What Is Blocking?
Blocking is short, solid framing installed between joists or other structural members to add support, keep materials aligned, or provide a firm attachment point. On a deck, blocking can stiffen the frame, support board ends, and help secure rail posts or other components where a single joist does not provide enough fastening space.
Quick Facts About Blocking
Category
Framing component
Used for
Support and attachment
Common confusion
Not a joist
Also called
Nailers, Cross-blocking
Often discussed with
Deck Construction
Key Takeaways About Blocking
- Blocking sits between framing members instead of spanning the full frame.
- It can stiffen a deck and support fasteners.
- Blocking is not the same as a joist.
How Blocking Works
Blocking works as a short piece of framing fitted between joists, beams, or other members. The pieces are cut to fit tightly, then fastened so they stay in place. Their position gives the frame extra support and creates a solid surface for screws or bolts.
Related glossary terms: Deck Ledger, Framing, Joist.
On a deck, blocking may sit between joists below a board seam. It can also sit where a guard post or stair connection needs more material behind the fastener. Joists carry the main span of the deck, while blocking supports nearby connections and limits movement. Proper layout keeps blocking flush and avoids conflicts with drainage or other deck parts.
Expert Note
When we build a deck frame, we place blocking where plans call for added stiffness or a secure fastening point. We check each piece for a tight fit, proper alignment, and solid connections before covering the frame with decking.
Blocking in Practice: A Real-World Example
A deck railing post lands beside a joist instead of directly over it. We add blocking between nearby joists so the post fasteners have solid wood behind them.
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