Picking the right screws is one of the cheapest ways to make a deck last. Use the wrong ones and you get snapped heads, split board ends, rust streaks and boards that work loose after a winter or two. This guide is about the decking job itself. It covers which screw goes in the boards and which in the frame, how long they should be, how many you need and how to fix them, using the TIMCO decking range we stock.
The Short Answer: What Screws Should I Use for Decking?
- Softwood deck boards: exterior-coated decking screws, 4.5mm diameter, such as TIMCO green Decking Screws (PZ) or TIMCO C2 Deck-Fix.
- Hardwood, oak or cedar boards: TIMCO A2 Stainless Decking Screws, or C2 Deck-Fix, which TIMCO lists for hardwood and softwood. Pre-drill hardwood.
- Coastal or very exposed decks: stainless steel for the boards, and A4 stainless timber screws for the frame.
- Length: about two and a half times the board thickness. That's 60–65mm for most 28mm softwood boards.
- Frame (joists, bearers, posts): not decking screws. Use exterior hex timber screws or coach screws.
- How many: two screws per board, at every joist.
What You’ll Need
What you’ll need to fix deck boards
- decking screws: see the full decking screws range
- exterior timber screws or coach screws for the frame
- a cordless drill driver or impact driver, and a PZ2, TX20 or TX15 bit to match your screws (C2 Deck-Fix tubs and cylinder-head screws come with a bit)
- a 3mm wood drill bit and a countersink bit for hardwood and board ends
- a tape measure, string line or straight edge and a pencil to mark joist lines
- spacers for an even board gap (an offcut of the right thickness works)
- safety glasses and gloves
For the right drivers and bits, see Essential Tools for Working with Wood Screws.
Boards, Joists and Frame: Three Different Jobs
The most common decking mistake is using one screw for everything. A deck has three types of joint, and each needs a different fixing:
| Joint | What it does | What to use |
|---|---|---|
| Board to joist | Holds the walking surface down and stops boards cupping or lifting | Decking screws, 4.5mm, partly threaded with a ribbed or cylinder head: green PZ, C2 Deck-Fix, A2 stainless |
| Joist to joist, rim or ledger | Builds the frame and carries the load to the bearers and posts | Exterior hex or wafer-head timber screws (6.7mm) or coach screws: green hex timber screws, wafer-head timber screws |
| Frame to posts, wall or masonry | Ties the deck to its supports | Heavy-duty timber screws or coach screws; coach screws with a suitable plug into masonry: heavy-duty timber screws, exterior coach screws |
Decking screws are made for the top layer only. TIMCO's own decking guide describes its C2 Deck-Fix as designed to cut into the board, clear debris through the helix, countersink with the ribs under the head and clamp the board to the joist. That's a board job, not a structural one. See Screws for the deck frame below.
C2 Deck-Fix vs Green PZ vs A2 Stainless: Which Decking Screw?
We stock three main TIMCO decking screws for boards. All are 4.5mm (gauge 9), partly threaded so they pull the board down tight, and made to BS EN 14592. Here's how they differ, from each product listing:
| Green PZ Decking Screws | C2 Deck-Fix (green) | A2 Stainless Decking Screws | |
|---|---|---|---|
| Best for | Softwood and treated timber decking | Softwood, hardwood and composite boards; impact drivers | Softwood, tropical hardwood, cedar, green oak; coastal or corrosive settings |
| Finish | Green organic plating | Multi-layer green organic plating | A2 (304) stainless steel |
| Corrosion (TIMCO/listing) | Up to 500 hours' salt spray; rating 3 for low-salt environments | Up to 1,000 hours' salt spray; rating 3 (urban and industrial, low salt) | Rating up to 4 (urban and industrial) |
| Point | 25° sharp point | Patented twin-cut point for fast pick-up and less splitting | 25° single slash point for low-torque entry near edges |
| Head | Ribbed double countersunk | Ribbed countersunk, strengthened against shearing with an impact driver | Ribbed double countersunk, self-countersinking |
| Drive | PZ2 | TX20 (bit included in tubs) | PZ2 |
| Lengths | 50, 60, 70, 80mm | 50, 65, 75, 80mm | 50, 65mm |
| Shop | Green PZ | C2 Deck-Fix | A2 Stainless |
In short: green PZ screws are the economical choice for a standard softwood deck. C2 Deck-Fix doubles the salt-spray rating, adds the twin-cut point and has a Torx drive that's less likely to cam out, which helps on bigger decks or hardwood. Stainless is the choice for hardwoods such as oak and cedar, for coastal sites, and wherever you want the most corrosion resistance. TIMCO also says its stainless Classic decking screws have been salt-spray tested for 1,000 hours for industrial environments with a moderate salt atmosphere.
