Research on Micro-Intervention Strategies for Energy-Saving Renovation of the Envelope Structures in Existing Brick–Wood Ancient-Style Buildings

Abstract

In the global low-carbon era, building energy conservation has achieved significant success. However, especially in the culture and tourism industry, there are many brick–wood buildings that imitate ancient styles. As their appearance authenticity and structural safety must be maintained, energy-saving retrofits face multiple constraints. For such buildings, regulating building energy consumption through the renovation of the enclosure structure has practical value in supporting the achievement of carbon peaking and carbon neutrality goals. This study addresses the contradiction between the preserving architectural forms and improving energy efficiency in the energy-saving renovation of brick–wood buildings that imitate ancient styles. It presents a “Three-Micro” technical system grounded in the minimum-intervention principle, integrating micro-intervention implantation, micro-realignment regulation, and micro-renewal iteration. Through modular node design, it combines traditional construction with modern energy-saving techniques and systematically devises an energy-saving retrofit plan for such existing buildings. Through simulation and verification using the case of the Northwest Corner Tower in the Imperial City of Shengjing, the results show that the energy-saving rate of the building itself is 58.47%, while the comprehensive energy-saving rate is 87.56%. Both meet the evaluation criteria for ultra-low energy consumption buildings under the relevant standards, which proves the feasibility of the “Three-Micro” technical system. It provides solutions for the energy-saving renovation of similar buildings, especially those brick–wood buildings that imitate ancient styles and have a high degree of completion (a high level of imitation of ancient architecture). At the same time, it also holds important reference value for the energy-saving renovation of some non-core ancient buildings that are commonly used in everyday life, such as those serving as ticket offices, exhibition halls, administrative offices, etc.

1. Introduction

The building sector accounts for 30% of total societal energy consumption [1], establishing itself as a critical domain for energy conservation and emissions reduction. Currently, governments, enterprises, and various sectors of society are increasing investments to promote R&D and implement energy-efficient technologies, leading to substantial progress in reducing energy consumption and carbon emissions across the sector. However, energy retrofits for imitation ancient buildings, particularly brick–wood structures, remain significantly underdeveloped. This lag is mainly reflected in the lack of relevant technical strategies and research guidance, as well as the inefficient use of a large number of commonly used antique buildings, resulting in inefficient energy consumption. The underlying challenges stem from the inherent constraints of traditional brick–wood structures, coupled with preservation requirements for architectural forms and components, which collectively escalate the technical complexity of energy retrofitting—especially for high-fidelity imitation ancient buildings.

The “transformation” involved in renovating existing ancient-style buildings and the “preservation” of their original appearance and features, restoring them to look as authentically aged as they originally were, have become key issues in the renovation of existing ancient-style buildings. The contradiction between “preservation and transformation” is mainly reflected in aspects such as the conflict between form and function, the selection of materials and technologies, and the conflict between usage requirements and protection measures. Therefore, it is necessary to find a balance between the demand for energy-saving renovation and the protection of historical value. Based on this, we introduce the minimum intervention theory. Rooted in the “anti-restoration” philosophy proposed by 19th-century British architect William Morris and systematized through the 1964 Venice Charter, the minimum intervention theory has evolved into a cornerstone principle of international cultural heritage conservation [2]. Its contemporary conceptual extension encompasses three dimensions: (1) The ontological value dimension emphasizes the material authenticity of architecture as a “carrier of historical information”, and historical buildings carry rich cultural information and historical value. It requires that the construction traces of different historical periods be preserved to avoid the loss of the historical value of buildings [3]. (2) The technical ethics dimension: follow the technical ethics of “recognisable, reversible and readable” and give priority to non-invasive or least invasive means of transformation to reduce the impact on building components and structures [4]. (3) Cultural memory dimension: preserve the intangible cultural elements embedded in the architectural space, such as traditional construction techniques, space-use modes, and other living heritage elements, and integrate new elements discretely into the overall form of the building, not only to maintain its authenticity, but also to enhance its functionality and aesthetics.

