GAD Editorial · Published ·
For most of architectural history, the roof was the one part of a building the public was never meant to touch. Three projects from the last two decades reversed that rule, and in doing so they asked an uncomfortable question: what does a building owe the city that surrounds it — the view back?
Snøhetta's Oslo Opera House, opened in 2008, made the answer literal. The building is a wedge of white marble and glass that rises out of the Oslo fjord like a glacier, and its roof is a public plaza: anyone can walk up the sloping stone surface, all the way to the top, without a ticket. Its most revealing achievement was behavioral — the roof became the city's living room, a place for sunbathing, protest marches, and wedding photos. The opera inside is excellent; the opera outside, the one performed by citizens walking on the building, turned out to be the main event. It is a cultural institution that makes a substantial part of its exterior a shared civic surface.
The High Line in New York, whose first section opened in June 2009, approached the same idea from the opposite direction: not a new building you can climb, but an old piece of infrastructure the city refused to demolish. Designed by James Corner Field Operations with Diller Scofidio + Renfro and planting designer Piet Oudolf — the team was selected in 2004 — the elevated freight rail line was converted into a linear park floating above Manhattan's West Side. Where Oslo's roof is a single gesture, the High Line is a sequence: a mile and a half of choreographed walking, with the city framed, cropped, and revealed like a film. Its popularity also sharpens a question for urban policy: how can a celebrated public amenity sit alongside development without excluding the residents it is meant to serve? A walkable building needs a housing and access policy around it, not just a photogenic route.
CopenHill, BIG's waste-to-energy power plant in Copenhagen, opened in October 2019, is the strangest and most ambitious of the three. BIG describes a facility designed to convert 440,000 tons of waste annually into electricity and district heating — and it wears a ski slope on its 85-meter roof, plus a climbing wall on its facade. It won World Building of the Year at the 2021 World Architecture Festival. The concept, which Bjarke Ingels calls "hedonistic sustainability," is that green infrastructure should be fun enough to visit: the chimney doesn't just disappear into the skyline, it becomes a destination. Whether that is a genuine reconciliation of industry and public life or a very expensive piece of public relations depends on your view of the smokestack, but as an idea it is undeniably potent: the most honest roof is the one that admits what the building actually does.
There is a harder question behind the climb: what makes an elevated public space accessible in practice? Slopes, weather, distance, rest stops and maintained lifts all matter. The High Line provides benches, ramps and elevators; its experience is not reserved for people who can take stairs. CopenHill distinguishes paid skiing from free access for walking, running or taking the elevator to its rooftop café during opening hours. Those distinctions matter more than the image of an athletic visitor on a dramatic roof. A democratic gesture needs reliable routes, clear opening information and ways to rest. The view from the top is only part of the public offer.
Three strategies, three verdicts. Oslo offers the roof as civic gift — culture you can stand on. The High Line offers the roof as reclaimed memory — infrastructure the city learned to love too late to leave alone. CopenHill offers the roof as alibi — proof that even a furnace can be a playground. What unites them is the recognition that in the dense contemporary city, the ground plane is under pressure. Looking up can reveal public-space possibilities that a conventional building footprint conceals. The question each project answers differently is whether that new public space belongs to everyone, or just to the view.