16th May 2023 -

When installing new decking in your garden, one of the first steps to success is ensuring a solid supporting framework. Whatever the intended use of your decking, by taking the time to lay robust groundwork and using excellent quality timber, your decking will be structurally sound and less likely to sag or collapse.

We supply a huge selection of treated decking frame timber in a range of sizes to suit your needs, all delivered quickly across the UK.

What Is the Best Timber to Use for a Decking Frame?

To build a decking frame which is fit for use, there are several factors to consider before choosing what timber to use. Some key points to keep in mind include:

  • Treated Wood: When choosing the best timber to use in decking joists, it’s important to opt for treated wood. This ensures that your decking will be more resistant to insects and rot, resulting in a longer-lasting structure. Timber is typically pressure-treated to ensure full saturation with treatment chemicals.
  • Decking Elevation: The appropriate timber for your frame will vary depending on the intended elevation of your decking. As a general guide, decking constructed on a low level should use C16 timber joists, measuring approximately 45mm x 95mm (4" x 2"). Alternatively, raised decking requires 45mm x 145mm timber (6" x 2").
  • Structural Grading: The ideal timber for decking joists is C16 or C24. This timber grading provides increased strength resulting in a more robust and stable decking able to withstand regular usage.
decking frame timber

Our Range of Decking Frame Timber

At Building Materials Nationwide, we supply a huge range of quality graded timber which is ideal for structural purposes, including building a robust decking frame. Across our entire range, the timber is kiln-dried resulting in a low moisture quotient, and pressure-treated to ensure the greatest resistance against insects and rot when used outdoors.

We supply only the highest quality timber and offer a range of timber graded to different strengths, including C16 treated timber and C24 treated timber, as well as sawn treated timber battens.

Our timber supplies also come in a range of measurements to suit any decking project, no matter the size of your outdoor space. From smaller measurements (47mm x 100mm) to larger sizes (75mm x 225mm), our structural graded timber is designed to provide excellent strength.

Browse our full range of decking frame timber online today. If you’re searching for something and you haven’t spotted it in our range, our dedicated team is on hand to help you find exactly what you’re looking for. Get in touch today for more information and support.

Want to view our range?


    • Ideal for general construction, fencing, garden and leisure timber applications
    • Pressure-treated
    Price from: £1.00 £1.20

    • Ideal for general construction, fencing, garden and leisure timber applications
    • Pressure-treated
    Price from: £4.20 £5.04
  3. £3.11 £3.73

View All Structural Graded Timber

Browse Our Full Timber Decking and Accessories Range

With a huge range of building and landscaping materials available in our online catalogue, we can help to supply your entire decking project beyond the decking framework. Within our range, you’ll also find:

  • Timber Decking Boards: We supply a wide range of pre-cut timber deck panels in a variety of sizes to complete your decking area. All of our timber decking boards come in the standard ridged style giving your decking an attractive finish, and are pressure-treated using tanalith E for enhanced protection.
  • Anti-Slip Timber Decking Boards: Whatever the intended use for your timber decking, our anti-slip timber decking boards provide a fantastic solution to reduce the risk of slipping if your decking gets wet. Whilst our anti-slip timber decking is also pressure-treated and comes in the same dimensions as our regular timber decking, the boards have an added anti-slip inlay to reduce slip hazards.
  • Timber Decking Fixings: You’ll find a fantastic range of timber decking screws and fixings on the Building Materials Nationwide website. Screws are typically easier to use for decking frames, allowing you to move joists after fitting if needed.

  1. Price from: £16.69 £20.03
  2. 1 - 2 Week Delivery

    • Made from 316 stainless steel for durability
    • Facilitates easy and efficient installation
    Price from: £22.00 £26.40

View All Decking

Get Extra Benefits With a Professional Trade Account

To truly enjoy our many benefits, you can apply for a Building Materials Nationwide trade account. Giving you access to a catalogue of over 25,000 products, our trade accounts are the best way to save you and your business time when you need it the most.

We strive to be your one-stop shop for construction and landscaping materials, including decking frame timber. When you sign up for a trade account with us, you’ll be assigned a dedicated account manager who will do the legwork for you, ringing around suppliers to source the products you need most, and getting in touch with you when they say they will.

You’ll also enjoy access to our speedy delivery services, reducing wasted time spent waiting for deliveries. With 30-day interest-free credit for all of our trade members, there’s no better way to shop with us than through a trade account. 

Sign up today to start enjoying our excellent benefits.


What size decking joists do I need?

The size of decking joist you’ll require is influenced by your decking’s intended use. For example, for an average deck which will only need to hold a table and chairs, joists measuring 4" x 2" will typically be sufficient. On the other hand, for deckings intended to support heavier objects, joists measuring 5" x 2" or 6" x 2" would be recommended to provide optimal strength.

How far apart do deck joists need to be?