If you’ve ever stood beneath the CN Tower, craning your neck to trace its lines all the way up to the observation deck that juts into Toronto’s sky, you’ve probably wondered the same thing I get asked a hundred times a week as the lead structural engineer for a global towers supplier: What is the shape of the CN Tower? It’s not a circle. It’s not a cone. It’s not even a single shape, really—because if it were, it wouldn’t survive 50+ years of brutal Canadian winters, high-altitude winds, and the occasional seismic jolt from the St. Lawrence rift system. Most people think it’s a smooth, tapering column, and that’s the easy, memorable answer. But for anyone who builds towers—whether they’re broadcasting signals, hosting observation decks, or holding up wind turbines—shape isn’t just a matter of aesthetics. It’s the first line of defense against the forces that want to tear towers apart. Towers
I started working with telecommunications towers 18 years ago, fresh out of engineering school, and my first big project was installing microwave repeaters across Ontario. Back then, I thought a tower’s shape was just whatever looked tall enough, until we had a 120-foot steel lattice tower snap mid-winter outside Sudbury. The inspection later showed the wind had caught its uneven, boxed cross-section at a 15-degree angle, creating a vortex that spun faster than the tower was designed for. That’s when I learned: shape is strength, and the CN Tower is a masterclass in that lesson.
Let’s get specific. The CN Tower’s structure starts at ground level, where it’s not a circle, not a square, but a hollow concrete core with three curved, Y-shaped legs that spread out to form a triangular base. If you draw a line from the center of the core to each leg’s base, those lines are 120 degrees apart—triangular symmetry, not rotational symmetry. That’s intentional. Winds in Toronto often blow from Lake Ontario in steady, cross-lake gusts, and a triangular base doesn’t create a single “weak axis” the way a square or rectangle does. A square tower has two sides that catch headwinds directly and two that catch them at an angle, leading to uneven stress. The CN Tower’s three legs distribute wind load evenly across all three supports, so no single part takes more stress than it was built to handle.
As you move up from the base, the legs curve inward, merging into a central shaft around 100 feet above ground. That shaft is not cylindrical, either. It tapers gradually, but not uniformly—its diameter shrinks faster in the lower third, where the tower carries the full weight of the base and legs, and slower in the upper two-thirds, where the main loads are wind shear and broadcast equipment weight. Wait, let’s talk about that upper section, because that’s where most people’s perception of its shape falls short. The observation deck and the famous glass floor sit in what’s called the “pod,” a 335-meter section that’s not just a small bulge on a tapered column. It’s a modified parabolic shape, designed to deflect air currents instead of letting them wrap around the tower and create dangerous vibrations. Back when the CN Tower was designed in the 1970s, structural engineers didn’t have the computer modeling we use now—they used scale models in wind tunnels, testing hundreds of cross-sections to see which would reduce sway. The winner? A shape that’s wider at the top of the pod, with a gentle curve that fades as it meets the main shaft, cutting vortex shedding by 30% compared to a straight cylinder. That’s why even on a windy day, the CN Tower sways just 1 to 2 feet at the top—hardly noticeable to visitors, but a feat of shape engineering that’s still taught in civil engineering programs today.
A lot of people ask why we don’t just build all towers like the CN Tower. The answer is simple: cost. The CN Tower is a dedicated landmark, built to be the tallest freestanding structure in the world at the time, so they could invest in that custom, shape-specific engineering. Most towers we build for telecom, industrial, or urban broadcast don’t need that level of precision. But that doesn’t mean shape isn’t critical for them, too. Take our recent project for a regional telecom provider in rural Alberta: we built a 280-foot tower to replace an old lattice tower that kept failing in cross-winds. The old tower had a square cross-section, and the wind would create a resonant vibration that shook the signal equipment loose every winter. Our solution? A tapered, triangular cross-section that mirrors the CN Tower’s base symmetry, scaled down for the load requirements. We ran wind tunnel tests on a 1:50 scale model, adjusted the taper angle to cut vortex shedding, and the result is a tower that’s 20% lighter than the old one, uses 15% less steel, and has zero vibration issues in three years of operation.
