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Decking Joists

Decking joists are an integral part of the structure of your decking. C16 and C24 structural graded, treated decking joists are perfect for a decking project that is designed to last.

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  • Rough Sawn Timber UC3u Treated Green Unseasoned FSC 22 x 100mm Rough Sawn Timber UC3u Treated Green Unseasoned FSC 22 x 100mm

    Rough Sawn Timber UC3u Treated Green Unseasoned FSC 22 x 100mm

    £1.74 - £13.32 (Ex VAT)
    £2.09 - £15.98 (Inc VAT)
    Treated timber is suitable to be used externally and is suitable for wet areas or areas where the timber will be coming into contact with the ground. Examples of treated timber uses are outdoor decking, shed bases, posts, sleepers. Carcassing is a...
  • Rough Sawn Timber UC3 Treated Green Unseasoned FSC 22 x 125mm Rough Sawn Timber UC3 Treated Green Unseasoned FSC 22 x 125mm

    Rough Sawn Timber UC3 Treated Green Unseasoned FSC 22 x 125mm

    £1.99 - £15.22 (Ex VAT)
    £2.39 - £18.26 (Inc VAT)
    Treated timber is suitable to be used externally and is suitable for wet areas or areas where the timber will be coming into contact with the ground. Examples of treated timber uses are outdoor decking, shed bases, posts, sleepers.
  • Rough Sawn Timber UC3u Treated Green Unseasoned FSC 22 x 150mm Rough Sawn Timber UC3u Treated Green Unseasoned FSC 22 x 150mm

    Rough Sawn Timber UC3u Treated Green Unseasoned FSC 22 x 150mm

    £2.61 - £19.98 (Ex VAT)
    £3.13 - £23.98 (Inc VAT)
    Treated timber is suitable to be used externally and is suitable for wet areas or areas where the timber will be coming into contact with the ground. Examples of treated timber uses are outdoor decking, shed bases, posts, sleepers. Carcassing is a...
  • Rough Sawn Timber UC3 Treated Green Unseasoned FSC 22 x 200mm Rough Sawn Timber UC3 Treated Green Unseasoned FSC 22 x 200mm

    Rough Sawn Timber UC3 Treated Green Unseasoned FSC 22 x 200mm

    £3.57 - £27.40 (Ex VAT)
    £4.28 - £32.88 (Inc VAT)
    Treated timber is suitable to be used externally and is suitable for wet areas or areas where the timber will be coming into contact with the ground. Examples of treated timber uses are outdoor decking, shed bases, posts, sleepers.
  • Rough Sawn Timber UC3 Treated Green Unseasoned FSC 22 x 225mm Rough Sawn Timber UC3 Treated Green Unseasoned FSC 22 x 225mm

    Rough Sawn Timber UC3 Treated Green Unseasoned FSC 22 x 225mm

    £4.02 - £30.83 (Ex VAT)
    £4.82 - £37.00 (Inc VAT)
    Treated timber is suitable to be used externally and is suitable for wet areas or areas where the timber will be coming into contact with the ground. Examples of treated timber uses are outdoor decking, shed bases, posts, sleepers.
  • Rough Sawn Timber UC3u Treated Unseasoned FSC 22 x 75mm Rough Sawn Timber UC3u Treated Unseasoned FSC 22 x 75mm

    Rough Sawn Timber UC3u Treated Unseasoned FSC 22 x 75mm

    £1.30 - £9.99 (Ex VAT)
    £1.56 - £11.99 (Inc VAT)
    Sleepers are always a popular product due to their versatility. They are often used as garden retainers, horizontally or sometimes dug into the ground and used vertically. Other popular applications are for steps and increasingly for growing vegetables...
  • Rough Sawn Timber UC3u Treated Unseasoned UK FSC 25 x 50mm Rough Sawn Timber UC3u Treated Unseasoned UK FSC 25 x 50mm

