Billions of pounds have been spent building state-of-the-art arenas to showcase the world’s best athletes during the 2012 Summer Olympic Games. But what happens to those buildings after the last medal is handed out and the last fireworks of the closing ceremonies fade?

That question was considered during the design process, and architects behind three of the most high-profile venues recently discussed how the structures will be adapted, or even dismantled, once the Games are over.

The architects shared their thoughts during “The Architecture of the Olympics,” hosted (and webcast) by LSE Cities, a research center at the London School of Economics and Political Science. From the start, they said, London’s Olympic Development Authority pushed for permanent structures that would serve the community, semi-permanent buildings that would change in form or function after the Games, and temporary arenas that would vanish after the Games.

Ricky Burdett, director of the center, said the London 2012 organizers looked at cities like Munich and Barcelona, which have smoothly integrated venues once the Olympics were over, and at Beijing and Athens, which have struggled in that effort.

“Beijing needed to put itself on the map at many levels,” he said. “It hadn’t built a major stadium for about 40 or 50 years. But at the same time they were building things like the CCTV (Central China Television) headquarters in order to make a statement about the new China, the new confidence. In Athens, to design a taekwondo stadium, only for taekwondo, that no one can use after the games, that’s what you get. A waste of infrastructure and a waste of investment.”

The first Olympic Park venue to be completed was the velodrome, home to track cycling, a sport Great Britain dominated in 2008 when it took seven gold medals. London’s new velodrome, which opened in February, contains one of the fastest tracks in the world but has also gained attention for its energy-efficient exterior.

The distinctive roof that gives the building its nickname – “the Pringle” – is remarkably lighter than those on any recent Olympic velodromes. Where the Laoshan Velodrome in Beijing contained 85 kilograms per square meter of steel in its domed roof, London’s velodrome has just 30, thanks to a web of steel cables that supports a series of lightweight panels in the roof. The beam that rings its signature roof was a recycled gas pipeline from the American oil industry.

It will remain on site as the centerpiece as the London Velopark, which will include a BMX track, a road course, and a mountain bike track. Michael Taylor of Hopkins Architects, the designer of the velodrome, knew from the beginning that he wanted to retain a connection between the indoor track and outdoor park.

“For me, one of the most exciting things about the project is the idea that a child in the East End could walk to up that glass, look in, still be in the park and see the likes of Chris Hoy training inside,” Taylor said.

The Aquatics Centre straddles the line between a permanent building and one designed exclusively for a two-week Olympic run. The swooping design by Pritzker Prize-winning architect Zaha Hadid houses a pair of 50-meter swimming pools along with a 25-meter diving pool. Those elements will remain in place when the Games are over, while the two steep wings of stadium seats will be removed, turning a 17,500-capacity competition venue into a facility that can focus more on everyday use.

The building’s footprint will be reduced by nearly 50 percent after the seating areas are removed, which also allows the curved roof to be about half as big as originally designed. Again, there’s a stark difference between London’s swimming center and the Water Cube of the Beijing Olympics, a 7.8-acre site that has been partially converted into a water park.

When it comes to real sustainability, however, London’s basketball arena is the real star of the Games. While Britain does have a professional basketball league, there are no teams with a fan base big enough to consistently fill the 12,000-seat hall in Stratford. The solution was a structure that could be broken down after the Olympics and reassembled somewhere else or recycled for the raw materials. The basketball arena is the largest of the Games’ temporary structures, which include the 5,000-seat water polo arena.

Designer Jim Eyre of WilkinsonEyre Architects pushed for a modular geodesic dome design that could be disassembled and shipped to another location, perhaps even the 2016 Olympics in Rio de Janeiro. He settled for a more traditional looking building that still carries plenty of sustainable credentials.

Rather than drive hundreds of piles into the ground to be left after the Games, the builders came up with a system to drill down into the soil, fill the area with rocks and use those as a base for the foundation. And the arena’s 110-foot by 24-foot facades are clad in a series of recyclable PVC arches lit from the inside, making the most of the building’s appearances on prime-time TV.

Once the basketball arena is removed, up to 800 units of housing are planned for the site. That transition fits with the views organizers have had from the very beginning, of turning the downtrodden wards of East London into a new piece of the city.

“What you have is a very resilient fabric, and in the middle of it is a series of jewels, most importantly apart from the buildings is the park itself, “ Burdett said. “If you put those things together, perhaps you do have a cocktail which over time will sustain even things we don’t know about. That’s what good cities are about.”