 inches thick, or attached to a full‑depth header/band/rim joist, or other lateral support to prevent rotation (§ R502.7). In Seismic Design Categories D0, D1 and D2, lateral restraint is required at each intermediate support (see exceptions). § R502.7.
- Joists larger than nominal 2" × 12" must have lateral support (solid blocking, diagonal bridging, or continuous 1" × 3" strip across bottoms) at intervals not exceeding 8 feet. § R502.7.1.
Tables control span decisions
- Use:
- Table R502.3.1(1) for sleeping/attic areas with live load = 30 psf and L/Δ = 360.
- Table R502.3.1(2) for living areas with live load = 40 psf and L/Δ = 360.
These tables list allowable clear spans by species, grade, joist size and spacing. § R502.3.1.
Decision‑relevant quick reference table
| Decision item | Typical value / threshold | Where to apply / Code Reference |
|---|---|---|
| Joist span tables (sleeping) | Live load 30 psf, L/Δ = 360 | Table R502.3.1(1) — § R502.3.1 |
| Joist span tables (living) | Live load 40 psf, L/Δ = 360 | Table R502.3.1(2) — § R502.3.1 |
| Minimum bearing on wood/metal | 1 1/2 in. | § R502.6 |
| Minimum bearing on masonry/concrete | 3 in. | § R502.6 |
| End lap for opposing joists | 3 in. lap + three 10d face nails | § R502.6.1 |
| Blocking for separated double joists | 2 in. nominal blocking spaced not more than 4 ft. o.c. | § R502.4 |
| Lateral restraint for large joists | Lateral support at intervals ≤ 8 ft. for joists > 2" × 12" | § R502.7.1 |
| Allowable girder/header spans | See Tables R602.7(1)–(3) (applies to R502.5) | § R502.5 |
(Use the full tables in the code to get the precise allowable span for the species/grade/size/spacing you plan to use — Table references are shown above.)
Exceptions & special cases
- If you use engineered products (I‑joists, trusses, glulam, SCL, CLT), follow the manufacturer’s design and installation instructions; some lateral restraint/bridging requirements are replaced by manufacturer recommendations. § R502.1.2 and R502.7 exceptions.
- For joists under bearing partitions: double joists must be sized to carry the partition and, if separated for piping, must be full‑depth solid‑blocked with 2‑inch nominal lumber spaced ≤ 4 ft. o.c. § R502.4.
- Girder/header spans for dimension lumber are not taken from the joist tables — the code directs you to header/girder tables (R602.7 series). If the top of a header/girder is not laterally braced, special multipliers or design are required (see referenced header/girder provisions). § R502.5.
- Subfloor panel span/attachment rules and allowable spans for panels are in Section R503 and its tables; do not assume a joist span is acceptable for subfloor panel support without checking those provisions. § R503.2 / Table R503.2.1.1.
Common mistakes
- Relying on a single span lookup without matching the correct table: use the 30 psf table only for sleeping/attic (fixed stair) scenarios and the 40 psf table for living areas. See § R502.3.1.
- Forgetting minimum bearing distances (common: assuming any bearing is OK). Minimums are 1 1/2 in. on wood/metal and 3 in. on masonry/concrete — § R502.6.
- Omitting required blocking/bridging or using incorrect spacing for blocked double joists under partitions (blocking ≤ 4 ft. o.c.). § R502.4.
- Using joist span tables for headers/girders — the code points you to different tables for those members (see § R502.5).
- Cutting/notching holes beyond limits for solid sawn members or altering engineered members contrary to manufacturer guidance (see § R502.8).
Worked example — concrete scenario with numbers
Scenario: second‑floor living area (regular occupied living space) — use prescriptive tables.
Given:
- Use Douglas fir‑larch, grade SS (special/select), floor joists sized 2 × 8.
- Joist spacing: 19.2 inches (a table spacing option).
- Design loads: live load = 30 psf (sleeping/attic table) or 40 psf (living area table). We will use the sleeping/attic table (30 psf) for this worked example.
Step 1 — pick correct table:
- For a sleeping/attic condition with live load 30 psf, use Table R502.3.1(1) per § R502.3.1.
Step 2 — read the table for the chosen species/grade/spacing/size:
- Table R502.3.1(1) lists for joist spacing 19.2 in., Douglas fir‑larch SS, the maximum clear spans (format: 2×6, 2×8, 2×10, 2×12). From that table the allowable span for a 2 × 8 is 14 ft‑1 in. for the 30 psf/10 psf dead‑load case. See Table R502.3.1(1).
Step 3 — verify bearing & blocking:
- Ensure joist ends have at least 1 1/2 in. bearing on wood or metal (or 3 in. on masonry) and provide required blocking or header support per § R502.6 and § R502.7.
