Deck Footing and Piers in CA

Y ou can quickly figure the amount of concrete needed to fill a tube by multiplying the following factors by the height of the tube in feet:

• 8-inch pier: .013 cu. yd. (0.6 80-pound bags of concrete mix per lin. ft.)
• 10-inch pier: .02 cu. yd. (0.9 bags per lin. ft.)
• 12-inch pier: .029 cu. yd. (1.3 bags per lin. ft.)

For rectangular footings, use these amounts per footing:

• 8x16x16-inch footing: .044 cu. yd. (2 bags each)
• 10x20x20-inch footing: .086 cu. yd. (3.8 bags each)
• 12x24x24-inch footing: .15 cu. yd. (6.75 bags each)

As an example, say you have four tubes and that they’re 8 inches in diameter and 4 feet deep. With a total lineal footage of 16 feet, the tubes will require 9.6 bags of concrete mix (0.6 bags per foot). The four 8x16x16 footings will require a total of 8 bags (2 bags per footing). So you’ll need 18 bags to complete the job.

Pier diameter.
A rule of thumb for pier diameter is “one inch per foot of span.” Thus a deck that spans 8 feet will stand comfortably on 8-inch-diameter piers, while a deck that spans 10 feet requires 10-inch-diameter piers. .

Footings.
F ootings help keep the structure from settling; to leave them out risks having a railing or rim joist that looks like a roller coaster. For most decks, a pier footing should be as thick as the pier’s diameter, with sides that measure twice that much. So an 8-inch pier should rest on a footing that’s 8 inches thick and 16 inches square, while a 12-inch pier should rest on a footing that’s 12 inches thick and 24 inches square.

Post Bases.
PBS44A or equivalent standoff bases cast into the (pier) footing

Most decks can be supported here in Ca with 24x24 concrete pads 12" deep into undisturbed soil for the footings & blocks or poured piers 6" above grade to the posts.
We add piers rather than blocks to get the posts 8" above typically and also place #4 rebar 2 vertical in the piers & 4 horizontal in the footing.

Note for Hillside Piers & footings:
Codes UBC1806.5.2 & IRC 403.1.7
Setbacks & clearences to slopes : >1 vert to 3 horiz
Translated... from the bottom of the footing go out 5 feet horizantal & level, (for a typical pier), now measure down at that point vertical to the ground.
That height on the slope to the level line is the depth the footing should be.

PIER PADS: UBC Table 18.I.C. Same as footings.
FOOTING/PIER SETBACK FROM SLOPE: UBC 1806.5.3. Footings adjacent to slopes shall be founded in firm material with an embedment and setback sufficient to provide vertical and lateral support. See Table 18-I-1.

COLUMNS AND POSTS: UBC 2306.5. Columns and posts located on concrete or masonry floors or decks exposed to the weather or to water splash or in basements shall be supported by concrete piers or metal pedestals projecting above floors unless approved wood of natural resistance to decay is used. The pedestals shall project at least 6” above exposed earth and at least 1” above such floors. Individual concrete or masonry piers shall project at least 8” above exposed ground unless the columns or posts, which they support, are of approved wood of natural resistance to decay or treated wood.

Difference in elevation between flat spot/yard of uphill house compared with flat spot/yard of downhill house times one half, is greater than the distance from bottom of slope/hill to closest downhill housewall.
{403.1.7; NA; fig.18-I-1}

Difference in elevation between flat spot/yard of uphill house compared with flat spot/yard of downhill house times one third, is greater than the distance from top of slope/hill to uphill house footing