Metal Roofing Screws

Fasteners are the cheapest part of a metal roof and the part most likely to sink it. For metal roofs, fasteners make up less than 1% of the total cost of installation, yet they can result in 100% of the roof’s failure. Pick the wrong screw — wrong substrate, wrong material, wrong length, or drive it badly — and you get leaks, rust streaks, and callbacks. Get it right and the roof outlives the loan.

A metal roof screw isn’t an ordinary fastener. Metal roofing screws are essential fasteners designed to secure metal panels on roofs and other structures, ensuring durability and resistance against weather and corrosion — from residential homes to commercial buildings and agricultural pole barns. What makes one watertight is the bonded rubber washer. The best metal roofing screws have a neoprene washer to help minimize leaks. That washer compresses against the panel and seals the hole. Screws also beat nails on a metal roof for one reason: roofing screws have a higher hold strength compared to nails — roofing screws are specifically for metal roofs, and roofing nails are typically used to secure asphalt shingles.

For most Montana roofs — galvanized or painted steel panels over a wood deck or wood purlins — a galvanized metal-to-wood screw with a Type 17 point and an EPDM or neoprene washer is the workhorse. The stainless and coastal worries you’ll read about elsewhere don’t apply inland. What matters here is matching the screw to your substrate and panel, getting the length right, and not wrecking the washer with an impact driver.

Knowing the Anatomy and the Types

Before you can spec a screw, you need to read one. The main components are: diameter (the shank diameter, not the head); threads per inch — a #12-14 is a #12 diameter with 14 threads per inch; length, measured from the underside of the head and including the drill point and sealing washer; head style — most common are hex head, hex washer head, and pancake head; drill point style — self-drilling, self-tapping, or self-piercing; material — carbon steel and stainless steel are the two most common; coating, with galvanized being the most common and the head usually painted to match the panel; and the sealing washer.

The single biggest buyer mistake is matching the point to the wrong substrate. Here’s how the point styles break down:

Screw type	Point	What it fastens into
Metal-to-wood	Type 17 (T17) / sharp	Wood framing, OSB, plywood decks
Self-drilling (SD / Tek)	Drill-bit point	Steel purlins, light-gauge framing
Self-tapping (ST)	No drill point, taps own threads	Pre-drilled or soft material
Self-piercing (SP)	30° sharp point	Light-gauge metal, then wood below
Stitch screw	Short	Overlapping panel seams only

Metal to wood roofing screws typically have a T17 point that promotes faster drivability. For steel framing, you need a drill point instead. Self-drilling (SD) screws have a drill point in the tip of the fastener. Self-tapping (ST) screws do not have a drill point but are able to tap their own threads into the attachment material. Self-piercing (SP) screws pierce through light gauge metals then self-tap into the material below. Self-drilling screws are made to bite heavier steel — common Tek-style options will penetrate steel up to .210” thick, with heavy-gauge versions rated for heavy gauge steel up to .500” thick.

Stitch screws do one job. They are typically used for stitching of sidewall and roofing laps or securing flashing or other components to sheeting. These types of fasteners are often used with sealants or washers to draw the joint tight.

Panel system also dictates the screw. The type of fastener depends on whether you are installing exposed fastener panels or concealed fastener panels. Wavy corrugated and R Panel are examples of exposed fastener panels. Standing seam or flush wall panels are concealed. Exposed panels — the corrugated and R-panel you see on most shops, barns, and pole buildings around here — use fasteners with rubber sealing washers to increase the weathertightness of the panels and keep water out. Standing seam is different: concealed fastener panels that use clip attachments, such as snap lock standing seam, generally use pancake head style fasteners, typically 1” pancake heads to fasten the clips.

Material, Coating, and Galvanic Corrosion

Mismatched metals rust out a roof from the fastener up. This effect is known as galvanic corrosion and is often a result of corrosion between the dissimilar metals that are in contact with each other. The rule is simple: fasteners should be made of the same material as the roof or wall systems whenever possible. At the very least, the fastener should display equivalent corrosion resistance to the material being fastened into.

Carbon steel is the standard body for most inland jobs. Carbon steel metal roofing screws offer superior hardness and clamping load capacities while also being cost-effective. However, they are more susceptible to rust. To counter this, many carbon steel metal roofing screws come with a zinc-capped head to enhance corrosion resistance. That zinc-alloy (ZAMAC) cap is what keeps the head from streaking red rust down a panel. The zinc alloy cap head eliminates red rust while protecting the integrity of the connection.

Match the screw material to the panel:

Panel material	Recommended screw
Standard galvanized steel	Zinc-plated (galvanized) screws, head painted to match
Aluminum	304 stainless — never 410
Copper	410 stainless, copper-plated
Corten	Stainless with dark brown painted head

For aluminum roofing, use stainless steel type 304 screws with matching paint color on the heads — never use 410 stainless on an aluminum roof. For copper, use type 410 screws that are copper-plated. For standard metal roofing, use zinc plated (galvanized) screws, with heads painted the same color as your panels.

Two coating cautions worth burning into memory. First: electroplated zinc plated screws are not for use in exterior applications and will corrode quickly. Don’t confuse cheap electroplated zinc with a proper galvanized roofing screw. Second, the Galvalume compatibility note — per the MCA tables, unpainted Galvalume steel should not be paired with plain zinc-plated screws; organic-coated, zinc-alloy head, or stainless-head screws are the compatible picks instead.