Conclusion: Using the prescriptive CRC table, a Douglas fir‑larch SS 2×8 at 19.2" o.c. in a sleeping/attic application can span up to 14'‑1" (refer to Table R502.3.1(1) per § R502.3.1). Confirm species/grade, spacing and live/dead loads match your project before applying the table value.
Related provisions (quick pointers)
- § R502.1 — Material identification and product requirements for lumber and engineered wood.
- § R502.3 / Tables R502.3.1(1) & (2) — Allowable joist spans (sleeping 30 psf; living 40 psf).
- § R502.4 — Joists under bearing partitions (double joists, blocking).
- § R502.5 — Allowable girder/header span reference (see Tables R602.7(1)–(3)).
- § R502.6 – R502.7.1 — Bearing, framing laps, joist support and lateral restraint / bridging.
- § R502.8 — Limits on notches and bored holes in joists (solid sawn vs engineered).
- Section R503 — Subfloor panel span and installation rules (panels, underlayment).
Code references
Grounded in the retrieved California Residential Code — click a citation to read the verbatim passage:
CRC § 2304.8 High relevance — show source text
Span is permitted to be 24 inches on center for floors where 11/2 inches of cellular or lightweight concrete is applied over the panels.|
TABLE 2304.8(4)—ALLOWABLE SPAN FOR WOOD STRUCTURAL
PANEL COMBINATION SUBFLOOR-UNDERLAYMENT (SINGLE FLOOR)a
(Panels Continuous Over Two or More Spans and Strength Axis Perpendicular to Supports)Col2 Col3 Col4 Col5 Col6 IDENTIFICATION MAXIMUM SPACING OF JOISTS (inches) MAXIMUM SPACING OF JOISTS (inches) MAXIMUM SPACING OF JOISTS (inches) MAXIMUM SPACING OF JOISTS (inches) MAXIMUM SPACING OF JOISTS (inches) IDENTIFICATION 16 20 24 32 48 Species groupb Thickness (inches) Thickness (inches) Thickness (inches) Thickness (inches) Thickness (inches) 1 1/2 5/8 3/4 — — 2, 3 5/8 3/4 7/8 — — 4 3/4 7/8 1 — — Single floor span ratingc 16 o.c. 20 o.c. 24 o.c. 32 o.c. 48 o.c. For SI: 1 inch = 25.4 mm, 1 pound per square foot = 0.0479 kN/m2.
a. Spans limited to value shown because of possible effects of concentrated loads. Allowable uniform loads based on deflection of1/360 of span is 100 pounds per square foot
except allowable total uniform load for 11/8-inch wood structural panels over joists spaced 48 inches on center is 65 pounds per square foot. Panel edges shall have approved
tongue-and-groove joints or shall be supported with blocking, unless1/4-inch minimum thickness underlayment or 11/2 inches of approved cellular or lightweight concrete is
placed over the subfloor, or finish floor is3/4-inch wood strip.
b. Applicable to all grades of sanded exterior-type plywood. See DOC PS 1 for plywood species groups.
c. Applicable to underlayment grade, C-C (plugged) plywood, and single floor grade wood structural panels.For SI: 1 inch = 25.4 mm, 1 pound per square foot = 0.0479 kN/m2.
a. Spans limited to value shown because of possible effects of concentrated loads. Allowable uniform loads based on deflection of1/360 of span is 100 pounds per square foot
except allowable total uniform load for 11/8-inch wood structural panels over joists spaced 48 inches on center is 65 pounds per square foot. Panel edges shall have approved
tongue-and-groove joints or shall be supported with blocking, unless1/4-inch minimum thickness underlayment or 11/2 inches of approved cellular or lightweight concrete is
placed over the subfloor, or finish floor is3/4-inch wood strip.
b. Applicable to all grades of sanded exterior-type plywood. See DOC PS 1 for plywood species groups.
c.CRC § 5-1 High relevance — show source text
The state agency does not adopt sections identified with the following symbol: †
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5 FLOORS
User notes:
About this chapter: Chapter 5 provides the requirements for the design and construction of floor systems that will be capable of supporting minimum required design loads. This chapter covers wood floor framing, wood floors on the ground, cold-formed steel floor framing and concrete slabs on the ground. Allowable span tables are provided that greatly simplify the determination of joist, girder and sheathing sizes for raised floor systems of wood framing and cold-formed steel framing. This chapter also contains prescriptive requirements for wood-framed exterior decks and their attachment to the main building.
SECTION R501—GENERAL
R501.1 Application. The provisions of this chapter shall control the design and construction of the floors for buildings, including the floors of attic spaces used to house mechanical or plumbing fixtures and equipment.
R501.2 Requirements. Floor construction shall be capable of accommodating all loads in accordance with Section R301 and of transmitting the resulting loads to the supporting structural elements.
