The Köppen Aw climate is a tropical climate with a dry winter, characterised by mean monthly temperatures above 18 degrees Celsius year round and a marked dry season. In the Nigerian Middle Belt this manifests as a single rainy season, roughly April to October, separated by a dry season during which the Harmattan, a dust-laden north-easterly wind, depresses humidity and widens the gap between daytime and night-time temperatures. Table 1 summarises indicative climate characteristics for representative savannah settlements, illustrating the internal variation between lowland cities such as Lokoja and Makurdi and the cooler Jos Plateau.

Two features of this regime drive the design problem. The first is the intensity and verticality of solar radiation, which loads horizontal surfaces, above all the roof, far more heavily than vertical walls. Savannah-specific measurement confirms that the roof can account for the majority of fabric heat gain in low-rise buildings, with one classroom study attributing close to 70 per cent of total heat gain to the roof (Abba 2020). The second is the seasonal asymmetry of the cooling task: the dry season rewards strategies that buffer the diurnal swing, whereas the humid wet season rewards strategies that maximise air movement and limit moisture retention. Figure 1 maps the principal heat-transfer pathways and the points at which passive interventions act.

How comfort is defined determines which design targets are judged adequate. The static, heat-balance approach formalised in the Predicted Mean Vote, and applied in studies such as Abilkhassenova et al. (2023), treats comfort as a narrow band of operative temperature largely independent of occupant adaptation. The adaptive paradigm, by contrast, holds that occupants of naturally ventilated buildings tolerate and indeed prefer a wider, climate-tracking comfort range because they adjust clothing, activity and openings (López-Pérez et al. 2019; Aqilah et al. 2025). For savannah residential buildings, the great majority of which are naturally ventilated for at least part of the year, the adaptive model is the more defensible baseline, and its use materially enlarges the comfort space that passive design can satisfy. Reviews of naturally ventilated comfort confirm that air movement can extend the acceptable temperature ceiling by several degrees (Abuhussain et al. 2024; Aqilah et al. 2022). The choice of model is not a technicality: a design judged a failure against a fixed 24 degree set point may be a clear success against an adaptive criterion, and much of the apparent inadequacy of passive buildings in the corpus stems from the use of inappropriately static baselines.

The central analytical lens of this review is what may be termed the savannah seasonal-duality problem. The bioclimatic tradition associated with Olgyay and Givoni treats the building envelope as a filter to be tuned to a prevailing climate, but the savannah does not present one climate; it presents two in annual alternation. A heavyweight envelope with high thermal mass damps the large dry-season diurnal swing and, if coupled with night ventilation, can flush stored heat before dawn. The same mass, however, can trap warmth during humid wet-season nights when outdoor temperatures no longer fall far enough to discharge it, leaving occupants warmer than a lightweight, well-ventilated alternative would. Figure 4 (Section 5) renders this tension graphically. The implication, developed throughout the analysis, is that the optimal savannah envelope is not a fixed compromise but an adaptive or switchable system whose behaviour changes with the season.

The study is a systematic literature review reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA 2020) statement. A systematic design was chosen over a narrative one because the research questions require an auditable, reproducible mapping of a dispersed evidence base rather than an illustrative selection. The protocol comprised four stages: identification, screening, eligibility assessment and inclusion, with explicit criteria applied at each transition. The complete flow, with record counts, is presented in Figure 2.

Two complementary sources were interrogated. Scopus was selected as the primary index for its quality control, structured metadata and reliable Digital Object Identifiers, which support verifiable referencing. Google Scholar was added as a secondary source precisely because of its broader, less filtered coverage, which captures regional Nigerian journals, theses and grey literature that Scopus omits and which are disproportionately important for an under-researched climate zone. The Scopus export was retrieved on 15 June 2026 and returned 181 records; the Google Scholar export returned 106 records, of which 98 carried usable bibliographic metadata. Table 2 sets out the search architecture, combining concept blocks for passive design, thermal performance, building type and geographic-climatic scope using Boolean operators.

