Anatomy of a Deck: From Substructure to Surface

October 11, 2021
HomeOutdoor Living IdeasAnatomy of a Deck: From Substructure to Surface

The anatomy of a deck includes components both the substructure (framing under the deck) and the deck surface. Each part plays a vital role in the structural integrity of your deck as well as its aesthetics.

Benefits of Understanding Deck Components 


Understanding what the deck components are and why they matter to the overall structure of your deck can help you in several situations, including: 

✓ Designing a new deck 

Inspecting your deck 

✓ Repairing an existing deck 

DIY-ing a deck build 

✓ Working with a contractor to build your deck 

Learn more about the anatomy of a deck, and why each piece is important to the whole. 

Anatomy of a Deck: Terms You Need to Know

The anatomy of a deck has two major parts: the deck substructure and the deck surface. The deck substructure is the frame and structural support for the deck surface. 

Anatomy of a deck labeled image by TimberTech

Within the substructure and deck surface are several individual parts, which include:

Substructure:Deck Surface:
1. Footings 
2. Support posts 
3. Beams 
4. Bridging / blocking 
5. Joists 
6. Hardware 
7. Ledger board 
8. Flashing 
9. Decking  
10. Railing posts 
11. Railing  
12. Stairs 

Substructure Components

Anatomy of a deck Inspecting deck floor joists

The substructure is the framework underneath your deck boards. It provides the structural support your deck needs to be safe and secure. Different deck layouts will require variations in substructure construction.  

Substructure deck components are usually constructed of traditional wood, which is vulnerable to moisture damage and weathering. Because of this, regular inspections of your substructure – and all its components listed below – should be performed at least once a year.  

1.) Footings

Footings provide a solid foundation to help spread the load of your deck over a greater surface area. Typically, the best type of footing is a concrete pillar that is poured into a hole you dig in the ground. In cold climates, the bottom of your footings will need to extend below the frost line, which varies across different areas, to prevent the concrete from shifting as the ground freezes and thaws. 

2.) Support Posts

Support posts are deck components part of the anatomy of a deck

Support Posts Support the Deck Frame

As their name suggests, support posts support the frame of the deck.  

They are typically attached to the tops of footings with metal brackets and sit above grade (ground-level).

Taller decks (taller than 8’) or those built over a slope may require bracing to keep the support posts from buckling under the load. Always check with your local building code department to ensure you’re adhering to your local code requirements.  

3.) Beams

Beams, also called girders, are deck components that support the frame of the deck. Beams are installed alongside the rim joists (joists at the perimeter) or below the joists to support the frame of the deck. For larger decks, more beams may be installed intermittently for extra support. 

4.) Blocking / Bridging   

Anatomy of a deck includes blocking

Blocking Provides Support to Joists 

Blocking, also called bridging, refers to the small blocks of wood installed between the joists. Blocking is essential to the anatomy of a deck as it prevents twisting or movement of the joists over time.  

Blocking should be installed about every 4’ to 6’ in between joists. Always make sure joists and blocking are level and in plane across the tops.  

5.) Joists

Joists are one of the most prominent parts of the anatomy of a deck as provide structural support to your deck floor. Joists are installed between beams and are typically spaced at 16” on center, but can be spaced 12” for a sturdier foot feel.  

IMPORTANT
Always refer to the installation guide for your chosen decking line for joist spacing and spanning guidance as different materials may have different requirements. GET INSTALLATION GUIDANCE 

The number of joists your deck will depend on the size of your deck and how the deck boards are arranged on the surface. For example, deck patterns, such as a herringbone pattern, will require specific joist spacing and blocking to support the intricate pattern.   

Create a Look All Your Own 

Explore deck patterns to inspire your design.  

6.) Hardware

Hardware is just as important to the anatomy of a deck as the boards that make up the frame.  

TimberTech deck building TOPLoc fastener installation

Hardware Keeps Your Deck Secure

Hardware pieces include the fastenersjoist hangers, and screws that secure your deck components to one another. Using the proper fasteners is essential for your deck’s structural integrity.  

7.) Ledger Board

The anatomy of a deck includes the ledger board

Connecting Deck to House

The ledger board is a piece of wood that secures the deck to your house, making it an essential part of the anatomy of a deck.  

Over time, potential issues such as rot in the ledger board or loose fasteners can cause your deck to pull away from your home, putting its structural integrity at risk. Annual deck inspections can help catch any issues early and prevent a full-fledged deck replacement.  