SECTION R502—WOOD FLOOR FRAMING
R502.1 General. Wood and wood-based products used for load-supporting purposes shall conform to the applicable provisions of this section.
R502.1.1 Sawn lumber. Sawn lumber shall be identified by a grade mark of an accredited lumber grading or inspection agency and have design values certified by an accreditation body that complies with DOC PS 20. In lieu of a grade mark, a certificate of inspection issued by a lumber grading or inspection agency meeting the requirements of this section shall be accepted.
Note: See Section R301.1.1.1 for limited-density owner- built rural dwellings.
R502.1.1.1 Preservative-treated lumber. Preservative treated dimension lumber shall be identified as required by Section R304.2.
R502.1.1.2 End-jointed lumber. Approved end-jointed lumber identified by a grade mark conforming to Section R502.1.1 shall be permitted to be used interchangeably with solid-sawn members of the same species and grade. End-jointed lumber used in an assembly required elsewhere in this code to have a fire-resistance rating shall have the designation “Heat-Resistant Adhesive” or “HRA” included in its grade mark.
R502.1.2 Prefabricated wood I-joists. Structural capacities and design provisions for prefabricated wood I-joists shall be established and monitored in accordance with ASTM D5055.
R502.1.3 Structural glued-laminated timbers. Glued-laminated timbers shall be manufactured and identified as required in ANSI A190.1, ANSI 117 and ASTM D3737.
R502.1.4 Structural log members. Structural log members shall comply with the provisions of ICC 400.
R502.1.5 Structural composite lumber. Structural capacities for structural composite lumber shall be established and monitored in accordance with ASTM D5456.
R502.1.6 Cross-laminated timber. Cross-laminated timber shall be manufactured and identified as required by ANSI/APA PRG 320.
CRC § 5-9 High relevance — show source text
Linear interpolation shall be permitted for ground snow loads other than shown.|
R502.4 Joists under bearing partitions. Joists under parallel bearing partitions shall be of adequate size to support the load. Double joists, sized to adequately support the load, that are separated to permit the installation of piping or vents shall be full-depth solid blocked with lumber not less than 2 inches (51 mm) in nominal thickness spaced not more than 4 feet (1219 mm) on center. Bearing partitions perpendicular to joists shall not be offset from supporting girders, walls or partitions more than the joist depth unless such joists are of sufficient size to carry the additional load.
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R502.5 Allowable girder and header spans. The allowable spans of girders and headers fabricated of dimension lumber shall not exceed the values set forth in Tables R602.7(1), R602.7(2) and R602.7(3). R502.6 Bearing. The ends of each joist, beam or girder shall have not less than 1 [1] / 2 inches (38 mm) of bearing on wood or metal, have not less than 3 inches of bearing (76 mm) on masonry or concrete or be supported by approved joist hangers. Alternatively, the ends of joists shall be supported on a 1-inch by 4-inch (25 mm by 102 mm) ribbon strip and shall be nailed to the adjacent stud. The bearing on masonry or concrete shall be direct, or a sill plate of 2-inch-minimum (51 mm) nominal thickness shall be provided under the joist, beam or girder. The sill plate shall provide a minimum nominal bearing area of 48 square inches (30 865 mm [2] ).
R502.6.1 Floor systems. Joists framing from opposite sides over a bearing support shall lap not less than 3 inches (76 mm) and shall be nailed together with a minimum three 10d face nails. A wood or metal splice with strength equal to or greater than that provided by the nailed lap is permitted.
R502.6.2 Joist framing. Joists framing into the side of a wood girder shall be supported by approved framing anchors or on ledger strips not less than nominal 2 inches by 2 inches (51 mm by 51 mm).
R502.7 Lateral restraint at supports. Joists shall be supported laterally at the ends by full-depth solid blocking not less than 2 inches (51 mm) nominal in thickness; or by attachment to a full-depth header, band or rim joist, or to an adjoining stud or shall be otherwise provided with lateral support to prevent rotation.
Exceptions:
- Trusses, structural composite lumber, structural glued-laminated members and I-joists shall be supported laterally as required by the manufacturer’s recommendations.
- In Seismic Design Categories D 0, D 1 and D 2, lateral restraint shall be provided at each intermediate support.
R502.7.1 Bridging. Joists exceeding a nominal 2 inches by 12 inches (51 mm by 305 mm) shall be supported laterally by solid blocking, diagonal bridging (wood or metal), or a continuous 1-inch by 3-inch (25 mm by 76 mm) strip nailed across the bottom of joists perpendicular to joists at intervals not exceeding 8 feet (2438 mm).