Shop these at DIY Refurb
- TIMCO Decking Screws, PZ, Green: 4.5 x 50 to 4.5 x 80, boxes of 200
- Decking Screws Industry Pack, 4.5 x 60 (1,000) for bigger decks
- TIMCO C2 Deck-Fix, Countersunk, Green: 4.5 x 50 to 4.5 x 80, tubs and boxes
- C2 Collated Deck-Fix (SQ2) for autofeed screwdrivers
- TIMCO A2 Stainless Decking Screws: 4.5 x 50 and 4.5 x 65, tubs of 250
Softwood, Hardwood and Composite Boards
Softwood (treated pine or spruce): the most common UK deck board. Green PZ decking screws are listed for softwood and treated timber, and their sharp point starts without pre-drilling in softwood.
Hardwood, oak and cedar: dense hardwoods split more easily and some, such as oak and cedar, react with ordinary steel and stain. Use A2 stainless decking screws, which are listed for tropical hardwood, cedar and green oak, or the stainless A2 cylinder-head decking screws, listed for corrosive woods such as oak and cedar. C2 Deck-Fix is also listed for hardwood. Always pre-drill hardwood.
Composite boards: follow the board maker's fixing instructions first, as many use their own clip systems. For face-fixing, the A2 cylinder-head screws are listed as ideal for composite decking, and C2 Deck-Fix cylinder-head and countersunk screws are both listed for composite boards.
For more on how timber type affects screw choice, see Does the Type of Wood Affect Which Screws You Should Use?.
What Length Decking Screw Do I Need?
A decking screw needs enough thread in the joist to hold the board down. The usual rule is a screw about two and a half times the board thickness, and at least twice the thickness. All the TIMCO decking screws we stock are partly threaded. The 4.5 x 50 green screw has about 32mm of thread, the 4.5 x 60 about 42mm, and the C2 4.5 x 75 about 50mm, so most of the thread ends up in the joist.
| Board thickness (typical, check your boards) | Suggested length | TIMCO sizes |
|---|---|---|
| 19–21mm (thin hardwood boards) | 50mm | Green PZ 4.5 x 50, C2 4.5 x 50, A2 4.5 x 50 |
| 25–28mm (most softwood boards) | 60–65mm | Green PZ 4.5 x 60, C2 4.5 x 65, A2 4.5 x 65 |
| 32mm (thicker boards) | 75–80mm | Green PZ 4.5 x 70 or 80, C2 4.5 x 75 or 80 |
Worked example: a 28mm softwood board x 2.5 = 70mm, so a 65mm or 70mm screw is ideal, and 60mm is the minimum (more than twice the board). If your joists are 47mm deep, 65mm leaves the tip well inside the joist.
Board sizes vary, so measure yours before you buy. Sizes in this table are typical. Check the pack and your board maker's guidance.
For the general rules on screw length, see the length section of our wood screws guide.
How Many Decking Screws Do I Need?
Work it out as joists x boards x 2, then add about 10% for mistakes and offcuts.
Worked example: a 3m x 3m deck
- Joists at 400mm centres across 3m: 3,000 ÷ 400 = 7.5, so 8 spaces and 9 joists
- Boards 144mm wide with 5mm gaps across 3m: 3,000 ÷ 149 = about 20.1, so 21 boards
- Screws: 9 x 21 x 2 = 378, plus 10% = about 420 screws
- That's three boxes of 200 green PZ screws, or two 250 tubs of C2 Deck-Fix
Joist spacing and board sizes here are typical. Check your own design and the board maker's guidance.
How to Fix Deck Boards: Spacing, Pilot Holes and Countersinking
- Mark your joist lines. Snap a string line or use a straight edge so every row of screws runs straight across the deck.
- Two screws per board at every joist, set in about 15–20mm from each edge (typical, check your board maker's guidance). Keep them in line along the deck for a neat finish.
- Gap the boards evenly with spacers, typically around 5mm. Timber moves with the weather.
- Pre-drill near board ends and in all hardwood. A pilot of around 3mm suits a 4.5mm decking screw (typical, check the pack). Twin-cut and slash points are made to cut splitting near edges, but pre-drilling the last 50mm or so of a board is still good practice.
- Countersinking: the ribs under TIMCO's decking screw heads countersink the head as it's driven, so you don't usually need a countersink bit in softwood. In hardwood, countersink the pilot hole so the head sits flush without crushing the surface.
- Drive until flush, then stop. Set your driver's clutch or ease off the impact driver so heads finish level with the surface, not sunk deep where water can sit.
- Use the right bit: PZ2 for green PZ and A2 stainless screws, TX20 for C2 Deck-Fix countersunk, TX15 for cylinder-head screws and SQ2 for collated C2.
Once the deck is down, give it a coat of decking oil or stain to protect the boards, such as Barrettine Decking Oil. Then see The Seasonal Guide to Caring for your Decking for year-round care.
Screws for the Deck Frame
Joists, rim joists, bearers and post connections carry the weight of the deck and everyone on it. Use heavy-duty exterior fixings here:
- Exterior hex timber screws: TIMCO Timber Frame & Landscaping Screws, Hex, Green (6.7mm, 60–250mm) are listed for decking subframes and joists, and start without pre-drilling in most softwoods.
- In-Dex-style hex flange timber screws: TIMCO Timber Screws, Hex Flange, Green (6.7 x 100–200mm) are designed as an alternative to the traditional coach screw, with 1,000-hour salt-spray plating. TIMCO says its In-Dex timber screws are 20 times faster to fit than a standard coach screw.
