Metal roofing screws are not interchangeable with standard fasteners — using the wrong screw on a metal roof causes leaks, panel pull-through, and premature failure. The right metal roofing screws match the substrate (wood vs. metal), have an EPDM sealing washer, and are long enough to penetrate the structural member beneath. Here's exactly what screws you need for a metal roof and how to install them correctly.
Metal-to-Wood Screws: The Most Common Type
Metal-to-wood screws are the most common type used in residential and agricultural metal roofing. They attach metal roofing panels to wood purlins or plywood decking. Metal-to-wood roofing screws are self-drilling — they penetrate the metal panel and thread into the wood beneath without pre-drilling. The standard configuration is a hex washer head with an EPDM rubber sealing washer bonded to the underside of the head.
Wood roofing screws must penetrate the wood purlin or sheathing by at least 1 inch — and 1.25 inches for structural connections. Screw length should allow at least one inch of penetration into the wood substrate. Add the metal panel thickness to the required wood penetration to determine the minimum screw length and round up to the nearest half- or quarter-inch size.
Metal-to-Metal Screws (Tek Screws)
Self-drilling screws are used for metal-to-metal applications — attaching metal panels to steel purlins, attaching trim to metal framing, and panel-to-panel sidelap connections. Metal-to-metal screws have a drill point tip sized for the steel gauge being fastened, which allows Tek screws to drill their own holes and form mating threads. For light-gauge steel framing (up to 1/4"), a #3 or #4 drill point is standard. For heavier structural steel, a #5 drill point handles up to 1/2" steel.
Pre-drilling is not required for metal-to-metal self-drilling screws in most gauges. However, pre-drill holes when fastening near panel edges to prevent the drill tip from walking and tearing the panel — point walking is when the tip skips across the metal surface before engaging, damaging the panel and mislocating the hole.
Lap Screws
Lap screws are used to attach panel sidelaps in exposed fastener systems — they stitch adjacent metal panels together at their overlapping edges. Lap screws are typically smaller diameter fasteners with a low-profile head that doesn't interfere with the panel's corrugation. They prevent panels from lifting at the sidelap under wind uplift and seal the side seam against water infiltration when used with the panel's sidelap sealant.
EPDM Sealing Washers: Critical for Leak Prevention
Use screws with rubber sealing washers for exposed fastener panels — this is non-negotiable. The EPDM washer compresses when the screw is driven, sealing the hole against water intrusion. Using sealing washers prevents roof leaks effectively. EPDM washers last 2–3 times longer than neoprene under UV exposure, making EPDM the correct specification for metal roofing. Drive screws firmly to seat the washer without crushing it — an over-driven screw collapses the washer and creates a leak path; an under-driven screw leaves the washer uncompressed and doesn't seal.
Hex Washer Head vs. Pancake Head
The two main head styles for metal roofing screws are hex washer head and pancake head (low-profile head):
| Head Type | Application | Notes |
|---|---|---|
| Hex washer head | Standard exposed fastener panels | Driven with nut driver; includes EPDM washer; most common type |
| Pancake / low profile head | R-panel, corrugated, trim screws | Lower profile reduces snag risk; still uses sealing washer |
| Cupped hex washer head | High-load applications | Cupped washer seat improves seal under thermal movement |
A hex washer head allows for strong and even-pressure holds across the sealing washer. Hex head screws for metal roofing are measured from the bottom of the head (since the head remains above the panel). Flat head screws for other applications are measured from the top of the head.
Screw Materials: Carbon Steel vs. Stainless Steel
Metal roofing screws are available in carbon steel (with various coatings) and stainless steel. Carbon steel screws with galvanized or other corrosion-resistant coatings are adequate for most inland applications. Stainless steel screws are essential within 3 miles of saltwater — coastal environments consume galvanized and standard coated screws rapidly. Stainless steel screws provide the best corrosion resistance for metal roofing near the coast and wherever the panels are aluminum or contain dissimilar metals that could accelerate galvanic corrosion.
Galvanized screws are appropriate for general agricultural and rural metal roofing where salt air isn't a factor. Using the wrong fastener can lead to leaks and structural issues — not just from environmental corrosion, but from galvanic corrosion when incompatible metals contact each other under moisture.
Color-Matched Screws
Color-coated screws match metal panel colors for aesthetics — exposed fastener metal roofing has visible screw heads, and matching the screw head color to the panel color creates a clean, professional appearance. Color matching is particularly important for residential metal roofing where the screws are visible from the ground. Most major roofing screw manufacturers offer color-matching systems for major metal panel brands.
How Long Should Metal Roof Screws Be?
Screw length depends on panel profile and substrate. For metal-to-wood installations: add the panel depth (typically 1/2" to 1-1/4" for corrugated and R-panel profiles) to the required wood penetration (1" minimum). A standard installation on 1" thick purlins requires screws at least 1-1/2" to 2" long depending on panel profile. For metal-to-metal: the screw only needs to penetrate and thread the steel purlin, so shorter screws are used — typically 3/4" to 1-1/4".
Can I Screw Metal Roofing Directly on Plywood?
Yes — metal roofing can be screwed directly to plywood decking using metal-to-wood screws. Plywood sheathing (typically 5/8" or 3/4" OSB or plywood) provides adequate holding depth for standard metal-to-wood roofing screws. The screw must penetrate through the panel and through the full plywood thickness with at least 1" of thread engagement. Self-drilling screws work on plywood without pre-drilling; the drill point penetrates wood easily. Some installers pre-drill the metal panel only (not the plywood) to prevent the drill tip from walking before it engages the panel's ribs.
Screw Spacing for Metal Roofing
Screws should be spaced every 12 to 18 inches horizontally along each purlin line for most residential and agricultural applications. In high-wind zones, closer spacing or additional fasteners at panel ends and ridgelines are required per local building codes. Screw placement should be in the flat section of panels (in the valley, not on the rib) for exposed fastener systems — screws driven through the rib crown are prone to leak. Always consult the panel manufacturer's installation instructions for approved fastener patterns, as requirements vary by panel profile and structural span.
How Many Screws for a 1,500 Sq Ft Metal Roof?
On a typical residential metal roof with panels spaced 12–18 inches at each purlin, plan approximately 80–100 screws per square (100 sq ft). For a 1,500 sq ft roof, that's roughly 1,200–1,500 screws. Actual count varies with panel profile, purlin spacing, hip and valley cuts, and the number of trim pieces requiring additional lap screws. Trim screws should have rubber sealing washers for any weather-exposed trim connections. Order 10–15% extra to account for waste, trim cuts, and replacement of any damaged screws during installation.
Best Way to Screw Down a Metal Roof
Drive screws with a screw gun or impact driver set to a low-torque clutch setting — metal roofing screws reach the correct seating depth quickly, and over-driving is the most common installation mistake. Drive screws perpendicular to the panel surface; angled screws don't compress the washer evenly and leak under rain. Replace old screws that have stripped holes or failed washers before they become active leak points — using the wrong screws or worn-out washers will cause leaks as soon as water hits the roof.
Shop Metal Roofing Screws at jakesales.com
Find metal-to-wood screws, metal-to-metal self-drilling screws, lap screws, and color-matched roofing fasteners with EPDM sealing washers at jakesales.com. Carbon steel and stainless steel options in every length for residential, agricultural, and commercial metal roofing projects.