Guided by the minimum intervention theory, this study proposes the micro-intervention principle for the energy-saving retrofit of existing brick–wood ancient-style buildings. The core approach is to micro-divide the building’s internal space and divide the energy-saving system into units, thus avoiding the conflict between the energy-saving system and the original form. Moreover, by implementing low-intrusive micro-intervention construction measures, a balance, and a breakthrough, can be found between authenticity protection and functional retrofit. This offers solutions for the long-overdue energy-saving retrofit of existing brick–wood ancient-style buildings, especially those with a high degree of authenticity.

2. Micro-Intervention Strategy Under the Minimum Intervention Theory

2.1. Analysis of the Limiting Factors in the Energy-Saving Renovation of the Envelope Structure of Existing Brick–Wood Ancient-Style Buildings

Compared with other buildings, the lag in the development of energy retrofitting for brick–wood imitation ancient buildings is due to the following aspects: (1) Constraints on architectural form: to preserve the historical architectural style, the dimensional proportions of building components in imitation antique architecture cannot be significantly altered by the application of energy-efficient materials, resulting in strict limitations on material selection for energy conservation [5]. (2) Component limitations: the attachment of energy-saving materials during retrofitting may cause certain damage to original building components, particularly wooden elements, which are vulnerable to structural compromise [6]. (3) Structural complexity: the intricate construction morphology of imitation ancient buildings presents substantial challenges to achieving adequate airtightness in the building envelope system [7,8].

2.2. Thoughts on the Renovation of Ancient-Style Buildings Under the Minimum Intervention Theory

In light of the theory of the minimum intervention theory, this paper proposes the following ideas for the energy-saving renovation of the envelope structures of existing brick–wood ancient-style buildings:

(1)

Establish a reversible technical system based on historical value assessment. Improve thermal performance through a micro-intervention construction logic, ensuring that the technical measures form a separable physical interface with the building’s main body. Develop a plan for installation and disassembly with minimal impact on the original structure.

(2)

Create an adaptable energy-saving space based on the morphological and spatial characteristics of the ancient-style buildings themselves, thus achieving minimum intervention in the energy-saving usable space at the envelope interface of the main building.

(3)

Construct an adaptable technical translation mechanism. Use parametric design to translate modern energy-saving technologies into cultural symbols that conform to the form paradigm and adopt compatible new structures and forms to meet the form-related and cultural requirements of ancient-style buildings.

(4)

Select an energy-saving system and materials suitable for the characteristics of ancient-style buildings, thereby achieving minimum intervention at the interface of the main building in terms of form, load, etc.

2.3. Micro-Intervention Strategies Under the Minimum Intervention Theory

Based on the above-mentioned theories and principles, this study proposes three micro-intervention strategies for the energy-saving renovation of the envelope structures of existing brick–wood ancient-style buildings: ”micro-intervention”, “micro-realignment”, and “micro-renewal”, so as to achieve the effective renovation of this type of buildings.

2.3.1. Micro-Intervention

The concept of “minimally invasive” emphasizes reducing physical intrusion and traumatic control on existing structural components. Specific measures to achieve this goal involve the following aspects: (1) Rigorous material selection. First, lightweight, high-efficiency insulation materials are preferred to minimize impacts on existing structures in terms of load-bearing capacity and cladding thickness [9]. Second, materials in direct contact with occupants must exhibit high impact resistance to protect original components. Third, the newly applied materials should provide protective functions, such as corrosion resistance and fireproofing, to safeguard existing structures. (2) Attachment method optimization. Lightweight materials form the foundation of minimally invasive design, while protective construction methods under safe and reliable conditions are prioritized. Common attachment strategies include wrapping, bonding, and minimally invasive implantation, with rational integration of these techniques being critical to successful implementation [10]. (3) Reversible structural design. Reversibility refers to the design of energy-efficient structures that allow non-destructive disassembly. This ensures that maintenance activities are conducted without causing subsequent damage to original components while preserving their authenticity.

