Deck footing options compared

The five options at a glance

The poured-pier prices assume 60 lb bags at about $7.50, a 4 ft form tube and a post base, which is how the deck footing calculator and the concrete footing bags calculator price them. Helical piles are always a contractor job; get a quote that includes the engineer's load figure for each pile.

How deep, and how much concrete

Footings must reach below the frost line, which runs from about 12 inches in the South to 42-60 inches in the North; the deck footing depth guide explains how to find yours. Depth is what drives the concrete count. For one 12 inch round pier with 4 inches above grade, the concrete footing bags calculator gives:

Going from 12 to 16 inches across raises the concrete by about three quarters, so use the larger size only where the beam span or the soil calls for it. The sonotube calculator counts form tubes for any diameter.

How many footings a deck needs

The count comes from the beams and the post spacing, not from the area. Here is the same 16 ft by 12 ft deck built three ways, using the takeoff in the deck materials calculator and the deck block calculator:

Shorter post spacing means more footings but a smaller beam, so the cheapest layout depends on lumber prices; the deck post spacing calculator and the beam span chart let you compare.

Worked example: three footings for an attached 12x16 deck

An attached 16x12 deck in a 42 inch frost zone needs three 12 inch piers. At 8 bags each that is 24 bags of 60 lb concrete, three 4 ft tubes and three post bases.

For a deck this size the poured piers are cheapest by a wide margin. Helical piles earn their price on wet clay, sites a mixer cannot reach, or a deck that has to be built in winter.

What inspectors look for

• The bottom of the hole at or below frost depth, on undisturbed soil, inspected before any concrete goes in.
• Footing size to suit the load: the inspector checks the area each footing carries against your soil's bearing value.
• A metal post base holding the post off the concrete. Posts buried in concrete rot at the collar and are not allowed in many places.
• Manufacturer evaluation reports for helical piles and ground screws, with the rated load per anchor.

If the deck needs a permit, take the footing plan with you; the deck permit guide lists what to bring.

Choosing

• Attached or raised deck, normal soil: poured piers in tubes.
• Soft soil or a heavy load such as a hot tub: piers on spread footings; see hot tub on a deck.
• Low freestanding deck with no permit: deck blocks on gravel, as in the ground-level deck guide.
• Wet ground, no access for digging, or a winter build: helical piles.
• A small platform where your code allows them: ground screws.