The Complete Guide to Stainless Steel Screws for Pressure-Treated Decks That Never Fail

Pressure treated lumber lasts 25 years. Your screws shouldn't fail in five. The chemicals protecting wood from rot destroy cheap fasteners faster than you'd think.

After nearly three decades building decks, we've watched this happen hundreds of times. Someone saves $30 on screws for a $5,000 deck. Bad math.

This guide covers what you need: permitted fasteners, why regular screws fail, galvanized versus stainless steel, 304 versus 316 grades, correct screw sizes, and installation techniques that prevent splitting and snapping.

Why should you use stainless steel screws for PT decking?

Because everything else corrodes. Copper preservatives in treated lumber attack metal fasteners through galvanic corrosion. Coated screws fail once the coating breaks down and rust starts. Stainless steel doesn't have a coating. The chromium is mixed into the entire fastener.

304 has 18% chromium, 316 has 16% chromium plus 2-3% molybdenum. That molybdenum is what stops pitting in saltwater.

What this means for your deck:

• Copper in treated wood won't corrode stainless steel
• Strength stays constant at 95,000+ PSI throughout its life
• Meets building codes

Which grade to use:

• 304 stainless: inland decks, dry climates
• 316 stainless: coastal areas, high humidity, anywhere near saltwater

Galvanized costs a third of what stainless runs. But we've rebuilt enough decks where galvanized fasteners failed prematurely that we won't use them anymore on treated lumber. Stainless costs more upfront and eliminates the callback when screw heads start snapping off.

What type of fasteners is permitted to be used with pressure treated wood?

IRC Section R317.3 requires hot-dipped galvanized minimum G90 coating or stainless steel grades 304, 316, or 410 for pressure treated lumber.

While silicon bronze and copper technically qualify under building codes, they're rare in fastening deck boards because they cost 3-4 times more than stainless without offering better performance. Nobody's spending that kind of money when stainless does the job.

Never mix stainless and galvanized fasteners in the same structure. Galvanic corrosion accelerates and the galvanized fastener corrodes way faster when touching stainless.

What happens if you use regular screws in pressure treated decking?

Regular screws corrode from the inside out. Copper-based preservatives in modern treated wood attack metal fasteners through galvanic corrosion. Within 2-3 years for cheap screws, 5-10 years for better ones, the fasteners rust away while the wood stays intact.

The failure looks like this: orange rust stains bleeding through deck boards, screw heads snapping off when you step on the board, and structural connections that look fine on the surface but have no holding power underneath.

Why does this happen?

In 2004, the lumber industry replaced CCA (which contained arsenic) with ACQ and CA-B preservatives. These new chemicals pack up to four times more copper into the wood. We watched fastener failures start piling up within a few years.

The corrosion process:

When pressure treated wood gets wet, it becomes a battery:

• Copper in the treated wood acts as the cathode
• Your steel fastener becomes the anode
• Moisture creates the electrical connection
• Electrochemical reaction destroys the metal

USDA Forest Products Lab tested ACQ extract on galvanized fasteners. 95% surface corrosion. CA-B treated wood was even worse. Research found ACQ-treated wood is significantly more corrosive than old CCA formulation for every type of metal tested.

What accelerates the corrosion?

Three conditions speed up fastener failure in pressure treated wood:

• High copper content in the wood (ground-contact rated lumber)
• Constant moisture that doesn't dry out
• Heat and humidity combined

Florida and California decks get all three, which is why fastener failure happens faster in those climates. Jobs in those regions taught us early on that standard galvanized won't cut it anymore.

Do stainless steel screws rust in pressure treated wood?

304 and 316 stainless won't rust in treated lumber. The chromium creates a passive oxide layer that self-heals when scratched. You might see surface tea staining (brown discoloration from tannins in the wood), but that's not corrosion. Wipe it off. Your SS pressure treated decking screws are still durable.

How to screw into pressure-treated deck boards using stainless steel screws?

Stainless steel screws work differently than coated fasteners. They snap clean when overtorqued instead of bending. Set your impact driver to 1200-1500 RPM max. If you're using a drill, stop when the screw head sits flush. One more turn and it snaps.

Should you pre-drill holes?

Yes. Always pre-drill when using stainless steel screws in pressure treated lumber. This prevents splitting, reduces installation stress, and keeps screws from snapping.

Where pre-drilling is mandatory:

• Anywhere within 2 inches of a board end
• All hardwoods like ipe or cumaru
• Dense pressure treated lumber that's dried out

The wood grain near board ends can't handle the wedging force from screws without splitting. Use a drill bit slightly smaller than your screw's shank diameter. For #8 screws (0.164" diameter), drill 0.144" pilot holes, that's a #27 bit. For #10 screws (0.190" diameter), use 0.161" holes, that's a #20 bit.

What about mid-board locations? Fresh pressure treated lumber is soft enough that you might get away without holes. But if your boards have been drying for a few weeks, the wood gets harder. Pre-drilling protects your fasteners.

How long should deck boards dry before screwing?