2.3.2. Micro-Realignment

The “micro-shaping” strategy places significant emphasis on controlling the deformation degree of components subsequent to renovation. It primarily attains the enhancement of both functionality and aesthetics by conducting detailed treatments on architectural components and other details. Additionally, through the subdivision at the spatial level, this strategy effectively circumvents the conflict between energy-saving structures and shape-defining components. Key technical measures include the following:

(1)

Structural micro-realignment: at the same time, structural components, either entirely or locally, that pose safety hazards are reinforced [11,12]. Traditional and new reinforcement technologies are combined to maintain concealment [13], while enhancing energy efficiency, seismic resistance, and durability [14].

(2)

Implementing micro-realignment: the energy-saving renovation of the envelope structure of existing brick—wood ancient-style buildings can be divided into two major parts: ① additive energy-saving elements, referring to components requiring additional insulation systems (e.g., walls, roofs, suspended ceilings, and floors) to achieve energy efficiency; ② intrinsic energy-saving elements, denoting self-sufficient energy-efficient components such as windows/doors [15].

For additive energy-saving elements, considering the damage and deformation of the components, the thermal insulation material should be lightweight and high-strength. Secondly, the thermal conductivity of the material should be low enough to reduce the thickness of the material and the influence of deformation caused by the increase in thickness. Thirdly, the conflicts caused by deformation can be reduced or optimized through hidden structural measures.

For intrinsic energy-saving elements, high-simulation replacement materials and highly permeable secondary door and window systems are energy saving measures to ensure shape consistency. Traditional wooden doors and windows, whether in terms of solid frame materials or transparent glass panes, can hardly achieve energy-saving transformation on their own. First of all, the thermal conductivity of the window frame itself is unsatisfactory and it is not suitable for the addition of an insulation layer. Secondly, it cannot support energy-saving glass. Third, issues such as frame length deformation and poor airtightness cannot be solved.

Therefore, severely deteriorated wooden fenestration may be replaced through historically accurate replication, utilizing contemporary replication techniques that preserve original formal characteristics, material authenticity, and historical patina, while achieving energy efficiency. For heritage-grade components that require preservation, integrating high-transparency supplementary fenestration on the interior, together with overhead ceiling interfaces, establishes a complete energy-efficient envelope system: retaining cultural heritage by preserving original elements while enhancing thermal performance through secondary installations. The optical neutrality of supplementary systems maintains minimal visual intervention, realizing effective micro-realignment.

(3)

Spatial micro-realignment: the inherent complexity of timber–brick structural joints in historic-style buildings renders conventional envelope retrofits inadequate for addressing thermal bridging and airtightness deficiencies without inducing fundamental morphological alterations [16]. This study proposes a spatial energy compartmentalization strategy (Figure 1), implementing three-dimensional zoning to create discrete thermal boundary units. Each compartment achieves systemic energy optimization through dual-layer interventions: material-layer reconfiguration with gradient insulation assemblies and high-performance sealing technologies; and spatial-layer optimization employing modular thermal bridge interruption mechanisms to regulate energy transfer pathways.

Each compartment forms an independent thermal closed-loop system that enables targeted optimization of critical components—exterior walls, roofs, adjacent ground surfaces, and fenestration systems—while preserving architectural integrity. Systematic enhancements include wall assemblies upgraded through high-efficiency insulation materials with optimized stratification; fenestration performance improved via advanced sealing technologies and energy-efficient glazing; roof/ground interfaces reinforced with thermal insulation, moisture-proofing, and thermal buffering measures. This compartmentalized approach transcends conventional holistic retrofitting through a fractal-based zonal control framework, achieving a symbiotic integration of heritage morphology with contemporary energy technologies. Through this compartmentalization method, the conflict between the energy-saving construction layer and the shape-defining components is reasonably circumvented, and the closure of the thermal insulation body and the airtight construction system is achieved.

2.3.3. Micro-Renewal

“Micro-renewal” strategy. Focused on technological integration and intelligent enhancement, this approach employs modern technical interventions to elevate building energy efficiency through two principal implementations: (1) Intelligent control systems: The implementation of smart control systems enables real-time performance monitoring and regulation of building envelopes. For instance, smart windows with automated aperture modulation responsive to outdoor illuminance and indoor thermal conditions significantly reduce HVAC and lighting energy consumption [17]. (2) Sustainable maintenance and renewal: The strategy emphasizes long-term envelope preservation through intelligent data-driven management [18]. Embedded sensors continuously monitor aging patterns, declining energy efficiency performance, and material degradation, enabling predictive maintenance, which eliminates structural overhauls while extending service life and reducing lifecycle costs.

