NUS SDE 1 & 3: Net-Zero Retrofit Lessons for Interiors

Singapore’s greenest building is often the one that already exists. The retrofit of the National University of Singapore’s School of Design and Environment (SDE) 1 and 3 is one of the clearest local demonstrations of that idea. Rather than demolish two ageing 1970s blocks on the Kent Ridge campus, NUS reinvented them as super-low-carbon, net-zero energy teaching buildings, keeping the original structures and rethinking how the spaces are shaded, ventilated and cooled.

The project was designed by the NUS College of Design and Engineering in collaboration with CPG Consultants, through an academia-industry partnership launched in 2015, and formally opened in February 2023. It has since won the Society of Façade Engineers’ 2024 Project of the Year award for International Sustainability. For architects, interior designers and facility owners, it is a useful case study in what a deep retrofit asks of interior materials.

The short version: SDE 1 & 3 kept its 1970s structures, wrapped them in deep external screens, removed suspended ceilings and switched to hybrid cooling at warmer set points. That approach saves embodied and operational carbon, but it also changes the brief for interiors. Finishes must tolerate a wider humidity range, control sound in exposed, hard-surfaced rooms and support fresh, healthy air, while lasting long enough to justify the carbon already invested.

From 1970s Blocks to Net-Zero Energy

SDE 1 and 3 are among the oldest buildings on the NUS campus. Together they cover around 22,000 square metres of gross floor area. The design team’s “less is more” approach focused on what could be kept and improved rather than replaced:

• Structure retained. Keeping the original concrete frames avoided the large embodied carbon of new construction. The team used life cycle analysis to measure the savings from structural reuse.
• A deep external veil. Distinctive external screens now wrap the buildings, providing sun shading, glare control, daylight shelves and porous ventilation.
• Ceilings opened up. Suspended ceilings up to 1.8 metres deep were removed, giving taller, brighter rooms and freeing space once taken by ductwork.
• Hybrid cooling. Major teaching areas now combine light air-conditioning at around 26 to 28 degrees Celsius with quiet, energy-efficient ceiling fans and a single-pass fresh air system.
• Solar power. Rooftop photovoltaic panels help SDE 1 generate more electricity than it uses.

The results are striking. SDE 1 has recorded an energy use intensity of around 45 kWh per square metre per year, a fraction of a typical Singapore institutional building. In February 2023 it received the BCA Green Mark 2021 In Operation Platinum Positive Energy award. SDE 3 began operating in January 2023. The retrofit sits beside SDE4, NUS’s earlier new-build net-zero energy building, and shows that existing stock can reach similar performance.

Why Retrofit Beats Rebuild on Carbon

A new building starts with a large carbon debt. The cement, steel and glass in its structure and envelope are emitted before anyone moves in. Retaining a structure keeps that embodied carbon in use, and a well-designed retrofit then cuts operational energy too. This is the logic behind Singapore’s growing interest in whole-life carbon, explained in our whole-life carbon fit-out guide, and the reason so many owners now ask whether a building can be refurbished before it is demolished. Our guides to refurbishment without demolition and adaptive reuse explore the same idea for commercial buildings.

Lesson 1: Specify for a Wider Humidity Range

Conventional air-conditioned buildings in Singapore hold interiors at low, stable humidity. Hybrid-cooled spaces like SDE 1 & 3 deliberately allow a wider temperature and humidity range, closer to outdoor conditions at times. That saves significant energy, but it changes how finishes behave:

• Wallcoverings should be moisture-tolerant and mould-resistant. Commercial vinyl and PVC-free wallcoverings with breathable or antimicrobial options suit these conditions better than delicate paper or natural-fibre papers.
• Flooring should be dimensionally stable in humidity. Resilient vinyl and carpet tiles on stable backings handle fluctuating conditions better than solid timber.
• Upholstery in breakout and teaching areas benefits from performance fabrics that resist mildew and are easy to clean.
• Adhesives and installation must be rated for the expected conditions, with moisture testing of existing slabs before new floors are laid.

Lesson 2: Exposed Ceilings Need Acoustic Thinking

Removing suspended ceilings brings daylight, height and better airflow. It also removes one of a room’s main sound absorbers. Exposed concrete soffits, hard floors and open, naturally ventilated edges can make teaching spaces echoey, and ceiling fans add a background hum. In a learning environment, speech clarity matters.