CRC § 25.4 High relevance — show source text
Tabulated uplift values are permitted to be reduced by multiplying by a factor equal to 2 divided by the actual
backspan ratio provided (2/backspan ratio).
e. Linear interpolation shall be permitted for ground snow loads other than shown.|For SI: 1 inch = 25.4 mm, 1 pound per square foot = 0.0479 kPa.
a. Spans are based on No. 2 Grade lumber of Douglas fir-larch, Southern pine, hem-fir, and spruce-pine-fir for repetitive (three or more) members.
b. Ratio of backspan to cantilever span shall be not less than 2:1.
c. Connections capable of resisting the indicated uplift force shall be provided at the backspan support.
d. Uplift force is for a backspan to cantilever span ratio of 2:1. Tabulated uplift values are permitted to be reduced by multiplying by a factor equal to 2 divided by the actual
backspan ratio provided (2/backspan ratio).
e. Linear interpolation shall be permitted for ground snow loads other than shown.|For SI: 1 inch = 25.4 mm, 1 pound per square foot = 0.0479 kPa.
a. Spans are based on No. 2 Grade lumber of Douglas fir-larch, Southern pine, hem-fir, and spruce-pine-fir for repetitive (three or more) members.
b. Ratio of backspan to cantilever span shall be not less than 2:1.
c. Connections capable of resisting the indicated uplift force shall be provided at the backspan support.
d. Uplift force is for a backspan to cantilever span ratio of 2:1. Tabulated uplift values are permitted to be reduced by multiplying by a factor equal to 2 divided by the actual
backspan ratio provided (2/backspan ratio).
e. Linear interpolation shall be permitted for ground snow loads other than shown.|R502.4 Joists under bearing partitions. Joists under parallel bearing partitions shall be of adequate size to support the load. Double joists, sized to adequately support the load, that are separated to permit the installation of piping or vents shall be full-depth solid blocked with lumber not less than 2 inches (51 mm) in nominal thickness spaced not more than 4 feet (1219 mm) on center. Bearing partitions perpendicular to joists shall not be offset from supporting girders, walls or partitions more than the joist depth unless such joists are of sufficient size to carry the additional load.
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R502.5 Allowable girder and header spans. The allowable spans of girders and headers fabricated of dimension lumber shall not exceed the values set forth in Tables R602.7(1), R602.7(2) and R602.7(3). R502.6 Bearing. The ends of each joist, beam or girder shall have not less than 1 [1] / 2 inches (38 mm) of bearing on wood or metal, have not less than 3 inches of bearing (76 mm) on masonry or concrete or be supported by approved joist hangers. Alternatively, the ends of joists shall be supported on a 1-inch by 4-inch (25 mm by 102 mm) ribbon strip and shall be nailed to the adjacent stud.
CRC § 25.4 High relevance — show source text
Applicable to all grades of sanded exterior-type plywood.|For SI: 1 inch = 25.4 mm, 1 pound per square foot = 0.0479 kPa.
a. Plywood continuous over two or more spans and face grain perpendicular to supports. Unsupported edges shall be tongue-and-groove or blocked except where nominal1/4-
inch-thick wood panel-type underlayment, fiber-cement underlayment or3/4-inch wood finish floor is used. Fiber-cement underlayment shall comply with ASTM C1288 or ISO
8336 Category C. Allowable uniform live load at maximum span based on deflection of1/360 of span is 100 psf.
b. Applicable to all grades of sanded exterior-type plywood.|2025 CALIFORNIA RESIDENTIAL CODE 5-13
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R503.2.2 Allowable spans. The maximum allowable span for wood structural panels used as subfloor or combination subfloor underlayment shall be as set forth in Table R503.2.1.1(1), or APA E30. The maximum span for sanded plywood combination subfloor underlayment shall be as set forth in Table R503.2.1.1(2).
R503.2.3 Installation. Wood structural panels used as subfloor or combination subfloor underlayment shall be attached to wood framing in accordance with Table R602.3(1) and shall be attached to cold-formed steel framing in accordance with Table R505.3.1(2).
R503.3 Particleboard.
R503.3.1 Identification and grade. Particleboard shall conform to ANSI A208.1 and shall be so identified by a grade mark or certificate of inspection issued by an approved agency. R503.3.2 Floor underlayment. Particleboard floor underlayment shall conform to Type PBU and shall be not less than [1] / 4 inch (6.4 mm) in thickness.
R503.3.3 Installation. Particleboard underlayment shall be installed in accordance with the recommendations of the manufacturer and attached to framing in accordance with Table R602.3(1).
SECTION R504—PRESSURE PRESERVATIVE-TREATED WOOD FLOORS (ON GROUND)
R504.1 General. Pressure preservative-treated wood basement floors and floors on ground shall be designed to withstand axial forces and bending moments resulting from lateral soil pressures at the base of the exterior walls and floor live and dead loads. Floor framing shall be designed to meet joist deflection requirements in accordance with Section R301.