3. Project Profile

The Northwest Corner Tower of Shengjing Imperial City was a product of the reconstruction of Shenyang City during the fifth year of Tiancong reign in the Qing Dynasty (1631). It was destroyed during the Russo-Japanese War in 1905 and reconstructed on its original site with authentic appearance by Shenyang City in 2001. As shown in Figure 2, this six-story structure features brick masonry walls in its lower three stories and wooden construction in the upper three stories. The tower adopts a hip-and-gable roof system surrounded by auxiliary eaves, with a plank door along the central axis in the north-south orientation and lattice wooden windows arranged around the perimeter [19]. Through data acquisition, BIM-based refined modeling, and component library establishment, this study carried out multi-scale digital reconstruction and preservation of existing historic architecture (Figure 3).

The renovation project focused on floors 1–5 of the structure, including components of the brick city wall (floors 1–3) serving as exhibition halls and wooden tower components (floors 4–5) functioning as office spaces. The sixth floor remains a permanently open religious ritual space excluded from energy-saving modifications, in compliance with China’s ultra-low energy consumption building standards specified in GB/T51350-2019 [20].

This study investigates the energy-efficient retrofitting of the Northwest Corner Tower in Shengjing Imperial City. Through field surveys and the application of the minimum intervention theory, innovative techniques were implemented: optimized insulation materials and systems, compartmentalized airtightness control, reversible cladding for wood components, and high-efficiency heat recovery ventilation. This research emphasizes envelope structure optimization strategies, providing theoretical references for green retrofitting of brick–wood imitation heritage architectures and non-core historical buildings.

4. Methods

4.1. Micro-Intervention

4.1.1. Insulation System Selection

As illustrated in the figure, the external envelope of the building demonstrates significantly greater complexity compared to the simply enclosed interior spaces. From the perspective of heritage conservation, the facade presents challenges for implementing energy-efficient modifications. Consequently, the adoption of an interior insulation system for the building envelope emerges as a more feasible solution, which ensures the preservation of the structure’s external architectural form while maintaining technical implementability.

4.1.2. Insulation Material Selection

The success of micro-interventions within internal structures primarily depends on the selection of insulation materials, with thermal insulation performance, non-combustibility (or flame retardancy), lightweight properties, thin profile, and high strength being essential evaluation criteria.

Table 1. Comprehensive comparison of insulation material performance.

	Vacuum Insulation Panels	Rock Wool Board	Foamed Cement Board	Foamed Ceramic Plate	Extruded Polystyrene Boards	Resin Plate
Thermal conductivity (W/mK)	0.010	0.044	0.060	0.080	0.030	0.040
Dry density (kg/m3)	60	140–200	300	280	30	100
Fire rating	A	A	A	A	B	B
Equivalent insulation thickness (cm)	2–3	11–13	10–14	15–18	7–9	10–11
Tensile strength (MPa)	0.27	0.015	0.1	0.25	0.2	0.1
Compressive strength (MPa)	0.34	0.06	0.35	0.3	0.2	0.1
Environmental protection property	Does not produce toxic substances; can be recycled	Pulverized materials pollute the air	Fragile, polluting the environment	Pollute the environment	The production of polystyrene as a raw material poses certain environmental and health risks	The main components of phenol and formaldehyde pollute the environment
Maintenance performance	Not easy to crack, good thermal stability, low maintenance rate	Prone to cracking and powdering, high maintenance rate	Fragile and difficult to maintain	Fragile and difficult to maintain	Easy to expand, high maintenance rate	Prone to breaking and detachment
Comprehensive analysis	Physical, thermal insulation, fire performance is excellent	Poor physical performance	Physical and thermal insulation properties are poor	General physical properties, good fire performance, insulation performance is poor	Good thermal insulation performance, poor fire performance	The physical and thermal insulation properties are average

