1. INTRODUCTION

Energy efficiency in buildings is one of the fundamental pillars for ensuring adequate conditions of habitability, comfort and environmental sustainability, especially in extreme climatic contexts. In Latin America, most countries lack specific and enforceable regulations regarding thermal design of homes, leading to inefficient construction and high exposure to thermal discomfort [1]. This problem is exacerbated in high mountain regions, such as the Peruvian highlands, where extremely low temperatures are persistent and directly affect the health and well-being of the population.

In the Peruvian context, the Ministry of Housing, Construction and Sanitation (MVCS) has introduced regulation EM.110 “Energy-efficient thermal and lighting comfort” [2], later reformulated as “Thermal envelope” [3], with the aim of promoting technical criteria for thermally efficient buildings. However, the effective application of this regulation in housing remains limited, both due to economic constraints and the lack of integration of thermal criteria into conventional architectural design.

Several studies [4], [5] in the country have demonstrated the positive impact of incorporating thermal insulation in walls, ceilings and windows, showing that the reduction of thermal transmittance using unconventional materials significantly improves thermal performance of living spaces. Several studies [6], [7] have proposed passive solutions based on local construction techniques and low-cost materials, with favourable results obtained through dynamic simulations. Likewise, other research [8], [9], have validated the use of bioclimatic envelopes in experimental homes located in Puno, highlighting their ability to achieve acceptable levels of thermal comfort even at high altitudes. For their part, [10] highlight that building energy simulation systems allow for the analysis of both the environmental quality and the energy demand of buildings. In the same vein, [11] show an energy-economic assessment that considers the predominant construction materials in the city under study. Similarly, [12] compared different material configurations considering variables such as orientation and shading. In [13], it is suggested that, in order to improve thermal comfort in housing developments, direct solar incidence should be reduced in warm climates and, conversely, favoured in cold climates. Finally,[14] carried out an energy assessment of homes during the period 1960–2011, managing to define a thermophysical model based on dynamic simulations.

From an adaptive comfort perspective, theories such as that of Fanger [15] serve as a reference for evaluating the thermal well-being perceived by users, considering not only physical parameters but also subjective, cultural and occupancy conditions. In high Andean areas, studies [16] have highlighted the specific sensitivity of inhabitants to draughts and sudden changes in temperature, with a comfort range slightly different from that of other latitudes.

Within this context, the purpose of this study is to analyse the effect of implementing a thermal envelope with insulation in a dwelling located in a cold high mountain area, in order to provide empirical evidence on its technical and economic viability. This work is part of a perspective of improving housing through passive strategies, proposing replicable alternatives that can be considered in future regulatory updates.

2. MATERIALS AND METHODS

The study adopts a quantitative and exploratory approach, using the case study technique. The research is carried out from an empirical perspective with on-site measurements and energy simulation. The methodological choice is justified by the need to understand the actual thermal behaviour of an existing housing before and after a passive intervention in its envelope.

The case study is located in the city of Puno, Peru, at 3,827 metres above sea level, corresponding to the Bioclimatic Zone 6 – Very cold continental according to the classification of the National Building Regulations [3]. The selected housing was built in 1986, has four levels and handmade brick walls with cement plastering, without previous thermal insulation.

Figure 1 shows that the vertical enclosures and openings of the building are composed of handmade brick, cement mortar and Moduglass system glass.

The sample selection was convenience non-probabilistic, given the accessibility of the property and the willingness of the occupants to participate in the study. The unit of analysis was a thermally intervened room and a control room, both with similar construction conditions.

Figure 1. Exterior condition of the dwelling before the intervention.

Source: Own elaboration

2.3 Ethical Considerations

The study was conducted with the authorisation of the occupants and under the ethical principles of informed consent. No interventions were made that could compromise the health or safety of the residents during the study.

2.4 Phases of the Study

The research was conducted over four months during the summer season and was structured in four methodological phases, according to the research model proposed by Wieser et al. [9]:

Phase 1. Synthesis

First, a regulatory review [3], [15] was carried out to identify the established criteria and their applicability in cold high mountain areas, a technical review of the theoretical framework of thermal comfort and a qualitative analysis of the dwelling.

Phase 2. Contrast

In the second phase, the current state of the dwelling was diagnosed through direct observation, architectural and thermal data collection through thermographic inspection, and energy simulation in DesignBuilder v7.3.1.003.

Phase 3. Exploration

A prototype thermal insulation envelope was then implemented using accessible materials and construction techniques adapted to the local context: a system consisting of a wall clad with insulation, a ceiling with EPS, high-density fireboard (HDF) floating floor with 0.5 cm insulation, exterior cladding, and replacement of windows with a double-glazed Moduglass system with an air chamber.

