You Want a Deck but Dread Digging Post Holes
Imagine this: you’ve finally decided to build that dream deck in your backyard. You have the plans, you’ve picked out the perfect composite boards, and you can already picture summer barbecues. Then, you remember the hardest part—digging. The thought of renting an auger, wrestling with rocky soil, and setting posts in concrete is enough to make you reconsider the whole project.
What if there was a way to build a solid, stable deck without ever pouring a single bag of concrete or digging below the frost line? That’s the promise of deck blocks. These simple, pre-formed concrete blocks are a game-changer for DIYers and professionals alike, offering a faster, cleaner, and more adjustable foundation for many types of decks.
If you’re searching for “how to use a deck block,” you’re likely looking for a practical escape from the mess and permanence of traditional footings. This guide will walk you through everything you need to know, from choosing the right blocks to securing your final beam, ensuring your floating deck is both strong and perfectly level.
What Exactly Is a Deck Block?
Before we dive into installation, let’s clarify what we’re working with. A deck block, often called a pier block or a deck foundation block, is a precast concrete footing with a specific shape designed to hold wooden beams or posts. They are not just random concrete blocks; they have a molded top with a saddle or notch that cradles standard dimensional lumber.
The most common design features a square base for stability and a U-shaped or slotted top. This slot is precisely sized to hold a 2×6, 2×8, or 2×10 beam securely in place, preventing lateral movement. Some advanced models even include built-in plastic saddles or adjustable brackets for finer tuning.
The core idea is brilliant in its simplicity. Instead of embedding a post in the ground, you place the block on a prepared gravel base. Your deck’s support beam then sits neatly inside the block’s saddle. The weight of the deck itself pushes down, locking the beam into the block and providing remarkable stability for low-to-the-ground structures.
When Deck Blocks Are the Perfect Choice
Deck blocks excel in specific scenarios. They are the ideal foundation for what’s known as a “floating” or “freestanding” deck. These are decks that are not attached to your house and are typically built less than 30 inches off the ground.
Think of a ground-level patio deck, a platform around a fire pit, or a simple walkout deck from a shed. Because they sit on the ground and can shift slightly with frost heave or soil settlement, they are perfect for blocks, which can be re-leveled if necessary. They are also fantastic for building on uneven or sloped ground, as you can adjust the height of each block with gravel or patio stones.
When to Avoid Using Deck Blocks
It’s crucial to know the limits. Deck blocks are not a substitute for code-approved deep footings in many situations. You should generally avoid them for:
– Decks attached to your house (ledger boards require immovable, frost-proof footings).
– Decks built high off the ground (over 30 inches), where lateral stability becomes critical.
– Areas with very soft, muddy, or unstable soil that cannot support the concentrated load.
– Regions with strict building codes that mandate below-frost-line footings for any permanent structure.
Always check with your local building department before starting. They can tell you if deck blocks are permitted for your project and what the load requirements are.
Gathering Your Tools and Materials
Success starts with preparation. You don’t need a garage full of specialty tools, but having the right equipment will make the job smooth and precise.
For tools, you’ll need a standard set: a shovel, a rake, a 4-foot level, a string line, a tape measure, a carpenter’s pencil, and a circular saw or miter saw for cutting lumber. A hand tamper or a plate compactor is highly recommended for compacting the gravel base. For marking, a can of spray paint is useful for outlining block locations on the ground.
Your material list is straightforward:
– Deck blocks (quantity depends on your deck size and beam span).
– Pressure-treated lumber for your beams (joists) and rim joists (typically 2×6 or 2×8).
– Crushed gravel or stone dust (often called “crusher run”) for the base.
– Landscape fabric (optional but recommended to prevent weed growth).
– Galvanized or stainless steel deck screws or nails for assembly.
– Concrete patio slabs or solid concrete blocks (optional, for building up height on sloped sites).
The Step-by-Step Guide to Installing Deck Blocks
Now for the main event. Follow these steps methodically for a professional-looking, stable foundation.
Prepare the Building Site
Start by clearing the area where your deck will sit. Remove all grass, sod, roots, and large rocks. You want to work on bare, stable soil. For a neat finish and to prevent future weeds, roll out a layer of landscape fabric over the entire area. This fabric allows water to drain while blocking plant growth.
Next, use your string lines and batter boards to mark the exact perimeter of your deck. This outline is your guide for everything that follows. Accuracy here prevents compounding errors later.
