Diamond Piers were developed to provide builders with a footing system that took a fraction of the time and energy of a concrete footing. Digging and dirt removal, concrete curing time, and large unsightly cardboard tubes are all eliminated when switching from a concrete Sonotube footing to a Diamond Pier.
Diamond Piers work by setting a special 12" concrete block a few inches into the ground and driving metal pipes through it with a jackhammer. When a post with a load is placed on the top of the block, the pins take on that load and transfer the load to a larger area, much like a tree root does.
Diamond Piers can be installed at any point, as long as you know where your deck framing will land. They're often installed once the deck rims and beam are installed and temporarily braced up, and a plumb line can be set to find the footing locations. Fortunately, since no large machinery is require to dig holes, the pier can be set even if it's next to a temp post, or close to the bottom of a retaining wall.
Since Diamond Pier installation can be verified by an inspector after it's installed, you don't need to have a separate footing inspection. When you submit your permit plans that include Diamond Piers and it gets approved, you can build your entire deck, and get footings inspected at the final inspection. The inspector will simply stick a tape measure down one or more of the pins to verify its length, which proves that it's been installed according to manufacturer specifications.
Helical footings, like Diamond Piers, are fast and versatile, especially compared to concrete. Unlike helicals, Diamond Piers can be installed by the deck builder, with no need to schedule a third party service, and are about half the cost of helicals.
If you're considering deck blocks or other pre-made footing blocks, know that those will have no uplift capacity and will move with the ground, whereas Diamond Piers are rated to withstand a frostline of 48"-60", depending on the pin length. DPs are also laterally stable, unlike a surface-set block, which is especially important when a deck is on an incline.
