REFERENCE STANDARD RS 10–9 PLYWOOD CONSTRUCTION

1.   DEFINITIONS—

(a) Plywood—Plywood is a laminated board or panel, consisting of a number of veneer sheets bonded together with either a water-resistant or waterproof adhesive that forms a bond stronger than the wood itself.

(b) Plywood component—A plywood component, for purposes of this standard, shall be defined as an element of a structural member formed by the assembly of plywood parts or of plywood parts with parts of wood or other materials so as to form an integral assemblage.

2.   CONFORMANCE WITH STANDARD—Materials, design, and fabrication shall conform to Reference Standard RS 10–53, RS 10–54, RS 10–56 or RS 10–57, except that the word "should" in the standards shall be mandatory.

3.   EXTERIOR USE—All plywood when permanently exposed in outdoor applications shall be of exterior type. Plywood used for covering the exterior of outside walls and applied directly to supports shall be at least 1/2 in. nominal thickness, or comply with specifications for 303 Specialty Siding published by the American Plywood Association. Panel joints shall be backed solidly by studs or by nailing pieces at least 2 in. wide (nominal), except over sheathing or where applied as lapped siding, or when otherwise made waterproof. Plywood siding applied over sheathing shall be not less than 1/4 in. thick.

4.   ROOF SHEATHING—Where plywood is used as roof sheathing the spans shall not exceed the values given in Table RS 10–9.1.

TABLE RS 10–9.1a
Allowable Spans for Plywood Floor and Roof Sheathing
Continuous Over Two or More Spans and Face Grain
Perpendicular to Supports a

Panel Span Rating, b Roof/Floor Span	Thickness (inches)	Roof Maximum Span (inches)
		Edges Blocked c	Edges Unblocked
12/0	5/16	12.2	12.2
16/0	5/16, 3/8	16.2	16.2
20/0	5/16, 3/8	19.2	19.2
24/0	3/8	24.2	20.2
24/0	15/32, 1/2	24.2	24.2
32/16	15/32, 1/2	32.2	28.2
	5/8
40/20	19/32, 5/8	40.2	32.2
	3/4
48/24	23/32, 3/4	48.2	36.2

 

Panel Span Rating, b Roof/Floor Span	Load (psf)
	Total	Live	Floor Maximum Span e (inches)
12/0	135	130	0 f,g
16/0	80	65	0 f,g
20/0	70	55	0 f,g
24/0	60	45	0 f,g
24/0	60	45	0 f,g
32/16	50	35	16 f,g
40/20	40 d	35 d	20 f,g
48/24	40 d	35 d	24 f,g

 

Notes:

a These values apply for C-D Sheathing Structural I and II and C-C grades only. Spans shall be limited to values shown because of possible effect of concentrated loads.

b Span rating appears on all panels in the construction grades listed in footnote b.

c Edges shall be blocked with lumber or other approved type of edge support.

d For roof live load of 40 psf or total load of 55 psf, decrease spans by 13 percent or use panel with next greater span rating.

e Edges of plywood floor sheathing shall have approved tongue-and-groove joints or shall be supported with blocking, unless 1/4-inch minimum thickness underlayment of 1 1/2 inches of approved cellular or lightweight concrete is installed, or finish floor is 25/32-inch wood strip. Allowable uniform load based on deflection of 1/360 of the span is 165 psf.

f Maximum shall be 24 inches if 25/32-inch wood strip flooring is installed at right angles to joist.

g For joists spaced at 24 inches on center, plywood sheathing with span rating numbers 40/20 or greater shall not be used for subfloors except when supporting 1 1/2 inches of lightweight concrete.

5.   PLYWOOD SUBFLOORS—Where plywood is used as structural subflooring the maximum spans shall not exceed the values given in Table RS 10–9.1. If resilient flooring or carpeting is to be applied directly to a plywood subfloor without separate underlayment, the panels shall be underlayment grade, C-C plugged, or any sanded grade of exterior type plywood. The thickness shall not be less than the values prescribed for the given spans and loads shown in Table RS 10–9.2.

6.   SPECIAL 1 1/8 IN. PLYWOOD SUBFLOORING FOR 48 IN. SPAN—Such material, if conforming to design specifications of the American Plywood Association special 2–4–1 panel, may be used over girders spaced not more than 48 in. on centers, with edges on 2 in. x 4 in. blocking securely attached to main girders, provided the total floor load does not exceed 65 psf. A tongue and groove joint may be used in lieu of blocking.