Inclusion and exclusion criteria, summarised in Table 3, were defined before screening. Studies were eligible if they addressed at least one passive architectural parameter, reported a thermal-performance or comfort outcome, and were relevant to tropical conditions, with priority given to savannah and wider Nigerian residential evidence. Cross-climate and non-residential studies were retained where they carried transferable mechanistic insight, for example envelope or phase-change-material reviews but were weighted accordingly in synthesis (Gupta and Deb 2023; Lamrani et al. 2021; Lai et al. 2023). Purely materials-science studies with no building-scale outcome, and method-only machine-learning papers without a design-parameter focus, were excluded.

The two exports were combined, yielding 287 records. Duplicate detection by title, author and DOI removed 41 records, several of which appeared in both databases, leaving 246 unique records for screening. Title and abstract screening against the eligibility criteria excluded 150 records, predominantly studies set in non-savannah climates, focused on non-residential buildings without transferable value, or confined to materials characterisation. Of the 96 reports sought for full assessment, 12 could not be retrieved or lacked sufficient detail. The remaining 84 underwent full eligibility assessment, from which 22 were excluded for the reasons recorded in Figure 2. Sixty-six studies were retained for synthesis.

Synthesis was thematic rather than meta-analytic, because the heterogeneity of climates, building types, metrics and methods in the corpus precludes statistical pooling. Data were extracted into a parameter-by-study matrix recording the mechanism examined, the reported direction and where available the magnitude of the thermal effect, the method used, and the climatic setting. Findings were then aggregated by parameter family and interpreted through a structured vote-counting logic that weighted savannah and Nigerian residential evidence most heavily, hot-dry and hot-humid Nigerian evidence next, and transferable cross-climate evidence least. This weighting is the basis of the sensitivity ranking developed in Section 5. The approach has limitations, discussed in Section 7, notably the inclusion of regional grey literature for which DOIs were unavailable, a deliberate trade-off accepted to improve savannah coverage.

Orientation and form are the cheapest of all passive measures because they are decided at the sketch stage and cost nothing to implement, yet their leverage is bounded. In the savannah the design objective is to minimise the area of envelope, especially glazing, exposed to the low-angle morning and afternoon sun on the east and west elevations, while presenting longer faces to the north and south where overhangs can exclude high-angle radiation. Simulation of residential orientation in north-eastern Nigeria found measurable cooling-load reductions from re-orienting the long axis, although the gains were modest relative to fabric measures (Alkali et al. 2021). Work on contemporary low-rise housing in tropical Enugu reaches a similar conclusion from the opposite climate zone, treating orientation and form as the foundational layer of a climate-responsive strategy rather than as a substitute for fabric measures (Nwalusi et al. 2022). Built form interacts with this: a compact plan with a low surface-to-volume ratio reduces total heat exchange, but compactness conflicts with the deep cross-ventilation that the wet season demands. This early tension foreshadows the duality problem and explains why orientation, though foundational, ranks below the fabric and ventilation measures that follow.

Wall performance in the savannah is governed less by steady-state U-value than by thermal mass and its phasing relative to the diurnal cycle. The ubiquitous sandcrete hollow block, assessed as a walling material in tropical Nigeria, performs poorly in isolation because its moderate mass and conductivity allow daytime heat to reach the interior with little useful delay (Muhammed et al. 2024). Indigenous and stabilised-earth alternatives consistently outperform it. Optimisation of residential envelopes using indigenous materials delivered both improved comfort and construction-cost savings (Jegede and Taki 2022), and comparative testing of stabilised latscrete against sandcrete blocks confirmed the thermal advantage of the earth-based option (Okereke and Ike 2025). Material reviews extend the logic to agro-industrial wastes and unfired earth blocks (Jannat et al. 2020) and to rice-husk-ash masonry, which improved building energy performance (Onyenokporo et al. 2024b). Investigations of the relationship between building materials and indoor cooling in Nigerian homes reinforce that material selection is among the most consequential envelope decisions (Okonta 2023; Egbum et al. 2023).

