There’s a lot that goes into a solid metal roof, but screw placement? That’s the part people second-guess the most.
Flat or rib? How far apart? What actually matters?
If you’ve been asking those questions, you’re in the right place. We’ll break down where to screw metal roofing and how to do it in a way that holds up.
Key Notes
- Screws go in flat sections (valleys), not ribs, for better structural grip and sealing.
- Standard spacing: 24 inches vertically, every 3rd rib horizontally for corrugated panels.
- Use drill drivers with adjustable torque, not impact drivers, to avoid overdiving screws.
- Proper technique requires perpendicular angle and EPDM rubber washers for watertight seal.
Rib or Flat? The Screw Placement Debate
Let’s start with the big one: where to screw metal roofing panels – on the rib or in the flat?
Most manufacturers (and seasoned pros) agree: place screws in the flat section, also called the valley. This is the part of the panel that sits flush against the roof deck or purlins.
Yes, some roofers prefer the rib. And yes, there are certain exceptions. But for standard exposed-fastener panels? The flat is where it’s at.
| Location | Main Advantages | Main Disadvantages |
|---|---|---|
| Flat/Valley | Secure grip, better seal, even load, less flexing | May sit in standing water if washers fail |
| Rib | Keeps screws out of water, allows some expansion | Less structural grip, harder to seal properly |
Quick Tip: Always follow your panel manufacturer’s guide. That’s the rulebook that matters most – not doing so can void your warranty.
Why Screws Go in the Flat (Most of the Time)
There are solid reasons why the flat section is the go-to:
- Better Structural Grip: The flat sits right on the solid roof deck or purlin. Screwing here gives the fastener something substantial to bite into.
- Stronger Seal: Screwing into the flat allows the washer to compress evenly, which is key for a watertight seal. On a rib, that washer often ends up distorted.
- Less Flex = Fewer Loose Screws: Fastening through the flat reduces stress on the panel and minimizes movement from wind or temperature changes.
- Even Load Distribution: Panels stay anchored and balanced, improving overall durability.
When Screws Might Go in the Rib (Rare Exceptions)
While the flat is standard, some manufacturers do specify rib fastening for particular panels.
A few reasons why:
- It keeps screws higher, away from any potential standing water.
- Some panel profiles are designed to flex more and need that rib fastener spacing.
- Rib screws can help with expansion/contraction of panels in large-span buildings.
But these are exceptions – not the rule. Always check the install manual for your specific panel.
How to Space Screws: Vertical & Horizontal Guidelines
Vertical (Up the Slope):
- Standard spacing: 24 inches on center
- High-wind or snow zones: Go tighter – 18 or 12 inches on center
- Installing over purlins? Place screws at every purlin line (usually 24 inches apart)
Horizontal (Across the Panel):
- Corrugated panels: Screw into every third rib
- Flat-type panels (like R-panel, PBR): Screw into every flat
- Edges and overlaps: Always place screws on both sides of the overlap, and at every edge
| Spacing Direction | Typical Value | Notes |
|---|---|---|
| Vertical (up panel) | 24 in O.C. | Reduce spacing in high-wind or heavy snow areas |
| Horizontal (across panel) | Every 3rd rib or every flat | Always screw near edges and overlaps |
Ideal Screw Pattern for Metal Roofing
The goal is clean, straight vertical lines of screws. This is called a “screw line” pattern, and it’s important for both structure and appearance.
- Screws go in vertical rows every 24 inches
- Each row includes 4–5 screws spaced across the panel width (depending on panel type)
- No staggered screws – keep it aligned for even load and seal
- Screws near overlaps and edges should be closer together (every 6 to 12 inches)
How to Drive Screws for a Watertight Seal
This part matters. More than you think.
- Straight, not slanted: Screws must go in perpendicular to the panel. Angled screws = leaks.
- Tight, but not too tight: Compress the washer just enough so it flattens under the screw head. If it bulges or breaks? You’re overdoing it.
- Use screws with EPDM rubber washers: This rubber is flexible, UV-resistant, and built to last.
- Clean up shavings: Metal debris left on the roof can cause rust.
What Tool Should You Use?
Use a drill driver, not an impact driver.
Impact drivers might feel faster, but they can overdrive screws, damage panels, and crush washers. Drill drivers with adjustable torque are safer and give you more control.
Screw Placement by Panel Type
| Panel Type | Screw Placement |
|---|---|
| Corrugated/Ribbed | Flat section (valley), every 3rd rib |
| R-Panel/PBR | Each flat, aligned vertically |
| Standing Seam | Concealed clips (no exposed screws) |
| Metal Shingles | Manufacturer-specified spots |
Screw location can change based on what kind of metal panel you’re working with:
- Corrugated / Ribbed Panels: Screws go in the flat sections. Spaced every third rib across, every 24 inches up.
- R-Panel / PBR / Western Rib: Screws go in each flat section across. Standard vertical spacing applies.
- Standing Seam Panels: No exposed screws. Fasteners are hidden beneath clips.
- Metal Shingles: Screws go into marked points near the top lip. Always follow the product guide.
What Happens If You Get It Wrong?
A lot, unfortunately:
- Leaks: Bad angles or loose washers = water getting in
- Rust: Improper screws or leftover shavings can start corrosion
- Loose panels: Without proper grip, wind and temperature shifts can dislodge panels
- Voided warranty: Manufacturers will not back a roof that doesn’t follow install guidelines
Moral of the story: It’s worth taking the time to get screw placement right the first time.
Weather & Climate Considerations
Hot/Cold Weather:
- Metal expands in heat and contracts in cold.
- Screws on the flat help prevent panel flexing and movement over time.
- Avoid installing in extreme temps – torque can be off due to expansion or contraction.
Windy Conditions:
- Go tighter with screw spacing near edges and overlaps
- Follow local code for wind uplift requirements
- Always double up on screws at panel ends
Screw Maintenance: How Often Should You Check?
- Inspect screws twice a year (spring and fall are great times)
- Also check after major storms
- Look for: loose screws, lifted washers, rust, and missing fasteners
If a screw is loose, retighten it. If a washer is damaged or crushed, replace the whole screw.
Frequently Asked Questions
Can I reuse old screw holes when replacing metal roofing?
No, reused holes typically won’t hold screws securely and may leak. It’s best to shift panels slightly or patch old holes with sealant and install new screws nearby.
Do I need to pre-drill holes for metal roof screws?
Not always, but pre-drilling can help with accuracy and cleaner finishes, especially on thinner panels or when attaching to metal purlins. It also reduces the risk of stripping or panel damage.
Are self-tapping screws okay for metal roofing?
Yes – in fact, most roofing screws are self-tapping. Just make sure they’re designed specifically for metal roofing and come with high-quality rubber washers.
How many screws do I need per metal roofing sheet?
It depends on panel size and spacing, but a typical 36″ wide panel needs 4–5 screws per row, spaced every 24″ vertically. That averages around 80–100 screws per 100 square feet of roofing.
Conclusion
When it comes to where to screw metal roofing, the safest bet (across most standard panels) is the flat section. It offers the most secure grip, better seal, and longer-lasting performance.
But getting it right isn’t just about where you place the screws. Spacing matters. So does the angle, the tool you use, the type of washer, and how tight you go.
Small details like these are what separate a roof that lasts decades from one that fails early.
If you’re planning a repair or replacement and want it done right from the start, book a free appointment with our team. We’ll check your screw pattern, spacing, and overall setup – no guesswork needed.