October 11, 1975 - CN Tower Construction Progresses in Toronto

By October 11, 1975, you're looking at a fully structurally complete CN Tower — 553.3 metres of concrete, steel, and antenna rising above Toronto's skyline after just 40 months of round-the-clock construction. Workers topped off the antenna on April 2, 1975, and the main concrete shaft was finished as early as February 1974. The project cost roughly CA$63 million and employed over 3,000 workers. There's far more to this engineering story than meets the eye.

Key Takeaways

• The CN Tower was declared structurally complete and ready on October 11, 1975, marking a major construction milestone.
• Construction spanned approximately 40 months of round-the-clock shifts, five days a week, with rotating crews.
• The tower topped off at 553.3 metres on April 2, 1975, with the final antenna piece installed that day.
• Over 1,537 contractors and 1,500 Canadian National workers contributed to completing the project.
• Despite structural completion in 1975, the CN Tower's public opening was scheduled for June 26, 1976.

Where Did CN Tower Construction Stand on October 11, 1975?

By October 11, 1975, the CN Tower had already wrapped up its structural construction, having topped off on April 2, 1975, at 553.3 metres (1,815.3 feet).

You're looking at a structure that became fully complete by this date, following the antenna's installation in 39 separately lifted pieces.

Workers had spent over two years shaping this 118,000-tonne landmark on Toronto's former railway lands.

Its urban impact on downtown Toronto was undeniable, reshaping the city's skyline dramatically.

Engineers and crews guaranteed public safety throughout finishing work before the tower's planned public opening. The tower was designed to broadcast radio and television signals over tall new buildings that had emerged during Toronto's 1960s construction boom.

That opening wouldn't arrive until June 26, 1976, but structurally, the CN Tower stood complete and ready. The project had cost approximately CA$63 million, a sum that would be fully repaid within fifteen years of operations.

How 40 Months of Around-the-Clock Work Built the CN Tower

Over 40 months of round-the-clock effort, 1,537 contractors and 1,500 Canadian National workers built the CN Tower in four distinct phases: foundation, shaft, sphere, and antenna. Labor rotation kept crews moving continuously, five days a week, 24 hours daily. Wage escalation rewarded those working at dangerous heights:

1. Base wage started at $8 hourly
2. Workers at 1,000 feet earned standard rates
3. Workers at 1,450 feet earned $9 hourly
4. Workers at 1,630 feet earned $10 hourly

You can appreciate how this structured pay system incentivized crews tackling the tower's most demanding elevations.

Each phase demanded specialized expertise, from excavating 56 tonnes of earth for the foundation to hoisting 44 antenna pieces via helicopter, completing the structure on April 2, 1975. The tower was originally built by the Canadian National Railway Company to resolve telecommunications interruptions caused by the growing number of taller buildings transforming Toronto's skyline.

How the Slipform Technique Built the CN Tower's Concrete Shaft

With the workforce and wages in place, the real engineering challenge was figuring out how to build a concrete shaft nearly 1,500 feet tall without stopping. Engineers solved this using continuous slipforming, a process where hydraulic jacks lifted the formwork incrementally as concrete hardened beneath it.

Starting June 26, 1973, crews worked 24-hour shifts, advancing the forms in 20-25 millimeter strokes. Up to 54 hydraulic jacks powered the platform early on, reducing to 24 as the tapered shaft narrowed. The rig reached 446 meters by February 22, 1974, averaging roughly 6 meters daily.

You'd also notice post-tensioning methods reinforcing the shaft throughout most of its height, with grout vents installed every 100 feet. Plumb bobs maintained vertical alignment, while 547 concrete cylinder sets verified structural strength continuously. The slipform itself was designed by Doug Sumner and supplied by Scanada, aka Heede International at the time. The tower was completed in 1975 and subsequently opened to the public the following year.

The CN Tower's Seven-Storey Sphere and Observation Deck Construction

Once the 335-metre concrete shaft was complete, crews shifted focus in August 1974 to building the seven-storey sphere that would house the observation decks and 360 Restaurant.

Using 45 hydraulic jacks, workers raised 318 metric tons of steel and wood up the tower's sides.

The construction sequence followed four key stages:

1. Twelve bracket forms lifted over one week
2. Forms tied together with a steel truss system
3. Concrete poured into wooden frames reinforced with rebar and a steel compression band
4. Second-level floor slab and ring beam poured on brackets

The completed sphere featured an observation lounge, glass flooring, and technical areas, all positioned below the upper SkyPod. Visitors can explore structures like the CN Tower through informative category tools that organize historical and scientific facts by topic for quick retrieval.

Steel cable bundles running the full leg height guaranteed structural integrity throughout. The tower's triangular-based legs were also engineered to taper toward the observation pod, splitting and deflecting wind forces to protect the structure during high winds.

How a Sikorsky Helicopter Completed the Antenna and Broke the World Height Record

As the sphere took shape atop the concrete shaft, one final challenge remained: mounting the antenna that would push the CN Tower to its record-breaking height. The helicopter logistics fell to a Sikorsky Sky Crane, nicknamed "Olga," which crews selected for its heavy-lift precision. Workers assembled each antenna section at ground level, and Olga lifted them sequentially into place starting in March 1975.

Before the final lift, you'd have witnessed a signature ceremony where the public signed the last antenna section. On April 2, 1975, Olga executed a precise fly-by before hoisting that final piece into position. The completed antenna stretched the tower to 553.33 meters, surpassing the existing world record and officially making the CN Tower the tallest freestanding structure on Earth.

How 1,500 Workers Kept CN Tower Construction Running Around the Clock

Behind the CN Tower's rapid rise stood over 1,500 workers who kept construction moving 24 hours a day, five days a week across 40 months. Worker rotation guaranteed no phase stalled, while weather resilience kept crews operating through Toronto's harsh conditions.

You'd notice their discipline reflected in four critical priorities:

1. Maintaining continuous concrete pouring for slipform progression
2. Monitoring hydraulic climbing jacks without interruption
3. Rotating skilled crews to sustain precision alignment
4. Pushing through difficult weather without halting operations

This relentless scheduling produced measurable results. The main concrete structure reached completion by February 1974, the seven-storey sphere was added by August 1974, and the antenna finished by April 1975. A specially outfitted helicopter was used to install the antenna as the final step to reaching the tower's full height.

Over 56 metric tonnes of excavated earth set the foundation that made this disciplined effort possible. Much like Radio City Music Hall, which opened in 1932 as a landmark of Art Deco design, the CN Tower was built with an ambition to cement its place as a defining structure in cultural and architectural history.

The Records the CN Tower Broke and Why They Still Matter

When the CN Tower topped off at 553.3 meters on March 31, 1975, it didn't just surpass Moscow's Ostankino Tower—it claimed the Guinness-certified title of world's tallest freestanding structure and held it for 32 years until September 12, 2007.

Its engineering legacy extends beyond that single record. You can trace its influence through multiple Guinness certifications: world's tallest tower from 1975 to 2009, world's highest wine cellar since 2006, and world's highest external walk via EdgeWalk since 2011. It remains the tallest freestanding structure in the Western Hemisphere today.

Its cultural impact is equally enduring—recognized as one of the seven wonders of the modern world, the tower transformed Toronto's skyline into an internationally recognized landmark that continues drawing millions of visitors annually.