The Bioclimatic Technology on Residential Building in Mandailing Natal District, North Sumatera

2.1 Lighting system

Lighting guidelines on buildings issued by the National Standardization Agency (BSN) through SNI 03-6197-2000 [13], which were established in 2000, are intended to obtain an illumination system with optimal operation; therefore, energy use can be efficient without reducing or changing the buildings’ functions, comfort, and occupant productivity.

The standard procedure for designing daylighting systems in buildings described in SNI 03-2396-2001 [14] aims to obtain a natural daylight illumination system that is in accordance with health and comfort requirements. Natural illuminance during the day can be considered good if, between 08:00 and 16:00 local time, there is enough light entering the room, and the distribution of light in the room is fairly even and does not cause disturbing contrasts.

In SNI 03-2396-2001 [15], natural illuminance factors during the day include three components: the sky factor, outer reflection, and inner reflection. The sky factor is a number that compares the level of illumination directly from the sky with the level of illumination from the bright sky on a flat plane. The measurement is conducted at two measuring points: the Main Measurement Point (Titik Ukur Utama/TUU) and the Side Measurement Point (Titik Ukur Samping/TUS).

TUU is located in the middle between the two side walls, at a distance of 1/3 d of the effective light field, while TUS was taken at a distance of 0.50 meters from the side wall, which is also at a distance of 1/3 d from the field of effective light holes, with d being a measure of the depth of the room, as shown in Figure 1. The requirements for the sky factor in a residential house must be met, as can be seen in Table 1. The average illuminance level, rendering, and color temperature recommended can be seen in the following Table 2.

Table 1. Sky factor values for residential buildings

Table 2. The average of illuminance levels, rendering, and color temperature for homes

Figure 1 illustrates the measurement layout used for assessing indoor daylight availability (sky factor/daylight factor) in residential rooms. The evaluation is performed on a horizontal working plane located 0.75 m above the finished floor level (section view). In plan, the room depth is defined as d (from the façade/opening plane to the rear wall), and the measurement line is positioned at 1/3 d from the opening. Along this line, one main measuring point (TUU) is placed in the central zone of the room, while two side measuring points (TUS) are located near the lateral boundaries, each at 0.5 m from the side walls. This configuration is intended to capture daylight conditions representative of both the central and peripheral areas of the space.

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tu_pian_2.png

Figure 1. Distance of d at TUS and TUU

Comparison of the level of natural illuminance in the room and natural illuminance on a flat surface in an open field is determined by the geometric relationship between the measuring point and the light hole, the size and position of the light hole, the distribution of the skylight, and the sky that can be seen from the measuring point [11].

Table 3. Relationship between Light Holes’ Height (TTCL) and Relative Sky Factor Values (NFLR)

The value of the sky factor and the distribution of light into the room are greatly influenced by the location and shape of the light hole. The same large light hole has a higher fl value at a higher position [16]. The relationship between the height of the light hole and the relative value of the sky factor can be seen in Table 3.

Research on daylighting by Aljawder and El-Wakeel [17] demonstrated a pronounced trade-off between visual privacy requirements and daylight availability in Bahraini dwellings. Their study evaluates the acceptability of contemporary mashrabiya, reflective glazing, and related measures. These findings are highly relevant for discussing the culturally driven privacy compromises (e.g., curtains or closed shutters) that frequently occur in tropical housing and their implications for both natural ventilation and daylighting.

Complementarily, García Fernández et al. [18] proposed a mathematical framework for daylighting design that can be adapted to our methods section or included as an analytical appendix. Employing this framework would strengthen the quantitative weighting of key design variables—specifically, opening configuration, room depth, and shading devices—in our study.

2.2 Natural ventilation system

Natural ventilation has benefits, such as circulating outside airflow into buildings, reducing harmful substances, and being beneficial to health [16]. Natural ventilation can channel O₂, prevent the concentration of CO₂, bacteria, and odors, and transfer heat in space [19]. Natural ventilation also creates thermal comfort because the air that moves over the body can help evaporate moisture from sweat on the surface of the skin. In addition, natural ventilation can serve as a structural cooler because direct air movement can continuously cool the structure and skin (covering) of the buildings [16].