The critical qualification is seasonal. High mass is an asset in the dry season, when large night-time temperature drops allow stored heat to be purged, but a liability in the humid wet season, when night temperatures stay high and the same mass re-radiates warmth indoors. Studies of traditional versus modern dwellings capture this ambivalence, finding heavyweight traditional construction superior under some conditions but not universally (Okafor et al. 2022). The envelope conclusion is therefore conditional rather than absolute: mass should be specified for the dry-season-dominant interior cities and moderated, or paired with assured night ventilation, where the wet season governs comfort.

If a single surface deserves design priority in savannah housing it is the roof. Because solar radiation is near-vertical for much of the day, the roof intercepts the largest radiant load, and savannah measurement attributes the majority of fabric heat gain to it (Abba 2020). Three roof parameters are actionable. Reflectivity, achieved through light-coloured or specially coated surfaces, reduces absorbed radiation at source and is among the most cost-effective single interventions. Insulation interrupts the conductive path to the ceiling and is repeatedly identified as the highest-impact envelope measure in tropical reviews (Gupta and Deb 2023); Nigerian assessment of aerogel indicates the upper bound of what high-performance insulation can deliver, while illustrating the cost barrier that limits its residential use (Bashir and Leite 2022). Geometry and ventilated cavities matter too: numerical analysis of roof slope shows that pitch and the provision of a ventilated attic alter both gain and the need for high-performance roofing materials (Lapisa et al. 2022). The combined deployment of reflective and insulated roofing with mechanical ventilation was central to the savannah-specific optimisation of Xi et al. (2025), which targeted Kaduna directly. The roof thus offers the rare combination of high leverage and comparatively low cost that places it at the top of the sensitivity ranking.

Windows are simultaneously the route for solar gain and the means of ventilation and daylight, which makes their design a balancing act rather than a minimisation. The window-to-wall ratio is the master variable: tropical envelope reviews identify it, alongside glazing properties, as a leading determinant of cooling load (Gupta and Deb 2023). Glazing selection compounds the effect, and Nigerian simulation of window glass thermal properties combined with fixed external shading demonstrates that material choice can meaningfully reduce indoor solar penetration (Olaniyan et al. 2023). Façade-level remodelling in Abuja's low-income housing shows that window size, position and shading act as a coupled system, improving daylight while lowering indoor thermal stress (Abdulkareem et al. 2018). The most striking finding in this family, however, is behavioural rather than technical. Examining the prevalence of climatically appropriate glazing in practice, Wingrove et al. (2025) document a sustained disconnect between passive-solar theory and what is actually built, with glazing routinely sized and oriented without regard to climate. This gap, revisited in Section 5, signals that the binding constraint on fenestration performance is not knowledge but its application.

Shading addresses the gain that orientation and glazing cannot eliminate, and it does so before radiation strikes the building. External devices, overhangs, fins, verandahs and screens, are markedly more effective than internal blinds because they intercept radiation outside the thermal envelope. A scoping review of external shading optimisation for residential buildings in Nigeria sets out the geometric and material considerations and stresses context-specific calibration to local sun paths (Onwuzuligbo et al. 2025), while the coupling of fixed shading with appropriate glazing has been shown to suppress indoor temperatures in Nigerian conditions (Olaniyan et al. 2023). The deep verandah, a recurring feature of indigenous Nigerian housing, is in effect a vernacular shading and buffer space whose logic modern practice has too often abandoned (Oluwarotimi 2026). Shading ranks highly because it is climatically robust across both seasons and moderate in cost, although its benefit is contingent on correct geometric design for the specific latitude and elevation.

Ventilation is the principal heat-removal mechanism available to a passive building, and in the savannah it carries a double role: convective cooling of occupants and, through night purging, discharge of heat stored in the fabric. Effective cross-ventilation depends on the placement, size and rhythm of openings as much as on their total area. Experimental work in low-rise Nigerian housing demonstrates that the rhythm and arrangement of window openings materially shape the indoor airflow pattern, not merely its volume (Oforji et al. 2023). Low-cost strategies to enhance natural ventilation can improve indoor environmental quality without capital-intensive plant (Mabdeh et al. 2020), and field study of overheating in low-income Abuja dwellings found that passive measures, ventilation prominent among them, stabilised peak indoor temperatures around 28 degrees Celsius (Adaji et al. 2022). The courtyard, examined across hot-dry and humid settings, is a powerful ventilation and micro-climate device whose multilevel variants enhance stack-driven airflow (Chidiadi and Taki 2025). Ventilation does, however, expose the duality directly: night purging is highly effective in the dry season but far less so in the humid wet season, when the outdoor air is itself warm and moist, and security and dust concerns frequently lead occupants to keep openings closed, negating the design intent.

