The Best Sizes, Spacing, and Strength Grades For Building a Timber Decking Frame
Are you wanting to build a beautiful decking in your garden but don’t know where to start? Our guide explains the basics of decking framing and the best sizes, spacing, and strength grades to create professional-looking and stable decking.
What Makes Up a Timber Decking Frame?
In order to figure out the right size timber for your decking, you need to know the different components of a decking subframe.
Joists
Joists are the backbone of your deck’s structure, playing a crucial role in timber framing. They are sturdy beams that support your decking, making sure everything stays strong and level. Typically running perpendicular to your house, they’re attached to the ledger board with joist hangers. Proper placement and spacing of joists ensure even weight distribution, which is vital for sturdy and durable decking.
Ledger Board and Rim Joists
A ledger board is a critical component in decking, as it anchors the deck to your house, supporting the joists that run perpendicular to it. Rim joists are the outermost joists that frame the deck, helping to keep the deck’s structure rigid and secure by connecting the ends of the internal joists.
Beams
Beams run along the edge of the decking or underneath to support the whole frame by transferring the load from the joists. Larger decks will need more beams to be structurally solid.
Joist Bridge/Blocking
Joist blocking, or bridging, involves placing small pieces of wood between deck joists to connect them. This helps prevent the joists from twisting or warping, especially under heavy loads or over time due to changes in moisture. Blocking strengthens the deck's structure by evenly distributing weight and reducing movement, ensuring a stable, long-lasting deck.
Decking Boards
Decking boards are the planks laid on top of the decking frame, forming the visible and walkable surface. These are most commonly made from timber but can also be made from composite PVC.
How Far Apart Should Your Joists Be Spaced?
Joists
"On centre" refers to the distance from the centre of one joist to the centre of the next. This measurement is crucial for ensuring even support and alignment across the deck. You can either mark up the centre of each joist and measure between them, or measure from the outer edge of one joist to the outer edge of the next. Typically, timber joists are spaced 16” on centre, which is standard for most decking. However, for a stronger deck capable of bearing more weight, spacing can be reduced to 12” on centre. This closer spacing increases the deck’s strength and stability, particularly for heavier loads.
Blocking
Joist blocking, or bridging, should be installed between decking joists to reduce movement and prevent warping. These blocks, or "noggins," are typically spaced 100 to 150mm apart. For joists spaced 16” on centre, blocking is usually recommended at 145mm, and for joists spaced 12” on centre, blocking is recommended around 100mm. Properly installed blocking helps to ensure a structurally sturdy and durable decking.
What Size Timber Do I Need For Decking Framing?
When choosing timber for decking framing, the size of the timber is crucial for structural integrity and depends on the deck's load requirements. Common joist sizes include:
For standard decks that only support light furniture, 2x4 (47x100mm) joists are typically sufficient. However, for heavier loads, such as hot tubs, 2x5 (47x125mm) or 2x10 (47x250mm) joists provide additional strength. Ledger boards and rim joists should match the joist size, usually 2x8 (47x200mm) or 2x10 (47x250mm), to ensure a uniform and strong frame.
For decking boards, the most common sizes are:
What Sizes of Timber Do Covers Offer?
We supply a wide range of treated carcassing timber in different sizes that would be perfect for your decking joists. Our depots also offer timber-cutting services, so you can easily get the exact size of timber you need for your decking project.
Explore our CoverDek range for top-quality, affordable supplies to create your dream decking.
What Is Timber Nominal Dimension?
When it comes to timber sizing, it’s important to understand the two different dimensions you may see for the same piece of timber. A nominal dimension in timber refers to the original, rough-cut size of a piece of wood before it’s planed or finished. For example, a board labelled as 2x4 is initially cut to those dimensions; however, after the wood is dried and smoothed, the actual or "dressed" size is somewhat smaller, typically losing around 10mm on each side. This discrepancy between nominal and actual dimensions is standard practice and very helpful to know when choosing the right size for your decking.
What Type of Timber Should I Use For My Decking Frame?
When choosing timber for your decking, it's important to pick strength-graded wood to ensure it can safely handle the weight of people and furniture. C16 timber is generally a good choice for most decking projects, but this can depend on your joist size, spacing, and the load the deck will bear. If you're planning for a heavier load or wider joist spacing, you might want to consider C24 timber for extra strength.
Additionally, using treated wood, or treating it yourself, is key to making sure your deck withstands the elements. Treated timber is much more resistant to mould, rot, and insect infestations, meaning your deck will stay strong and look great for years to come, no matter what the weather throws at it.
Are There Regulations About Timber Decking Sizing?
In the UK, garden decking is generally considered permitted development under Class E, meaning you usually don't need planning permission if it meets specific criteria. The decking must not exceed 0.3 metres in height, and it must be incidental to the enjoyment of the house, meaning it is a minor additional element that does not impact the primary use of the home. As long as these conditions are met, decking can be added without formal planning approval, but it is always best to check with your local council in regard to your specific situation.
Build Your Dream Decking With Covers
Explore our wide selection of top-quality timber and building materials to create a gorgeous, sturdy, and durable decking. Speak to our friendly team of experts for any advice and help you need.
At Covers Builders Merchants, you can rely on our 175 years of industry experience and our commitment to quality. When you visit your nearest Covers depot, you’ll experience the difference of shopping at a family-run business.