The amount of air change that will occur in a room is determined by the area of the opening, the direction of the incoming wind, and the speed of the wind [20]. Boutet [20] also revealed that the comparison of the dimensions of the opening area between the inlet and outlet will affect the airflow rate. The value of the effectiveness of openings related to the inlet-outlet comparison can be seen in Table 4 below:

Table 4. Value of opening effectiveness in inlet-outlets

Several other studies examining natural ventilation and thermal comfort in tropical or near-tropical settings include those investigated single- versus double-loaded corridors through simulations and occupant surveys in Malaysian secondary schools [21-23]; their results show that single-loaded corridors enhance air movement, reduce indoor temperatures, and yield higher comfort levels. These findings support our argument that residential massing and spatial layout—particularly corridor configuration and opposing openings—can be leveraged to maximize cross-ventilation in Mandailing [22]. Meanwhile, Hlaing and Kojima evaluated wind-catcher-type shading devices for hot-humid housing by comparing three shading configurations; they found that wind-catcher variants reduce hours of thermal discomfort while still admitting breezes. This evidence informs our proposed façade elements that simultaneously mitigate solar gains and capture wind, aligning with locally appropriate bioclimatic technologies. Finally, Ali et al. [23] analyzed shading and airflow in eight Libyan dwellings, assessing orientation, solar protection, and ventilation. Their straightforward recommendations underscore the primacy of orientation, shading, and cross-flow in lowering energy demand, providing a cross-climatic benchmark that helps justify our guidance on orientation and settlement-scale layout.

2.3 Bioclimatic architecture and energy conservation

Bioclimatic architecture [24-26] is an architecture that considers aspects of climate and the environment in carrying out its functions to obtain thermal comfort. Bioclimatic architecture always employs architectural design strategies that take into account environmental conditions and are beneficial in reducing the use of electrical energy, CO₂ pollution, NO₂, and the use of artificial equipment that tends to change climate and environmental conditions.

Therefore, according to Jones [16], bioclimatic architecture has a close relationship with energy conservation efforts, especially in energy utilization. Another opinion put forward by DeKay et al. [27] is that bioclimatic architecture is a study of climate aspects that are used to obtain thermal comfort conditions through the collaboration of air temperature, air humidity, airflow velocity, and solar heat radiation. These four aspects can be used to study the role and utilization of natural (climate) potential in an environment, as shown in the comfort zone model in Figure 2.

Energy conservation is an action that aims to save energy in the operation and maintenance of buildings. Conservation does not have to change the buildings’ function, comfort, or work productivity of residents and must consider cost aspects.

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Figure 2. Thermal comfort zone [27]

Figure 2 Bioclimatic comfort chart showing the relationship between air temperature (℃, vertical axis) and relative humidity (% RH, horizontal axis) for light work/indoor activity. The central ‘comfort zone’ indicates the range of temperature–humidity combinations in which most occupants are expected to experience thermal comfort. Areas below this zone indicate conditions where additional solar gain (‘sunshine needed’) is beneficial, while areas above and to the sides indicate conditions where shading and/or increased air movement (‘winds needed’) are required and where the environment may become too dry or too humid.

2.4 Environmentally friendly

Environmentally friendly design concepts in Indonesia and elsewhere have long drawn on local wisdom to respond to climate. For example, Mandaka et al. [28] examined the typology of courtyard houses in Lasem, Central Java (Indonesia), documenting courtyard configurations and their relationships to the primary building masses in the Chinese settlements of Lasem—implying adaptations to both climatic and cultural contexts. This work provides an Indonesian regional reference for the role of courtyards/voids in facilitating natural ventilation and daylighting in dwellings. Likewise, Alhmoud [29] analyzed the effects of climatic conditions on vernacular architectural strategies in Egypt and Spain, synthesizing classical measures such as thermal mass, light-colored surfaces, small openings, shading, vegetation and water features, orientation, and the use of courtyards. Taken together, these strategies constitute a bioclimatic toolkit that is also pertinent to humid tropical regions [30].

