Section R503

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

5-12 2022 CALIFORNIA RESIDENTIAL CODE

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FLOORS

TABLE R503.2.1.1(1) ALLOWABLE SPANS AND LOADS FOR WOOD STRUCTURAL PANELS FOR ROOF AND

SUBFLOOR SHEATHING AND COMBINATION SUBFLOOR UNDERLAYMENT ^{a, b, c}

SPAN RATING	MINIMUM NOMINAL PANEL THICKNESS (inch)	ALLOWABLE LIVE LOAD (psf)h, I		MAXIMUM SPAN (inches)		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 for ¹⁵ /32- and ¹ /2-inch panels. h. Maximum span 24 inches where ³ /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 nominal ¹ /4-inch-thick wood panel-type

underlayment, fiber-cement underlayment with end and edge joints offset not less than 2 inches or 1 ¹ /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 of ¹ /360 of span, is 100 psf. k. Unsupported edges shall have tongue-and-groove joints or shall be supported by blocking unless nominal ¹ /4-inch-thick wood panel-type underlayment, fiber cement underlayment with end and edge joints offset not less than 2 inches or ³ /4-inch wood finish flooring is installed at right angles to the supports. Fibercement underlayment shall comply with ASTM C1288 or ISO 8336 Category C. Allowable uniform live load at maximum span, based on deflection of ¹ /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.

FLOORS

TABLE R503.2.1.1(2) ALLOWABLE SPANS FOR SANDED PLYWOOD COMBINATION SUBFLOOR UNDERLAYMENT ^a

IDENTIFICATION	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 nominal ¹ /4-inch-thick wood panel-type underlayment, fibercement underlayment or ³ /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 of ¹ /360 of span is 100 psf. b. Applicable to all grades of sanded exterior-type plywood.

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).