Pressure treated deck boards arrive soaking wet, sometimes holding 40-60% moisture. Fresh treated lumber ships at 35-75% moisture content. That water needs to go somewhere.

Stack boards off the ground with spacers between each layer for 2-4 weeks minimum. Air needs to circulate. KDAT (kiln-dried after treatment) lumber dries faster, maybe a week to ten days.

You might get advice to feel when it's dry or do the water spray test. If water beads up instead of soaking in, it's still too wet. They might also tell you to weigh boards and wait till the weight stops dropping. Honestly? That's guessing.

Get moisture content below 19% before installing. You need it below 19% because that's fiber saturation point where free water is gone but cell walls are still saturated.

Buy a cheap moisture meter. Runs $20-50 for a basic pin-type. Prevents you from rebuilding your deck when boards shrink and create half-inch gaps. Twenty bucks versus ripping out a whole deck? Easy call.

What happens if you skip drying time?

Gaps between boards will open up to a quarter inch or more within six months. A 5.5-inch wide treated board loses about 3/16 inch in width as it dries from 40% to 15% moisture. That's roughly 3% shrinkage across the grain. Screw heads stay put but boards pull away from fasteners as they shrink. The deck creaks with every step because boards are loose.

Wet lumber splits easier too. Wood fibers are swollen and stressed. Even with pilot holes, you'll see more cracks near screw heads. Let it dry first.

If you must install wet boards:

• Install them touching with zero gap
• They'll shrink and create spacing naturally
• Wood shrinks across the grain, not lengthwise
• A 6-inch wide board might lose 1/4 inch in width but almost nothing in length

How should deck boards be spaced and fastened?

Two screws per joist, minimum. Place them about 3/4 inch from each board edge. IRC Table R507.7 requires maximum 16-inch joist spacing for 5/4 deck boards, 24 inches for 2-inch boards. Two screws per joist isn't just best practice, it's code in most jurisdictions. Single-screw installations allow boards to rotate and cup.

Use a chalk line to keep screws aligned. Mark first and last screw positions, stretch string between them, then use it as a reference while you work.

Spacing based on moisture content:

• Wet boards: install touching with no gap
• Dry boards: 3/16 inch gap for 4-inch widths
• Dry boards: 1/4 inch gap for 6-inch widths

A 16-foot pine board can shrink roughly 1/4 inch in width as it dries. Get the math wrong and you'll either have boards touching (no drainage) or gaps big enough to lose your keys through.

How do you prevent screws from breaking when deck boards shrink?

Board dries out, shrinks across its width, but screws stay exactly where you put them. Something has to give. Usually the screw or the board itself.

Stainless steel doesn't flex like softer metals. When wood movement puts stress on the fastener, it snaps instead of bending.

How do you fix this? Pre-drilling slightly oversized pilot holes gives screws a bit of clearance. Not so big you lose holding power, but enough that minor wood movement won't immediately stress the fastener to breaking.

For wet lumber that's going to shrink, drill pilot holes 1/32 inch larger than normal. A #10 screw normally gets a 0.161-inch hole, bump it to 0.192 inches (that's a 3/16-inch bit). Gives the screw wiggle room as wood moves.

Thermal expansion and contraction adds to this. Wood swells when humid, contracts when dry. Temperature swings make it worse. Summer to winter cycles in Ontario or northern California put continuous stress on every fastener.

Pro Tip: After the first month, walk your entire deck and check for screws that have backed out slightly as boards settled. Tighten them back down before moisture gets underneath and starts rot. We make this a standard follow-up visit because roughly 10% of fasteners need minor adjustment after initial installation.

What size screws for pressure treated deck boards?

For standard 5/4 inch pressure treated deck boards, use 2.5 inch long screws. 5/4 deck boards measure 1 inch actual thickness after milling. Building codes require minimum 1.5 inches of fastener penetration into joists. That's why 2.5-inch screws are standard: 1 inch through the board, 1.5 inches into the joist.

Should you use #8 or #10 gauge screws for pressure treated deck boards?

For treated pine decking, use #8 or #9 gauge screws. For dense pressure treated lumber, step up to #10 gauge.

What length screws for pressure treated deck boards?

Standard 5/4 inch pressure treated boards measure about 1 inch thick after planing. For 1-inch thick boards, use 2.5 inch screws. For 2-inch thick pressure treated boards, use 3 inch screws.

Simple rule: multiply your board thickness by 3 to get the right screw length.

This gives you at least 1 inch of penetration into the joist below. A 2.5 inch screw through 1-inch decking provides 1.5 inches of penetration, which prevents screws from pulling out when pressure treated boards shrink or warp.

What's the best stainless steel screws for PT decking?

The best stainless steel screws for PT decking are Eagle Claw stainless steel screws.

We've sold tens of millions over the years to professional deck builders who know the difference between fasteners that hold and ones that fail. The math never works out when you're replacing corroded screws five years later. 

Grab our free sample pack and test them on scrap pressure treated lumber before you buy. Eagle Claw is made by contractors for contractors, which is why returns basically never happen. We know once you drive five of these, you're ordering more!