7.   PLYWOOD WALL SHEATHING—Plywood may be applied either horizontally or vertically and as indicated in building code provisions for the bracing of exterior walls.

8.   FASTENING—Plywood sheathing and subflooring—Plywood sheathing and subflooring shall have the maximum fastener spacing on framing as prescribed in Table RS 10–9.3.

TABLE RS 10–9.1b
Allowable Loads for Plywood Roof Sheathing
Continuous Over Two or More Spans and Face Grain
Parallel to Supports a

	Thickness (inches)	No. of Plies	Span (inches)	Total Load (psf)	Live Load (psf)
	15/32	4	24	30	20
	15/32	5	24	45	35
Structural I	1/2	4	24	35	25
	1/2	5	24	55	40
	15/32	5	24	25	20
	1/2	5	24	30	25
Other grades	19/32	4	24	35	25
covered in	19/32	5	24	50	40
DOC PS-1	5/8	4	24	40	30
	5/8	5	24	55	45

 

Note:

a Uniform load deflection limitations: 1/180 of span under live load plus dead load, 1/240 under live load only. Edges shall be blocked with lumber or other approved type of edge supports.

TABLE RS 10–9.2
Minimum Thickness for Plywood
Combination Subfloor—Underlayment a
(Plywood continuous over two or more spans and face grain perpendicular to supports)

 

Species Group	Maximum Spacing of Supports (in.)
	16	20	24
1	1/2 in.	5/8 in.	3/4 in.
2,3	5/8 in.	3/4 in.	7/8 in.
4	3/4 in.	7/8 in.	1 in.

 

Notes:

a Applicable to underlayment grade, C-C (plugged) and all grades of sanded exterior type plywood. Spans limited to values shown because of possible effect of concentrated loads. Allowable uniform load based on deflection of 1/360th of span is 100 psf. Plywood edges shall have approved tongue and groove joints or shall be supported with blocking, unless 1/4-inch minimum thickness underlayment is installed, or finish floor is 25/32-inch wood strip. If wood strips are perpendicular to supports, thickness as shown for 16- and 20-inch spans may be used on 24-inch span.

Except for 1/2 inch, Underlayment grade and C-C (plugged) panels may be of nominal thicknesses 1/32 inch thinner than the nominal thicknesses shown when marked with the reduced thickness.

TABLE RS 10–9.3
Fastening Schedule

Thickness (in.)	Common Nail and Staple Size/Type	Fastener Spacing (in.)a
		Panel Edges	Intermediate Support
Roof and Wall Sheathing
1/2 or less	•   6d Smooth or deformed	6 1/2	12
5/8 or greater	•   8d Smooth or deformed	6 1/2	12
5/16, 3/8, 1/2	•   16 gage galvanized wire staples, 1/8 in. minimum crown. Length of one in. plus plywood thickness except 1 1/4 in. for 5/16 in. plywood	4 1/2	8
1/2	•   6d Smooth or deformed	6 1/2	12
5/8, 3/4, 7/8	•   8d Smooth or 6 deformed	6 1/2	12
1, 1 1/8	•   10d Smooth or 8d deformed	6 1/2	6
1/2	•   16 gage galvanized wire staples, 3/8 in. minimum crown	4 1/2	7
5/8	•   1 5/8 in. long	2 1/2	4

 

Note:

a Where spans are 48 in., or more, nails shall be spaced at 6 in. at all supports.

9.   PLYWOOD SIDING—Plywood siding shall be applied and nailed as prescribed in Table RS 10–9.4.

TABLE RS 10–9.4
Plywood Siding

 

Type of Siding	Plywood b, c Thickness (in.)	Nail Size	Nail Type	Nail Spacing (in.)
				Panel Edges a	Intermediate Supports
Panel Siding	3/8 d	6d	Corrosive resistant box or casing nails	6	12
	1/2, 5/8 and thicker	8d		6	12
Lap Siding	3/8	6d	Corrosive resistant box or casing nails		One nail per stud for width 12 in. or less.
	1/2 and thicker	8d		4	8 in. for width greater than 12 in.