Phase 4. Conclusion

Finally, a comparative analysis was carried out by monitoring thermal behaviour with MadgeTech RHTemp101A sensors to record temperature and relative humidity under three conditions: (1) no insulation, (2) partial insulation, and (3) complete insulation.

Figure 2. Interior condition of the case study before the intervention, where the walls are made of handmade brick, cement plaster, and the windows are Moduglass system with 6 mm thick single glazing.

Figure 2. Interior condition of the case study. a) Room to be intervened with thermal insulation, b) Control room.

Source: Own elaboration

2.5 Instruments and materials

The instruments used were:

A FLIR i50 thermal imaging camera, with an accuracy of ±2% and thermal sensitivity of 0.1°C, as shown in Figure 3.

Figure 3. Flir I60 thermal imaging camera.

Source: Own elaboration

MadgeTech RHTemp101A sensors, with a measurement range of –40 °C to +80 °C with an accuracy of ±0.3 °C temperature and ±3 % relative humidity, as shown in Figure 4.

Figure 4. Madgetech Data Logger sensor.

Source: Own elaboration

DesignBuilder software for energy simulation and thermal performance analysis. Finally, Python Jupyter in Google Colab was used for data processing.

2.6 Thermal insulation system and costs

The thermal envelope was designed using low-cost, easy-to-install materials adapted to local construction techniques. It was based on technical criteria proposed by [17], prioritising efficiency, availability and speed of implementation. The final system included:

• Exterior plastering: PEN 1,200.00
• Insulated wall cladding (internal panels): PEN 1,528.80
• 8.3 mm HDF flooring with insulation: PEN 600.00
• 1" EPS ceiling: PEN 160.50
• Replacement of windows with double glazing with air chamber: PEN 2,000.00

2.7 Analysis variables and indicators

The data were processed using Python (Pandas, Matplotlib). Anomalous thermal behaviour, interior thermal stability and level of compliance with regulatory thresholds were identified.

3. RESULTS

During the contrast stage, the initial thermal state was evaluated using thermographic inspection and energy simulation with DesignBuilder software. The most relevant findings are detailed below:

The thermographic image shows significant thermal differences between window frames, walls and construction joints, suggesting the presence of critical thermal bridges. Surface temperatures range from 14°C to 22°C. The cold areas, represented in violet and blue tones (approximately 14°C), correspond to surfaces with high heat loss, such as single glazing and uninsulated walls. In contrast, the warmer areas, shown in orange, red and yellow tones (up to 22°C), indicate heat accumulation on surfaces exposed to solar radiation or with high thermal inertia. The central cursor registers temperatures of 19.8°C and 20.5°C. These images allow the identification of deficiencies in the building envelope, especially in windows and joints between walls and structural elements, where the lack of insulation facilitates unwanted heat transfer, affecting indoor thermal stability. This analysis is key to establishing the baseline thermal behaviour prior to passive intervention.

Figure 5 shows significant thermal differences between frames, walls and construction joints, highlighting thermal bridges and areas with high heat loss.

Figure 5. Thermographic analysis of heat loss. a) Room to be renovated. b) Control room without intervention.

Source: Own elaboration

Figure 6 shows the digital representation of the dwelling modelled in DesignBuilder, used to analyse the initial thermal behaviour through energy simulation.

Figure 6. Energy simulation model in Design Builder.

Source: Own elaboration

During the same analysis period, the energy model in DesignBuilder showed heat losses through walls, ceilings and floors, especially at night when the outside temperature drops. Cold discomfort was detected, with operating temperatures dropping to 16 °C, which is insufficient to ensure thermal comfort, especially when resting or wearing light clothing. At this altitude, sensitivity to cold is greater. Although indoor temperatures remain between 16 °C and 18 °C, according to Fanger's criteria, these conditions do not reach acceptable comfort levels.

The simulation showed a thermal transmittance of 2.96 W/m²·K in walls and 1.26 W/m²·K in floors. The EM.110 standard establishes maximum values of 2.7 W/m²· K for walls, 1.20 W/m²·K for floors and 0.8 W/m²·K for ceilings in zone 6 (very cold continental climate), as well as an acceptable range of indoor comfort from 18°C, a threshold that is not always reached according to the results of the simulation and monitoring. After the passive intervention, the thermal transmittance values improved significantly: walls with 0.44 W/m²·K, ceiling with 0.64 W/m²·K and floor with 0.78 W/m²·K, reflecting a substantial improvement in the thermal envelope and, therefore, in indoor comfort, as shown in Figure 7.

Figure 7. Thermal envelope. a) Wall. b) Ceiling. c) Floor.

Source: Own elaboration

In the conclusion stage, thermal behaviour was monitored using MadgeTech RHTemp101A sensors. In condition (1) without insulation, recorded in December 2024, outdoor temperatures ranged from 20°C (maximum) to -2°C (minimum).

