Deck blocks—sometimes called pier blocks or elephant feet—are a favourite for fast, no-dig deck foundations across Canada. But the real debate starts when builders (DIY or pro) must choose: pair them with 4x4 posts, 6x6 posts, or skip deck blocks altogether? This is a critical structural decision that can impact not just the safety and stability of your deck, but also how much ongoing maintenance or re-leveling you'll need to deal with in our freeze-thaw climate.
What Exactly Are Deck Blocks—and What Are They Not?
- Deck blocks are precast concrete bases that spread the weight of your deck into the soil. They make installs quick for floating decks, small platforms, stairs, and sometimes pergolas—without the messy work of digging below the frost line.
- They come in several shapes, but most commonly a pyramid style with slots for wood posts or beams.
- The Deck Block 10x10x7 is our go-to at The Ultimate Deck Shop because it’s sized for both 4x4 and 6x6 posts.
- Deck blocks do not protect against frost heave in cold climates like Saskatchewan, nor do they count as a below-frost foundation for code when decks are attached to a house.
- They aren’t suitable for heavy, high, or permanent structures in most regions.
The Real Differences Between 4x4 and 6x6 Posts
- 4x4 posts (actual dimensions: 3.5" x 3.5") are lighter, cost-effective, and common for small, low deck projects.
- 6x6 posts (actual: 5.5" x 5.5") are much more rigid/durable, and have become the standard on larger, taller, or heavily loaded decks and pergolas.
| Factor | Typical Use for 4x4 on Deck Blocks | Typical Use for 6x6 on Deck Blocks |
|---|---|---|
| Deck Height | Best if 24–30 in or under | Tall decks, 24 in and up; always above 36 in |
| Load | Small, light decks, landings | Larger/heavier decks, pergolas, shade structures |
| Stability | Needs strong bracing, prone to wobble if tall | Much more stable, resists twist and sway |
| Code | Usually allowed for small floating projects | Often recommended or required for structure |
When 4x4 Posts on Deck Blocks Make Total Sense
If you’re building a true floating deck that’s small, low, and lightly loaded, 4x4s are absolutely fine—sometimes even required by code for a minimal footprint. Here’s when we typically recommend it:
- Deck height is no higher than 24 inches above finished grade.
- Deck area is 10 x 10 ft or less, with no hot tub or outdoor kitchen.
- Project is disconnected from the house foundation (not attached by ledger).
- Posts are relatively short (ideally 18–20 inches exposed).
- Lots of lateral bracing (cross bracing or connection to deck framing).
- Local code allows it for floating decks on deck blocks at your project's size and height.
For example, a backyard 8 x 8 ft landing, 18 inches high, with 4x4 posts in Deck Block 10x10x7 units, is a practical and safe choice, especially when paired with proper bracing and blocking.
Red Flags for Using 4x4s:
- Deck exceeds 30 inches in height or covers large areas requiring longer spans.
- You need to support guard (railing) loads of any significant force.
- Posts will support a heavy load (hot tub, kitchen island, etc).
- Structure will see a lot of people or movement.
As soon as one of these is true, we advise moving to 6x6. In many municipalities, it’s a code requirement.
This is Where 6x6 Posts Shine On Deck Blocks
Moving up to 6x6 posts is a big jump in both cost and capability. Here’s what makes 6x6 right on deck blocks:
- The deck is 24–36 inches high or more (but still a floating deck, not attached).
- You’re adding a shade structure or pergola (especially for wind/uplift).
- You want a more solid feeling—less flex, less risk of movement over time.
- Decks larger than 100–120 sq ft, or supporting higher live loads.
For example, a floating 12 x 12 ft deck with a pergola needs 6x6 posts in our Deck Block 10x10x7, placed at corners and midspan, to keep the structure safe and reduce "wobble" over the years.
Choosing the Right Block and Setup: Why Size and Footprint Matter
Not all blocks are created equal—a deck block must be heavy and wide enough to spread loads, accept post sizes, and keep your structure stable in prairie soils.
We often recommend combining a deck block with a large patio stone, like the Keystone Patio Block 24" x 24" x 2", underneath.
