Green roofs are often discussed in terms of their environmental benefits, from reducing heat absorption to managing stormwater. But successfully implementing a green roof on an existing structure can be considerably more complex.

At Sentosa, GWS Living Art was commissioned by Sentosa Development Corporation (SDC) as part of the Cooling Sentosa roadmap to deploy its proprietary Gaiamat soilless green roof system across multiple existing sheltered walkways and public infrastructure.

The project presented a unique set of challenges. The structures had limited load-bearing capacity, permanent water supply points were not available across all installation zones, and construction had to take place without disrupting one of Singapore’s busiest tourist destinations.
The resulting installation spans 2,908 m² across eight zones and 26 individual roof surfaces, demonstrating how engineered green infrastructure can be adapted to complex retrofit environments.

The Challenge: Greening Existing Structures Without Overloading Them

Green Roof Systems along Tanjong Beach Walk

One of the first considerations was structural; many of the sheltered walkways and existing infrastructure within the project could not accommodate the additional loads associated with conventional green roof assemblies. A retrofit solution therefore needed to provide the benefits of a vegetated roof without imposing excessive structural weight.

The Gaiamat™ system was selected for its lightweight construction, weighing approximately three to four times less than conventional green roof assemblies. This lightweight construction made Gaiamat particularly suited to retrofit applications where structural loading is a key consideration.

Rather than requiring an entirely new roof structure, the system could be installed directly onto the existing roof surfaces, allowing SDC to introduce vegetation across existing infrastructure.

Choosing Plants for Heat, Drought and Long-Term Performance

Structural suitability was only one part of the equation.

SDC required the finished green roofs to be low-maintenance, visually lush and horticulturally vibrant. This meant plant selection had to account for both environmental resilience and visual quality.

GWS evaluated species against three primary criteria:

1. 1) Resilience under high solar irradiance and elevated temperatures
2. 2) Ability to withstand extended periods without supplementary irrigation
3. 3) Ability to create a layered canopy with variation in texture, height and colour

The selected species were also trialled in-house on the Gaiamat substrate. Candidate plants demonstrated sustained vitality for a minimum of 14 days without irrigation, helping establish their suitability for a low-maintenance green roof environment.

A) Cyanotis cristata, B) Bidens alba, C) Sphagneticola trilobata, D) Dianella ensifolia
(Photo Credits: NParks)

The final planting palette included four species:

(A) Cyanotis cristata formed the primary groundcover, creating a dense purple-toned mat across the roof surface.

(B) Bidens alba provided vertical growth and colour variation while also contributing ecological value as a pollinator-attracting species.

(C) Sphagneticola trilobata offered a robust, spreading groundcover with glossy foliage and bright yellow flowers.

(D) Dianella ensifolia added height and textural contrast through its upright, strap-like foliage, as well as small blue-purple flowers and ornamental berries.

The result was a planting strategy designed not only to survive the conditions of an exposed green roof, but also to create a visually varied landscape.

Solving the Irrigation Challenge Without Permanent Water Infrastructure

A) GWS staff installing portable irrigation pipe / B) Drip irrigation pipe

Another challenge emerged from the site’s existing infrastructure.
The installation zones did not have permanent water supply points suitable for a conventional timed irrigation system connected to mains water.

Instead of allowing this constraint to limit the deployment, the GWS team developed a portable irrigation methodology adapted from dry riser firefighting infrastructure.

The approach allowed water to be distributed to the roof installations without requiring permanent irrigation infrastructure.
The planting strategy supported this approach. Because the selected species had demonstrated drought tolerance, daily irrigation was unnecessary.

Under standard conditions, irrigation was carried out approximately twice a week, with frequency increased to three times weekly during prolonged dry periods or drought conditions.

Combined with the moisture-retention properties of the Gaiamat system, this approach created a maintenance regime that reduced the infrastructure and resource requirements normally associated with irrigating multiple green roof sites.

Installing 2,908 m² Without Disrupting Sentosa

The technical design also had to account for the realities of working within an active tourist destination.

Sentosa experiences significant visitor traffic, particularly around its beaches, transport connections and public walkways. Construction activities therefore had to be carefully scheduled to minimise disruption.
Installation works were restricted to night-time operations, commencing after 22:00 each day.

The Gaiamat assembly was installed sequentially across the roof surfaces, beginning with the root barrier, followed by the drainage and moisture-management layers and finally the pre-grown vegetated layer. Perimeter termination was completed using L-profile edging to secure the assembly.

In total, the project covered:
– 2,908 m² of green roof area
– 8 designated zones
– 26 individual roof surfaces
– 4 drought-tolerant plant species

More Than a Green Roof: Managing Heat and Stormwater

While the project was designed around the practical requirements of retrofitting green infrastructure, the completed system also provides environmental functions beyond vegetation. Including stormwater management and ambient heat reduction.

The Gaiamat assembly can retain and absorb water within its substrate layers. Under storm event conditions, the installed system demonstrated a peak flow absorption capacity of up to 25.80 L/m², helping attenuate surface runoff and reduce the hydraulic load transferred to conventional drainage infrastructure.

The vegetated layer also contributes to thermal regulation.
Once established, the vegetation and substrate work together to reduce the rate at which solar energy is absorbed by the underlying roof surface. The system acts as a thermal buffer between direct solar radiation and the roof structure.

However, understanding how these surface-level temperature reductions translate into ambient heat mitigation requires further measurement. As part of the Sentosa project, GWS Living Art installed sensors to monitor temperature and assess the system’s cooling performance in the surrounding environment.

Designing Green Infrastructure Around Real-World Constraints

The Sentosa project illustrates an important consideration for urban greening: successful nature-based solutions must work within the constraints of the built environment.

At Sentosa, this meant developing a system that was lightweight enough for retrofit applications, selecting plants capable of surviving Singapore’s heat and intermittent drought conditions, developing an irrigation strategy without permanent water infrastructure, and completing installation works around the operating requirements of a major tourist destination. The result is an islandwide green roof deployment that integrates vegetation into existing infrastructure without treating greening as an isolated aesthetic addition.

If you’d like to learn more about our approach to green engineering and nature-integrated design solutions, get in touch with us at hello@gwslivingart.com.