What Size Screws To Use For Metal Roofing?

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Size is one of the first things that comes to mind when shopping for fasteners for your next roofing project.

Of course, the best size depends on the type of roof. But what else should you consider? Also, how do you measure screw length and thickness, and does the screw type matter? We answer these and other common roofing screw size questions below.

What size screws for metal roofing

The 1 1/2-inch screw is the standard size for metal roofing jobs. It is used throughout the metal roofing project, offering a 1 1/4-inch penetration to hold the metal panels strongly in place. However, 1-inch and 2-inch screw sizes aren’t uncommon, especially for thinner and thicker roofing sheets. 

What are Metal Roofing Screws?

Metal roofing screws are special screw fasteners used to secure metal roof panels to the building structure, whether wood or metal substrates.

They are made from various metals and some from a combination of metals. For instance, standard metal roof fasteners are constructed from a carbon steel base. Meanwhile, long-life fasteners are stainless steel screws. Hardened steel screws and chrome steel screws are other options.

Finally, we often use bimetallic screws for complete corrosion resistance. They feature a stainless steel head and shank and a carbon steel tip to easily penetrate the steel roof panel and the wood or metal substrate.

Anatomy of Roofing Sheet Screws

Like other screws, metal roofing screws comprise two main parts, the head, and the shank. However, a few additional features make the screws unique. These are;

  • A sealing washer to protect the surface from water penetration
  • A corrosion-resistant coating to prevent surface corrosion
  • The screws are available in different colors to match the roof.
  • Drill points (for metal substrates) and sharp points (for wooden substrates) enable faster penetration.

Benefits of Metal Roofing Screws

Originally, roofers used nails for metal roof panels. But later, the fasteners evolved into nails with washers for leak protection. Then manufacturers began making threaded nails with sealing washers for greater holding power and weather tightness.

The evolution hasn’t stopped. Today, metal roofing screws are preferred because they are easier to install and offer greater holding power. Moreover, modern-day roofing screws are beautiful and corrosion-resistant.

Above all, screws are more resistant to wind pullout but easy to remove with drills and other tools. Also, unlike nails, you can lift screws off a metal roof without damaging the panels. Therefore, previously screwed metal panels are more reusable than nailed panels.

Fastener Identification: What is “Screw Size?”

Screw “size” primarily refers to the screw’s diameter and length. Screw diameter refers to the shank and head diameter, while the length solely refers to the shank length. However, we don’t dwell on the head diameter as all head diameters are practical for metal roofing projects.

  • Screw diameter: The screw diameter is the shank diameter measured at the thickest point. The higher the value, the thicker the screw.
  • Screw length: Screw length is measured differently depending on whether it’s a flex head screw or flat head screw. For hex head screws, the “screw length” is the distance from the bottom of the screw head to the screw tip. Meanwhile, for flat-head screws, the length is measured from the top of the head to the screw tip.

Screw sizes in the US follow ASME/ANSI guidelines, forming the Unified Thread Standard (UTS). Meanwhile, the rest of the world follows ISO standards.

Factors Impacting Metal Roof Screw Size Choice

Various factors impact the choice of metal roofing screw length. However, the two main factors are the metal panel and substrate properties.

  • Metal roof panel properties: You need thicker screws for heavier roof panels. Otherwise, the panels put excessive strain on the screws. Also, you need longer screws for thicker metal panels for a strong substrate attachment.
  • Substrate properties: Typically, the screw must penetrate the substrate up to an inch or more. That’s why 1 1/2-inch screw fasteners are the most popular. In addition, we prefer longer screws for thicker substrates to achieve a stronger joint. Thinner screws work better for wooden substrates, while metal substrates require thicker, stronger screws to reduce the risk of broken screws.
  • Exposed vs concealed metal roof paneling: Exposed fastener panels give you more freedom to use larger screws to achieve the desired results. However, standing seam or concealed roofs require tinier, low-profile fasteners.
  • Other factors to consider when shopping for metal roof screws are climate and personal preferences. For instance, you need longer, thicker screws in windy climates or cold areas with heavy ice loads.

What’s the Correct Screw Length for a Metal Roof?

As we’ve seen, the “right screw size” depends on various factors, including panel type, substrate properties, and climate. Nevertheless, the following are appropriate-sized screws for standard applications;

  • Standing seam roofing – 1-inch long pancake head screws are the best choice for fastening standing seam roof clips.
  • 1/2-inch corrugated roofing panels: 1 1/2-inch screws are used for standard 1/2-inch corrugated roofing projects. This is because the screw fastens go on the high/rib of the roofing panel, which is 1/2-inch high. So, you need extra length to achieve a strong attachment.
  • 7/8-inch corrugated roofing panels: 7/8-inch corrugated panels have 7/8-inch high ribs, requiring even longer screws for maximum attachment strength. Therefore, we recommend 2-inch long roof screws.
  • R-panel/AG panels/7.2 panel: Screws go on the low of R-panels, AG panels, and 7.2 panels. So, you don’t need unnecessarily long screws. For this reason, we recommend 1-inch metal screws.

