The authors screened 6,377 records from six academic databases for studies published between 2015 and 2026. After removing duplicates, filtering document types and assessing titles, abstracts and full texts, they retained 60 studies reporting passive strategies in warm-humid, hot-humid, tropical, equatorial or closely comparable climates. Because buildings, climate sub-zones, metrics and research methods varied substantially, the team used a narrative synthesis rather than statistical meta-analysis. It separated measured, simulated and occupant-reported evidence and appraised each study with instruments appropriate to its design, treating uncalibrated simulations as weaker evidence than field measurements or validated models. The review was conducted under PRISMA 2020 guidance, although it was not registered on PROSPERO because the protocol did not fall within that registry’s health-related scope.

Ventilation produced the clearest and most consistent signal. It appeared in 36 studies, more than any other strategy, and the review rated natural and cross ventilation as the most consistently supported passive approach in the core warm-humid evidence. In Malaysian vernacular houses, field measurements showed that open-window cooling often worked through increased air movement and convection rather than a large reduction in air temperature. A mixed-method study in Tangerang, Indonesia, likewise found that natural ventilation and solar shading lowered indoor temperature and cooling demand, while highlighting the importance of airtightness. In Chongqing, a measurement-and-simulation study estimated that intermittent night-purge ventilation reduced annual sensible cooling load by 24.5%, from 61.6 to 46.5 kWh/m², compared with continuous ventilation, although the result came from a single study in a marginal humid-subtropical climate stratum. The review also found that occupant-reported evidence generally favoured natural ventilation over mechanical cooling in mixed-mode housing.

That distinction matters because stacked modules are not simply conventional tropical buildings compressed upward. Their lightweight assemblies generally have low thermal mass, while repeated module-to-module joints can create thermal bridges and unpredictable airtightness. Measurements of modular mock-ups found poor airtightness that varied with the wall-assembly method, and a study of prefabricated bamboo cabins still encountered thermal-comfort problems. Stacking also narrows the cross-sectional paths through which air can move, restricts the courtyards and semi-open transition spaces found in many vernacular precedents, and means that the roof—an important cooling surface in low-rise tropical housing—represents a declining share of the total envelope as height increases. A six-storey building, for example, has roughly one-sixth of the roof area per dwelling of a single-storey house, making roof-focused evidence less directly transferable to tall modular blocks.

The review’s largest reported effects also came from its least verified evidence. An unvalidated conceptual simulation of a 25-storey tower in Karachi reported an 8 °C reduction in indoor temperature and a 96% reduction in cooling and heating energy, but it combined changes to massing, orientation, envelope and shading, so no individual mechanism could be isolated. A framework study based on case studies reported a 59% reduction in cooling load from insulation, shading and combined ventilation. By comparison, mixed-method studies that paired measurements with calibrated simulations generally produced more conservative results of 14–20%. The authors therefore describe the extreme 96% figure as a possible maximum in an unvalidated model, not a realistic expectation, and they regard about 50–60% from more controlled studies as the stronger basis for discussing integrated passive design. The comparison remains qualitative because the review used different appraisal instruments for simulation and empirical study designs.

Among individual envelope measures, shading had one of the most directly usable findings. A parametric EnergyPlus study of 12 overhang configurations for opaque walls in Bangkok found an optimum depth-to-space ratio of approximately 1:1.15. Roof interventions also performed better than façade-only changes in a Dominican Republic study: modifying the roof increased comfort hours by 17.86%, compared with a smaller gain from façade treatment. Phase-change-material roofs produced estimated peak ceiling-temperature reductions of 3.25 K in Cox’s Bazar, 4.7 K in Dhaka and 6.6 K in Jashore, with peaks delayed by two to three hours, but this evidence came from computational modelling or laboratory-scale prototypes rather than occupied full-scale housing. A ventilated attic or double roof offers a smaller benefit; one marginal-stratum study reported a 5.8% reduction in annual sensible cooling load. These results support treating roof design as an initial priority while recognising that its relative contribution changes with building height.

