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Chapter 5 — FLOORS

Section R503 — FLOOR SHEATHING

2025 California Residential Code (Title 24, Part 2.5) · 2025 edition · updated 2026-07-29 · California

Italicized text is a California amendment to the model code, as printed in the official publication.

R503.1 Lumber sheathing.

Maximum allowable spans for lumber used as floor sheathing shall conform to Tables R503.1, R503.2.1.1(1) and R503.2.1.1(2).

TABLE R503.1—MINIMUM THICKNESS OF LUMBER FLOOR SHEATHING

JOIST OR BEAM SPACING
(inches)		 MINIMUM NET THICKNESS MINIMUM NET THICKNESS
JOIST OR BEAM SPACING
(inches)		 Perpendicular to joist Diagonal to joist
24 11/16 3/4
16 5/8 5/8
48a 11/2 T & G N/A
54b 54b 54b
60c 60c 60c
For SI: 1 inch = 25.4 mm, 1 pound per square inch = 6.895 kPa.
N/A = Not Applicable.
a. For this support spacing, lumber sheathing shall have a minimum_Fb_ of 675 and minimum E of 1,100,000 (see ANSI AWC NDS).
b. For this support spacing, lumber sheathing shall have a minimum_Fb_ of 765 and minimum E of 1,400,000 (see ANSI AWC NDS).
c. For this support spacing, lumber sheathing shall have a minimum_Fb_ of 855 and minimum E of 1,700,000 (see ANSI AWC NDS).

R503.1.1 End joints. End joints in lumber used as subflooring shall occur over supports unless end-matched lumber is used, in which case each piece shall bear on not less than two joists. Subflooring shall be permitted to be omitted where joist spacing does not exceed 16 inches (406 mm) and a 1-inch (25 mm) nominal tongue-and-groove wood strip flooring is applied perpendicular to the joists.

R503.2 Wood structural panel sheathing.

R503.2.1 Identification and grade. Wood structural panel sheathing used for structural purposes shall conform to CSA O325, CSA O437 DOC PS 1 or DOC PS 2. Panels shall be identified for grade, bond classification and Performance Category by a grade mark or certificate of inspection issued by an approved agency. The Performance Category value shall be used as the “nominal panel thickness” or “panel thickness” wherever referenced in this code.

R503.2.1.1 Subfloor and combined subfloor underlayment. Where used as subflooring or combination subfloor underlayment, wood structural panels shall be of one of the grades specified in Table R503.2.1.1(1). Where sanded plywood is used as combination subfloor underlayment, the grade, bond classification, and Performance Category shall be as specified in Table R503.2.1.1(2).

5-12 2025 CALIFORNIA RESIDENTIAL CODE

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

FLOORS

TABLE R503.2.1.1(1)—ALLOWABLE SPANS AND LOADS FOR WOOD STRUCTURAL
PANELS FOR ROOF AND SUBFLOOR SHEATHING AND COMBINATION SUBFLOOR UNDERLAYMENTa, b, c

SPAN
RATING		 MINIMUM
NOMINAL
PANEL
THICKNESS
(inch)		 ALLOWABLE LIVE LOAD
(psf)h, I		 ALLOWABLE LIVE LOAD
(psf)h, I		 MAXIMUM SPAN
(inches)		 MAXIMUM SPAN
(inches)		 LOAD
(pounds per square foot,
at maximum span)		 LOAD
(pounds per square foot,
at maximum span)		 MAXIMUM SPAN
(inches)
SPAN
RATING		 MINIMUM
NOMINAL
PANEL
THICKNESS
(inch)		 Span
@ 16″ o.c.		 Span
@ 24″ o.c.		 With edge
supportd		 Without edge
support		 Total load Live load Live load
Sheathinge Sheathinge Rooff Rooff Rooff Rooff Subfloorj
16/0 3/8 30 — 16 16 40 30 0
20/0 3/8 50 — 20 20 40 30 0
24/0 3/8 100 30 24 20g 40 30 0
24/16 7/16 100 40 24 24 50 40 16
32/16 15/32, 1/2 180 70 32 28 40 30 16h
40/20 19/32, 5/8 305 130 40 32 40 30 20h, i
48/24 23/32, 3/4 — 175 48 36 45 35 24
60/32 7/8 — 305 60 48 45 35 32
Underlayment,
C-C plugged, single floore		 Underlayment,
C-C plugged, single floore		 Rooff Rooff Rooff Rooff Combination
subfloor
underlaymentk
16 o.c. 19/32, 5/8 100 40 24 24 50 40 16i
20 o.c. 19/32, 5/8 150 60 32 32 40 30 20i, j
24 o.c. 23/32, 3/4 240 100 48 36 35 25 24
32 o.c. 7/8 — 185 48 40 50 40 32
48 o.c. 13/32, 11/8 — 290 60 48 50 40 48

