Leslie Massey
When building a deck, it is important to consider the size of the bearers and joists to ensure the structure is stable and durable. Decking bearers and joists form the backbone of the deck, providing support and distributing weight. The size of the bearers and joists will depend on factors such as the span between supports, the type of timber used, and the load requirements of the deck. In Australia, timber is a popular material for construction due to its functionality, sustainability, and health benefits. When selecting the appropriate size of bearers and joists for a deck, it is crucial to refer to span tables, local regulations, and proper installation techniques to ensure the safety and longevity of the outdoor structure.
| Characteristics | Values |
|---|---|
| Bearer and joist size | Determined by how far they need to span between supports |
| Bearer size | Calculated based on the floor load width and post spacing |
| Joist size | Calculated based on the spacing between joists |
| Bearer and joist spacing | Based on the size and load requirements of the deck; improper spacing can compromise structural integrity |
| Bearer and joist material | H3 treated pine framing is recommended for protection against termites and fungal attack |
| Joist spacing | 450mm is commonly used as it provides ample support; 400mm spacing can be used with clear treated pine due to its flexibility |
| Bearer and joist function | Provide stability and longevity to the deck by distributing weight and load |
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What You'll Learn
- Bearer and joist size is determined by how far they need to span between supports
- Use timber span tables to determine bearer and joist size
- Use H3 treated pine framing for bearers and joists
- Bearer and joist spacing is important for structural integrity
- Bearer and joist spacing facilitates proper drainage
Bearer and joist size is determined by how far they need to span between supports
When building a deck, it is important to select the correct bearer and joist sizes to ensure the safety and longevity of your structure. The size of bearers and joists is determined by how far they need to span between supports, with the required size increasing as the distance between supports increases. This is because longer spans require stronger and larger materials to bear the weight and maintain structural integrity.
Span tables are an excellent tool to determine the required bearer and joist sizes based on the width of the span and the anticipated load. These tables provide guidance on the appropriate member sizes, ensuring the structure meets building safety standards. The Australian Standards provide span tables that are specifically designed for decking applications, taking into account the unique considerations of outdoor construction.
The type of timber used for bearers and joists also plays a crucial role in determining the required size. Treated pine is a popular option for outdoor decks due to its affordability and resistance to rot and termites. However, hardwood options like spotted gum or ironbark offer greater durability and strength, providing better protection from the elements. The choice of timber should consider the specific environmental factors and load requirements of the deck.
In addition to the span and load, the thickness of the flooring joists depends on what is placed on top of them. For example, joists below end-matched joints must be at least 35mm thick to support the weight of the flooring adequately. It is important to consult the relevant Australian Standards or online calculators to determine the appropriate thickness and size for your specific application.
The spacing of the bearers and joists is another critical factor in ensuring the structural integrity of your deck. The spacing will depend on the size of the members used and the span of the bearers and joists. The Australian Standards provide guidelines for the maximum spacing of bearers and joists to ensure optimal safety and performance. Correct calculations of the stiffness and strength of the internal timbers are vital, as the load placed on a deck can sometimes be very large.
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Use timber span tables to determine bearer and joist size
Timber span tables are a crucial tool for determining the appropriate bearer and joist sizes for your deck. These tables outline the maximum span distances for different types of timber, ensuring your deck's structural integrity and safety. Here's a step-by-step guide on how to use timber span tables effectively:
Step 1: Understand the Key Components of a Deck
Before delving into span tables, it's essential to grasp the fundamental elements of a deck. Bearers and joists are the primary structural components. Bearers are horizontal supports that rest on posts or pedestals and bear the weight of the joists above. Joists, in turn, are horizontal members that support the decking boards.
Step 2: Refer to the Correct Span Table
When determining bearer size, use the bearer span table, and for joist size, refer to the joist span table. These tables will indicate the maximum span distance for each type of timber.
Step 3: Check Timber Material and Grade
Identify the specific timber you plan to use, including its grade. Common timber grades include MGP10, F7 hardwood, or LVL (Laminated Veneer Lumber). Ensure the timber grade specified in the span table matches your chosen material.
Step 4: Find the Timber Size
Locate the size of the timber you intend to use in the span table. For instance, you might be using 140x45mm timber. This dimension is crucial for determining the appropriate span distance.
Step 5: Determine Span Distance
Using the bearer span table, find the maximum span distance for your chosen timber size. This value indicates how far a bearer can span between supports. Similarly, for joists, refer to the joist span table to determine the maximum span distance between bearers.
Step 6: Ensure Adequate Support Spacing
Check that your selected timber will be supported within the allowable span distance specified in the table. If you require longer spans, consider increasing the calibre of timber or opting for hardwood, which can typically span greater distances.
Step 7: Calculate Floor Load Width
To establish the required bearer size and post spacing, calculate the floor load width. This calculation depends on the size of the deck you plan to build. For example, a deck that is 1 metre wide and 10 metres long will have a different floor load width than a smaller deck.
Step 8: Consider Continuous Span Bearers
If your deck has bearers supported at more than two points along their length, they are considered continuous span bearers. This design is common for longer decks and requires careful calculation of bearer size and post spacing.
Step 9: Consult Local Regulations
Remember to check with your local council before commencing any construction. There may be specific regulations or standards, such as BAL ratings in bushfire-prone areas, that you must adhere to when building your deck.