The concept of environmentally friendly design is one of the important aspects of efforts to reduce surface temperatures and minimize global warming. This concept has long been implemented by the ancestors of the Indonesian people throughout the archipelago. The ancestors of the Mandailing community in Manambin, Hutagodang, and Habincaran in the Mandailing Natal District have also long used environmentally friendly materials as part of their building practices. The strategy to use environmentally friendly materials can still be seen in the structures, especially in residential buildings or heirlooms (old houses) in the three villages, as revealed by Nuraini [31].

The use of environmentally friendly materials in Mandailing community residential buildings is carried out in three parts of the dwelling: the bottom of the building, the middle part, and the top of the building [31]. According to Nuraini [31], the strategy includes the use of local stones as foundations, local wood (ingui wood) as pillars, beams, windows, doors, stairs, and roof structures, and the use of gogat (local bamboo) as wall and floor material.

A brainstorming study conducted with the Mandailing ethnic community on the model of the growing house design offered shows that the Mandailing ethnic community provides input and advice to architects who will build a house in the Mandailing area; therefore, they can continue to use local materials as part of the residential buildings that are built in stages [31]. This shows that the concept of environmentally friendly design has become part of the life and culture of the Mandailing people.

Based on the research problem formulation, namely: how to utilize bioclimatic aspects, particularly in terms of natural lighting and ventilation in residential buildings, the results section begins by answering the problem formulation. The first section will discuss natural illumination, natural ventilation, and then about the building layout patterns. The explanation is as follows:

4.1 Research samples

The results of field observations that have been carried out indicated that there are three residential units in Manambin, four residential units in Hutagodang and two residential units in Habincaran which are used as research samples for measurements of illumination and natural ventilation. Details of the research samples can be seen in Table 5.

Table 5. Details of research samples

Name of the Place	Case Number	Drawing of Residential Floor Plan
Manambin	1	tu_pian_4.jpg tu_pian_5.jpg
	2	tu_pian_6.jpg tu_pian_7.jpg
	3	tu_pian_8.jpg   tu_pian_9.jpg
Hutagodang	4	tu_pian_10.jpg tu_pian_11.jpg
	5	tu_pian_12.jpg tu_pian_13.jpg
	6	tu_pian_14.jpg tu_pian_15.jpg
	7	tu_pian_16.jpg tu_pian_17.jpg
Habincaran	8	tu_pian_18.jpg tu_pian_19.jpg
	9	tu_pian_20.jpg tu_pian_21.jpg

4.2 Natural illuminance

Across all observation cases, daylight served as the primary source of illumination in living rooms, bedrooms, dining/kitchen areas, and bathrooms/lavatories during daytime periods. Measurements at the standard working plane show that living, sleeping, and dining/kitchen spaces consistently achieved usable natural illuminance with a relatively even spatial distribution, as summarized in Table 6. Bathrooms/lavatories exhibited greater variability—reflecting smaller apertures or borrowed light—yet still benefited from functional daylight for general use. Minor differences between dwellings were attributable to orientation, opening size/placement, and shading conditions, without altering the overall finding that the principal living spaces are both daylight-reliant and evenly lit (Table 6).

Table 6. Strength of illumination received

Based on the field observations, it was found that the residents of the house and family members spend more time in the front room. The distribution of natural illumination is quite even due to the existence of a continuous interior space without walls. In all research cases, it also shows that there were no activities utilizing artificial lights or lighting from 07:00 to 17:00 Western Indonesian Time (WIB).

Comfortable conditions for natural illuminance in all occupancy cases are obtained from openings in the form of windows on two crossed sides. This is also supported by the presence of vegetation on one side of the opening; therefore, the incoming light is not too glaring.

4.3 Natural ventilation

Across all cases, natural ventilation was established by the ingress of outdoor air through opposed openings—combinations of vents, windows, and/or doors—creating cross-flow paths that traverse the depth of the dwellings. The front/living room consistently showed the least flow resistance and the most reliable air movement, reflecting its adjacency to the primary façade and relatively larger or more operable apertures. Adjoining rooms benefited to varying degrees, depending on opening size, placement, and internal partitions.

