Deck Floor Joist Spans

If you are designing a deck, one of the calculations that you need is the size of the lumber required to span the distances between the deck supports or deck supports and wall.

The lumber span is from the inside of the support on one end to the inside of the support on the other end, as shown in Figure 1.

Additional information on decks with hot tubs or spas.

Deck floor joist span

There are seven factors that enter into choosing the correct lumber size.

Figure 2 - Deck floor joist spacing

1. Species of the lumber
2. Grade of the species
3. Length of the span
4. Spacing between Joists (Figure 2)
5. Dimensions of the lumber
6. Pounds per square foot (psf) - live load
7. Pounds per square foot (psf) - dead load

Check with your local building department to find out the psf requirement in your area.

Following are tables for the two most common required psf loads for 12 inch joist spacing. Both tables are based on the use of #2 grade lumber.

Table 1 is for 40 psf live load and 10 psf dead load.

Table 2 is for 60 psf live load and 10 psf dead load.

Table 1

12″ Joist Spacing, 40 psf live load & 10 psf dead load - Grade #2 lumber

Length In Feet	2 × 6
8
9
10
12
14
16

Length In Feet	2 × 8
8
9
10
12
14
16

Length In Feet	2 × 10
8
9
10
12
14
16

Length In Feet	2 × 12
8
9
10
12
14
16

Table 2

12″ Joist Spacing, 60 psf live load & 10 psf dead load - Grade #2 lumber

Length In Feet	2 × 6
8
9
10
12
14
16

Length In Feet	2 × 8
8
9
10
12
14
16

Length In Feet	2 × 10
8
9
10
12
14
16

Length In Feet	2 × 12
8
9
10
12
14
16

Continued... 16″ & 24″ Joist Spacing