The idea for Oasia’s unusual design came about rather quickly. Can you tell us more?

Phua Hong Wei (HW): The brief from the client was to create something unique and identifiable. We wanted to encapsulate the whole idea of a garden city in the building. As this was designed for a government land sales site with a submission deadline, there wasn’t a lot of time. It was one of those Eureka moments when we did a quick sketch and went to the client the next day. They accepted the idea almost instantly as they recognised the merits of the design.

The original sketch of the building was almost similar to what we built: the idea for L-shaped stacks, sky terraces and a green envelope.

A façade of green creepers helps Oasia stand out in a site that is hemmed in by skyscrapers all around. How did the context of the site play a role in shaping its design?

We wanted to create a new building typology that stands out from the rest. Not in a sculptural sense but creating a vertical liveable space that is integrated with urban planning. We knew there was going to be a linear park extending from the neighbouring Tanjong Pagar Centre in the future, so we responded to the context with a building that would blend seamlessly with the ground. This is also why we brought the façade and planters down to the ground to look as if the greenery grows from the ground to the top. When you stand at the foot of Oasia and look up, you can hardly discern any building because it looks like a huge tree. You don’t see any hard surfaces, because it is softened by the façade of greenery.

The green façade goes beyond the trend of having plants on buildings. What other roles does it perform?

HW: We worked closely with our consultant to bring in more than 20 species of creepers and greenery for the façade and they are located based on suitability to sun and shade. The façade is more than greenery being a cosmetic treatment for buildings. We see buildings as a component of the city and they can be civic and generous. Guests will have views of greenery from their window or at the sky terraces, while people on the street have something nice to look at instead of another hard, glass-curtained building.

When I was giving a public presentation on this building, a member of the audience said he lived in the nearby public housing that looked out to Oasia and was energised to see this big “tree” when he looked out of his window every morning. These are things you can’t predict or design for, but they show what a building can do for the surroundings.

The building does not just look like a tree, it performs like one too. As we have over 50 species of greenery within the building, it attracts bees, birds, and sometimes squirrels! That’s delightful, especially in an urban context. The variety of greenery is intentional, but the biodiversity wasn’t something we predicted.

Oasia uses an innovative L-shaped floor plan to configure its three programmes: office, hotel rooms and club rooms. As cities shift away from buildings that only have a singular use, how can architecture enable such mixed-use developments?

HW: Mixed-use development is the way forward because we cannot afford to have isolated buildings with singular use. The challenge is bringing the different programmes together and to finish up the building holistically, so that it doesn’t look like two or three different components stacked together.

This is what Oasia does perfectly. Each programme is a stack based on L-shaped floor plans. By flipping them into opposite corners and inserting sky terraces in between them — on levels 6, 12 and 21— this creates openings that offer views to various parts of the city. The sky terraces offer both distant and intimate views by acting like huge “urban windows” that frame views of greenery in the foreground and the city skyline in the background. They are also in-between spaces that are not just functional divisions of the different programmes but shared spaces for the building’s users.

Tell us more about these sky terraces. What is the value of buildings having such spaces?

HW: Such elevated ground spaces are important because they are the in-between spaces of buildings. In a mixed-use development like this, we need to weave in and value-add the spaces between different programmes and offer shared spaces for the guests and the public. As the city intensifies and buildings get taller, there’s a detachment from the ground. It’s important to bring such spaces into the building so that there’s intimacy and human scale.

The approach of our design for Oasia is not just looking at sky terraces with a lot of greenery but rethinking the façade as another surface for greenery too. When we counted the surfaces, both horizontal and vertical, it achieved more than 1,000 per cent that of the site area. It is a unique achievement for a building. The sky terraces are important because they duplicate the ground four times vertically. We even created a sky terrace on the rooftop by tucking the building services underneath and there is a pool for guests and a restaurant for the public. Each sky terrace covers almost the same footprint as the ground, so building users and the public will enjoy more land space.