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| Design Values & Spans for Pressure-Treated Southern Pine |
Design values published in the SPIB Grading Rules for Southern Pine
Lumber, 2002 Edition, apply to both treated and untreated Southern Pine.
Design values for dimension lumber are based on normal use conditions
(moisture content of 19% or less). These values are intended for use in covered
structures or where the moisture content in use does not exceed 19% for an
extended period of time. For applications where the moisture content will
exceed 19% for an extended period, tabulated Southern Pine design values
must be multiplied by the appropriate wet-service factor, CM . Refer to Table A-2 below.
WET SERVICE ADJUSTMENT FACTORS 
Table A-2: Wet-Service Factor, CM
For lumber 2" to 4" thick; applies to all values
|
Extreme
Fiber Stress
in Bending
Fb
|
Tension
Parallel
to Grain
Ft
|
Horizontal
Shear
Fv
|
Compression
Perpendicular
to Grain
Fc⊥
|
Compression
Parallel
to Grain
Fc
|
Modulus
of
Elasticity
E
|
| 0.851 |
1.00 |
0.97 |
0.67 |
0.802 |
0.90 |
Decks are built in all shapes and sizes. The basic structural system is
generally the same: decking is supported by joists, joists are supported by
beams, which in turn are supported by posts. Posts are then connected or
anchored to a foundation or footing, transferring loads from the deck structure
to the ground. Recommended maximum span for Southern Pine decking is
24" o.c. (2x4, 2x6, R.E.D.). Typical joist spans are listed in Tables 14, 15 and 16 below,
incorporating the wet-service factor CM for adequate structural design in
high-moisture conditions. For additional deck design details (beams, posts, connections) refer to the Forest Products Laboratory Wood Decks Manual.
TREATED SOUTHERN PINE SPAN TABLES
Decks; Moisture Content exceeds 19%
Maximum Spans given in feet and inches; inside to inside of bearings
| Table 14: Wet-Service Floor Joists - 40 psf live load, 10 psf dead load, l/360 deflection |
Size
inches
|
Spacing
inches on center |
Grade |
| Select Structural |
No. 1 |
No. 2 |
No. 3 |
| 2 x 6 |
12 |
10-9 |
10-7 |
10-4 |
9-4 |
| 16 |
9-9 |
9-7 |
9-5 |
8-1 |
| 24 |
8-7 |
8-5 |
7-10 |
6-7 |
| 2 x 8 |
12 |
14-2 |
13-11 |
13-8 |
11-11 |
| 16 |
12-11 |
12-8 |
12-5 |
10-3 |
| 24 |
11-3 |
11-1 |
10-2 |
8–5 |
| 2 x 10 |
12 |
18-1 |
17-9 |
17-5 |
14-0 |
| 16 |
16-5 |
16-2 |
15-10 |
12-2 |
| 24 |
14-4 |
13-6 |
13-1 |
9-11 |
| 2 x 12 |
12 |
22-0 |
21-7 |
21-2 |
16-8 |
| 16 |
20-0 |
19-8 |
18-10 |
14-6 |
| 24 |
17-6 |
16-1 |
15-5 |
11-10 |
TREATED SOUTHERN PINE SPAN TABLES
Decks; Moisture Content exceeds 19%
Maximum Spans given in feet and inches; inside to inside of bearings
| Table 15: Wet-Service Floor Joists - 60 psf live load, 10 psf dead load, l/360 deflection |
Size
inches
|
Spacing
inches on center |
Grade |
| Select Structural |
No. 1 |
No. 2 |
No. 3 |
| 2 x 6 |
12 |
9-5 |
9-3 |
9-1 |
7-11 |
| 16 |
8-7 |
8-5 |
8-1 |
6-10 |
| 24 |
7-6 |
7-4 |
6-8 |
5-7 |
| 2 x 8 |
12 |
12-5 |
12-2 |
11-11 |
10-0 |
| 16 |
11-3 |
11-1 |
10-6 |
8-8 |
| 24 |
9-10 |
9-7 |
8-7 |
7-1 |
| 2 x 10 |
12 |
15-10 |
15-6 |
15-2 |
11-10 |
| 16 |
14-4 |
13-11 |
13-7 |
10-3 |
| 24 |
12-7 |
11-5 |
11-1 |
8-5 |
| 2 x 12 |
12 |
19-3 |
18-10 |
18-5 |
14-1 |
| 16 |
17-6 |
16-7 |
15-11 |
12-3 |
| 24 |
15-3 |
13-7 |
13-0 |
10-0 |
TREATED SOUTHERN PINE SPAN TABLES
Decks; Moisture Content exceeds 19%
Maximum Spans given in feet and inches; inside to inside of bearings
| Table 16: Wet-Service Floor Joists - 100 psf live load, 10 psf dead load, l/360 deflection |
Size
inches |
Spacing
inches on center |
Grade |
| Select Structural |
No. 1 |
No. 2 |
No. 3 |
| 2 x 6 |
12 |
7-11 |
7-9 |
7-6 |
6-3 |
| 16 |
7-2 |
7-1 |
6-6 |
5-5 |
| 24 |
6-4 |
6-1 |
5-3 |
4-5 |
| 2 x 8 |
12 |
10-5 |
10-3 |
9-8 |
8-0 |
| 16 |
9-6 |
9-4 |
8-4 |
6-11 |
| 24 |
8-4 |
7-8 |
6-10 |
5-8 |
| 2 x 10 |
12 |
13-4 |
12-10 |
12-6 |
9-5 |
| 16 |
12-1 |
11-1 |
10-10 |
8-2 |
| 24 |
10-4 |
9-1 |
8-10 |
6-8 |
| 2 x 12 |
12 |
16-3 |
15-4 |
14-8 |
11-3 |
| 16 |
14-9 |
13-3 |
12-8 |
9-9 |
| 24 |
10-4 |
10-4 |
10-4 |
8-0 |
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