R504.1.1 Unbalanced soil loads. Unless special provision is made to resist sliding caused by unbalanced lateral soil loads, wood basement floors shall be limited to applications where the differential depth of fill on opposite exterior foundation walls is 2 feet (610 mm) or less.
R504.1.2 Construction. Joists in wood basement floors shall bear tightly against the narrow face of studs in the foundation wall or directly against a band joist that bears on the studs. Plywood subfloor shall be continuous over lapped joists or over butt joints between in-line joists. Sufficient blocking shall be provided between joists to transfer lateral forces at the base of the end walls into the floor system.
CRC § 6.1 High relevance — show source text
SPAN
USE HANGER IF HEADER
SPANS MORE THAN
6 FT.||||||| |||HEADER-DOUBLE IF
MORE THAN 4 FT. SPAN
USE HANGER IF HEADER
SPANS MORE THAN
6 FT.||||||| |||HEADER-DOUBLE IF
MORE THAN 4 FT. SPAN
USE HANGER IF HEADER
SPANS MORE THAN
6 FT.||||||| |||HEADER-DOUBLE IF
MORE THAN 4 FT. SPAN
USE HANGER IF HEADER
SPANS MORE THAN
6 FT.||||||| |||HEADER-DOUBLE IF
MORE THAN 4 FT. SPAN
USE HANGER IF HEADER
SPANS MORE THAN
6 FT.||||||| |||HEADER-DOUBLE IF
MORE THAN 4 FT. SPAN
USE HANGER IF HEADER
SPANS MORE THAN
6 FT.|||||PIER|PIER| |||||||||| |||||||||| |||||||||| |||||||||| ||LAP JOIST 3 IN. MIN. OR
SPLICE–SEE SECTION
R502.6.1|LAP JOIST 3 IN. MIN. OR
SPLICE–SEE SECTION
R502.6.1|LAP JOIST 3 IN. MIN. OR
SPLICE–SEE SECTION
R502.6.1|||||| |||||||||| ||||||||||JOISTS–SEE SECTION
R502.7.1
PROVISION FOR PIPES
AND VENTS
DOUBLE JOISTS UNDER BEARING
PARTITIONS. IF JOISTS ARE SEPARATED FOR PIPES, BLOCK
4 FT. ON-CENTER MAXIMUM
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm.
R502.2.1 Framing at braced wall lines. A load path for lateral forces shall be provided between floor framing and braced wall panels located above or below a floor, as specified in Section R602.10.8.
R502.2.2 Blocking and subflooring. Blocking for fastening panel edges or fixtures shall be not less than utility grade lumber. Subflooring shall be not less than utility grade lumber, No. 4 common grade boards or wood structural panels as specified in Section R503.2. Fireblocking shall be of any grade lumber.
R502.3 Allowable joist spans. Spans for floor joists shall be in accordance with Tables R502.3.1(1) and R502.3.1(2). For other grades and species and for other loading conditions, refer to the AWC STJR.
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R502.3.1 Sleeping areas and attic joists. Table R502.3.1(1) shall be used to determine the maximum allowable span of floor joists that support sleeping areas and attics that are accessed by means of a fixed stairway in accordance with Section R318.7 provided that the design live load does not exceed 30 pounds per square foot (1.44 kPa) and the design dead load does not exceed 20 pounds per square foot (0.96 kPa). The allowable span of ceiling joists that support attics used for limited storage or no storage shall be determined in accordance with Section R802.5.
|TABLE R502.3.
CRC § 2.1 High relevance — show source text
R502.2.1 Framing at braced wall lines. A load path for lateral forces shall be provided between floor framing and braced wall panels located above or below a floor, as specified in Section R602.10.8.
R502.2.2 Blocking and subflooring. Blocking for fastening panel edges or fixtures shall be not less than utility grade lumber. Subflooring shall be not less than utility grade lumber, No. 4 common grade boards or wood structural panels as specified in Section R503.2. Fireblocking shall be of any grade lumber.
R502.3 Allowable joist spans. Spans for floor joists shall be in accordance with Tables R502.3.1(1) and R502.3.1(2). For other grades and species and for other loading conditions, refer to the AWC STJR.
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R502.3.1 Sleeping areas and attic joists. Table R502.3.1(1) shall be used to determine the maximum allowable span of floor joists that support sleeping areas and attics that are accessed by means of a fixed stairway in accordance with Section R318.7 provided that the design live load does not exceed 30 pounds per square foot (1.44 kPa) and the design dead load does not exceed 20 pounds per square foot (0.96 kPa). The allowable span of ceiling joists that support attics used for limited storage or no storage shall be determined in accordance with Section R802.5.