Table 7. Measurement of wind speed

Spot measurements with a hand anemometer at seated head height confirmed perceptible indoor air velocities during occupied periods, corroborating occupant reports of improved comfort, particularly in the front/living room. Under the prevailing wind conditions and the observed opening states, airflow proceeded without notable obstruction, supporting routine activities in these spaces. Case-wise airspeed values and variability are summarized in Table 7, which aligns the quantitative readings with the observed continuity of cross-ventilation throughout the sampled dwellings.

4.4 Building layout pattern

Across the three settlements—Manambin, Hutagodang, and Habincaran—the residential layout exhibits a distinctive, site-responsive pattern. Dwellings are micro-sited and oriented to maintain inter-building spacing and opposed openings that promote cross-ventilation while preserving daylight access. Despite differences in façade orientation and street alignment, the resulting configurations enable outdoor air to traverse the living zones and admit diffuse natural illumination into primary rooms (see Figure 3).

Figure 3 presents several spatial configurations designed to facilitate cross-ventilation through strategic opening placement. In each layout, primary habitable spaces (bedrooms, living room, guest room) and high-moisture/heat-generating areas (kitchen) are equipped with openings on different sides of the envelope, creating pressure-driven flow paths across the room's depth. The red callouts indicate the rooms where cross-ventilation is intentionally enabled, demonstrating how window and door alignment, as well as façade distribution, can support passive cooling and indoor air renewal without mechanical assistance.

Bioclimatic assessment using standard psychrometric/comfort diagrams indicates that, during the observation periods, local environmental conditions generally fell within or near the comfort envelope when air movement is present. Field measurements recorded indoor air speeds of approximately 1.6–2.1 m/s, which are consistent with the levels of convective airflow typically associated with improved thermal acceptability in warm, humid climates.

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Figure 3. Samples of a living space that utilizes cross ventilation

Taken together, the settlement-scale morphology and dwelling-level aperture strategies yield robust pathways for cross-flow and daylight penetration across the three sites. While orientation varies from block to block, the combinations of spacing, opening placement, and internal porosity allow residents to experience reliable air movement and functional daylighting under the prevailing climatic conditions documented in this study.

6.1 Recommendations

They are grounded in the reported field evidence: daytime illuminance of approximately 150–250 lux, air velocities of approximately 1.6–2.1 m/s, and the role of cross-openings, reduced internal partitions, and micro-landscape elements (vegetation/water) in the sampled dwellings.

(1) Recommendations addressing study limitations

Broaden environmental and perceptual instrumentation. Augment airspeed and lux readings with indoor/outdoor dry-bulb temperature, relative humidity, and mean radiant temperature, and compute task-relevant indices (e.g., daylight sufficiency ratio, simple glare probability) collected concurrently with standardized interview prompts. This will reduce construct underrepresentation and permit triangulation between physical and perceived comfort.

Strengthen internal validity and generalizability. Adopt repeated diurnal/seasonal measurements (e.g., wet vs. dry season; clear vs. overcast) and stratified sampling across orientations, room typologies, and opening-to-room ratios. Where feasible, apply mixed-effects models to handle clustering (points within rooms within dwellings) and report effect sizes with 95% confidence intervals.

Document trade-offs and boundary conditions. Record potential countervailing factors (privacy, noise, security, insects) and acoustic and odor conditions. In parallel, log artifact use (curtains/blinds/fans) and window-opening behavior to clarify when cross-ventilation/daylight strategies are pragmatically constrained.

(2) Recommendations for future research

Simulation–measurement coupling. Pair field data with validated airflow/daylighting simulations to test sensitivity to aperture size/height, porosity, WWR, shading, and vegetation placement. Use scenario analysis to estimate performance under anticipated climate variability.