8.) Flashing

Flashing is often made of L-shaped sheets of stainless steel or vinyl that fit over the ledger to cover the gap between the ledger board and your home. Flashing not only helps protect the ledger board, but also channels water and moisture away from your home. For added protection against water damage, you can apply deck joist flashing tape to the top of your ledger board as well as your joists.  

Joist tape protects deck components of your substructure

Protect Your Substructure With Flashing Tape

Deck joist flashing tape, can be used on both your ledger board and the tops of the joists to keep moisture from penetrating your deck’s frame.  

PRO TIP
Apply deck joist flashing tape to the tops of your joists and ledger board to help protect your substructure from water damage. LEARN ABOUT JOIST TAPE 

Deck Surface

Anatomy of a deck includes deck components of the surface

The deck components of the surface refer to the visible parts of your build — most of which you can customize to suit your taste. When designing your deck, keep the overall look and feel you want to achieve in mind as you think through your deckingrailing, and stair designs. The combination of all these elements will create the aesthetic — and contribute to the atmosphere — of your outdoor living space. 

The anatomy of a deck and deck components depend on deck shape

Explore Curated Deck Designs 

Take a virtual 3D tour of completed deck builds for inspiration into how you can combine deck surface components to create a unique look and feel. 

9.) Decking

Decking refers to your deck boards, the most prominent part of the anatomy of a deck surface. Deck boards come in a wide variety of different materialscolors, and sizes.  

Anatomy of a deck includes the stairs

Decking Boards 101 

Need help deciding which decking boards are right for your style and build? 

Just like your substructure, decking will require fasteners for secure installation. Different deck board profiles (such as grooved boards) may only work with certain types of fasteners

Deck Board & Fastener Combinations 

Looking for a cheat-sheet of board and fastener pairings? Check out these projects from our Deck Building Resource Center for easy combinations.  

TOPLoc top-down fastener application with a drill

TimberTech® AZEK® With TOPLoc®

TOPLoc fasteners are color-matched screws that complement your deck color, giving you a blended-in look.  

Cortex hidden fastener application with plastic-tipped hammer

TimberTech AZEK With Cortex®

Cortex screws are hidden by collated plugs made of TimberTech AZEK decking for a seamless, polished surface.  

CONCEALoc hidden clip fastener application with a drill

TimberTech PRO®& EDGE® With CONCEALoc®

CONCEALoc Hidden Fasteners are clips that are installed between grooved boards for a fastener-free surface.  

10.) Railing Posts

Railing posts are typically made of 4” x 4” wood posts that are securely fastened to the frame or deck surface, depending on installation best practices. Depending on the style of your deck railing, wood posts can be covered by decorative composite post sleeves that give it a clean finish and help prevent moisture damage. Or you can opt for sleek aluminum posts which are narrower, giving you a more minimalist look.   

11.) Railing

A railing system includes the top rail, bottom rail, and infill (the section between the top and bottom rails) which are all installed between the posts. Material options for your rails and infills vary, allowing you to customize the look of your railing for a unique deck perimeter.  

Anatomy of a deck includes deck components like the railing

Does My Deck Require Railing? 

Railing is typically required for decks with a surface higher than 30” off the ground, but this can vary depending on your local building codes.  

As an element central to safety as well as design, proper installation of your railing is vital. Work with a contractor if you don’t feel confident installing a railing yourself

12.) Stairs

Stairs get you from your deck to your lawn or patio. Depending on your deck height, you may have only one to two steps, or a whole flight of stairs. Your deck height and shape play important roles in your deck stairs design, which can vary from straight stairs to wraparound stairs, and more. Before deciding on a stairs design, be sure to consult local building codes to ensure your design is compliant.  

Looking to Visualize Your Deck Design?

Use our 3D Deck Design Tool to play with deck height, shape, board color, and more.

Get Started Planning Your Deck Project 

Now that you understand the deck components that make up the anatomy of a deck, you’re ready to start planning for your build. Dive into our Deck Building Resource Center to get guidance on every step of the deck building process, from design to decking installation. Plus, watch helpful how-to videos that show you exactly what to expect for your build.  

Get the DIY Insight to Do Your Project Right

Dive into our Deck Building Resource Center for easy-to-follow tips, guided install videos, and more.

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