TABLE R502.3.1(1)—FLOOR JOIST SPANS FOR COMMON LUMBER SPECIES
(Residential sleeping areas, live load = 30 psf, L/Δ = 360)aCol2 Col3 Col4 Col5 Col6 Col7 Col8 Col9 Col10 Col11 ** JOIST SPACING**
(inches)** SPECIES AND GRADE** ** SPECIES AND GRADE** ** DEAD LOAD = 10 psf** ** DEAD LOAD = 10 psf** ** DEAD LOAD = 10 psf** ** DEAD LOAD = 10 psf** ** DEAD LOAD = 20 psf** ** DEAD LOAD = 20 psf** ** DEAD LOAD = 20 psf** ** DEAD LOAD = 20 psf** ** JOIST SPACING**
(inches)** SPECIES AND GRADE** ** SPECIES AND GRADE** ** 2 × 6** ** 2 × 8** ** 2 × 10** ** 2 × 12** ** 2 × 6** ** 2 × 8** ** 2 × 10** ** 2 × 12** ** JOIST SPACING**
(inches)** SPECIES AND GRADE** ** SPECIES AND GRADE** ** Maximum floor joist spans** ** Maximum floor joist spans** ** Maximum floor joist spans** ** Maximum floor joist spans** ** Maximum floor joist spans** ** Maximum floor joist spans** ** Maximum floor joist spans** ** Maximum floor joist spans** ** JOIST SPACING**
(inches)** SPECIES AND CRC § 2308.8 High relevance — show source text
2308.8 Floor framing. Floor framing shall comply with this section.
2308.8.1 Girders. Girders for single-story construction or girders supporting loads from a single floor shall be not less than 4 inches by 6 inches (102 mm by 152 mm) for spans 6 feet (1829 mm) or less, provided that girders are spaced not more than 8 feet (2438 mm) on center. Other girders shall be designed to support the loads specified in this code. Girder end joints shall occur over supports.
Where a girder is spliced over a support, an adequate tie shall be provided. The ends of beams or girders supported on masonry or concrete shall not have less than 3 inches (76 mm) of bearing.
2308.8.1.1 Allowable girder spans. The allowable spans of girders that are fabricated of dimension lumber shall not exceed the values set forth in Table 2308.8.1.1(1) or 2308.8.1.1(2).
TABLE 2308.8.1.1(1)—HEADER AND GIRDER SPANSa, b FOR EXTERIOR BEARING WALLS
(Maximum spans for Douglas fir-larch, hem-fir, Southern pine and spruce-pine-fir and required number of jack studs)Col2 Col3 Col4 Col5 Col6 Col7 Col8 Col9 Col10 Col11 Col12 Col13 Col14 Col15 Col16 Col17 Col18 Col19 Col20 GIRDERS AND
HEADERS
SUPPORTINGSIZE ALLOWABLE STRESS DESIGN GROUND SNOW LOAD,****pg(asd), (psf)e ALLOWABLE STRESS DESIGN GROUND SNOW LOAD,****pg(asd), (psf)e ALLOWABLE STRESS DESIGN GROUND SNOW LOAD,****pg(asd), (psf)e ALLOWABLE STRESS DESIGN GROUND SNOW LOAD,****pg(asd), (psf)e ALLOWABLE STRESS DESIGN GROUND SNOW LOAD,****pg(asd), (psf)e ALLOWABLE STRESS DESIGN GROUND SNOW LOAD,****pg(asd), (psf)e ALLOWABLE STRESS DESIGN GROUND SNOW LOAD,****pg(asd), (psf)e ALLOWABLE STRESS DESIGN GROUND SNOW LOAD,****pg(asd), (psf)e ALLOWABLE STRESS DESIGN GROUND SNOW LOAD,****pg(asd), (psf)e ALLOWABLE STRESS DESIGN GROUND SNOW LOAD,****pg(asd), (psf)e ALLOWABLE STRESS DESIGN GROUND SNOW LOAD,****pg(asd), (psf)e ALLOWABLE STRESS DESIGN GROUND SNOW LOAD,****pg(asd), (psf)e ALLOWABLE STRESS DESIGN GROUND SNOW LOAD,****pg(asd), (psf)e ALLOWABLE STRESS DESIGN GROUND SNOW LOAD,****pg(asd), (psf)e *ALLOWABLE STRESS DESIGN GROUND SNOW LOAD,***_pg(asd), CRC § 5-7 High relevance — show source text
2025 CALIFORNIA RESIDENTIAL CODE 5-7
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
FLOORS
TABLE R502.3.1(2)—FLOOR JOIST SPANS FOR COMMON LUMBER SPECIES
(Residential living areas, live load = 40 psf, L/Δ = 360)b—continuedCol2 Col3 Col4 Col5 Col6 Col7 Col8 Col9 Col10 Col11 ** JOIST SPACING**
(inches)** SPECIES AND GRADE** ** SPECIES AND GRADE** ** DEAD LOAD = 10 psf** ** DEAD LOAD = 10 psf** ** DEAD LOAD = 10 psf** ** DEAD LOAD = 10 psf** ** DEAD LOAD = 20 psf** ** DEAD LOAD = 20 psf** ** DEAD LOAD = 20 psf** ** DEAD LOAD = 20 psf** ** JOIST SPACING**
(inches)** SPECIES AND GRADE** ** SPECIES AND GRADE** ** 2 × 6** ** 2 × 8** ** 2 × 10** ** 2 × 12** ** 2 × 6** ** 2 × 8** ** 2 × 10** ** 2 × 12** ** JOIST SPACING**