What’s the Correct Fastener Shank Diameter (Gauge) for a Metal Roof?

Although metal screw shank diameters are measured in inches, you’re more likely to come across “gauge (#)” or “major diameter” measurements in the US.

Generally, anything less than 1/4-inch thick is labeled #0 to #12-gauge. For instance, a #0 screw has an outside diameter of 0.06 inches, while #12 screws have outside diameters of 0.216 inches.

Beyond #12 screws, the sizes are labeled in inches. For instance, half-inch screws are labeled 1/2-inch, and two-and-a-quarter-inch screws are labeled 2 1/4-inch. The only exception is 1/4-inch screws which are sometimes labeled #14.

The following are general selection guidelines to help you choose the right screw diameter for the right application;

  • #9 to #10 – Metal to wood screws: #9 screws are 11/64-inch thick while #10 screws are 3/16-inch thick. These screws are best for screwing metal panels to wooden substrates.
  • #12 – Metal-to-metal roofing sheet screw: #12 screws are 7/32-inch thick screws. We mainly used them for screwing metal panels to metal substrates.
  • #14 – For areas with heavier snow loads: #14 screws have 1/4-inch thick diameters. They work best in locations with strong winds and heavy snow loads.

What’s the Right Screw Head Diameter for a Metal Roofing Project?

Screw head diameters don’t matter much when roofing. Instead, the head style is more important as it determines the screw length.

Nevertheless, you may want to know that metal screw head diameters are twice the screw shank diameter. For instance, a #14 screw (1/4-inch shank diameter) has a 1/2-inch diameter head. Meanwhile, a #0 screw (1/16 inch shank diameter) has a 1/8-inch diameter head.

Matching Fastener to Application: General Guidelines 

Now that we know standard screw lengths and diameters, let’s match common screw sizes to popular metal roofing applications;

  • 2-inch metal roof screws: Two-inch screws are used where panels overlap because these sections require longer fasteners to penetrate two panels while penetrating the substrate to a sufficient depth. Also, they are the best choice for 7/8-inch corrugated panels.
  • 1 1/2 inch screws: 1 1/2-inch screw fasteners are ideal for thicker metal roof panels or when fastening metal panels to metal substrates. They are also great for 1/2-inch corrugated metal roofing sheets.
  • 1-inch screws: One-inch screws are the standard choice for standing seam roofing projects. They penetrate 3/4 inches into the substrate for excellent holding strength.
  • 5/16-inch screws: 5/16-inch screws are mainly used to stop larger screws from overlapping.
  • 1/4-inch screws: Quarter-inch size screws are primarily for affixing metal roof trim at two-foot increments.

Dangers of Choosing the Wrong Metal Roof Screw Size

Using the wrong metal screws for your roofing project can cause multiple issues. These include;

  • Roof leaks around the screw: Incorrect screw size is the second most common cause of leaking around roof screws after incorrect screw installation. For instance, thicker shanks can damage thinner roof panels.
  • Over or under-driven screws: Naturally, we want to underdrive longer screws and overdrive shorter ones. Unfortunately, over or underdriving roof screws only cause new problems.
  • Substrate damage: Longer or thicker screws can damage the roof components beneath the metal panels. For instance, splitting in wooden purlins is inevitable if the screws are too thick. Also, longer screws can piece the insulation, especially at the roof’s eaves.

Other Factors to Consider When Buying Metal Roofing Screws

As you’d expect, size is the first of many other factors you must consider when shopping for metal roof screws. Other factors to prioritize are;

  • Screw head types: Popular screw head types are hex washer head, flat head, pan head, oval head, round washer head, pancake head, and wafer head screws.
  • Threads per inch (TPI): The number of threads per inch (TPI) on the screw determines the coarseness or fineness of the screw. Generally, coarser screws are stronger and more suited for thicker metal panels. The opposite is true for fine screws.
  • Specialty screws: Some screws are designed for special purposes. For instance, we use lap screws (also known as the stitch screw) to attach the panel side lap on exposed fastener panels. Meanwhile, self-driving screws, better known as TEK screws, eliminate the need for pre-drilling.
  • Drill point style: Besides self-drilling screws, self-piecing and self-tapping screws are other popular drill point styles. A self-tapping screw taps threads into the material but doesnt drill through metal. Meanwhile, a self-piercing screw pierces light-gauge metal and taps threads into the material.

How to Use Roofing Screws

Ideally, you should hire a professional roofer for all roofing jobs. Nevertheless, knowing a few tips for a future DIY doesn’t hurt. So, the following are best practices for screwing metal roofs;

  • Avoid over or under-tightening roofing screws
  • Always install screws straight, not sideways
  • Pre-drill if attaching panels to a solid wood substrate
  • Always use a screw gun to fasten roofing screws

Summary

One-and-a-half-inch screws are the standard size for metal roofing. They provide sufficient penetration for strong panel attachment. #9 (11/64 inches) and #10 (3/16 inches) are the standard shank/shaft diameters for metal-to-wood, and #12 (7/32 inches) is the ideal shaft diameter for metal-to-metal roofing projects. Always speak to a professional if unsure.