Authors: Esma Hećimović-Huseinbašić and Irem Silajdžić
When mitigating climate impacts and improving urban comfort, discussions often centre on nature-based solutions (NbS) for cities. Large parks, green corridors and urban ecosystems effectively reduce heat and improve microclimates while also delivering co-benefits for stormwater, urban biodiversity and wellbeing. The challenge typically lies in densely built city centres, already consolidated neighbourhoods that generate and trap excess heat, where demolition or wholesale redevelopment is neither feasible nor desirable. Integrating NbS into the existing residential building stock, often older and energy-inefficient, through targeted retrofits offers a pragmatic and scalable alternative.
In our recent project in the region, our team screened several hundred multi-apartment buildings in a dense urban centre, using a contextual evaluation combining desktop analysis, site visits and stakeholder engagement. Key factors included building orientation, roof and facade condition, structural capacity and proximity to heat-island hotspots. Engagement with homeowners’ associations (HOAs) and building managers informed feasible interventions and governance pathways. From this process, the team developed tailored NbS packages matched to common building typologies, such as intensive and extensive green roofs for accessible and non-accessible roofs, inner-courtyard gardens and pocket tree planting to cool courtyards and improve air movement, climber systems for row blocks to shade facades and reduce surface temperatures and container-based green walls and planters where verge space is limited. These interventions can reduce roof and local ambient temperatures, improve stormwater retention and create communal green space that supports biodiversity and liveability. On ageing building stock typical of city centres however, NbS alone may yield only modest energy effects, but integrated with energy-efficiency (EE) measures, they realise their full potential. Beyond social and ecological co-benefits, such as usable shared space, urban biodiversity or CO₂ uptake, residents gain tangible outcomes: reduced energy use, longer envelope life and improved thermal comfort across seasons. From this project, the team drew several practical takeaways:
- Engaging residents and governance early: In dense historic centres, often with buildings 100+ years old, ownership is fragmented and common areas tend to sit in a long status quo. HOAs and their engagement are therefore pivotal to any NbS retrofit. Clear, concise onboarding materials that explain what is proposed, why, who will deliver it and when decisions are needed help secure HOA initiative and constructive decision-making.
- Planning maintenance from day one: Even well-designed NbS underperform without a maintenance regime that defines establishment, routine care, renewal cycles, inspection cadence, documentation, and budgets. Pairing specialist contractors with trained building managers and motivated HOA members from the outset sustains quality and stabilises costs.
- Bundling NbS with EE measures: Combining waterproofing, insulation, window upgrades and NbS into a single retrofit package streamlines permitting, financing, warranties and resident engagement and increases uptake. In many older, energy-inefficient buildings, full benefits are realised only when EE measures and NbS are implemented together, since NbS alone on poorly insulated buildings is unlikely to produce significant energy savings.
- Technical due diligence is indispensable for durable, high-performing NbS: Verifying structural loads, waterproofing integrity and drainage capacity before adding green systems is essential at the start of design. Designs should reflect local microclimate conditions, plan for safe access and include reliable seasonal irrigation with drought-tolerant planting to de-risk long-term performance.
- Using pilots and municipal alignment to scale: Visible, well-maintained pilot projects build trust and create reference sites that inspire neighbouring buildings and communities. Early alignment with municipal approval pathways and indicative timelines can shortens delivery and clarifies responsibilities.
Retrofitting NbS into existing building stock is a practical, scalable route to cooler, healthier cities where space is limited and heritage is valued. The key to all of this is disciplined delivery: early stakeholder engagement to secure HOA governance, rigorous technical due diligence, a maintenance plan defined from day one and bundling NbS with EE measures to maximise outcomes and minimise disruption. To accelerate adoption, pilot projects should be aligned with municipal processes and equipped with simple monitoring plans that feed results into reports or concise case studies for residents and city teams. Standardised details and specifications, together with permit templates and procurement checklists, could enable replication across similar buildings and districts. Phased rollouts, starting with high-impact rooftops and courtyards in heat-island hotspots, can build visible momentum, while outcome-based operation-and-maintenance contracts and seasonal commissioning keep performance on track. Coupled with clear communication of co-benefits, such as comfort, urban biodiversity, facade longevity and social space, this approach could provide a credible path to city-scale impact.