(inches)** SPECIES AND GRADE** ** SPECIES AND GRADE** ** Maximum floor joist spans** ** Maximum floor joist spans** ** Maximum floor joist spans** ** Maximum floor joist spans** ** Maximum floor joist spans** ** Maximum floor joist spans** ** Maximum floor joist spans** ** Maximum floor joist spans** ** JOIST SPACING**
(inches)** SPECIES AND GRADE** ** SPECIES AND GRADE** ** (ft-in)** ** (ft-in)** ** (ft-in)** ** (ft-in)** ** (ft-in)** ** (ft-in)** ** (ft-in)** ** (ft-in)** 19.2 Douglas fir-larch SS 9-8 12-10 16-4 19-10 9-8 12-10 16-4 19-6 19.2 Douglas fir-larch #1 9-4 12-4 15-0 17-5 8-10 11-3 13-8 15-11 19.2 Douglas fir-larch #2 9-2 11-8 14-3 16-6 8-5 10-8 13-0 15-1 19.2 Douglas fir-larch #3 7-0 8-11 10-11 12-7 6-5 8-2 9-11 11-6 19.2 Hem-fir SS 9-2 12-1 15-5 18-9 9-2 12-1 15-5 18-9 19. CRC § 25.4 Medium relevance — show source text
Other maximum span provided by an accredited lumber grading or inspection agency also allowed.
c. Individual wood deck boards supported by two joists shall be considered single span and three or more joists shall be considered multiple span.|For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 degree = 0.01745 rad.
a. Maximum angle of 45 degrees from perpendicular for wood deck boards.
b. Other maximum span provided by an accredited lumber grading or inspection agency also allowed.
c. Individual wood deck boards supported by two joists shall be considered single span and three or more joists shall be considered multiple span.|For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 degree = 0.01745 rad.
a. Maximum angle of 45 degrees from perpendicular for wood deck boards.
b. Other maximum span provided by an accredited lumber grading or inspection agency also allowed.
c. Individual wood deck boards supported by two joists shall be considered single span and three or more joists shall be considered multiple span.|For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 degree = 0.01745 rad.
a. Maximum angle of 45 degrees from perpendicular for wood deck boards.
b. Other maximum span provided by an accredited lumber grading or inspection agency also allowed.
c. Individual wood deck boards supported by two joists shall be considered single span and three or more joists shall be considered multiple span.|2025 CALIFORNIA RESIDENTIAL CODE 5-39
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
FLOORS
R507.8 Vertical and lateral supports. Where supported by attachment to an exterior wall, decks shall be positively anchored to the primary structure and designed for both vertical and lateral loads. Such attachment shall not be accomplished by the use of toenails or nails subject to withdrawal. For decks with cantilevered framing members, connection to exterior walls or other framing members shall be designed and constructed to resist uplift resulting from the full live load specified in Table R301.5 acting on the cantilevered portion of the deck. Where positive connection to the primary building structure cannot be verified during inspection, decks shall be self-supporting.
R507.9 Vertical and lateral supports at band joist. Vertical and lateral supports for decks shall comply with this section.
R507.9.1 Vertical supports. Vertical loads shall be transferred to band joists with ledgers in accordance with this section.
R507.9.1.1 Ledger details. Deck ledgers shall be a minimum 2-inch by 8-inch (51 mm by 203 mm) nominal, No. 2 grade or better pressure-preservative-treated Southern pine, incised pressure-preservative-treated hem-fir, or decay-resistant, naturally durable wood. Deck ledgers shall not support concentrated loads from beams or girders. Deck ledgers shall not be supported on stone or masonry veneer.
R507.9.1.2 Band joist details. Band joists supporting a ledger shall be a minimum 2-inch-nominal (51 mm), solid-sawn, spruce-pine-fir or better lumber or a minimum 1-inch (25 mm) nominal engineered wood rim boards in accordance with Section R502.1.7. Band joists shall bear fully on the primary structure capable of supporting all required loads.
