In 2013, Robert Downey Jr. commissioned Nicolò Bini to create a Malibu Binishell with thin-shell concrete; nine years later, the 6,500-sq-ft home was completed

Most celebrity homes take a year or two to complete. Robert Downey Jr.’s didn’t. It took nine years, an Italian father-and-son duo, and a process of blowing up concrete like a balloon. This same style of construction was studied in a 2022 conference paper from Politecnico di Milano, Domes of Air and Concrete: Aging and Durability, calling it one of the most unusual chapters in modern concrete design.

A house built like a balloon

The building is known as a Binishell and is designed around a huge balloon rather than wood formwork or metal beams. Workers put up a nylon-covered balloon and then pour wet concrete onto it. After the concrete is poured, workers inflate the balloon with air. The balloon expands, and the wet concrete rises with it, forming a domed structure. Within about an hour, the concrete sets and the dome holds its shape on its own. This technique was developed in 1964 by Dante Bini, an industrial designer from Italy. Dante went on to construct thousands of such domes all over the world over the following decades. Later on, his son, Nicolò Bini, improved upon this concept. He wanted the domes to meet current construction guidelines and offer more design flexibility than his father's simple symmetrical designs.

Why Downey Jr. wanted something different

Downey and his wife, Susan, own a seven-acre property in Malibu overlooking Zuma Beach. They wanted a second guest house for entertaining, separate from their main house. But the couple was not impressed when architects showed them standard house plans. They wanted something nobody had built before. A mutual friend introduced the pair to Nicolò Bini, who was already testing his updated Binishell system on a remote lot in Joshua Tree, California. The Downeys liked what they saw. In 2013, just as the "Iron Man" film trilogy was coming to an end, they hired him to build their dome.

Nine years from shell to home

Constructing the shell itself did not take long. Transforming the raw concrete shell into a comfortable home, however, was a process that took years. The shell reportedly sat on the property unfinished, with no flooring, windows, or interior walls, for a significant stretch before the interior work began. As interior designer Joe Nahem later described it, it was just a raw shell. Nahem's firm, Fox-Nahem, eventually took over the finishing of the interior. The team added two bedrooms, a home theater, and a kitchen built for hosting guests, all wrapped around the dome's curved walls. Since a Binishell has no straight lines and no right angles, all the doors, windows, and furniture had to be custom-made to fit the curves. It's also part of why the full project, from commission to move-in-ready home, spanned about nine years, wrapping up in 2022.

Why builders are watching concrete domes closely

Binishells are not just a quirky design trend. Engineers value curved, thin-shell concrete because it can enclose the same amount of space with less material than a flat-walled structure. In a 2014 paper in the journal Structural Concrete, ‘Pneumatic forming of hardened concrete – building shells in the 21st century,’ it is explained that curved shells spread the weight evenly across the surface. That geometry allows builders to use thinner concrete without sacrificing strength. That material efficiency applies to the dome shape itself; it doesn't mean a custom, unique build like Downey's is fast or cheap to finish. The custom-made curved doors, windows, and furniture required in such projects are another factor in terms of cost apart from the efficiency of the shell material used.

Efficiency is now even more important than it was in 1964. Concrete manufacture has become a considerable contributor to carbon emissions across the planet due to the amount of cement involved. According to research in the journal Buildings and Cities, ‘Embodied Carbon of Concrete in Buildings Part 1: Analysis of Published EPD,’ cement alone is a considerable emitter of greenhouse gases on a global scale. Saving concrete in the construction process is one of the ways in which the impact can be reduced.

A one-of-a-kind home, not a housing fix

None of this means Binishells will replace regular houses anytime soon. They’re expensive, slow to finish, and hard to build at scale. That’s why it took nine years to build Downey’s dome. But his home throws a spotlight back on a decades-old idea. It shows how thin-shell concrete, once a way to build cheap, quick shelters, can be transformed into a striking, custom-built home for anyone willing to wait. For people scrolling past yet another glass-box celebrity mansion, Downey’s balloon-shaped dome is set apart by one simple reason. It looks unlike most homes being built today, and in an industry so often criticized for repeating the same designs, that alone could be enough for a second look.