 

Notes:

a Minimum edge distance of 3/8 in.

b In direct-to-stud applications 5-ply panels of 1/2 in. nominal thickness or more

may be used over studs 24 in. o.c. if texturing does not penetrate through the face veneer. All other panels must be used over studs spaced not more than 16 in. on center.

c Special requirement: Nails on ship-lap edges of 5/8 in. and thicker panel siding 3/8 in. from exposed edge and slant driven towards edge; do not set.

d When separate sheathing is applied, 3/8 in. panel and 303 siding may be used over supports spaced 24 in. on center 1/4 in. over supports 16 in. on center.

10.   PLYWOOD DIAPHRAGMS—Plywood diaphragms may be used to resist horizontal forces in horizontal and vertical distributing or resisting elements, provided the deflection in the plane of the diaphragm, as determined by calculations, tests, or analogies drawn therefrom, does not exceed the permissible deflection of attached distributing or resisting elements. Diaphragms to resist earthquake loads may be designed and constructed in accordance with reference standard RS 10–58.

Permissible deflection shall be that deflection up to which the diaphragm and any attached distributing or resisting element will maintain its structural integrity under assumed load conditions; i.e., continue to support assumed loads without danger to occupants of the structure.

Connections and anchorages capable of resisting the design forces shall be provided between the diaphragms and the resisting elements. Openings in diaphragms that materially affect the strength of the diaphragms shall be fully detailed on the plans, and shall have their edges reinforced to adequately transfer all shearing stresses. Structural diaphragm shapes shall be limited to the proportions given in Table RS 10–9.5.

TABLE RS 10–9.5
Diaphragm Proportions

 

Type	Horizontal Diaphragms— Maximum Span-Width Ratios	Vertical Diaphragms— Maximum Height-Width Ratios
• Nailed all edges	4:1	3 1/2:1
• Blocking omitted at intermediate joints	4:1	2:1

 

Design—

Horizontal and vertical plywood diaphragms shall be used at shear values not exceeding those set forth in Tables RS 10–9.6 and RS 10–9.7 respectively or shall be designed by principles of stress analysis. Plywood thickness for horizontal diaphragms shall not be less than as set forth in Tables RS 10–9.1 and RS 10–9.2 for corresponding joist spacing and loading, except that 1/4 in. may be used where design analysis justifies.

All framing members shall be proportioned and spliced where necessary to transmit direct stresses. The width of framing members shall be at least 2 in. nominal. In general, panel edges shall bear on the framing members and butt along their center lines. Nails shall be placed at least 3/8 in. from the panel edges, and spaced not more than 12 in. apart along intermediate supports and 6 in. apart along the panel edge-bearings. All nails shall be firmly driven into the framing members. No unblocked panel less than 12 in. wide shall be used.

(See Tables RS 10–9.6 and RS 10–9.7).

11.   PLYWOOD COMPONENTS.—Plywood components shall be acceptable when designed and fabricated according to procedures in reference standard RS 10–55.

12.   STRUCTURAL USE PANELS.—Panels shall comply with Reference Standards RS 10–54 and RS 10–56 and shall include those manufactured using only veneer as in regular plywood, with veneer faces and a reconstituted wood core as in composite plywood, or using only reconstituted wood as in structural flakeboard, waferboard, oriented strandboard and particleboard.

13.   MARKING OF PANELS.—Structural-use sheathing panels shall be marked with a Span Rating symbol as required in RS 10–54 and RS 10–56. The left-hand number shall denote the maximum roof span in inches, and the right-hand number the floor span.

Structural-use panels designated for use as single-layer floor panels shall be marked with a floor Span Rating. Structural-use panels intended for use solely as wall sheathing shall be marked with a stud spacing of 16 o.c. or 24 o.c.

14.   PANEL SPANS.—Spans for structural-use panels used for floor or roof sheathing shall not exceed the Span Rating. Live loads on floors or roofs shall not exceed those specified in Tables RS 10–9.1a and RS 10–9.1b.

Spans for structural-use panels for wall sheathing may be applied either horizontally or vertically. Maximum stud spacing shall not exceed 16 inches o.c. for panels with a rated wall span of 16 inches or roof span of 16 or 20 inches, and 24 inches o.c. for panels with a rated wall span of 24 inches or roof span of 24 inches or more.

15.   HORIZONTAL SHEAR.—Structural-use panels may be used to resist horizontal forces and shall be assigned shear values equal to those for C-D plywood and other grades in Tables RS 10–9.6 and RS 10–9.7.

