Airspace development above existing buildings could bolster housing delivery potential, according to urban transformation researcher Dr Ehsan Noroozinejad MIEAust.
Australia’s housing debate is still dominated by two familiar options: expand outwards or redevelop existing sites from scratch. Both are slow, expensive and carbon-intensive. A third option deserves far more engineering attention: airspace development, also known as vertical extension, rooftop housing or upward extension.
In simple terms, vertical extension means adding new floors above an existing building. It is not a cosmetic rooftop addition. Done properly, it is an integrated structural, architectural, services, fire, acoustic, access and construction-management intervention that converts unused air rights into new floor area while retaining the embodied value of the existing asset.
Recent literature defines vertical extension as creating new floorspace on top of an existing base building, often using reserve structural capacity and lightweight construction systems.
The engineering logic is compelling. The National Housing Accord target is 1.2 million well-located homes over five years from mid-2024, yet recent approval data shows Australia approved 16,710 dwellings in April 2026, below the average 20,000 per month needed to stay on track. If we need more homes near jobs, transport and existing services, then the roofs of suitable buildings should be treated as part of the national housing infrastructure portfolio.
The first question for engineers is not “Can we build above?” but “Which buildings, under which load path, and with which intervention strategy?” A rigorous feasibility pathway should begin with document recovery, forensic survey, intrusive investigation where needed, material testing, GPR scanning, column and wall capacity checks, foundation and pile-capacity review, and assessment of historic code assumptions.
The critical issue is reserve capacity: unused strength in the existing gravity and lateral systems. This may arise from conservative original design, higher original design loads, change of use, load reduction opportunities, over-sized members, or historical detailing.
A recent study from UNSW simulated 25 vertical-extension scenarios across five existing buildings using concrete, steel, timber and hybrid systems. It found that one to nine additional storeys could be structurally viable when considering vertical loads, equivalent to 33-225 per cent additional floorspace. When lateral loads were considered, up to seven storeys remained viable.
The same study found structural embodied-carbon savings of 32-212 kgCO₂e/m² compared with demolish-and-rebuild alternatives, equal to a 34-94 per cent reduction. Lightweight steel and timber systems generally unlocked the largest additional floor areas.
This is where modern methods of construction become central. Vertical extensions are highly constrained sites: limited laydown area, occupied buildings below, tight cranage windows, services continuity, acoustic disruption and public-realm interfaces. Lightweight prefabricated systems, cross-laminated timber, glulam, light-gauge steel, steel-cross laminated timber (CLT) hybrids and volumetric modules, reduce dead load, compress site programs and improve quality control. They also make the temporary-works problem more manageable.
Raising the roof
Australia already has a strong proof of concept. At 55 Southbank Boulevard in Melbourne, WSP assessed concrete, composite and CLT options for a vertical extension above an existing 1989 concrete building. The CLT option enabled 10 additional storeys without exceeding pile capacity; a concrete option was feasible for only six storeys.
The project required strengthened core walls, new steel cores, a transfer deck and careful lateral-load design, but it delivered about 13,000 m² of new space through adaptive reuse rather than full demolition.
For structural engineers, vertical extension is therefore a multidisciplinary appraisal exercise, not simply a member-checking exercise. The existing building and the new addition must be treated as one coupled system. The interface between old and new is often the highest-risk zone: it carries vertical load transfer, diaphragm action, differential movement, waterproofing, fire separation, acoustic separation, services distribution and construction tolerances.
Research on vertical extensions describes this host-extension interface as both a difficulty and a solution because it concentrates uncertainty, adaptability and coordination risk.
Geotechnical engineers are equally central. Many schemes will fail or succeed at foundation level. Existing pile records may be incomplete, soil parameters may be uncertain, and the original design may not have anticipated higher overturning or long-term settlement effects. A defensible geotechnical strategy should consider pile load testing, settlement compatibility, uplift, lateral response, basement constraints, adjacent assets and staged strengthening options. In many urban buildings, avoiding new foundations may be the difference between viability and abandonment.
Construction managers also need to rethink delivery. Vertical extension above an occupied building requires a “surgical construction” mindset: short possessions, predictable lifting plans, high prefabrication, temporary weathering, tenant safety, vibration management, fire egress continuity and staged commissioning. The buildability plan should be developed alongside the structural concept, not after it.
Architecture and regulation are not secondary issues. Height limits, overshadowing, privacy, street character, façade articulation, heritage, access, lift upgrades, NCC compliance, fire resistance, disability access, waterproofing and energy performance all shape engineering feasibility.
In NSW, low- and mid-rise reforms already seek more housing within 800 m of nominated centres and transport hubs, with an expected contribution of up to 112,000 homes over five years. Airspace development could complement this policy direction by increasing density without requiring every site to be cleared and rebuilt.
Global opportunity
Internationally, Australia can learn from England’s permitted-development pathway, where certain works can proceed under national rights subject to conditions, limitations and prior approval where required. Sweden also offers useful lessons: timber-based vertical densification has been used to add homes above older buildings, with prefabricated volumetric systems craned into place.
These models are not directly transferable, but they show the value of codified approval pathways, lightweight construction, early resident engagement and repeatable technical guidance.
Australia should now move from isolated examples to an engineered system. The next step is a national airspace audit combining LiDAR, building-age data, planning controls, ownership structures, infrastructure capacity and preliminary structural screening. Suitable public buildings, car parks, retail centres, low-rise commercial blocks and strata assets should be prioritised for pilots.
The objective is not to build everywhere. It is to identify where vertical extension is structurally, economically, socially and environmentally justified.
For engineers, the opportunity is significant. Airspace development can create new housing where infrastructure already exists, extend the life of ageing assets, reduce demolition waste, lower embodied carbon and open a new field of high-value adaptive-reuse practice.
It will not solve the housing crisis alone. But without using the air above suitable buildings, Australia is ignoring one of the few remaining urban resources that is already serviced, already located and waiting to be engineered.
Dr Ehsan Noroozinejad MIEAust is Senior Researcher and Global Challenge Lead at Western Sydney University, Director of Research and Development at the Association of Rooftop & Airspace Development, and Coordinator of the NSW Affordable Housing Network.
