Deck Blocks vs Poured Concrete Footings

Deck blocks — precast concrete blocks with a notch or cup on top — let you build a floating deck on grade without digging holes or pouring concrete. They are legal and common in many jurisdictions, but they come with important limitations.

What is a floating deck?

A floating deck is a freestanding deck that is not attached to the house and does not have footings that extend below the frost line. It sits on top of the ground on deck blocks or crushed stone pads. Because it is not connected to the house structure, it shifts slightly with frost and seasonal soil movement — and that is acceptable, because there is nothing attached to prevent it.

When deck blocks are permitted

Deck blocks are typically permitted for: low-to-grade decks (usually within 30 inches of grade) that are freestanding (not attached to the house ledger), used for non-primary structures, and in jurisdictions with minimal frost depth requirements. Many jurisdictions allow deck blocks for decks below a certain size or height without a permit — confirm with your local building department before starting.

When deck blocks are not enough

• Attached decks must have footings below the frost line — if the deck moves, the house moves with it.
• Any deck tall enough to require a permit usually requires below-frost footings.
• Decks supporting a roof, pergola or any overhead structure need poured footings.
• Sites with poor drainage, expansive soils or high water tables need engineered footings.

Deck block installation

Compact the soil under each block location, add a 2-inch base of crushed gravel for drainage, and set each block level. Snap a chalk line across the tops of the blocks; shim with patio block shims to achieve level. Don't put deck blocks on organic soil or mulch — they will settle unevenly.