There’s a debate that’s been raging for decades, with no signs of slowing down: Should metal roofing screws go through the valleys of the corrugated metal or through the peaks? I’ve noticed those who prefer going through the peaks are vehement in their position. They insist there is no better way to do it, and anyone who thinks otherwise is an idiot. But are they right?
The first time someone told me to drive the screws through the peaks, I ignored their advice. It seemed counterintuitive to me. They told me the roof would leak if I didn’t do it that way, but that made no sense to me.
Why should I drive the screw through the part of the metal that’s the farthest away from the sub-deck? How is that going to prevent leaking, when it almost certainly will crimp the metal? I also thought about the rubber gasket right below the metal washer on the screw: Isn’t that supposed to sit flat? I thought this must just be a myth that has spread so far, many accept it as fact.
Around this same time, I was working with a lot of scrap metal; and more and more, I began to see old sheets of corrugated steel with holes through the peaks. I started to doubt my logic, so I began doing research… To my surprise, I found several modern videos, articles, forums, and comments saying you should go through the peaks. I also found the opposite.
So, what’s going on here? Who’s right? Well…
Before the invention of the self-tapping screw, there was a benefit to driving nails through the peaks instead of the valleys. Holes made by nails are very leaky, and since water runs through the valleys, if you drive the nails through the peaks, the holes won’t leak as much. However, since the advent of modern screws, this wisdom no longer applies. Continue reading to learn more…
The History of Corrugated Metal Roofing
Corrugated metal was invented in the 1840s by a British architect and engineer named, Henry Palmer. Back then, the panels were called CGI for short, which stood for “corrugated galvanized iron.”
Roofers in those days didn’t carry around cordless power drills with them, they carried hammers. The only practical way to fasten the panels was by driving nails through them. This created a problem, though… the roofs leaked like a barrel with a hole in the bottom.
Enter the lead head nail…
The Lead Head Nail
A lead head nail is exactly what it sounds like: It’s a regular nail with a lead head instead of a steel head. It was supposed to solve the leakage problem. Lead is an extremely soft metal, so when you hit the head with a hammer, it flattens out like a pancake, creating a sort of makeshift gasket.
Lead head nails worked better than other nails but they still leaked. Eventually roofers figured out that if they drove the lead head nail through the peak, it was less likely to leak. This lead to another problem, though – no pun intended.
Nails are good at holding things together, but they’re not that good at holding things down – there’s a difference. Roofs with lead head nails through the peaks didn’t leak as much, they just blew off. Pick your poison: Would you like a roof that leaks or blows off?
Enter the self-tapping metal roofing screw…
The Self-Tapping Metal Roofing Screw
In 1961, Black and Decker invented the cordless power drill. Construction workers no longer had to rely on hammers and nails, they could now take a drill with them anywhere. This meant using screws was no longer an inconvenience. Simply drill a hole and drive in the screw.
So in 1965, an inventor named, Carl H., invented the self-tapping metal screw. This solved both problems: no more leaks, no more panels blowing away. You could now drive a screw with a washer into the panel. The washer prevents leaking, and the screw threads prevent the fastener from being pulled out – screws are excellent at holding things down.
Even better: Modern metal roofing screws have an EPDM rubber gasket under the washer to completely eliminate leaking – though, they don’t last forever, sadly.
It was around this time that many roofers went back to driving through the valleys, though others relucted. It made more sense to once again go through the valleys because it didn’t crimp the corrugations and you got a tighter connection. Since the valleys sit flat against the wood, you can grab more material with less material doing it that way – i.e., you don’t need an extra long screw to drive it all the way into the substrate.
If you drive the screw through the peak, then only a small percentage of the threads actually penetrate the wood; unless you completely depress the peak until it’s flush with the wood, which basically defeats the purpose.
Why Do People Still Go Through the Peaks?
Now that we know why builders started going through the peaks, and why this no longer makes sense, it begs the question: Why do so many still insist on doing it this way? I think it has something to do with New Zealand.
It took a while for self-tapping screws to become the norm and for this new practice to catch on. For reasons I’m not particularly sure of, New Zealand was late to the game, so they just kept going about it the old way; and for reasons I don’t understand at all, even when they switched to screws, they still kept driving them through the peaks. Tradition, I suppose?
New Zealanders also migrated heavily to other nations throughout the 20th century – Australia, South Africa, America… and brought this tradition with them, perpetuating the pas·sé practice. As far as I can tell, to this very day, most New Zealanders insist on driving screws and nails – yes, they still sometimes use lead head nails – through the peaks, and so does everyone else they’ve spread this “knowledge” to.
The next time someone tells you it’s wrong to drive the screws through valleys, you can tell them the story of the lead head nail and how it was replaced by the self-tapping screw, and hopefully bring them into the modern era.
Corrugated Metal Roofing. History of Corrugated Metal Roofing. Retrieved from https://www.corrugatedmetalroofing.net/history.html
Google Patents. Self-tapping screw. Retrieved from https://patents.google.com/patent/US3398625A/en
Taylor Miller (October 31, 2020). History of Power Tools Series | Drill from the past to now. Retrieved from https://ronixtools.com/en/blog/history-of-power-tools-series-drill-from-the-past-till-now/
Origins. Immigration History from New Zealand to Victory. Retrieved from https://origins.museumsvictoria.com.au/countries/new-zealand/