Phase change materials (PCMs) extend the thermal-mass principle by storing and releasing latent heat at a chosen transition temperature, in effect adding tunable mass to a lightweight fabric. The corpus on PCMs is large and methodologically mature (Lamrani et al. 2021; Zhang et al. 2025; Yang et al. 2023), and includes work calibrated explicitly to the tropical-savannah climate. Bimaganbetova et al. (2020) identify a narrow band of PCMs suitable across savannah cities worldwide, and savannah-focused energy prediction has been built on PCM-integrated simulation (Nazir et al. 2023). Envelope-integration studies in tropical and semi-arid settings report meaningful reductions in cooling demand and improvements in comfort (Elenga et al. 2025; Laasri et al. 2024; Al-Yasiri and Szabó 2022; Kulumkanov et al. 2024). The decisive constraints for savannah housing are economic and practical rather than physical: PCMs remain costly, depend on correct selection of melting range for the local climate, and require supply chains and installation expertise that are not yet widespread in Nigeria. Recent synthesis of PCM integration within building elements reaches the same conclusion, identifying cost, selection and installation capacity rather than thermal performance as the limiting factors (Mohan et al. 2026). They are therefore positioned in this review as a high-potential but conditional measure, appropriate where budgets allow and where the transition temperature is matched to local conditions.

The final family acts partly at the building scale and partly at the scale of the immediate micro-climate. Shade trees, green roofs and vertical greenery reduce radiant loads and evaporatively cool surrounding air, and systematic reviews confirm the cooling benefit of urban tree canopy and green infrastructure (Yin et al. 2024; Ji et al. 2024). Surface albedo is a related lever: high-reflectance finishes reduce absorbed radiation, although savannah-specific simulation finds the effect uneven, with wall albedo reducing the Universal Thermal Climate Index by up to 2.8 degrees Celsius while ground albedo had a minimal effect and can in some configurations worsen outdoor comfort by reflecting radiation onto occupants (Bedra and Li 2025). This nuance, that a measure can help or harm depending on geometry, mirrors the conditional character of thermal mass and reinforces the review's central message that savannah passive design rewards calibration over the uncritical application of generic prescriptions. Vegetation and albedo measures rank lower in the hierarchy not because they are ineffective but because their benefit is the most context-dependent and the slowest to establish.

Aggregating the parameter analysis produces a clear ordering of design priorities for savannah residential buildings, presented in Figure 3. The roof occupies the top tier because it combines the largest addressable load with low to moderate cost. Natural ventilation follows, both for its direct convective effect and for its role in unlocking the benefit of thermal mass through night purging. External shading and the management of glazing and window-to-wall ratio form the next tier, being climatically robust and moderate in cost. Wall mass, orientation, phase change materials and vegetation occupy the lower tiers, not because they lack effect but because their benefit is either modest, conditional on season or budget, or highly sensitive to context. This hierarchy is the review's first contribution: it replaces the undifferentiated lists of strategies common in the literature with a prioritised sequence that tells a designer where to spend the first and most consequential decisions. Sensitivity-based evaluation of passive approaches for Nigerian residential buildings provides methodological precedent for this kind of ranking and arrives at a broadly comparable ordering of envelope priorities (Tambaya 2023). Parallel work on hot-arid Saudi housing likewise finds roof and glazing measures to dominate achievable cooling-demand reductions (Rodrigues et al. 2025).

