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Question DetailsAsked on 8/14/2017

what is the cost foot a deck footing 1' x 5' in clay dirt

I need 16 footings 5 feet deep 1 foot in diameter in clay dirt with rock and tree roots. What a good price per hole?

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1 Answer


In readily dug soil without large (say over 4 inch) stones, commonly about $20-40/hole in that quantity, using a 2-man post hole digging machine - though if lots of cobbles, larger rocks, or sicky clay 12" is getting awfully large for a hand-held machine.

If accessible to a tractor or bobcat with hydraulic auger, probably in the $30-40/hole range.

If larger rocks or boulders which do not come easily with an auger, or bedrock, then requires accessibility for a larger truck drill and more like $50-100/hole for 16 holes - up to $200-400 range in bedrock or essentially all large rock talus or boulders depending on hardness.

If large rocks or bedrock and NOT accessible to a truck drill (roughly the size of a long dumptruck or a gasoline tanker truck without trailer) or overhead power line interference or such which prohibits using a drill, so it requires hand digging then likely to be more a 2 foot diameter (so more concrete needed or sonotube with compacted stone backfill around it) dug with jackhammer with rock point and spade tips - so in that case more like $250-500/hole, at which point getting a small backhoe or bobcat in with backhoe and jackhammer attachments to dig the holes (which would be more about 3 feet in dimension in that case) would make more sense if at all possible to get access, even if it means removing some fencing temporarily. Ditto on removing fencing if that will get a drill rig in.

Note these are ballpark numbers - accessibility, local labor costs, competition for hole digging jobs (Excavator and Fencing would be the normal contractor Search the List categories for this type of work) and of course ground conditions all affect the cost.

I am assuming you are talking this deep of holes because these are going to support a building rather than a deck, or a deck in deep freezing conditions. If the latter and in hard to dig soil conditions, I would be looking at why so many holes - first any along the house foundation (assuming heated building) generally only have to go to the bottom of foundation elevation (commonly 3-4 feet) because they will be warmed by the foundation, and I would also look at (if for a deck) putting in fewer posts (maybe larger post size as needed) at wider spacing with larger carry beam to minimize the number of holes. For instance, my 12x48 deck has 6 posts total (house side hanging off house so no posts there) - granted, 4x12" perimeter beam which is begger than normal.

Also - if some of these posts are along the house - so entire deck is supported on posts, and the house side is not carried on a ledger board, then you could probably build the deck entirely free-standing weith only gap-filling trim and maybe flexible sway resistance linkage to the house. In which case I have never seen a building code requiring the deck footings go to below frost depth. For a free-standing deck (with adequate sway bracing), simple precast concrete post blocks embedded about 4-8 inches into the ground (assuming the clay is firm to hard, not mushy) so the wood posts are 4 inches clear of the ground would commonly be used.

I would also be looking at the 12" diameter thing - unless supporting a full multi-story house, 6-8" sonotube footings would be the more normal support size for a deck - but presumably these have been designed by an engineer, which is generally required for any house and for any deck more than from 1-3 feet off the ground, depending on local code.

Answered 3 years ago by LCD

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