By following these steps and referring to timber span tables, you can confidently determine the appropriate bearer and joist sizes for your deck, ensuring a safe and sturdy structure.
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Use H3 treated pine framing for bearers and joists
When building a deck, it is important to consider the materials used for the bearers and joists, as these provide the foundation and support for the entire structure. One option for Australian decks is to use H3 treated pine framing for the bearers and joists.
H3 treated pine is a type of timber that has been treated with preservatives and kiln-dried to enhance its durability. The "H" in H3 stands for "hazard," indicating the level of treatment required to protect the timber from various hazards. In this case, H3 is suitable for above-ground applications, providing protection against insect damage, decay, and fungi attacks. This treatment is particularly effective in preventing termite infestations, which is a common issue with timber structures in Australia.
Using H3 treated pine for your deck's bearers and joists offers several advantages. Firstly, it is a cost-effective option compared to other types of timber. Secondly, it provides long-term resistance to decay, ensuring that your deck remains solid and maintenance-free for many years. Additionally, H3 treated pine is easy to work with, especially if it is kiln-dried and laser-cut. This makes it a popular choice among builders and homeowners.
When using H3 treated pine for your bearers and joists, it is important to follow the span tables provided by timber suppliers. These tables specify the required size of the bearers and joists based on the length and width of your deck. For example, a deck that is 1 metre long and 1 metre wide may only require two bearers, one on each side. However, a longer deck, such as one that is 10 metres long and 6 metres wide, will need additional bearers and stumps for support.
In summary, using H3 treated pine framing for your deck's bearers and joists can be a durable, cost-effective, and practical choice. It provides protection against insects and decay, ensuring the long-term stability of your deck. However, it is important to follow the recommended span tables and seek advice from experienced builders or designers to ensure the structural integrity of your deck.
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Bearer and joist spacing is important for structural integrity
When building a deck, it's important to consider the size and spacing of your bearers and joists to ensure the structural integrity of your deck.
The size and spacing of your bearers and joists will depend on the load they need to support. The load put onto your deck can be very large, so correct calculations of the stiffness and strength of the internal timbers of your deck are essential.
For example, if you're using 190x45 bearers, you'll require posts every 2.1 metres along a 10-metre-long deck. This will result in a total of 6 posts per bearer. Alternatively, you can use 190x70 bearers, which will need a post every 2.6 metres (5 posts per bearer). The spacing between the floor bearers should not exceed 1.8 metres, and the maximum span of the floor bearer should not exceed 3.6 metres.
The spacing between your joists is also important. At Softwoods, they use 450mm spacing as a default as it provides ample support in almost all uses. They also use 400mm spacings with clear-treated pine as it is slightly more flexible than other decking materials.
Properly installed and spaced bearers and joists ensure the deck can safely accommodate loads without sagging or collapsing.
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Bearer and joist spacing facilitates proper drainage
When building a deck, it's important to consider the spacing of your bearers and joists not only for structural integrity but also for proper drainage. Drainage and drying are critical functions of deck board spacing. The bearers and joists are the foundational framework that supports the deck, and their spacing determines how water flows through the deck.
The required size of your bearers and joists is determined by how far they need to span between supports. A continuous span bearer is supported at more than two points along its length. For example, a 1-metre long and 1-metre wide deck will likely have two bearers, one on each side, and will be considered single span as each bearer is only supported at its ends. On the other hand, a 1-metre wide and 10-metre long deck will still have two bearers running the length of the structure but will need support along the 10-metre length, making it a continuous span.
The spacing of your joists is critical to ensuring your deck's structural integrity, long-term stability, and durability. Joists support the decking boards and distribute the load evenly across the frame, preventing sagging and structural failure. The optimal spacing between decking joists depends on several factors, including the type of decking material, the anticipated load, and local building regulations. For traditional decking materials like timber or composite boards, a typical maximum joist spacing of 16 inches (40.6 cm) on-centre is common.
Deck joist spacing is typically 16 inches (40.6 cm) apart on centre, but this can vary depending on the decking material and manufacturer's guidelines. For thicker or heavier decking materials or environments with significant loads, spacing can be reduced to 12 inches (30.5 cm) on-centre. For thinner or lighter decking materials, such as PVC or aluminium, spacing can be increased to 24 inches (61 cm) on-centre or even higher. Proper planning and consideration of environmental conditions such as moisture levels can help mitigate potential issues like wood expansion and contraction, ensuring your deck's longevity and proper drainage.
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Frequently asked questions
The required size of bearers and joists depends on how far they need to span between supports. The load that you put onto your deck should also be considered since it determines the stiffness and strength of the internal timbers.
For a low-level deck, you can use 90 x 45mm Pine timber for bearers or joists if they are supported every 1000mm.
If you want the supports further apart, you need to increase the calibre of the timber as per span tables. You can also swap to hardwood to extend the distance that the calibre of timber can span.
At Softwoods, 450mm spacing is used as a default since it provides ample support in almost all uses. 400mm spacing is also used with clear-treated pine as it is slightly more flexible than other decking materials.
Bearers and joists form the backbone of the deck, supporting the weight of people, furniture, and other loads. They ensure the deck can safely accommodate these loads without sagging or collapsing.