CRC § 3.3 Medium relevance — show source text
0 1 2 3 4
FIRE-RESISTANCE RATING (HOURS)
TABLE 3.3
FLOOR/CEILING ASSEMBLIES—WOOD JOISTCol2 Col3 Col4 Col5 Col6 Col7 Col8 Col9 Col10 ITEM
CODEMEMBRANE
** THICKNESS**CONSTRUCTION DETAILS PERFORMANCE PERFORMANCE REFERENCE NUMBER REFERENCE NUMBER REFERENCE NUMBER NOTES REC.
HOURSITEM
CODEMEMBRANE
** THICKNESS**CONSTRUCTION DETAILS LOAD TIME PRE-BMS-92 BMS-92 POST-BMS-92 POST-BMS-92 POST-BMS-92 F/C-W-1 3/8″ 12′ clear span, 2″ × 9″ wood joists 18″ o.c.; deck:
1″ T&G; filler: 3″ of ashes on1/2″ boards nailed to
joist sides 2″ from bottom; 2″ air space;
membrane:3/8″ gypsum board.60 psf 36 min 7 1, 2 1/2 F/C-W-2 1/2″ 12′ clear span, 2″ × 7″ joists 15″ o.c.; deck: 1″
nominal lumber; membrane:1/2″ fiberboard.60 psf 22 min 7 1–3 1/4 F/C-W-3 1/2″ 12′ clear span, 2″ × 7″ wood joists 16″ o.c.;
2″ × 11/2″ bridging at center; deck: 1″ T&G;
membrane:1/2″ fiberboard; 2 coats “distemper”
paint.30 psf 28 min 7 1, 3,
151/3 F/C-W-4 3/16″ 12′ clear span, 2″ × 7″ wood joists 16″ o.c. CRC § 23-40 Medium relevance — show source text
23-40 2025 CALIFORNIA BUILDING CODE
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
WOOD
TABLE 2308.8.2.1(2)—FLOOR JOIST SPANS FOR COMMON LUMBER SPECIES
(Residential living areas, live load = 40 psf, L/Δ = 360)—continuedCol2 Col3 Col4 Col5 Col6 Col7 Col8 Col9 Col10 Col11 JOIST
SPACING
(inches)SPECIES AND GRADE SPECIES AND GRADE DEAD LOAD = 10 psf DEAD LOAD = 10 psf DEAD LOAD = 10 psf DEAD LOAD = 10 psf DEAD LOAD = 20 psf DEAD LOAD = 20 psf DEAD LOAD = 20 psf DEAD LOAD = 20 psf JOIST
SPACING
(inches)SPECIES AND GRADE SPECIES AND GRADE 2 × 6 2 × 8 2 × 10 2 × 12 2 × 6 2 × 8 2 × 10 2 × 12 JOIST
SPACING
(inches)SPECIES AND GRADE SPECIES AND GRADE Maximum floor joist spans Maximum floor joist spans Maximum floor joist spans Maximum floor joist spans Maximum floor joist spans Maximum floor joist spans Maximum floor joist spans Maximum floor joist spans JOIST
SPACING
(inches)SPECIES AND GRADE SPECIES AND GRADE (ft. - in.) (ft. - in.) (ft. - in.) (ft. - in.) (ft. - in.) (ft. - in.) (ft. - in.) (ft. - in.) 19.2 Douglas Fir-Larch SS 9-8 12-10 16-4 19-10 9-8 12-10 16-4 19-2 19.2 Douglas Fir-Larch #1 9-4 12-4 15-0 17-5 8-10 11-3 13-8 15-11 19.2 Douglas Fir-Larch #2 9-1 11-6 14-1 16-3 8-3 10-6 12-10 14-10 19.2 Douglas Fir-Larch #3 6-10 8-8 10-7 12-4 6-3 7-11 9-8 11-3 19.2 Hem-Fir SS 9-2 12-1 15-5 18-9 9-2 12-1 15-5 18-9 19.
Frequently asked questions
How do I know whether to use the 30 psf or 40 psf joist table?
Use Table R502.3.1(1) (30 psf) for sleeping areas and attics accessed by fixed stairs as described in § R502.3.1; use Table R502.3.1(2) (40 psf) for normal living areas.
Can I span a joist farther by using a higher grade or different species?
Yes — the tables list spans by species and grade. If your lumber has a different grade/species than shown, either use the appropriate table entry or an engineered design (AWC STJR or RDP). See § R502.3.
What if my header or girder span isn't listed in the floor tables?
Header and girder spans for dimension lumber are taken from the header/girder tables (R602.7 series); § R502.5 directs you to those tables rather than the joist tables.
Are engineered joists (I‑joists) covered by the same tables?
No. Engineered members have manufacturer‑rated capacities and must be used per the manufacturer’s instructions or engineered design; see § R502.1.2.
Do I still need blocking if I use plywood subfloor?
Yes. Blocking and lateral restraint requirements for joists are independent of sheathing — follow § R502.7. Also check subfloor panel installation rules in § R503.
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