When building a deck, one of the most important considerations is how far apart to space the deck blocks that will support the decking boards. Proper deck block spacing is crucial for ensuring a safe, sturdy, and long-lasting deck. In this comprehensive guide, we will discuss the key factors to consider when determining deck block spacing, provide deck block spacing recommendations, and outline best practices for block layout.
What are Deck Blocks?
Deck blocks, also known as deck piers or footings, are structural supports that bear the weight of the deck. They transfer the load from the deck boards and framing down through the blocks into the ground. Deck blocks are designed to sit on the ground or surface below the deck and are made from concrete, plastic, or metal. Concrete deck blocks are the most common type.
Key Factors That Determine Deck Block Spacing
There are several important considerations when figuring out deck block spacing:
- Deck size and configuration – Larger decks and multi-level decks require closer spacing between blocks.
- Deck height – The higher off the ground the deck sits, the closer together the blocks should be.
- Type of decking material – Heavier decking like composite boards needs closer support than lighter woods.
- Amount of weight on deck – Decks built for hot tubs or crowded parties need tighter block spacing.
- Soil conditions – Weak or sandy soil requires closer block spacing than hard, compacted soil.
- Local building codes – Many areas have specific regulations for deck block spacing.
Recommended Deck Block Spacing
While deck block spacing can vary based on the factors above, there are some general recommended guidelines to follow:
For Low Decks (Less than 18 inches off ground)
- Maximum spacing on center: 8 feet
- Typical spacing on center: 6-7 feet
For Medium Decks (18 inches – 3 feet off ground)
- Maximum spacing on center: 6 feet
- Typical spacing on center: 4-5 feet
For High Decks (Over 3 feet off ground)
- Maximum spacing on center: 4 feet
- Typical spacing on center: 3-4 feet
For heavily loaded decks or weak soil conditions, closer block spacing is better. When in doubt, err on the side of extra blocks for maximum stability.
Best Practices for Deck Block Layout
Properly laying out the deck blocks is just as important as the spacing. Here are some key best practices to follow:
- Check local building codes for any deck block requirements.
- Space blocks evenly under all decking joists, not just perimeter joists.
- Align blocks properly under joists – don’t offset or stagger blocks.
- Use additional blocks under high load areas like stairs or hot tubs.
- Space blocks closer near ledger boards attached to structures.
- Use diagonal bracing blocks on very tall or heavily loaded decks.
- Cap all wood posts with deck blocks to spread load.
- Dig holes for blocks on loose soil to prevent shifting.
- Level and adjust blocks to keep deck surface even.
Deck Block Spacing for Specific Deck Types
Beyond the general spacing guidelines, block placement can vary for different deck designs.
Floating Deck Block Spacing
Floating decks are not attached to a structure and bear all their weight on the blocks. This requires closer block spacing:
- Maximum spacing: 4 feet on center
- Typical spacing: 2-3 feet on center
Attached Deck Block Spacing
Attached decks are connected to a structure like a house. The ledger board connection allows slightly wider spacing:
- Maximum spacing: 6 feet on center
- Typical spacing: 4-5 feet on center
Multi-level Deck Block Spacing
Multi-level decks should have tighter block spacing to support multiple structures:
- Maximum spacing: 4 feet on center
- Typical spacing: 2-3 feet on center
Octagon Deck Block Spacing
Octagon decks need evenly spaced blocks around the perimeter and interior:
- Maximum perimeter spacing: 3 feet on center
- Maximum interior spacing: 4 feet on center
Deck Block Spacing Code Requirements
Most areas adhere to building codes that dictate proper deck block installation. Common code requirements include:
- Maximum spacing between blocks – often 6-8 feet.
- Minimum block pier size – typically a 10″ x 10″ pad.
- Minimum depth below frost line – 12-24 inches deep.
- Concrete block minimum strength – often at least 2500 PSI.
- Proper cap plate installation on wood posts.
Always check your local building codes before construction to ensure your deck blocks meet all spacing and sizing requirements.
Choosing the Right Size Deck Blocks
Deck blocks come in a range of sizes and capacity ratings. Use these guidelines when selecting deck blocks:
- Small Decks – 12″ x 12″ x 4″ blocks rated at 1500-2000 lbs.
- Medium Decks – 16″ x 16″ x 4″ blocks rated at 4000 lbs.
- Large or Multi-level Decks – 20″ x 20″ x 4″ blocks rated over 5000 lbs.
Bigger blocks provide more load bearing support. For heavy loads, use tall blocks or stack blocks to disperse weight.
Deck Block Installation Process
Installing deck blocks properly is critical. Follow this process for each block:
- Dig hole 12-24 inches below frost line.
- Fill bottom 2 inches with gravel for drainage.
- Place block, level, and adjust height as needed.
- Backfill around block with compacted soil or gravel.
- Check level on multiple sides before moving on.
Taking care during block installation prevents shifting, sagging, and safety issues down the road.
Alternatives to Traditional Deck Blocks
Beyond basic deck blocks, there are a few other options:
Metal Pedestal Systems
Metal pedestals can be adjusted and spaced like blocks and provide great versatility. They can be more expensive but are very sturdy and long-lasting.
Deep Foundation Supports
For weak soils, helical piles screwed deep into the ground or poured concrete piers can provide stability and allow wider deck block spacing on top.
Floating Footings
Floating footings are pre-formed concrete pads that sit on the soil instead of being dug in. They simplify installation but may shift more easily.
Conclusion
Determining deck block spacing relies on the size, height, location, and use of the deck. Follow the recommendations in this guide based on your specific deck design needs. Adhering to proper deck block installation practices and meeting code requirements will result in a safe, enjoyable deck that stands the test of time.