    Rough Sawn Timber UC3u Treated Unseasoned UK FSC 25 x 50mm

    £0.99 - £7.60 (Ex VAT)
    £1.19 - £9.12 (Inc VAT)
    Treated timber is suitable to be used externally and is suitable for wet areas or areas where the timber will be coming into contact with the ground. Examples of treated timber uses are outdoor decking, shed bases, posts, sleepers. Carcassing is a...
  • C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 44 x 95 x 4800mm C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 44 x 95 x 4800mm

    C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 44 x 95 x 4800mm

    £3.48 - £26.72 (Ex VAT)
    £4.18 - £32.06 (Inc VAT)
    Our planed & regularised treated sawn timber is perfect for structural timber carcassing as it comes in��C24 grade. This timber is ideal for a number of uses in the home and garden. The pressure treatment on this timber protects it against wood...
  • C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 44 x 120mm C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 44 x 120mm

    C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 44 x 120mm

    £4.36 - £33.40 (Ex VAT)
    £5.23 - £40.08 (Inc VAT)
    Treated timber is suitable to be used externally and is suitable for wet areas or areas where the timber will be coming into contact with the ground. Examples of treated timber uses are outdoor decking, shed bases, posts, sleepers. Regularised timber has...
  • C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 44 x 145 x 4800mm C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 44 x 145 x 4800mm

    C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 44 x 145 x 4800mm

    £5.23 - £40.08 (Ex VAT)
    £6.28 - £48.10 (Inc VAT)
    Treated- Treated timber is suitable to be used externally and is suitable for wet areas or areas where the timber will be coming into contact with the ground. Examples of treated timber uses are outdoor decking, shed bases, posts, sleepers. C16 or C24...
  • C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 44 x 170mm C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 44 x 170mm

    C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 44 x 170mm

    £6.10 - £46.76 (Ex VAT)
    £7.32 - £56.11 (Inc VAT)
    Treated timber is suitable to be used externally and is suitable for wet areas or areas where the timber will be coming into contact with the ground. Examples of treated timber uses are outdoor decking, shed bases, posts, sleepers. Regularised timber has...
  • C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 44 x 195mm C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 44 x 195mm

    C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 44 x 195mm

    £6.97 - £53.43 (Ex VAT)
    £8.36 - £64.12 (Inc VAT)
    Treated timber is suitable to be used externally and is suitable for wet areas or areas where the timber will be coming into contact with the ground. Examples of treated timber uses are outdoor decking, shed bases, posts, sleepers. Regularised timber has...
  • C24 Timber Joists UC4 Treated Redwood 47 x 200 x 4800mm C24 Timber Joists UC4 Treated Redwood 47 x 200 x 4800mm

    C24 Timber Joists UC4 Treated Redwood 47 x 200 x 4800mm

    £44.60 - £341.96 (Ex VAT)
    £53.52 - £410.35 (Inc VAT)
    C24 deck joists are perfect for supporting your decked area. This timber is UC4 treated, meaning that not only is it ideal for outdoor use, but it is also suitable for direct contact with the ground. C24 graded timber is a premium loadbearing grade...
  • C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 44 x 220mm C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 44 x 220mm

    C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 44 x 220mm

    £7.84 - £60.11 (Ex VAT)
    £9.41 - £72.13 (Inc VAT)
    Treated timber is suitable to be used externally and is suitable for wet areas or areas where the timber will be coming into contact with the ground. Examples of treated timber uses are outdoor decking, shed bases, posts, sleepers. Regularised timber has...
  • C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 44 x 245mm C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 44 x 245mm

    C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 44 x 245mm

    £8.13 - £62.35 (Ex VAT)
    £9.76 - £74.82 (Inc VAT)
    Treated timber is suitable to be used externally and is suitable for wet areas or areas where the timber will be coming into contact with the ground. Examples of treated timber uses are outdoor decking, shed bases, posts, sleepers. Regularised timber has...
  • Rough Sawn Timber UC3u Treated Kiln Dried Regularised FSC 44 x 44mm Rough Sawn Timber UC3u Treated Kiln Dried Regularised FSC 44 x 44mm

