Deck fastener guide
Fasteners are the cheapest part of a deck and the most common cause of its failure. The two things that go wrong are galvanic corrosion, where two dissimilar metals eat each other in the presence of treated wood and water, and using a screw where the hardware specifies a nail.
Corrosion is a chemistry problem, not a quality problem
Modern pressure treatment is copper-based — ACQ, CA and the older CCA all rely on copper as the biocide. Copper is cathodic to zinc and to steel, so when a zinc-coated screw sits in wet treated wood, the zinc becomes the sacrificial anode and dissolves. The screw loses its coating, then its shank, and the deck board comes loose. Higher copper retention in ground-contact lumber accelerates it.
| Fastener coating | Works with | Do not use with |
|---|---|---|
| Electro-galvanised | Interior, untreated wood only | Any treated lumber, any exterior use |
| Hot-dip galvanised (ASTM A153) | Treated lumber above ground | Ground contact, cedar, ipe, coastal air |
| Stainless 304 | Cedar, redwood, most treated lumber | Coastal salt air, ipe (staining risk) |
| Stainless 316 | Everything, including coastal and ipe | Nothing — it is the safe default where budget allows |
| Ceramic / epoxy coated | Treated lumber, most composites | Check the coating's listed compatibility |
| Aluminium | Untreated dry wood | Treated lumber — rapidly corrodes |
Two rules follow from the table. Anything touching treated lumber needs at least hot-dip galvanised, and anything in ground contact or within a mile of salt water needs stainless. Where a stainless screw touches galvanised hardware, the stainless wins and the galvanised part corrodes — which is why you do not mix them in the same connection.
Length is a penetration question
The working rule for decking is that the fastener must penetrate the joist by at least 1″ after passing through the board. For a 1″ deck board that means a 2″ screw; for 5/4×6 at 1″ thick, a 2″ or 2½″ screw. Too short and the screw holds by the tip in the top fibres of the joist; too long and it exits the bottom of a 2×8 and creates a rust path.
For structural connections the rule changes: hangers, ties and post bases are tested with specific fasteners, and substituting a deck screw for a hanger nail voids the load rating. Hanger nails are hardened and have a full-diameter shank; deck screws are hardened differently and are brittle in shear.
How many fasteners a deck consumes
| Connection | Basis | Per 100 sq ft |
|---|---|---|
| Face screws, 16″ joists | 2 per board per joist crossing | ~350 |
| Hidden clips | 1 per board per joist crossing | ~175 |
| Joist hangers | 1 per joist end, 6–10 nails each | ~20 hangers |
| Ledger fasteners | 2 rows staggered, per fastener schedule | ~12 |
| Guard post anchors | 2 per post, 4 fasteners each | ~8 |
The face-screw figure assumes 5.5″ boards with 16″ joist spacing; it scales linearly with both, which is why the board calculator computes it from the actual row and joist count rather than from area. Buy 10% spare, because dropped and stripped screws are normal and a partial box never finishes the job.
Where fasteners are the wrong answer entirely
Some connections should not be made with screws or nails at all: a ledger to a house band, a beam to a post, and a guard post to a frame. Those want structural screws or bolts with a published load value, or a manufactured connector. A 3″ deck screw has no published shear capacity, so using one in a structural connection is not a shortcut — it is an unrated connection.
What fastener counts do not solve
- It does not give a fastener schedule. Ledger spacing is tabulated against joist span and species; the table is what the inspector will check, and it is in the code, not here.
- It does not rank brands. Coating classes are standardised; brands within a class differ far less than the classes do.
- It does not cover adhesives or concealed systems. Structural adhesives and proprietary rail systems have their own installation manuals, which override general advice.
Questions people actually ask
Can I use regular deck screws in treated lumber?
Only if they are rated for it — coated or stainless. Plain electro-galvanised screws will corrode away in wet treated wood within a few years, and the failure is hidden under the board until it lets go.
Do I need stainless screws for cedar?
Yes, or a coating rated for cedar. Cedar contains acids that attack zinc, and bare steel leaves black iron stains that bleed into the wood and cannot be sanded out.
Can I use deck screws for joist hangers?
No. Hangers are rated with specific hardened nails or manufacturer-approved structural screws. A deck screw has a thinner shank and no published load value in that application.
How long should deck screws be?
Long enough to penetrate the joist by 1″ after passing through the board. For 1″ decking over a solid joist, that is a 2″ screw; for 2″ material, 2½–3″.
How many screws per deck board?
Two per joist crossing for a standard 5.5″ board, and two per crossing for wider boards as well. The count grows with joist density, not with board width, which is why 12″ joist spacing costs nearly twice the fasteners of 16″.