16.   FASTENINGS.—Structural-use panels shall be fastened to the framing system in accordance with Table RS 10–9.3.

17.   FIRE RESISTANCE.—Structural-use panels SHALL NOT BE USED as an element of a fire resistive assembly unless it has been specifically tested and approved for such use.

Table RS 10–9–6 Allowable Shear for Wind for Horizontal Plywood Diaphragms a
(lbs. per ft. of horizontal run)

Plywood Grade	Common Nail Size	Minimum Nail Penetration in Framing (in.)	Minimum Nominal Plywood Thickness (in.)	Minimum Nominal Width of Framing Member (in.)	Blocked Diaphragms				Unblocked Diaphragms
					Nail Spacing at Diaphragm Boundaries (all cases) and Continuous Panel Edges Parallel to Load (Cases 3 & 4)				Nails Spaced 6 in. Maximum at Supported End
					6 in. Nail Spacing 6 in.	4 in. at Other 6 in.	2 1/2 in. Plywood 4 in.	2 in. Panel Edges 3 in.	Load Perpendicular to Unblocked Edges and Continuous Panel Joints (Case 1)	All Other Configurations (Cases 2, 3 and 4)
Structural I.	6d	1 1/4	5/16	2	185	250	375	420	165	125
			or 1/4	3	210	280	420	475	185	140
	8d	1 1/2	3/8	2	270	360	530	600	240	180
				3	300	400	600	675	265	200
	10d	1 5/8	1/2	2	320	425	640b	730b	285	215
				3	360	480	720	820	320	240
	6d	1 1/4	5/16	2	170	225	335	380	150	110
			or 1/4	3	190	250	380	430	170	125
			3/8	2	185	250	375	420	165	125
				3	210	280	420	475	185	140
Structural II. C-C Exterior, Standard Sheathing and other Grades covered in Product	8d	1 1/2	3/8	2	240	320	480	545	215	160
				3	270	360	540	610	240	180
			1/2	2	270	360	530	600	240	180
				3	300	400	600	675	265	200
Standard PS 1	10d	1 5/8	1/2	2	290	385	575b	655b	255	190
				3	325	430	650	735	290	215
			5/8	2	320	425	640b	730b	285	215
				3	360	480	720	820	320	240

 

Notes—

a These values are for short time loads due to wind and shall be reduced 25 percent for normal loading. Space nails 12 in. on center along intermediate framing members.

b Reduce tabulated values 10 percent when boundary members provide less than 3 in. nominal nailing surface.

Table RS 10–9–7 Allowable Shear for Wind for Vertical Plywood Diaphragms a,b
(lbs. per ft. of vertical run)

Plywood Grade	Nail Size (Common or Galvanized Box)	Minimum Nail Penetration in Framing (in.)	Minimum Nominal Plywood Thickness (in.)	Plywood Applied Direct to Framing Nail Spacing at Plywood Panel Edges (in.)				Nail Size (Common or Galvanized Box	Plywood Applied Over 1/2-inch Gypsum Sheathing Nail Spacing at Plywood Panel Edges (in.)
				6	4	2 1/2	2		6	4	2 1/2	2
	6d	1 1/4	5/16	200	300	450	510	8d	200	300	450	510
Structural I	8d	1 1/2	3/8	280	430	640	730	10d	280	430	640	730
	10d	1 5/8	1/2	340	510	770	870	—	—	—	—	—
Structural II, C-C Exterior, Standard Sheath-	6d	1 1/4	5/16	180	270	400	450	8d	180	270	400	450
ing, Plywood Panel Siding, and other grades	8d	1 1/2	3/8	260	380	570	640	10d	260	380	570	640
covered in Product Standard PS 1	10d	1 5/8	1/2	310	460	690	770	—	—	—	—	—
	Nail Size (Galvanized Casing)							Nail Size (Galvanized Casing)
Plywood Panel Siding in grades covered in	6d	1 1/4	5/16	140	210	320	360	8d	140	210	320	360
Product Standard PS 1	8d	1 1/2	3/8	160	240	360	410	10d	160	240	360	410

 

Notes—

a These values are for short time loads due to wind and shall be reduced 25 percent for normal loading. All panel edges backed with 2-inch nominal or wider framing. Plywood installed either horizontally or vertically. Space nails at 12 in. on center along intermediate framing members.

b For unblocked vertical plywood diaphragms use the values in the last column of Table RS 10–9–6.

Editor's note: For related unconsolidated provisions, see Appendix A at L.L. 1995/017.