This wider pad distributes weight on soft prairie soil, helps fight frost movement, and makes any future re-leveling much easier. Here’s how we do it:
- Excavate a square 26 x 26 in by 3–4 in deep
- Fill with compacted gravel
- Set the Keystone Patio Block
- Drop the deck block squarely in the centre
- Set your 4x4 and 6x6 post
How Many Deck Blocks for 4x4 vs 6x6?
The number of blocks you need is primarily driven by deck size, joist span, and beam span—not by 4x4 or 6x6 choice. But in practice, decks built with 6x6 posts are also heavier and need slightly closer support spacing. For a 12 x 12 ft deck, plan on 6–10 blocks depending on layout and local code.
- Small decks (about 8 x 8 ft): use 6 blocks (corners and midspans).
- Larger decks: add blocks every 4–6 ft along beams and joists.
With 6x6 posts or a top-heavy build like a pergola, additional blocks under beam lines minimize sag and shifting in our freeze-thaw cycles.
When You Shouldn't Use Deck Blocks—4x4 or 6x6 Doesn't Matter
Deck blocks are not the right answer everywhere. If any of the following apply, switch to a proper footing (poured pier, sonotube, or helical pile) below frost line:
- Your deck will be attached to a dwelling (ledgered to house).
- Your municipality or inspector requires below-frost foundations for any structure above a certain height, size, or with a cover.
- You’re in a deep frost region and want permanent, maintenance-free stability.
- You’re supporting extreme loads—hot tubs or outdoor kitchens.
In these cases, post size alone won’t save the project from heaving or shifting, and deck blocks of any size can compromise safety over time.
A Practical Decision Guide: 4x4 vs 6x6 on Deck Blocks
- Deck surface 0–18 in above grade, footprint < 100 sq ft: 4x4s are typically fine.
- Deck 18–30 in, especially with railing: 6x6 is smart.
- Above 30 in or with covers/pergolas or lots of occupancy: 6x6 posts or switch to below-frost footing.
- Heavy clay, wet, or uneven ground: Use more deck blocks, bigger base pads, or consider a different foundation.
How to Make Deck Blocks Work Best (Tips from the Field)
- Use string lines for perfect layout—deck squares are much easier to lay out at ground level before a single post is set.
- Level with a builder’s level, not just a short torpedo level on the block, to avoid cumulative errors.
- Add blocking and bracing for all posts, especially if taller than 2 feet.
- Avoid stacking blocks—instead, build up with framing.
- Place blocks on large patio stones (like the Keystone) over compacted gravel, especially on soft or expansive soils.
- Plan for some maintenance: floating decks on deck blocks in cold climates may shift a little each year—plan to re-level as needed after freeze and thaw. Keep the area clear of organic material to prevent rot and moisture. For a checklist on cleaning, sealing, and inspecting your deck, check our Deck Maintenance resources.
When In Doubt: Ask for Help (And Combine Smarts With the Right Materials)
If you’re balancing budget, size, or site challenges, here’s a quick rule from our years in the business:
- For tiny, low, budget decks: 4x4 posts in Deck Block 10x10x7 units can make perfect sense.
- For almost all backyard decks or pergolas: Scaling up to 6x6 posts feels more professional, is safer, and pays off over years (especially in clay or freeze/thaw soils)
- For anything large, tall, or attached: Upgrade to foundations below frost. Trust us, you want peace of mind when the prairie frost comes!
Resources for Planning and Building Your Deck
Still not sure if your project needs 4x4 or 6x6, or how many deck blocks you should order? At The Ultimate Deck Shop, we’re always happy to walk you through a plan, recommend a material list, or explain the differences for your unique use case—without upselling you on things you don’t need. You can also check out our free online resources, or reach out for a DIY consult.
Ready for more deck foundations advice?
- For step-by-step seasonal and structural care tips, visit our Deck Maintenance Checklist.
- For more on joist protection and waterproofing, read our guide to deck frame protection.
No matter what you build, your deck will thank you for matching the right block, post, and care plan. If you need materials or advice in Regina, Saskatoon, or beyond, stop by The Ultimate Deck Shop to get it right the first time.