Thermal mass remains unsettled, and humidity is the most uncomfortable blind spot in the evidence. Some tropical design guidance advises against heavy materials because they can retain heat when nighttime temperatures remain high, yet a Malaysian field study found the best measured operative-temperature range in a residence combining cross-ventilation with thermal mass. The disagreement may reflect whether mass can discharge heat through night ventilation or a courtyard rather than whether mass is inherently helpful. Humidity is even less settled. In Dominican social housing, passive packages reduced the daily temperature range by as much as 6.8%, but indoor relative humidity remained around 80–99% and changed by less than ten percentage points. Region-specific adaptive comfort models also performed better than conventional predicted mean value or ASHRAE 55 approaches for mixed-mode buildings, indicating that imported comfort thresholds may misjudge occupants’ responses. The review therefore warns that temperature improvements alone may not resolve the latent loads that distinguish warm-humid conditions.

Geographic coverage is uneven as well. Southeast Asia supplied 19 of the 60 studies, South Asia eight, East Asia six, Latin America and the Caribbean four, and sub-Saharan Africa nine, eight of them from Nigeria. Most African studies documented passive features in hospitals, libraries, places of worship or other non-residential buildings through observation and qualitative interviews rather than quantified performance in housing. A three-day field experiment and calibrated EnergyPlus study in Kaduna was a notable exception, but its savanna climate was not fully warm-humid. The absence of evidence is therefore not merely a shortage of publications; it reflects a shortage of instrumented residential studies from which locally applicable comfort models and design parameters could be developed. The review identified this as a priority because tropical African cities currently rely on evidence from Southeast Asia and Latin America whose transferability is plausible but untested.

Only 13 of the 60 studies addressed modular, prefabricated, container-based or precast construction, and the closest evidence to the target configuration was a simulation-only optimisation of stacked urban layouts in Singapore. A study of high-rise social housing in Cyprus monitored a conventionally built building and proposed, but did not implement, a modular retrofit. The available findings support several provisional starting points, including prioritising roof treatment, using opaque-wall shading, maintaining ventilation paths, using regionally derived adaptive comfort criteria and considering lightweight demountable façade panels, whose embodied energy was about 50% below the study average compared with more than twice the average for 120–150 mm solid precast concrete. These are hypotheses for testing, not validated rules for modular towers, and their transferability is especially uncertain where airtightness, thermal bridging, ventilation geometry or roof-to-dwelling ratios differ from the source buildings.

The review’s central conclusion is therefore both encouraging and cautionary: passive strategies are well founded in principle for warm-humid housing, but their performance in occupied stacked modular buildings remains unmeasured. The proposed research agenda calls for longitudinal monitoring of temperature, relative humidity, air velocity and energy use in occupied modular apartments, paired with occupant surveys; field-measurement studies of tropical African housing; dedicated investigation of passive humidity and latent-load control; and factorial tests that isolate thermal mass and interactions among combined strategies. Until such evidence exists, the passive-design literature can inform early design hypotheses for modular stacked housing, but it cannot establish whether a particular stack of modules will remain habitable without substantial mechanical cooling. The absence of direct evidence is not evidence that passive strategies are ineffective; it means that their performance in this configuration has not yet been measured.

Subject of Research: Systematic review of passive thermal design evidence for warm-humid modular stacked housing

Article Title: A systematic review of passive design strategies for modular stacked housing in warm-humid climates

Article References: Babalola, O. D., & Aremu, A. S. (2026). A systematic review of passive design strategies for modular stacked housing in warm-humid climates. Frontiers in Built Environment, 12, Article 1946962. https://doi.org/10.3389/fbuil.2026.1946962

Image Credits: AI Generated

DOI: 10.3389/fbuil.2026.1946962

Keywords: passive design, modular housing, warm-humid climates, natural ventilation, thermal comfort, cooling loads, humidity control, sub-Saharan Africa, systematic review, thermal mass, systematic, review