There are two ways to support a backyard deck.
Either the deck, or more specifically the deck’s platform, can be supported by beams and columns that rest on deck blocks, or these beams and columns can sit on poured concrete piers.
Deck blocks, often accompanied by an 18”x18” patio stone underneath, placed there in order to lessen the chance of the deck block sinking by strategically spreading the working load of the deck, create what’s known as a floating deck.
Concrete piers, poured about 48-54 inches deep into the soil, require the homeowner to first dig a hole in order to accommodate the sono-tube (cardboard cylinder) and accompanying Bigfoot base the concrete gets poured into.
Why a homeowner would dig, as opposed to float a deck, depends entirely on circumstance.
A Bigfoot base, or footing tube unit (plastic base and cylinder in one) demands such a large hole, you’re going to require the services of a backhoe. Don’t attempt to dig this hole by hand, or bother hiring the manual labour to do so, unless of course you’ve happened upon a band of migrant workers from some third-world country.
You likely shouldn’t be getting your heart rate up to the level of horsepower necessary to effectively move this amount of earth, while the chances of getting a local young person to drop her or his cellphone in exchange for a spade shovel, separating them from the outside world for the few hours this task will require, is conservatively estimated at zero.
Backhoes require space to manoeuvre, which will be a challenge if you’ve cut off access to your backyard by means of a fence or stone walkway. Then you’ll be faced with having to ask your neighbours for permission to have the backhoe access your backyard through their property, which could be awkward if ties are somewhat strained, due to you allowing your Rottweiler to regularly poop and basically run amok through their gardens for the past six months.
Then you’ll have to hire a crane to lift the backhoe over your home, dropping it into your backyard. It’s a quite spectacular and doable feat indeed – and perhaps costly – with you certainly forfeiting a little anonymity, if your goal was to build this deck under the radar of the local building inspector.
The advantage of having concrete piers is stability, being that it allows the builder to secure the balance of the deck’s weight to the home’s foundation.
Decks supported by poured concrete piers and ledgers attached to the home don’t generally move.
Plus, poured piers can accept tons of weight, which along with the proper engineering, will permit the -homeowner to transform an existing deck into the floor of a future three- or four-season sun room.
If you’re not thinking sun room in the future, or at least a screened in porch, you ought to be, it’s often the natural progression of a deck if as the homeowners, you plan on sticking around for the foreseeable future.
Because floating decks are subject to sinking or heaving up at certain times of the year, although quite mildly in most cases, they should work independently, and not be attached to the home. As a result, and to ensure your floating deck remains stable and level, the beams supporting the joists should be constructed of three-ply 2x10s, spaced no more than eight feet apart. This triple beam should rest on 6×6 timbers (4x4s are no longer permitted) which will sit in the heavier 6×6 deck block.
If the floating deck is to be three or more feet off the ground, homeowners should consider using adjustable post brackets. Basically, the 6×6 posts get locked into the U-shaped, adjustable brackets, which in turn rest in the deck blocks.
The adjustable brackets are insurance against severe sinking or heaving, since they allow the homeowner to adjust the height of the supporting beam with the simple turn of a nut.