The answer is to place absorption deliberately elsewhere:

• Suspended acoustic elements such as baffles or lightweight PET panels hung below exposed soffits restore absorption without reinstating a full ceiling. See our acoustic wall and ceiling panels guide.
• Acoustic wall treatments on the surfaces where sound reflects most.
• Carpet tiles in studios, seminar rooms and quiet zones to absorb footfall and chair noise. Our guide to acoustic carpet tiles explains how they help.

Lesson 3: Fresh Air Raises the Bar for Emissions

A single-pass fresh air system brings in outdoor air rather than recirculating it, which supports healthy indoor air. Low-emission interior materials are still essential, because the benefit of good ventilation is reduced if finishes release VOCs into occupied rooms. Specify flooring, wallcoverings, adhesives and furniture with recognised low-emission certification such as GREENGUARD Gold, FloorScore or CRI Green Label Plus. Our indoor air quality guide covers what each label means.

Lesson 4: Durability Protects the Carbon Investment

A retrofit that saves embodied carbon in the structure can lose some of that gain if interior finishes are replaced every few years. For institutional buildings, the best-value finishes are durable, repairable and modular:

• Modular carpet tiles let worn areas be replaced tile by tile.
• Commercial-grade wallcoverings and wall protection resist the scuffs of student traffic, furniture moves and exhibition set-ups.
• Products with Environmental Product Declarations give verified embodied carbon figures, helping project teams account for materials properly. See our guide to the whole-life carbon impact of flooring.

Our university and polytechnic interior material guide applies these principles across campus building types.

What Other Building Owners Can Take From It

SDE 1 & 3 is a university building with an academic team behind it, but its lessons apply widely. Offices, schools, community buildings and ageing commercial blocks across Singapore face the same choice between demolition and renewal. The project shows that the carbon case for keeping a structure is strong, that passive design and hybrid cooling can dramatically cut energy use in the tropics, and that interior materials must be chosen for the conditions a low-energy building actually creates, not the ones a conventional building would.

Final Thoughts

The NUS SDE 1 & 3 retrofit proves that net-zero energy is achievable in Singapore’s existing building stock, not just in new landmarks. It also shows that low-energy design changes the interior brief: finishes must handle humidity, control sound in open, exposed spaces, keep emissions low and last long enough to honour the carbon saved by keeping the building standing. For anyone planning a retrofit, those are the questions to put to every material on the schedule.

Planning an institutional or commercial retrofit? Book an appointment with Goodrich Global to discuss moisture-tolerant wallcoverings, acoustic solutions and durable flooring for low-energy buildings.

Project information: Archify Singapore (NUS School of Design and Environment 1 & 3), NUS College of Design and Engineering, and published project coverage. Project images are not reproduced here.

Frequently Asked Questions

What is the NUS SDE 1 & 3 retrofit?

It is the transformation of two 1970s buildings at the NUS School of Design and Environment into super-low-carbon, net-zero energy teaching spaces. Designed by the NUS College of Design and Engineering with CPG Consultants and opened in February 2023, it retained the original structures and added external screens, hybrid cooling and rooftop solar.

How energy efficient is NUS SDE 1?

SDE 1 has recorded an energy use intensity of about 45 kWh per square metre per year and generates more electricity than it consumes through rooftop solar panels. It received the BCA Green Mark 2021 In Operation Platinum Positive Energy award in February 2023.

What is hybrid cooling in a building?

Hybrid cooling combines light air-conditioning at warmer set points, around 26 to 28 degrees Celsius at SDE 1 & 3, with ceiling fans and fresh air supply. The air movement from fans keeps occupants comfortable at higher temperatures, which greatly reduces the energy needed for cooling.

What interior materials suit a net-zero retrofit in Singapore?

Choose moisture-tolerant, mould-resistant wallcoverings and stable resilient or carpet tile flooring for hybrid-cooled spaces, acoustic panels or baffles where suspended ceilings are removed, low-emission certified products for healthy indoor air, and durable, modular finishes that avoid frequent replacement.