For SI: 1 inch = 25.4 mm, 1 pound per square foot = 0.0479 kPa.
a. The allowable total loads were determined using a dead load of 10 psf. If the dead load exceeds 10 psf, then the live load shall be reduced accordingly.
b. Panels continuous over two or more spans with long dimension (strength axis) perpendicular to supports. Spans shall be limited to values shown because of possible effect of
concentrated loads.
c. Applies to panels 24 inches or wider.
d. Lumber blocking, panel edge clips (one midway between each support, except two equally spaced between supports where span is 48 inches), tongue-and-groove panel
edges, or other approved type of edge support.
e. Includes Structural I panels in these grades.
f. Uniform load deflection limitation:1/180 of span under live load plus dead load,1/240 of span under live load only.
g. Maximum span 24 inches for15/32- and1/2-inch panels.
h. Maximum span 24 inches where3/4-inch wood finish flooring is installed at right angles to joists.
i. Maximum span 24 inches where 1.5 inches of lightweight concrete or approved cellular concrete is placed over the subfloor.
j. Unsupported edges shall have tongue-and-groove joints or shall be supported with blocking unless minimum nominal1/4-inch-thick wood panel-type underlayment, fiber-
cement underlayment with end and edge joints offset not less than 2 inches or 11/2 inches of lightweight concrete or approved cellular concrete is placed over the subfloor, or
3/4-inch wood finish flooring is installed at right angles to the supports. 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.
k. Unsupported edges shall have tongue-and-groove joints or shall be supported by blocking unless nominal1/4-inch-thick wood panel-type underlayment, fiber-cement under-
layment with end and edge joints offset not less than 2 inches or3/4-inch wood finish flooring is installed at right angles to the supports. 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, except panels with a span rating
of 48 on center are limited to 65 psf total uniform load at maximum span.
l. Allowable live load values at spans of 16 inches on center and 24 inches on center taken from referenced standard APA E30,APA Engineered Wood Construction Guide. Refer to
referenced standard for allowable spans not listed in the table.

TABLE R503.2.1.1(2)—ALLOWABLE SPANS FOR SANDED PLYWOOD COMBINATION SUBFLOOR UNDERLAYMENTa

** IDENTIFICATION** ** SPACING OF JOISTS**
(inches)		 ** SPACING OF JOISTS**
(inches)		 ** SPACING OF JOISTS**
(inches)
** IDENTIFICATION** ** 16** ** 20** ** 24**
Species groupb — — —
1 1/2 5/8 3/4
2, 3 5/8 3/4 7/8
4 3/4 7/8 1
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.

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

FLOORS

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).

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▸ Contents — 2025 California Residential Code (Title 24, Part 2.5)
2025 California Residential Code (Title 24, Part 2.5)
  1. Chapter 1 — ADMINISTRATION
  2. Chapter 2 — DEFINITIONS
  3. Chapter 3 — BUILDING PLANNING
  4. Chapter 4 — FOUNDATIONS
  5. ▸ Chapter 5 — FLOORS
    Overview
    1. Section R501 — GENERAL
    2. Section R502 — WOOD FLOOR FRAMING
    3. Section R503 — FLOOR SHEATHING
    4. Section R504 — PRESSURE PRESERVATIVE-TREATED WOOD FLOORS (ON G…
    5. Section R505 — COLD-FORMED STEEL FLOOR FRAMING
    6. Section R506 — CONCRETE FLOORS (ON GROUND)
    7. Section R507 — EXTERIOR DECKS
  6. Chapter 6 — WALL CONSTRUCTION
  7. Chapter 7 — WALL COVERING
  8. Chapter 8 — ROOF-CEILING CONSTRUCTION
  9. Chapter 9 — ROOF ASSEMBLIES
  10. Chapter 10 — CHIMNEYS AND FIREPLACES
  11. Chapter 44 — REFERENCED STANDARDS
  12. Appendix AA — BOARD OF APPEALS
  13. Appendix AB — PERMIT FEES
  14. Appendix AC — RESERVED
  15. Appendix BA — RESERVED
  16. Appendix BB — TINY HOUSES
  17. Appendix BC — RESERVED
  18. Appendix BD — RESERVED
  19. Appendix BE — RADON CONTROL METHODS
  20. Appendix BF — PATIO COVERS
  21. Appendix BG — SOUND TRANSMISSION
  22. Appendix BH — AUTOMATIC VEHICULAR GATES
  23. Appendix BI — LIGHT STRAW-CLAY CONSTRUCTION
  24. Appendix BJ — STRAWBALE CONSTRUCTION
  25. Appendix BK — COB CONSTRUCTION (MONOLITHIC ADOBE)
  26. Appendix BL — HEMP-LIME (HEMPCRETE) CONSTRUCTION
  27. Appendix BM — 3D-PRINTED BUILDING CONSTRUCTION
  28. Appendix BN — EXTENDED PLATE WALL CONSTRUCTION
  29. Appendix BO — EXISTING BUILDINGS AND STRUCTURES
  30. Appendix CA — RESERVED
  31. Appendix CB — RESERVED
  32. Appendix CC — RESERVED
  33. Appendix CD — RESERVED
  34. Appendix CE — RESERVED
  35. Appendix CF — RESERVED
  36. Appendix CG — NONSEWERED SANITATION SYSTEMS
  37. Appendix CH — PRIVATE SEWAGE DISPOSAL
  38. Appendix CI — SWIMMING POOL SAFETY ACT
  39. Appendix CJ — EMERGENCY HOUSING
  40. Appendix CK — AREAS PROTECTED BY THE FACILITIES OF THE CENTRAL…

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