A deck can look well built on day one and still develop loose boards, stained timber or raised screw heads after its first wet winter. The difference is often in the details below and across the surface. This decking fixings guide explains how to choose fixings that suit your boards, frame and site conditions, so the finished deck stays safe, tidy and easier to maintain.
Decking fixings guide: start with the board material
The first decision is whether you are fixing timber or composite decking. They may look similar once laid, but they expand, drain and fasten differently. Using a fixing designed for one material on another can result in poor spacing, damaged board edges, or visible movement as the weather changes.
Timber decking screws
For traditional softwood decking, purpose-made decking screws are normally the most straightforward option. They are designed with a sharp point and coarse thread to pull the board firmly into the joist, while the head sits neatly at or just below the timber surface. A countersunk head is generally preferred because it reduces trip hazards and gives a clean, consistent finish.
Choose a screw long enough to pass through the board and secure it in the joist. As a practical rule, the fixing should penetrate the joist by around 35mm or more. For example, 28mm boards are commonly fixed with 60mm or 65mm decking screws. Board thickness, joist condition, and the manufacturer’s recommendation should always be given priority over a general rule.
Avoid ordinary bright zinc-plated screws. They are not made for wet outdoor conditions and can rust quickly, leaving dark streaks on the boards and weakening over time. Exterior-coated screws offer good value for many domestic timber decks. Stainless steel screws are a sensible step up for coastal locations, shaded gardens, damp areas, or premium timber, where staining would be particularly noticeable.
Composite decking clips and screws
Most grooved composite boards are intended to be installed with hidden clips. These sit in the groove at the board edge and fasten into each joist, creating even gaps without rows of visible screw heads. The result is a smart surface, but it is not simply a cosmetic choice. The clip system controls board spacing and allows the movement composite decking needs with changing temperatures.
Solid composite boards and some square-edge systems are face-fixed using screws instead. If so, follow the board manufacturer’s guidance carefully on pilot holes, screw type and spacing. Overtightening can distort the surface, while a screw placed too close to an end may split or crack the board. Beware: many composite brands have warranty stipulations regarding fixings, expansion spacing, and joist spacing, etc., so make sure to read all the small print.
Do not overlook structural fixings
Decking screws secure the walking surface. They are not a substitute for the fixings that hold the deck frame together. The subframe carries the load, so its connections deserve the same care as the visible finish.
Deck frame Joist hangers, a heavier version of the standard joist hanger (sometimes called deck joist shoes), structural timber screws, coach screws, bolts, and brackets all have their place, depending on the layout. A ledger board attached to a building, for example, needs properly specified structural fixings and suitable weather protection. It must not rely on a few general-purpose screws. Freestanding decks are not fixed to a house, so it is even more important that they have secure connections between posts, bearers and joists to hold the frame in shape.
Galvanised or stainless steel structural fixings are usually appropriate for external timberwork. For heavily exposed sites, near the coast, or where corrosion resistance is a priority, ask for advice on the most suitable grade. It is also worth checking compatibility with pressure-treated timber, as the preservatives used in modern treated timber can be harsh on unsuitable metals.
If a deck is raised, supports steps, has a handrail, or will carry heavy furniture such as a hot tub, the structure needs more than a standard garden-deck approach. In most cases, professional structural design advice and planning permission obtained will be needed.
Have a look at The Planning Portal; it has a lot of information for the DIYer.
Match the fixing to the environment
The South East has its share of wet winters, shaded gardens and exposed coastal plots. A deck in a sunny, open garden dries quickly after rain; one beneath trees or beside a north-facing wall may stay damp for days. That affects both the timber and the fixings.
Stainless steel is particularly useful where corrosion, black staining or long-term appearance is a concern. Coated decking screws remain a practical and cost-effective choice for many installations, provided they are made for exterior timber use. The key is to buy fixings suited to the whole job, rather than choosing on price alone.
Timber movement also matters. Freshly fitted pressure-treated boards can shrink as they dry, while established boards may swell in wet conditions. Leave consistent gaps between boards for drainage and airflow. For many timber decks, a gap of around 5mm to 8mm is common, although board width, moisture content and supplier guidance can alter this. Composite boards require their own specified expansion gaps, especially at board ends.
Good drainage protects fixings as much as it protects boards. Build a slight fall away from buildings, keep air moving beneath the deck and avoid trapping soil, leaves or standing water around the frame. No screw coating can compensate for timber that is constantly sitting in moisture.
Plan quantities before you start
Running short of screws halfway through laying boards is frustrating, but over-ordering without a plan can be expensive. Calculate from the joist layout, not just the deck area. Each timber board normally needs two screws at every joist it crosses. Wider boards may need additional care to prevent cupping, but do not add fixings randomly without checking the board guidance.
For a simple estimate, count the number of boards, multiply by the number of joists each board crosses, then multiply by two. Add 10 per cent for offcuts, awkward edges and the occasional dropped screw. Hidden composite clips are calculated in a similar way: one clip per board at each internal joist, plus starter clips, end clips and the correct screws for fascia and trim.
Keep structural fixings separate on the list. Include heavy deck joist hangers (not the lightweight internal ones) if you need them, angle brackets, bolts or structural screws, washers, post bases and handrail fittings where required. This makes it much easier to check that the frame can be completed before boards are laid.
Installation habits that prevent problems
Set out the first board carefully. A straight first run keeps every later board in line, whereas a small error at the start becomes obvious at the far end of the deck. Use spacers for consistent board gaps rather than judging them by eye.
With timber boards, pre-drilling is worthwhile near ends and edges, particularly with hardwood or dry boards. It reduces splitting and helps screws sit straight. Drive fixings square to the board and stop when the head is flush or only lightly recessed. A deeply buried screw head collects water and can create a rough depression as the timber weathers.
Check your joist centres before fixing. Boards that span too far can flex, even if every screw is tight. Composite products are especially dependent on the correct support spacing, which is often closer than for timber. Make sure you are inside the manufacturer’s maximum joist-centre recommendation and reduce it for diagonal board layouts where necessary.
For clean cuts around posts and edges, seal any freshly cut ends of treated timber with an appropriate end-grain preservative. This is a small job that helps protect the most vulnerable timber fibres. Keep the deck surface clear as you work, too. Grit caught under a board or clip can affect alignment.
When a hidden fixing is worth it
Hidden clips cost more than conventional screws and take a little more planning, but they can be worthwhile where appearance is central to the project. They are a strong choice for composite decking, contemporary garden spaces and barefoot areas where a smooth surface matters.
Face-fixed timber remains popular because it is familiar, secure and straightforward to repair. A damaged board can be removed by taking out its screws, while concealed systems may require more careful dismantling. There is no single best method - the right choice depends on the board type, desired finish, budget and how easily you may need to access the deck later.
The Team at the Crestala Fencing Centre can provide practical advice on fixings for the wooden and composite decking we supply. Contact the Team for a full itemised quote.
