// CODE SNIPPET
Section R503 Floor Sheathing
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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).
For SI: 1 inch = 25.4 mm, 1 pound per square inch = 6.895 kPa. N/A = Not applicable.
| 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 this support spacing, lumber sheathing shall have a minimum Fb of 675 and minimum E of 1,100,000 (see ANSI AWC NDS).
- For this support spacing, lumber sheathing shall have a minimum Fb of 765 and minimum E of 1,400,000 (see ANSI AWC NDS).
- 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).
For SI: 1 inch = 25.4 mm, 1 pound per square foot = 0.0479 kPa.
For SI: 1 inch = 25.4 mm, 1 pound per square foot = 0.0479 kPa.
| SPAN RATING | MINIMUM NOMINAL PANEL THICKNESS (inch) |
ALLOWABLE LIVE LOAD (psf)h, l |
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 | Subfloorl | ||||||
| 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 |
- 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.
- 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.
- Applies to panels 24 inches or wider.
- 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.
- Includes Structural I panels in these grades.
- Uniform load deflection limitation: 1/180 of span under live load plus dead load, 1/240 of span under live load only.
- Maximum span 24 inches for 15/32-and 1/2-inch panels.
- Maximum span 24 inches where 3/4-inch wood finish flooring is installed at right angles to joists.
- Maximum span 24 inches where 1.5 inches of lightweight concrete or approved cellular concrete is placed over the subfloor.
- 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.
- 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.
- 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.
| 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 |
- 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, fiber-cement 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.
- 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).
Related Code Sections
Section R503 Floors, Floor 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).
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