The acceptability of deck pier blocks instead of footings depends on two things deck height and frost level.
Pier blocks can be used instead of footings for a ground-level deck not requiring permits. Piers blocks can also be used if the frost level depth is less then the height of the pier block. Allowing you to set the pier block below the frost level on stable ground.
In Calgary, decks less than 24” above grade do not require a permit. The low height gives you total freedom in selecting the level of support for your deck. Any decks higher than 24” require concrete piles 10” in diameter and 48” below grade. These footing size requirements are to ensure enough soil bearing to prevent the joist from sinking in the ground. The depth requirement is to provide stable support for the deck below the frost level.
Regardless if a permit is required, it is better to build a deck with sufficient support. This is why I build all decks with concrete columns, 10” wide, and 48” deep. Yes, it may be a low deck, not requiring a permit or to meet code requirements, but you will never regret building a strong deck that can be enjoyed for years.
Yes, when you are digging down four feet to pour concrete piles below the frost level, you may be thinking O’ if I just use deck piers I will be able to enjoy my deck sooner but you will also be able to enjoy your deck less when it collapses and needs to be replaced. Build it right the first time, enjoy it for years.
In Calgary, all deck posts must bear on concrete columns extending 6” above grade. With a ground-level deck, you may be able to dig around the column for water does not pool around the post. This limits the use of deck piers because a deck post cannot be in ground contact. Meaning you cannot bury the pier and post below the frost level in the ground.
Using Deck Pier Blocks for a Floating Deck
You could use pier blocks for a floating deck less than 24” from grade and not attached to your house. It’s important that it is not attached to the house foundation if it’s a floating deck. As a floating deck will do exactly as its name says, it will float, rising and sink as the ground freezes and thaws. A floating deck attached to your house will increase stress on the house foundation, possibly causing the house foundation to fail. Then the extra work for concrete footings will seem like nothing compared to the work to repair the foundation.
To help stabilize deck piers under a floating deck, dig down to clay, removing all the loam, topsoil. Topsoil contains unstable organic matter. A deck supported on topsoil will sink unevenly into the ground. Organic matter also acts as a sponge absorbing water, increasing the level of expansion and contraction in winter and spring. Once below the topsoil dig and extra 6” out and fill with compacted gravel. The gravel will allow water to drain away from under the pier. Also, the space between the stones will provide room for water to freeze without pushing against the pier.
For a full step-by-step guide on how to build a floating deck. Click the link.