Building A Timber Decking Joist Sub Frame

Gone are the days when homeowners needed to hire a deck builder before they could enjoy the benefits of a nice deck on their property. This change is due to the availability of easy-to-use decking kits in stores or online and articles like this that direct homeowners on the steps to building a deck in their homes. 

The first step involves planning and preparing the area where the deck will be installed. This is done by identifying the space where the deck will be situated, clearing the area of objects that can obstruct the deck’s installation, and taking accurate measurements based on the deck size the homeowner desires. 

The next step is identifying the primary components that make up a deck and their functions. These components include: 

  • Joists: These are the pieces of timber laid down where the decking boards will be attached.
  • Joist frame: This is the structure that encompasses the joists.
  • Decking board: This is the board laid horizontally on the joists. It is for constructing the deck’s floor.
  • Balustrades and railings: They are used to barricade the deck.

This article will highlight the importance of joist subframes or joist frames and the steps to building a timber decking joist subframe. 

Importance of a Timber Decking Joist Sub Frame

There are specific reasons a joist subframe needs to be constructed when building a deck. These reasons include:

  1. Joist sub-frames provide a structurally sound frame for installing joists.
  2. Sub-frames provide an elevated structure for timber used in building decks. This is because not all classes of timbers can be laid directly on the ground without being damaged by specific factors like termites or water. The class of timber that can be laid directly on the ground are timbers belonging to Class-4.
  3. The joists are laid horizontally in a lateral pattern; thus, joist sub-frames offer lateral rigidity for joists.
  4. The structure provided by joist sub-frames prevents joists from sagging over time.

Steps for Building a Timber Decking Joist Sub Frame

There are specific steps to guide any homeowner when building a timber decking joist subframe. These steps include:

  1. Get the desired angle or gradient you want to lay the decking boards to facilitate proper water drainage. A gradient is essential if the homeowner intends to groove the decking boards.
  2. Lay the decking boards horizontally on the measured gradient.
  3. Construct a joist raft that will sit on the drainage oversite (inclined decking boards from above). This procedure is particular to ground-level decks
  4. Mount lightweight metal connectors/mini joist hangers at the elevated point of the inclined decking boards.
  5. Use noggins/connecting timber between each joist to give extra subframe rigidity.
  6. Install newel posts on/around the joist subframe depending on preference.
  7. Fit the base and top rail between the newel posts with the top rail 900mm above the base rail.
  8. Use infills to space the railing spindles 120mm apart.


After building and installing the joist subframes for your deck, the next step is caring for and maintaining the deck. Hence, it is essential that before installing a deck in a home, the homeowner knows what is involved in caring for a deck, especially timber decking.

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