- Wafer head for a low profile: TIMCO Wafer Head Timber Screws (6.7 x 95–150mm, TX30 bit included) clamp well and sit flatter than a hex head, which helps where a board sits on top.
- Heavy-duty connections: TIMCO Heavy Duty Timber Screws, Silver (8.0–10mm, up to 200mm) don't need a pilot hole into most wood types, according to the listing.
- Coach screws: TIMCO Exterior Green Coach Screws for timber-to-timber, or timber-to-masonry with a suitable plug.
Size frame fixings to the timber you're joining, and follow your deck design, Building Regulations where they apply, and any joist hanger maker's fixing instructions. For a raised deck, get the structure checked.
Shop these at DIY Refurb
Coastal and Exposed Sites
Salt air is hard on fixings. Coated screws carry a corrosion rating, and TIMCO's ratings describe where each one suits:
| Screw | Corrosion rating (listing) | Suits |
|---|---|---|
| Green PZ decking screws | 3, low salt (500 hours' salt spray) | Most inland gardens |
| C2 Deck-Fix (green) | 3, urban and industrial, low salt atmosphere (1,000 hours) | Inland and urban decks, harder-working sites |
| A2 cylinder-head decking screws | 4, urban and industrial, moderate salt atmosphere | Exposed and near-coastal decks |
| A4 stainless timber frame screws | A4 (316) marine grade | Frames in marine, coastal and high-humidity locations |
Near the sea, use stainless for the boards and A4 stainless for the frame, and check every fixing is rated for the site.
Hidden and Discreet Fixings
We don't currently stock clip-style hidden decking fixings. For a discreet face-fixed finish, cylinder-head decking screws have a much smaller head that sits just below the surface and an upper thread that clamps the board to the joist:
- C2 Deck-Fix Cylinder Head, Green, 4.5 x 60: twin-cut point, 1,000-hour green plating, TX15 bit included, for timber or composite boards
- A2 Stainless Cylinder Head, 4.5 x 60: head about 5mm across, corrosion rating 4, TX15 bit included
Fitting a handrail? The TIMCO Decking Handrail Bracket Kit is stainless steel, with 4 brackets and 16 screws, for the discreet fixing of handrails to decking posts.
Common Decking Screw Mistakes
- Using interior screws outside: zinc or yellow screws rust and stain the boards. Always use decking-rated or stainless screws.
- Using decking screws for the frame: they're made for boards. Use timber screws or coach screws for joists and posts.
- Screws that are too short: less than twice the board thickness and boards lift and cup.
- One screw per joist: two per board at every joist stops boards twisting.
- Fixing too close to the edge or end without a pilot: a recipe for splits, especially in hardwood.
- Overdriving: sunk heads hold water and can tear the board surface. Stop at flush.
- Ordinary steel in oak or cedar: use stainless to avoid black staining.
- No gap between boards: boards swell when wet. Leave an even gap.
- Wrong bit: a worn or wrong-size bit chews heads. Match PZ2, TX20, TX15 or SQ2 to the screw.
If you're repairing an older deck, check the timber is sound first. See Can Decking in the UK Get Woodworm?.
Frequently Asked Questions
What size screws for decking boards?
Most UK decking is fixed with 4.5mm screws. For typical 28mm softwood boards, a 60–65mm screw is a good choice. For thinner 19–21mm hardwood boards use 50mm, and for 32mm boards use 75–80mm.
Can I use normal wood screws for decking?
Not outside. Interior zinc or yellow screws rust and stain. Use exterior-coated decking screws or stainless steel, which also have the helix shank and ribbed head made for clamping boards to joists.
Should I pre-drill decking boards?
Pre-drill all hardwood and near the ends of any board. In softwood, decking screws with sharp, twin-cut or slash points can usually go straight in, away from the ends.
Are stainless decking screws worth it?
For hardwood, oak and cedar, coastal sites and decks you want to last, yes. For a standard inland softwood deck, coated screws such as green PZ or C2 Deck-Fix are a cost-effective choice.
Torx or Pozi decking screws?
Both work. Torx (TX) recesses, used on C2 Deck-Fix, grip the bit more positively and are less likely to cam out with an impact driver. PZ2 is the standard woodscrew drive used on green and A2 decking screws.
How far apart should decking screws be?
Two screws per board at every joist, set in about 15–20mm from each edge, with joists typically at 400mm centres. Check your board maker's guidance.
Can I use decking screws for fencing or pergolas?
C2 Deck-Fix is listed for pergolas, fences and sheds as well as decks. For posts and structural joints, use timber screws or coach screws.
Related Guides
- The Different Types of Wood Screws Explained (decking screws section)
- Does the Type of Wood Affect Which Screws You Should Use?
- Essential Tools for Working with Wood Screws
- The Seasonal Guide to Caring for your Decking
- Can Decking in the UK Get Woodworm?
Browse our full decking screws and screws ranges. Not sure which screw suits your deck? Get in touch with the DIY Refurb team and we'll point you in the right direction.
