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Anatomy of deck: know the deck structure and surface

Tuesday, January 04, 2022

When installing your own garden deck, it is a good idea to get to know the anatomy of the deck. The deck structure consists of two parts, the under-deck frame, and the deck surface. Where the frame under the deck is also known as the substructure.

Why is it important to understand the overall structure of the deck boards?

Some may ask why it is necessary to understand the different structures of the deck. This is because the individual parts of the deck are important to the overall structure of the deck and can help you make decisions in 4 situations. These 4 situations are.

1. designing a new deck building

2. Inspecting and repairing your outdoor deck boards

3. build a DIY garden deck

4. Get a contractor to build your outdoor deck

composite decking | deck design | top and bottom rails

Deck construction terminology

The structure of a deck has two main parts: the deck substructure and the deck surface. The substructure of the deck acts as the overall support for the deck.

The substructure and the deck surface are describe in more detail below.

Substructure components

The substructure is the framework beneath the deck. It provides safe and secure structural support for the deck. Different deck designs require different substructures.

Traditional deck components are usually constructed from traditional timber, which is susceptible to moisture rot and weathering. It is for this reason that we need to understand the structure of the deck so that we can carry out regular inspections of the deck.


The foundation provides a solid base for the deck and a strong foundation will make your deck safer and last longer. Usually, the best type of foundation is a concrete pillar, which is poured into a hole dug in the ground.

When building a foundation, the bottom of the foundation needs to extend below the frost line to prevent the concrete from shifting when the ground freezes and thaws. It is important to note that the frost line is different in different areas, so the construction of the foundations will depend on the actual situation.

Support columns

As the name suggests, support columns are the framing structures used to support the deck. They are located at ground level and are usually attached to the foundation with metal brackets.

Decks higher than 8 feet or decks built on a slope may require bracing to prevent the support posts from warping and buckling. Always apply to your local building regulations before building a deck board to ensure your deck meets local code requirements.


The crossbeam, also a deck component, supports the deck frame. The crossbeam is installed next to or under the edge joists to support the deck framing. For larger decks, more beams can be installed to provide additional support.

Baffles / Bridging

Bridging provides support for the joists. Baffles, also called bridging, are small blocks of wood fitted between the rim joists. The purpose of the blocking is to prevent the joists from twisting or moving over time.

Baffles are installed between the joists at approximately 4ft to 6ft intervals. Make sure that the joists and baffles are level and in-plane across the top.


The joists are one of the most prominent parts of the deck anatomy and provide structural support for the outdoor deck.  The joists are mounted between the crossbeams, with every two joists usually spaced 12″ to 16″ on center.

The number of joists depends on the size of the deck and how it is designed. Complex herringbone deck patterns, for example, require specific joist spacing and battens to support them.


Metal parts are very important to the structure of your deck anatomy, as it holds the sections in place and makes your deck more secure.

Hardware includes fasteners, joist hangers, and screws that hold your decking components to each other. Using the proper fasteners is vital to the structural integrity of your deck.

Step boards

Step boards serve to connect the deck to the house and secure the deck to your house.

After years of deck use, the step boards may become rotten from moisture or the fasteners may loosen. These problems can cause your deck to detach from your house and cause certain safety issues. An annual deck inspection will allow you to identify problems early and repair them in time to keep your deck safe for use.


Flashing is usually made of L-shaped sheets of metal material and it serves to cover the gap between the siding and the house. This not only helps to protect the deck but also draws water and moisture away from your home.

deck foundation | local building code

Deck surface

Although the appearance of the entire deck anatomy is the deck surface. The deck components of the surface can be customized to suit your own design ideas. When designing your deck you need to take into account design ideas for decking, railings, and stairs to make your outdoor living space more coherent and aesthetically pleasing.


Decking, also known as decorative decking, is the most important part of the deck’s surface structure. There are a variety of different materials, colors, and sizes of decking on the market for you to choose from.

Just like the deck substructure, the surface decking also requires fasteners for secure installation. Different decking boards may require specific types of fasteners.

Railing systems

Although the balustrade system consists of top rails, bottom rails, and infill, all installed between the balustrade posts. The choice of material for the rails and infill varies, allowing you to customize the look of the rails for a unique deck perimeter.

Not every deck floor needs a railing system, railings are usually used on decks where the surface is more than 30 inches above the ground and are intended to ensure people’s safety.

Deck stairs

If your decking boards are of a certain height then you will need to install a staircase. Depending on the height of the deck, your staircase may only have a few steps or it may have a full flight of deck stairs. The higher the deck height, the greater the variety of stair designs. For example a straight staircase or a wrap-around staircase.

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