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
TABLE R503.1 MINIMUM THICKNESS OF LUMBER FLOOR SHEATHING
| JOIST OR BEAM SPACING (inches) | MINIMUM NET THICKNESS | |
| Perpendicular to joist | Diagonal to joist | |
| 24 | 11/16 | 3/4 |
| 16 | 5/8 | 5/8 |
| 48a | 11/2 T & G | N/A |
| 54b | ||
| 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). |
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.
Wood structural panel sheathing used for structural purposes shall conform to DOC PS 1, DOC PS 2, CSA O437 or CSA O325. 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
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).
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
TABLE R503.2.1.1(2) ALLOWABLE SPANS FOR SANDED PLYWOOD COMBINATION SUBFLOOR UNDERLAYMENTa
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 | MAXIMUM SPAN (inches) | LOAD (pounds per square foot, at maximum span) | MAXIMUM SPAN (inches) | |||
| SPAN @ 16″ o.c. | SPAN @ 24″ o.c. | With edge supportd | Without edge support | Total load | Live load | |||
| Sheathinge | 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 | 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-andgroove 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 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 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, fibercement 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 reference standard APA E30, APA Engineered Wood Construction Guide. Refer to reference 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) | ||
| 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 C 1288 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. |
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).
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).
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.
Particleboard floor underlayment shall conform to Type PBU and shall be not less than 1/4 inch (6.4 mm) in thickness.
Particleboard underlayment shall be installed in accordance with the recommendations of the manufacturer and attached to framing in accordance with Table R602.3(1).