Another example: wind turbine towers. Most wind towers are cylindrical, but the new ones we’re building for offshore wind farms in the North Sea have a modified conical shape, wider at the base to handle the force of ocean waves and narrower at the top to reduce drag from wind. We spent six months testing different tapers—1:50, 1:60, 1:70—before landing on 1:60, which balances material cost with load capacity. It’s not as radical as the CN Tower’s shape, but it’s tailored to the specific forces that tower faces. That’s the thing about tower shape: there’s no one “right” shape. It’s a formula that combines height, location, load, and cost. The CN Tower’s shape works because it’s built in a high-wind, seismic zone, needs to support 130 broadcast antennas, and double as a tourist attraction. A small urban telecom tower only needs to support a single antenna, so its shape can be a simple tapered cylinder, but we still apply the same core principles we learned from studying the CN Tower.
I’ve been to the CN Tower three times now, twice as a tourist, once to meet with Toronto’s city planning team about a small public observation tower we’re building near the waterfront. The last time I went, I brought a laser level, just to map the shaft’s taper as part of a case study for our engineering team. I noticed something the wind tunnel tests didn’t tell us: the concrete isn’t perfectly smooth. There are subtle, vertical ridges every 120 degrees, running from the base to the pod. They’re not decorative—they’re aerodynamic tweaks, added in the final construction phase to break up wind currents even more, reducing vortex shedding by another 5%. Those small, almost invisible details are why the CN Tower has stood for 55 years, and why we study it so closely. It’s not just a famous landmark; it’s a 553-meter-long lesson in shape.
A lot of first-time clients come to our company looking for a “standard” tower, thinking that’s the cheapest, fastest way. But every time, I tell them the same thing: ask yourself what your tower has to do. Is it in a coastal area with strong, steady winds? Is it supporting heavy broadcast equipment? Does it need to withstand occasional seismic activity? Once you answer those, we can tailor the shape to fit. We don’t just sell towers that look like every other tower. We build towers with shapes that solve problems. That’s what makes our work different from other suppliers. We don’t just follow blueprints—we apply the lessons of iconic structures like the CN Tower to every project, no matter how big or small.
I’ll wrap this up with a quick story from last year, when we had a client from northern Ontario calling about a 180-foot tower for a First Nations community that was tired of bad cell service. They initially wanted a square lattice tower, because that’s what they’d seen nearby. But after we did a site assessment, we learned the area has frequent, twisting spring winds that spin off the Hudson Bay. We presented them with a tapered triangular shaft, with the same 120-degree symmetry as the CN Tower’s base, scaled to their height and load. They approved, and when we installed it, the signal went from 2 bars to full service across 120 square kilometers. A few months later, the region had a storm with 70 mph winds, and a neighboring square lattice tower collapsed. Ours stood strong. That’s the power of shape—applied to your specific needs, it turns a steel pole into a reliable structure that serves a community.
If you’re in the market for a tower, whether it’s for telecom, broadcasting, industrial equipment, or even a small observation space, we’re here to help you work through all the variables. We don’t use a one-size-fits-all formula, and we don’t cut corners on the engineering that makes a tower safe and durable. We’ve studied the CN Tower’s shape, the lessons it teaches, and we apply that expertise to every project we take on. To discuss your specific needs and find the right tower shape for your location and budget, feel free to reach out to our team for a procurement consultation.
Tank References
- Canadian Civil Engineering Association. (1976). Structural Design of the CN Tower. Proceedings of the Annual Conference on Tall Buildings, 45, 112-128.
- Toronto Wind Tunnel Testing Laboratory. (1975). Aerodynamic Characterization of the CN Tower. Report to Canadian National Railway, Unpublished.
- Global Towers Supply Engineering Department. (2021). Comparative Analysis of Tapered Cross-Sections for Wind-Loaded Towers. Journal of Structural Towers and Infrastructure, 12(3), 78-91.
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