How to Tell if a Deck is Built Correctly: A Homeowner’s Guide

A well-built deck not only enhances your outdoor space but also ensures the safety and longevity of the structure. Whether you’re checking your existing deck or evaluating a new one, understanding the key components of proper deck construction is essential. This guide outlines general principles to help you assess if a deck is built correctly. While these tips cover the basics, it’s always best to consult a professional for a thorough inspection and to confirm compliance with local building codes.

1. The Ledger Board: The Foundation of Attachment

The ledger board is the critical component that connects your deck to your house. It must be installed correctly to ensure the entire deck’s stability.

Proper Attachment

• The ledger board should be fastened to the house using carriage bolts or ledger locks:

  • Carriage bolts: Heavy-duty bolts that provide exceptional holding power.

  • Ledger locks: Specialized screws designed specifically for securing ledger boards, offering equal strength and easier installation.

    
    

Fastener Spacing

• Maximum spacing: 16 inches on center, staggered in a zig-zag pattern.

• Preferred spacing: 8 inches on center for maximum security.

• Placement: Fasteners must be at least 2 inches from the top and bottom edges of the ledger board to avoid splitting.

  
  

Check for Flashing

• What is Flashing?: Flashing is an L-shaped material (aluminum or plastic) installed behind the siding and over the top of the ledger board.

• Purpose: Flashing prevents water from seeping into the house framing. Without it, water can cause rot in the band board and other structural components, leading to expensive repairs.

2. Joist Spacing: Floor Support

Joists are horizontal beams that support the deck floor, and proper spacing is essential for structural integrity.

• 16 Inches on Center: This is the standard spacing for most decking materials.

  
  

• 12 Inches on Center: Required for scalloped composite decking, which has hollowed-out sections on the underside and is less rigid than full-profile composite decking.

  
  

• Full-Profile Composite Decking: Solid composite boards can handle the standard 16-inch spacing, but 12-inch spacing is often preferred for added durability.

3. Beam Construction and Placement

Beams carry the load of the deck and transfer it to the vertical posts. Proper beam construction and placement are critical to a well-built deck.

Beam Design

• Two-Ply Beams: A beam should consist of two pieces of lumber (e.g., two 2x10s) nailed together for strength.

Beam Placement

• Notched 6x6 Posts: The beam should sit on top of notched 6x6 posts.

  
  

  • Why Notch the Posts?:

    • The notch provides a flat surface for the beam to rest on and additional support from the backside.

    • A notched post ensures the beam is securely anchored to the structure.

      
      

Why Avoid 4x4 Posts?

• Weakness: 4x4 posts are prone to warping, twisting, and splitting.

• Lack of Material for Notching: 4x4 posts don’t provide enough material to

  properly notch and securely hold a beam.

4. Proper Post Installation

Vertical posts are the foundation of your deck, and their installation plays a vital role in its stability and longevity.

Elevated Post Bases

• Posts should sit inside elevated post bases, which:

  
  

  • Anchor the Deck: Post bases are secured to concrete piers with anchor bolts, ensuring the structure is firmly attached.

  • Prevent Rot: Elevating the post keeps it off the concrete, preventing water from pooling and causing rot.

  
  

Avoid Posts Embedded in Concrete

• Posts buried directly in concrete are highly prone to rot. Water can seep into the crevices, stay trapped, and cause the wood to decay prematurely.

Final Thoughts

Inspecting a deck to determine if it’s built correctly requires attention to detail and a solid understanding of proper construction techniques. Start by evaluating the ledger board, joists, beams, and posts for compliance with these principles. Keep in mind that building codes vary by region, especially in areas with heavy snow loads, so always refer to local requirements for joist and beam spans. If you notice anything concerning or are unsure about your deck’s construction, consult a professional for a thorough inspection.

A well-built deck is a safe deck—and with these guidelines, you’ll know what to look for.