At three stories high, the old commissariat near Wat Phnom is a chameleon of a building. Shrouded by battered green fencing and overgrown trees, the imposing 1910 Protectorate-era façade is painted a glorious colonial yellow but badly run down and almost hidden from view from the immaculate cream Post Office opposite. Standing inside the damp former entrance, white and russet chequered tiles leading off down separate hallways, one moment the interior of the former police headquarters seems to be brimming with restoration potential, the next, hopelessly decrepit. French shutters still grace some of the doors, while a ruined sweeping staircase unleashes a flurry of bats when treaded on.

Imagine, though, that the dimly lit staircase led to the second story of a beautifully restored public art gallery, and adjoining the one hundred year old house was a contemporary extension, designed to complement the period grandeur, while making its own statement to modern Phnom Penh.

This is what 21 Phnom Penh architecture students were asked to envisage when the Institut Français announced their annual design competition, the creation of a “heritage house” at the old police headquarters.

Third-year architecture students Phorn Rithy, Eng Pichenda and Kuoch Penglong, from Phnom Penh’s Pannasastra University, leapt at the chance. There are examples of contemporary symbiosis with classical buildings in almost every other city in the world – most famously, the Louvre in Paris. Though the competition has no bearing on the old headquarters (which is owned by businessman Kith Meng’s Royal Group) the task is an interesting design experiment into the potential development of the city’s remaining colonial architecture, the students say.

“We want to connect the past to the present,” says Pichenda, explaining the group’s decision to put a white, closed-in bridge connecting one building to the other.

“When you stand on the bridge it’s like a hole to the past. You can’t see anything – when you walk across the bridge you are walking from the past to the future.”

With just under two months to produce a cutaway plan, site drawings for all three levels of the old building and 3D modelling, the trio visited the house four or five times at different rimes of the day, looking at the structure, analysing traffic, trying to imagine what kind of experience they wanted visitors to have as they walked through its dilapidated rooms. The building famously posed as Gerard Depardieu’s guesthouse in the 2002 film City of Ghosts, for which it was painted its current yellow, according to the students, but they are unsure of its exact use in recent decades.

Currently the cavernous former police headquarters is home to an outdoor volleyball court. In the day time the building is alive with the yells and thumps of the competitive volleyball courts set up in the paved courtyard. At night, it is eerily silent, something 22-year-old resident Manh had to come to terms with when he moved into the premises two years ago to work as a referee on the volleyball courts.

There are no ghosts, he insists, but bats and capuchin monkeys from nearby Wat Phnom have made the second and third storeys their roaming ground, as he discovered when he was asked to cut back branches from the upstairs windows.

“At first I saw it was old building, and then became more used to it. There are six or seven of us living here, all the same age, and two children. I would probably go back to my homeland (Kampong Spieu) if it was knocked down.”

The question of preserving the city’s French colonial heritage is not especially a focus of the Institut Français , says Olivier Planchon, the centre’s cultural attaché. In past years the architecture competition has asked students to design a new airport for Sihanoukville, a contemporary art museum for Phnom Penh, and social housing.

“As a cultural centre we are interested in architectural ideas and problems. It is interesting in a city like Phnom Penh where there used to be very high quality architecture in the ‘60s and now, what’s built is not as interesting as what’s in Bangkok and Singapore. It could be that there will be a new architecture of great quality. So we’re betting on [the new generation], when we give them the space to create.”

Urban design lecturer Cheam Phanin, who will be one of the judges for the design competition this week, says heritage protection, which is divided into three categories, depends upon the proven historical significance of a building.

“We have a tendency to renovate buildings. They buy them for a cheap price and then put them on sale…[Brown riverside] is a good model of renovation. It gives new life to a building. Heritage buildings cost a lot of money and resources.”

In 2002 Phanin was a recipient of a design competition which took him to Paris, where he saw how successful the transformation of old architecture through modern designs was Penglong has similar hopes for Phnom Penh – though he is not a nostalgia-lover. The 23-year-old is passionate about sustainable design and fighting the city’s dire congestion issues, more than constructing future Vattanac monoliths.

“In the 1960s Phnom Penh… wasn’t going to be like Paris,” he concedes.

“But that was the year Mr Molyvann collaborated Khmer architecture with French architecture and it became New Khmer architecture.”

“He doesn’t destroy the old buildings. He created [heritage] zones,” adds Rithy. “Now it’s too late to turn back.”

Pachinda is optimistic: she thinks ideas like theirs will one day be used to restore the crumbling colonial heritage of the French quarter.

Though the Institut Français’ competition has no actual bearing on the future of the old police headquarters, which on a rainy weekday afternoon takes on a gloomy, ruminative aspect, the building itself looks set to become a hotel, with its original façade preserved, according to Royal Group.

The Heritage House architecture competition will be announced September 12. An exhibition of the designs runs from then until October 5 at Institut Francais du Cambodge, Street 218 Keo Chea.