Prototype trials and incremental retrofits. Implement low-cost, replicable interventions (e.g., transom vents, opposite façade openings, interior partition relief, light-colored finishes, vegetation trellises, or pergolas) in a subset of homes and evaluate pre/post changes in illuminance, air speed, and occupant satisfaction.

Settlement-scale morphology. Quantify how inter-building spacing, street width/orientation, and courtyard/void distribution influence wind availability and sky view at the room level. Develop morphological indicators (e.g., blockage/porosity indices) that planners can apply quickly during layout reviews.

Equity and adoption studies. Examine socio-cultural acceptance, maintenance burden, and affordability of passive tactics across income groups and life-cycle stages (new build vs. retrofit), identifying incentives and delivery models (self-build kits, community workshops).

(3) Implications for current settlement development in Mandailing Natal

Embed passive performance in village layout codes. Preserve or create true cross-ventilation paths by securing opposed façade openings at the dwelling level and ensuring adequate setbacks, street/corridor alignments with prevailing winds, and protected approach voids at the cluster/block scale. Use minimum spacing/height-to-width (H/W) ratios to safeguard sky views and diffuse daylight penetration into primary living spaces.

Issue practical design standards and retrofit guides. Publish illustrated guidelines for (i) opening geometry (size, sill height, head height, placement), (ii) partition management in front rooms (to reduce internal resistance to light/air), and (iii) micro-landscape elements (permeable, shade-casting vegetation and small water features positioned to temper glare and pre-cool incident air without introducing dampness). Align these with SNI daylighting and ventilation intent while keeping them accessible to self-builders.

Pilot “vernacular-plus” demonstration homes. Develop municipal or community pilots that showcase vernacular tactics enhanced with bioclimatic detailing (e.g., adjustable upper vents, ventilated clerestories, shaded courtyards), accompanied by monitoring dashboards and open-house training for local builders and residents.

Protect against maladaptive modernization. In permit reviews and housing programs, screen for over-glazed façades without shading, sealed envelopes, and deep plans with insufficient cross-flow, requiring remedial measures (external shading, operable vents, light-colored finishes, interior porosity) before approval.

Institutionalize measurement-informed planning. Establish a light-touch monitoring protocol (seasonal spot checks at standard heights/points) to track neighborhood-level daylight and airflow over time; integrate results into community action plans and retrofit prioritization (e.g., identify households where small, funded modifications would yield the largest comfort gains).

Together, these recommendations translate the study’s empirical insights into an implementable agenda: richer measurement for credibility, targeted experiments for proof of concept, and codified settlement-scale controls that keep Mandailing Natal’s housing both climate-responsive and culturally legible while guarding against high-energy, maladaptive design drifts.

6.2 Conclusion

This study shows that comfortable daylight and natural ventilation in Mandailing rural dwellings can be achieved through simple spatial and envelope tactics rather than mechanical systems. The combination of cross-ventilation openings, porous internal layouts, and micro-landscape elements keeps illuminance and air movement within ranges that occupants consistently perceive as comfortable.

In practical terms, the findings can be translated into several design guidelines for rural housing in similar tropical climates:

1. Prioritize true cross-ventilation pairs by placing openings on opposing or adjacent walls and combining doors/windows with high-level vents to ensure continuous air paths and balanced daylight distribution.
2. Integrate soft and hard micro-landscape elements—such as shade-casting vegetation and small water features—near openings to pre-cool incoming air, reduce glare, and maintain visual comfort without blocking sky views.
3. Maintain building layout patterns that preserve airflow corridors, including adequate spacing between houses, staggered building lines, and minimally obstructed approach paths that channel wind into primary living spaces.

For planners and policymakers, these strategies can inform rural housing guidelines, building codes, and retrofit programs that aim to reduce reliance on artificial lighting and mechanical cooling. Performance targets derived from this study (e.g., maintaining typical daytime illuminance and air-speed ranges associated with “comfortable” or “very comfortable” occupant responses) can be used as benchmarks in design review and post-occupancy evaluation. More broadly, recognizing and codifying these vernacular bioclimatic practices can help safeguard local knowledge while supporting the transition to climate-responsive, low-energy rural housing.