Length, Sizing, and Quantity

Too short and the screw never grabs; too long and you snap it driving. The rule of thumb is penetration. You want at least one inch of screw penetration into the material that you are fastening to. From there, the length is usually rounded up to the next half or quarter inch to ensure the fasteners are long enough. Don’t overshoot for its own sake — the longer the screw, the more torsional strain is produced during driving, and sometimes this can cause the fasteners to break during installation.

Length by panel profile, exposed-fastener applications:

Panel	Fastened at	Minimum screw length
Standing seam (clips)	Clip	1” pancake head
½” corrugated	High of the panel	1.5”
⅞” corrugated	High of the panel	2”
R-panel / 7.2 / Ag panel	Low of the panel	1” common

Those numbers come straight from the standard guidance: ½” corrugated fastens to the high of the panel; since the panel is ½” in height, you need at least a 1.5” screw. ⅞” corrugated also fastens to the high; at ⅞” in height, you need at least a 2” screw. R-panel, 7.2, and Ag panels fasten to the low of the panel, where screws 1” in length are the most common.

Common diameters run #10, #12, and #14, and they’re sold in bulk — Western Building Center carries metal-to-wood roof screws in #10 and #14 diameters, in 1”, 1‑1/2”, and 2” lengths, with painted heads in black, brown, charcoal, green, red, white, and plain galvanized to match panel colors. Bulk packs on the wider market typically run in packages of 250 or quantities up to 5,000.

One field tip for re-roof and repair work: when you’re backing out old, loosened screws, step up a size. So-called “rescue screws” — replaces loosened fasteners — are sized slightly larger to grab fresh material where the old threads stripped out.

Installation: Where Good Screws Still Fail

The right screw, driven wrong, leaks. Three rules carry most of the weight.

Drive into the flat, perpendicular, and don’t over-torque. On low-profile panels you fasten the flat, not the high rib, and you stop when the washer seats — avoid over-torquing, which damages the washer and causes leaks; the washer should sit like a neat, firm donut against the metal. A crushed or mushroomed washer is a future leak.

Leave the impact driver in the truck. Impact drivers are not recommended for fastening metal panels or composite panels. These tools can cause damage to the drill point, break screws, chip painted surfaces, and strip threads on Type 300 stainless steel screws. And again — over driven screws also damage the EPDM sealing washer and could potentially cause leaks. Use a depth-sensing or torque-controlled screw gun instead.

Spacing tightens up at the edges, which matters a lot under Montana snow and chinook wind. Spacing typically ranges from 12 to 24 inches in the field and 6 to 12 inches at edges, ridges, and overlaps — always consult your manufacturer’s guidelines. The eaves, ridges, and overlaps take the wind uplift and the snow drag, so that’s where you go tighter.

One more reason the washered screw matters in this climate: metal panels move. These screws accommodate thermal expansion and contraction to prevent leaks — exactly what a panel does through Montana’s swing from a January cold snap to an August roof deck baking in the sun. A sound EPDM washer flexes with that cycling instead of cracking around the hole.

Frequently Asked Questions

What’s the difference between roofing screws and roofing nails? Roofing screws have a higher hold strength compared to nails, but nails offer faster installation. Roofing screws are specifically for metal roofs, while roofing nails are typically used to secure asphalt shingles.

How long should a metal roofing screw be? Aim for at least one inch of bite into the substrate. You want at least one inch of screw penetration into the material you’re fastening to, and the length is usually rounded up to the next half or quarter inch. For reference, ½” corrugated needs about a 1.5” screw at the high rib, ⅞” corrugated needs about 2”, and R-panel fastened at the low commonly uses a 1” screw.

What screw do I use for wood versus steel framing? For wood framing, OSB, or a plywood deck, use a metal-to-wood screw. Metal to wood roofing screws typically have a T17 point that promotes faster drivability. For steel purlins, use a self-drilling Tek screw with a drill-bit point — common versions penetrate steel up to .210” thick, with heavy-gauge options rated to .500”.

Why is my new metal roof leaking around the screws? Usually the washers. A roof can fail from broken fasteners, incorrectly installed fasteners, worn out sealing washers, or the simplest of errors: using the wrong screws. Over-driving is the common culprit — the washer should sit like a firm donut, not a flattened, squeezed-out ring.

Can I use an impact driver to speed things up? No. Impact drivers are not recommended for fastening metal panels. They can damage the drill point, break screws, chip painted surfaces, and strip threads. Over driven screws also damage the EPDM sealing washer and could potentially cause leaks. Use a screw gun with depth or torque control.

What screws go with a standing seam roof? Concealed clip-fastened systems use low-profile pancake heads. Snap lock standing seam generally uses pancake head style fasteners — 1” pancake heads are the most typical for fastening the clips.

Do screw color choices matter beyond looks? Color is mostly appearance, and matching is straightforward. Screws are available with color-coated fastener heads to match the color of your metal panels, so the fasteners blend in for a more polished, neat appearance. Function still comes first — get the substrate, material, length, and washer right, then match the color.