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The biggest risk of using deck blocks is movement beneath the deck. Surface-set concrete blocks may seem like a quick, inexpensive foundation, but Minnesota’s freeze-thaw cycles, shifting soil, and drainage conditions can cause individual supports to settle or heave. That movement can leave a deck uneven or strain its framing and connections. At UglyDeck, we encourage homeowners planning a permanent deck to evaluate properly designed footings—such as poured concrete, helical piers, or an approved proprietary system—rather than assume deck blocks will work for every project. Deck blocks can still be appropriate for certain small, low, freestanding decks where local requirements allow them. Below, we explain the main failure risks and how to choose a suitable foundation.
What Are Deck Blocks?
Deck blocks, also known as pier blocks, are precast concrete blocks designed to provide a simple base for decks. They eliminate the need for digging holes and pouring concrete footings. Essentially, deck blocks are set directly on the ground, and the deck’s posts rest on top of them. This method is often advertised as a quicker and more affordable option compared to traditional footings.
The Appeal of Deck Blocks
For many, the appeal of deck blocks lies in their simplicity. They are readily available at most home improvement stores and don’t require specialized skills or heavy equipment to install. This makes them a popular choice among DIYers looking to save time and money on their deck projects.
The Risks of Using Deck Blocks
Despite their allure, deck blocks come with several risks that can compromise the integrity and safety of your deck.
Stability Issues
One of the most significant concerns with deck blocks is stability. Since they sit directly on the ground, they are susceptible to shifting due to soil movement, freeze-thaw cycles, and erosion. This can lead to an uneven deck surface, structural weaknesses, and, in the worst cases, collapse.
Weight Limitations
Deck blocks have manufacturer-specific load and installation limits. The size of a post alone does not determine whether a foundation is adequate: deck loads, block bearing area, soil capacity, connections, and the approved design all matter. A hot tub, elevated deck, or other heavily loaded structure needs a foundation designed for those loads, not an assumed deck-block capacity.
Code Compliance
Many local building codes have specific requirements for deck foundations. Deck blocks may not meet these regulations, leading to potential legal and safety issues. Ensuring compliance with local codes is crucial to avoid fines and ensure the safety of your deck.
Alternatives to Deck Blocks
Fortunately, there are safer and more reliable alternatives to using deck blocks, each offering greater stability and support.
Concrete Footings
Concrete footings are the traditional choice for deck foundations. Although they require more effort and resources to install, they provide a stable, durable base that can support heavy loads. By digging holes below the frost line and filling them with concrete, you create a solid footing that minimizes the risk of shifting and settling.
Helical Piers
Helical piers are an innovative alternative that offers the benefits of concrete footings with easier installation. These screw-like steel rods are driven into the ground, providing strong support without the need for extensive digging. They are especially useful in areas with difficult soil conditions.
Diamond Pier Foundation System
Diamond Pier is a proprietary precast concrete footing system that uses driven steel pins to transfer loads into the soil. It can reduce excavation for some projects, but its suitability depends on the specific product, soil conditions, structural loads, and acceptance by the local building department.
How Deck Block Failures Can Happen
For example, a low deck supported by surface-set blocks may initially appear level. If the soil beneath one block settles, washes away, or heaves during freezing weather, that support can shift relative to the others. The result may be uneven framing, movement, or costly corrective work. This is an illustrative failure scenario, not a documented UglyDeck customer case.
The Cost of Cutting Corners
While deck blocks might seem like a cost-effective option upfront, the potential for failure can lead to expensive repairs and replacements. Investing in a more reliable foundation from the start can save you money and stress in the long run.
Ensuring a Successful Deck Project
To ensure the success of your deck project, consider the following tips:
Plan Thoroughly
Before starting your project, take the time to plan carefully. Consider the size, weight, and intended use of your deck. Consult local building codes to ensure compliance and obtain any necessary permits.
Choose the Right Foundation
Select a foundation method that suits your deck’s requirements and your local soil conditions. While deck blocks may seem appealing, investing in a more stable foundation like concrete footings or helical piers will pay off in the long run.
Seek Professional Advice
If you’re unsure about the best foundation for your deck, consult with a professional. They can assess your specific situation and recommend the most suitable option. Their expertise can help you avoid costly mistakes and ensure a safe, durable deck.
Consider Hiring UglyDeck.com to Install Your Footings For You
Want to build your own deck without tackling the foundation alone? With UglyDeck’s DIY assistance options, Twin Cities homeowners can get help with qualifying footing, ledger, and framing work, then take on the remaining steps themselves. It’s a practical way to keep the hands-on DIY experience while getting professional help with critical structural work.
Explore UglyDeck DIY Assistance
For related guidance, see Are Deck Blocks a Good Idea? for a balanced comparison, or How to Use Concrete Deck Blocks for appropriate installation considerations.
Conclusion
While deck blocks might seem like a convenient solution for your deck project, the potential risks far outweigh the benefits. Stability issues, weight limitations, and code compliance challenges make them a less-than-ideal choice, especially for supporting larger structures like 6×6 posts. By opting for more reliable foundation methods like concrete footings, helical piers, or the Diamond Pier system, you can ensure the safety and longevity of your deck. So, before you embark on your next deck-building adventure, consider the long-term implications and make an informed choice that will enhance your outdoor living space for years to come.