    Rough Sawn Timber UC3u Treated Kiln Dried Regularised FSC 44 x 44mm

    £1.76 - £13.48 (Ex VAT)
    £2.11 - £16.18 (Inc VAT)
    Treated timber is suitable to be used externally and is suitable for wet areas or areas where the timber will be coming into contact with the ground. Examples of treated timber uses are outdoor decking, shed bases, posts, sleepers. Carcassing is a...
  • C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 47 x 75mm C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 47 x 75mm

    C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 47 x 75mm

    £2.61 - £20.04 (Ex VAT)
    £3.13 - £24.05 (Inc VAT)
    Treated timber is suitable to be used externally and is suitable for wet areas or areas where the timber will be coming into contact with the ground. Examples of treated timber uses are outdoor decking, shed bases, posts, sleepers. Regularised timber has...
  • C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 72 x 97mm C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 72 x 97mm

    C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 72 x 97mm

    £5.56 - £42.63 (Ex VAT)
    £6.67 - £51.16 (Inc VAT)
    Treated timber is suitable to be used externally and is suitable for wet areas or areas where the timber will be coming into contact with the ground. Examples of treated timber uses are outdoor decking, shed bases, posts, sleepers. Regularised timber has...
  • C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 72 x 145mm C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 72 x 145mm

    C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 72 x 145mm

    £8.34 - £63.95 (Ex VAT)
    £10.01 - £76.74 (Inc VAT)
    Treated timber is suitable to be used externally and is suitable for wet areas or areas where the timber will be coming into contact with the ground. Examples of treated timber uses are outdoor decking, shed bases, posts, sleepers. Regularised timber has...
  • C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 72 x 170mm C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 72 x 170mm

    C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 72 x 170mm

    £9.73 - £74.61 (Ex VAT)
    £11.68 - £89.53 (Inc VAT)
    Treated timber is suitable to be used externally and is suitable for wet areas or areas where the timber will be coming into contact with the ground. Examples of treated timber uses are outdoor decking, shed bases, posts, sleepers. Regularised timber has...
  • C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 72 x 195mm C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 72 x 195mm

    C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 72 x 195mm

    £11.12 - £85.27 (Ex VAT)
    £13.34 - £102.32 (Inc VAT)
    Treated timber is suitable to be used externally and is suitable for wet areas or areas where the timber will be coming into contact with the ground. Examples of treated timber uses are outdoor decking, shed bases, posts, sleepers. Regularised timber has...
  • C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 72 x 220mm C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 72 x 220mm

    C16 Timber Joists UC3u Treated Kiln Dried Regularised FSC 72 x 220mm

    £12.51 - £95.93 (Ex VAT)
    £15.01 - £115.12 (Inc VAT)
    Treated timber is suitable to be used externally and is suitable for wet areas or areas where the timber will be coming into contact with the ground. Examples of treated timber uses are outdoor decking, shed bases, posts, sleepers. Regularised timber has...
  • Rough Sawn Timber UC3u Treated Unseasoned UK FSC 25 x 38mm Rough Sawn Timber UC3u Treated Unseasoned UK FSC 25 x 38mm

    Rough Sawn Timber UC3u Treated Unseasoned UK FSC 25 x 38mm

    £0.75 - £5.77 (Ex VAT)
    £0.90 - £6.92 (Inc VAT)
    With a long and proud tradition of supplying quality timber, timber products, and associated services, Howarth Timber & Building Supplies has established an enviable reputation for its versatility, reliability and expertise. Quality and range of...

Decking Joists

The deck joist size that you require will depend on your project size, we have multiple length options in stock and available for delivery from any of our branches. When planning your decking joist spacing, a good rule of thumb for timber decking 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).

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.