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Decking Joists

Browse our range of timber flooring joists and floor timbers, offering reliable support for floors, roofs, and outdoor projects. Perfect with joist hangers for secure connections, our durable timber joists are ideal for decking, structural work, and garden builds.

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    C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 47 x 100mm (4x2)

    Discover the incredible strength and versatility of our C16 Timber Joists. These structural wood pieces are kiln dried and expertly pressure treated, making them resistant to wood-destroying fungi and ideal for both indoor and outdoor projects. With...
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    C16 Timber UC3u Treated Kiln Dried Regularised FSC 47 x 75mm (3x2)

    Due to the size of this 3x2 C16 graded timber carcassing, we recommended using it purely for vertical non-load bearing stud positions. C16 Timber Joists, expertly crafted for those who seek durability and reliability in construction projects. These...
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    C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 47 x 150mm (6x2)

    Transform your outdoor spaces with our Timber Floor Joist, designed specifically for external use, making them perfect for decking joists. These robust timber joists are your go-to solution for projects requiring reliable structural support in...
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    C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 47 x 125mm (5x2)

    C24 Graded Timber C16 and C24 are strength grades; the higher the grade, the better the load bearing quality it has. C16 is normally the grade that is produced from faster grown UK timber. C24 is a premium product as the wood is slower grown and is also...
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    C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 47 x 200mm (8x2)

    C16 and C24 are strength grades; the higher the grade, the better the load bearing quality it has. C16 is normally the grade that is produced from faster grown UK timber. C24 is a premium product as the wood is slower grown and is also denser. Higher...
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    C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 47 x 225mm (9x2)

    Treated timber is suitable to be used externally and is suitable for wet areas or areas where the timber will not be coming into contact with the ground. Examples of treated timber uses are outdoor decking, shed bases, posts, sleepers. Regularised...
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    C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 47 x 175mm (7x2)

    C16 and C24 are strength grades; the higher the grade, the better the load bearing quality it has. C16 is normally the grade that is produced from faster grown UK timber. C24 is a premium product as the wood is slower grown and is also denser. Higher...
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    C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 75 x 100mm (4x3)

    C16 and C24 are strength grades; the higher the grade, the better the load bearing quality it has. C16 is normally the grade that is produced from faster grown UK timber. C24 is a premium product as the wood is slower grown and is also denser. Higher...
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    C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 75 x 150mm (6x3)

    C16 and C24 are strength grades; the higher the grade, the better the load bearing quality it has. C16 is normally the grade that is produced from faster grown UK timber. C24 is a premium product as the wood is slower grown and is also denser. Higher...
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    C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 75 x 175mm (7x3)

    These C16 carcassing timber lengths are UC3u treated timber, meaning they perfect for outdoor use providing it is above ground. Carcassing is a generic trade term which refers to the use of a species of timber. Spruce/Pine and Fir are used to form...
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    C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 75 x 200mm (8x3)

    These C16 carcassing timber lengths are UC3u treated timber, meaning they perfect for outdoor use providing it is above ground. Carcassing is a generic trade term which refers to the use of a species of timber. Spruce/Pine and Fir are used to form...
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    C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 75 x 225mm (9x3)

    These C16 carcassing timber lengths are UC3u treated timber, meaning they perfect for outdoor use providing it is above ground. Carcassing is a generic trade term which refers to the use of a species of timber. Spruce/Pine and Fir are used to form...

Decking Joists

When choosing the right decking joists for your project, the size you need will depend on the overall dimensions of your deck. We offer a variety of decking and joists in different lengths, all available for delivery from any of our branches. For timber decking, a good rule of thumb for decking joist spacing is 450mm centres (or 400mm if using a chevron pattern). For composite decking joists, spacing should be 400mm centres, or 300mm when opting for a chevron pattern.

Additionally, consider using deck joist tape to protect the joists from moisture, and joist hangers for decking to ensure a secure and durable installation.

Frequently Asked Questions

What size deck joists?
The deck joist size required depends on your project design. Our most popular sizes are 47x100mm, 47x125mm, and 47x150mm. These are available from every Howarth branch in lengths of 3m, 3.6m, 4.2m, and 4.78m. We also have availability of 5.4m and 6m at select branches
What size screws for decking joists?
Camo deck screws are perfect for fastening deck boards to joists. For the framing, structural wood screws will do a great job.
How far apart should deck joists be?
When designing how far apart your deck joists should be, a good timber decking spacing is 450mm centres (or 400mm centres is using a chevron pattern), and 400mm centres for composite decking (or 300mm centres if using a chevron pattern).
How many decking joists do I need?
The number of decking joists needed is dependant upon the size of the decking project. It can be calculated based on spacing of 450mm centres for timber decking (400mm centres for chevron pattern) and 400mm centres for composite decking (300mm centres for chevron pattern).
What wood to use for deck joists?
C16 or C24 timber is ideal for decking joists. It is structural graded and when well put together will keep the decking strong and stable.
How thick should decking joists be?
Decking joists are most commonly 47mm in size.
Should I stain deck joists?
We always recommend treating timber and maintaining it over time, this includes decking joists. This will increase the longevity of the decking structure. Don’t forget to protect the ends!

How to guides

How to build a deck

How to build a decking using our timber products. 

How to build a raised deck

A step by step guide on how to build your own raised decking area.