The hierarchy is necessary but not sufficient, because the savannah does not present a stable target. Figure 4 illustrates why. During the dry season the wide gap between daily maximum and minimum temperatures rewards thermal mass and night ventilation, which together shift the indoor peak away from the hottest hours and discharge stored heat before dawn. During the wet season the diurnal range collapses, night temperatures remain elevated and humidity rises, so that the same mass becomes a heat reservoir that cannot discharge, and the design priority shifts decisively towards maximised airflow and moisture control. A single fixed envelope optimised for one season is therefore necessarily suboptimal for the other.

The constructive implication is that savannah residential design should favour adaptive or hybrid solutions over single strategies: moderate rather than maximal mass, paired with generous and secure openings that allow occupants to switch behaviour between seasons, and resilient measures such as roof performance and shading that pay off in both regimes. This reframing explains several apparently contradictory findings in the corpus, in which heavyweight construction outperforms lightweight in one study and underperforms in another (Okafor et al. 2022; Muhammed et al. 2024); the contradiction dissolves once the governing season is specified. The seasonal-duality framing is the review's second contribution and a corrective to the climate-as-singular assumption embedded in conventional bioclimatic prescription.

The most sobering theme across the corpus is that robust evidence has not translated into practice. In a study of high-rise residential buildings in Lagos, only 28.6 per cent of cases had adopted passive design strategies despite their documented benefit (Dimuna et al. 2025). Wingrove et al. (2025) demonstrate a systematic disconnect between passive-solar theory and built glazing practice, and surveys of office and residential adoption in Nigeria report only moderate awareness among the property owners and managers who commission and operate buildings (Adegoke et al. 2025; Oluwatayo and Miracle 2025). A structured review of the motivators and challenges of passive design extracted far more barriers than drivers in hot, dry and humid developing-country contexts (Juffle and Rahman 2023). The same asymmetry appears at continental scale, where feasibility assessments of passive systems across African countries identify cost, capacity and regulatory constraints rather than technical limits as the binding obstacles (Lazaro and Li 2025).The barriers are familiar: weak enforcement of building energy codes, a construction culture habituated to sandcrete and air-conditioning, the low first-cost priorities of a housing market facing a deficit exceeding seventeen million units (Oluwarotimi 2026), and a shortage of designers trained in climate-responsive method. The gap is not evidential but institutional, which means it will not close through more simulation studies alone.

The corpus also reveals weaknesses in how savannah passive design is studied. There is a heavy dependence on building simulation, valuable for its control but only as reliable as its weather files and calibration, set against a relative scarcity of longitudinal field measurement in occupied savannah dwellings; the field studies that do exist, such as those in Abuja classrooms and low-income housing, are notable partly for their rarity (Mustapha 2023; Adaji et al. 2022). Comfort baselines are inconsistently defined, with static and adaptive models used interchangeably and few studies adopting a Nigeria-specific adaptive standard. Sampling is frequently small and convenience-based (Oluwatayo and Miracle 2025), limiting generalisation. Future-climate testing is uncommon, even though warming will intensify the cooling task (Aloshan 2026; Lee and Ng 2025b). And the residential focus is thin: a substantial share of Nigerian passive-design evidence is drawn from classrooms, offices, libraries and places of worship (Mohammadpourkarbasi et al. 2022; James et al. 2022), from which residential inferences must be drawn cautiously. These weaknesses define the research agenda set out in Section 7.

Finally, the savannah passive-design problem is inseparable from an equity problem. The households least able to afford continuous mechanical cooling are those most exposed to overheating, and social and low-cost housing is repeatedly shown to perform poorly in use (Simões et al. 2021; Callejas et al. 2023; Lee and Ng 2025a). Passive design is, in this light, not merely an energy strategy but a public-health and affordability strategy, and the measures that matter most for low-income housing, roof performance, ventilation, shading and locally available materials, are precisely those at the top of the sensitivity hierarchy and the bottom of the cost scale. Retrofit packages developed for existing Nigerian housing demonstrate that meaningful improvement is achievable within tight budgets (Onyenokporo and Ochedi 2019; Chung-Camargo et al. 2024; Adaji and Adekunle 2025), and upcycled and waste-derived materials extend that reach further (Onyenokporo et al. 2024a). Aligning the design hierarchy with the affordability constraint is thus not a compromise but a convergence.