Mark and Excavate for Each Block
Your deck’s support beams will run perpendicular to your deck boards. You need to place deck blocks in a grid to support these beams. A common layout is a row of blocks along the outside edges of the deck and additional rows spaced no more than 6 to 8 feet apart for the interior beams.
Using your plan, mark the center point for each deck block on the ground with spray paint. At each mark, dig out a shallow area about 2-3 inches deep and twice the width of the block. This excavation is for your gravel base, not for burying the block.
Create a Solid and Level Gravel Base
This is the most critical step for long-term stability. Fill each excavated hole with 2-3 inches of crushed gravel. Do not use round pea gravel, as it does not compact well and will shift. Use your hand tamper or plate compactor to firmly pack the gravel down. A solid, well-compacted base distributes the deck’s weight and prevents individual blocks from sinking.
After tamping, use a long, straight 2×4 and your level to check that all your gravel pads are roughly even with each other. You don’t need them perfect yet, but they should be in the same general plane.
Set and Level the Blocks
Place a deck block centered on each compacted gravel pad. Now comes the precision work. Run your string lines along the length and width of your deck at the exact height where the top of your beam will sit.
Using a scrap piece of your beam lumber, place it into the saddle of a block. Check its height against the string line. To adjust a block that is too low, lift it and add a little more gravel underneath, then re-tamp. For a block that is too high, you must remove it and take away some gravel. Never shim a deck block with wood; it will rot and create an unstable point.
Work your way around the perimeter, getting all the outside blocks perfectly level with each other and at the correct height. Then, level the interior blocks to the same plane. Use your 4-foot level placed on the scrap beam across multiple blocks to ensure everything is flat and even.
Install the Beams and Frame the Deck
With all blocks perfectly set and level, you can begin framing. Carefully lower your long, pressure-treated beams into the saddles of the blocks. The weight of the beam will help seat it. At this point, you can optionally secure the beam to the block. Some builders use a bead of construction adhesive in the saddle, while others use a metal strap or bracket screwed from the block into the beam side.
Once all primary beams are in place, you can build the rest of your deck frame on top of them. Attach your rim joists and interior joists using standard joist hangers and galvanized fasteners, following your deck plan. The solid, level foundation provided by the blocks makes this framing stage straightforward.
Troubleshooting Common Deck Block Issues
Even with careful planning, you might encounter a few hiccups. Here’s how to solve the most common problems.
Dealing with Sloped or Uneven Ground
If your yard has a slope, you can still use deck blocks. The key is to create level pads at different heights. For a gentle slope, you may simply need to excavate deeper on the high side and add more gravel on the low side.
For a more severe slope, you can “stack” a solid concrete patio slab underneath a deck block to raise it up. Ensure the slab is perfectly level and the block is centered on it. Never stack deck blocks on top of each other, as this creates a dangerous shear point.
What If a Block Sinks Later?
This is the advantage of a floating deck. If you notice a low corner or a wobbly feel after a season, the repair is relatively simple. You will need to temporarily support the deck’s beam near the sinking block using screw jacks or sturdy blocks of wood.
Once the weight is off, lift the deck block out of its saddle. Excavate around it, add more crushed gravel, compact it thoroughly, and reset the block. Lower the deck back onto it. This adjustability is a major benefit over permanent concrete piers.
Preventing Movement and “Bounce”
A deck that feels springy or moves laterally usually points to a framing issue, not the blocks themselves. Ensure your joists are spaced appropriately (16 inches on center is standard) and that you’ve used proper joist hangers at every connection. For added rigidity on longer spans, install solid blocking (bridging) between the joists at the mid-span of the deck.
Also, double-check that your beams are fully seated in the block saddles and, if desired, mechanically fastened. A loose beam can shift and create instability.
Your Path to a Perfect Floating Deck
Using deck blocks demystifies deck building, turning a daunting excavation project into a manageable weekend endeavor. By understanding their purpose, preparing a solid base, and taking the time to level each block meticulously, you create a foundation that will support years of enjoyment.
The process boils down to patience with the leveling stage. Rushing the gravel base and block placement is the single biggest mistake you can make. Invest time there, and the rest of the construction will flow smoothly. Remember to always prioritize safety, consult local codes, and use pressure-treated lumber for all components in contact with the blocks and ground.
Now, with your blocks set and beams secured, you’re ready for the rewarding part: laying down the decking boards and finishing your outdoor living space. Your stable, level, and hassle-free floating deck is just a few more steps away.