The indoor temperatures in the control room fluctuated between 17°C and 10°C, while the relative humidity varied between 70% and 30%. Channel 2, located on the interior window sill of the main façade, showed the greatest thermal variability, indicating a less protected area or one with greater exposure to the environment, as shown in Figure 08.

Figure 8. Temperature comparison by channel – Bedroom 03 (control room).

Source: Own elaboration

In the room to be renovated, average indoor temperatures ranged between 22 °C and 10 °C, with relative humidity between 70% and 20%, as shown in Figure 9. Also, channel 2 in this room showed greater thermal variability due to its critical location.

Figure 9. Temperature comparison by channel – Bedroom 02 (room to be refurbished).

Source: Own elaboration

A slight downward trend in temperature was observed towards the end of the period, possibly due to a seasonal or climatic change, despite it being the summer season. The thermal waves in both rooms show divergent behaviour. In addition, discrepancies were identified between the simulation results and the data obtained through monitoring.

During the exploratory phase, a thermal envelope was implemented consisting of: insulated wall cladding, EPS ceiling, insulated HDF floating floor, exterior cladding and window replacement (from a Moduglass system to double glazing without thermal break), as shown in Figure 10.

Figure 10. Thermal envelope construction detail. a) Interior wall cladding, where: INT = Interior, YL = Plasterboard, AT = Glass wool thermal insulation with vapour barrier, C = Air chamber, EMC = Cement mortar plaster, EXT = Exterior. b) Ceiling, where: EXT = Exterior, PC = Floating floor, AT = Thermal insulation, CA = Reinforced concrete, LKK = King Kong brick for ceiling, CRY = Plaster ceiling, EPS = Expanded polystyrene. c) Floor, where: EXT = Exterior, PC = Floating floor, Li = Polystyrene foam, AT = Thermal insulation, CA = Reinforced concrete, LKK = King Kong brick for ceiling, CRY = Plaster ceiling.

Source: Own elaboration

Figure 11 shows the implementation of the thermal envelope in exterior walls through cement plastering.

Figure 11. Implementation of the thermal envelope in exterior walls.

Source: Own elaboration

Figure 12 shows bedroom 02 refurbished with the thermal envelope in the floor, wall and ceiling.

Figure 12. Implementation of thermal insulation in the floor, interior walls and ceiling. a) Interior walls with drywall cladding consisting of EPS, glass wool, vapour barrier and plasterboard. b) Floor with insulating foam and HDF laminate flooring (8.3 mm, 19.3 x 1.20 cm); replacement of windows with aluminium double glazing (6 mm) with air chamber without thermal break; ceiling with EPS ceiling (1").

Source: Own elaboration

The total cost of implementing the thermal envelope is PEN 9,000.00, as shown in Table 1. According to Ipsos [18], the average monthly income in Peru ranges from PEN 12,000.00 for socio-economic status A to PEN 1,300 for socio-economic condition E. Therefore, the total cost would be less than one salary for class A and almost seven salaries for class E.

Table 1. Thermal envelope cost for interior renovation

Source: own elaboration.

In condition (3) with complete insulation, sensors were placed at various points on the envelope to evaluate its thermal performance.

Figure 13 shows the location of the channels: Channel 1 in the dividing wall with the neighbour, Channel 2 in the window sill of the main façade, Channel 3 in the dividing wall with bedroom 03, Channel 4 on floor level 02, Channel 5 on the ceiling. Control room without thermal insulation: Channel 1 on the dividing wall with bedroom 03, Channel 2 on the main façade window sill, Channel 3 on the dividing wall with the neighbour, Channel 4 on floor level 02, Channel 5 on the ceiling.

Figure 13. Floor plan of the house – location of the sensors (channels).

Source: Own elaboration

In February and March 2025, outdoor temperatures ranged from 18 °C (maximum) to 3 °C (minimum). The indoor temperatures in the control room fluctuated between 17°C and 11°C, while the relative humidity varied between 75% and 55%. Channel 2, located on the interior window sill of the main façade, showed the greatest thermal variability, indicating a less protected area or one with greater exposure to the environment, as shown in Figure 14.

Figure 14. Temperature comparison by channel – Bedroom 03.

Source: Own elaboration

In the room refurbished with interior thermal insulation, indoor temperatures ranged from 20°C to 12°C, with relative humidity between 70% and 45%. Also, channel 2 in this room showed greater thermal variability due to its critical location. However, the temperature waves remain uniform in the other channels, demonstrating that thermal comfort has increased inside the room, as shown in Figure 15.

Figure 15. Temperature comparison by channel - Bedroom 02.

Source: Own elaboration