compares the insulation performance of various materials in the construction field [21]. Through comprehensive analysis, vacuum insulation panels (VIPs) demonstrate advantages such as lightweight characteristics, minimal thickness (energy efficiency calculations indicate that only 30 mm VIPs are required to meet ultra-low energy consumption retrofit requirements for this project, compared to 135 mm for rock wool and 90 mm for extruded polystyrene (XPS) boards under equivalent conditions), reliable combustion performance, and structural strength. These properties ensure minimal alterations to the building’s internal configuration while fulfilling multi-objective retrofit requirements, including energy conservation, protection, and fire resistance [22,23]. Additionally, VIPs can achieve a minimum thickness of 10 mm, facilitating curved installations adapted to wooden column dimensions. Consequently, VIPs were selected as the insulation material for walls and columns in this project. Considering the potential damage from numerous suspension rods and equipment fasteners above the ceiling, rock wool was chosen for concealed insulation applications to meet both thermal and acoustic insulation needs. XPS boards were adopted for perimeter ground insulation layers due to their advantages, such as compressive resistance and moisture prevention.

4.1.3. Reversible Attachment System

(1)

External wall insulation attachment structure

The retrofitting measures for the exterior walls of the 1–3-story masonry structure section are illustrated in Figure 4. While retaining the original exterior walls, an internal insulation layer is added. During construction, the substrate is first treated with a treatment agent, followed by leveling and bonding using polymer-modified cement mortar. The waterproof layer employs a cement-based permeable crystalline waterproofing coating. Vacuum insulation panels are installed and secured with polymer-modified cement mortar for leveling and bonding. The finish layer adopts staggered joint splicing. Thermal insulation spacers are positioned above the bonding layer, with expansion screws drilled into each steel plate to fix mounting brackets, and gaps are densely filled with foamed polyurethane.

The retrofitting measures for the 4–5-story historic building section are shown in Figure 5. A 30 mm thick vacuum insulation panel (pre-attached with simulated wooden windowsill boards) is installed near exterior window openings and fixed using galvanized cement nails and metal corner guards.

(2)

Micro-intrusive reversible construction of wooden components

For attaching the timber member insulation system, non-invasive or minimally invasive reversible modifications are implemented with minimal alteration to the original components.

The existing wooden columns are encapsulated with a waterproof breathable membrane. On one hand, this membrane prevents moisture in the air from eroding the internal structure of the columns, thereby avoiding mold growth, condensation, and damage caused by moisture intrusion. When moisture permeates into the insulation layer, it gradually degrades the thermal performance of the insulation material while allowing internal moisture to dissipate through the air-permeable protective layer. On the other hand, in cold and humid environments, cement mortar is prone to efflorescence [24], and prolonged contact may induce corrosive effects on wooden members. The installation of the waterproof breathable membrane beneath effectively mitigates the impacts of such phenomena, thereby enhancing the service life of timber members and endowing them with improved corrosion resistance.

This study employed galvanized cement nails for the “column wrapping” of timber members. First, galvanized cement nails with a diameter of 1.8 mm were selected to fasten the wire mesh layer onto a 1 m² spruce wood column at intervals of 250 mm, 200 mm, and 150 mm, with a nail penetration depth of 20 mm. It was found that the 200 mm interval fixation method satisfied both the requirements of structural stability and cost-effectiveness. Second, as described above, the number of nails per square meter was 25, and the pull-out resistance of each nail was 294 N [25,26,27] (Equation (1)). According to Equation (2), the bonding strength of the nails in the 1 m² spruce wood was calculated to be 0.00735 MPa.

$$P_{rw,\alpha }=\phi {\displaystyle \frac{0.8·\delta {\left(b·0.84·\rho \right)}^2·d·l_{ef}·{10}^{-6}}{si{n}^2\alpha +\frac{4}{3}co{s}^2\alpha }}·K_D·K_{SF}$$

(1)

In Formula (1):

$P_{rw,\alpha }$ is the pulling capacity of galvanized cement nail, N;

$b$ is 1 (for D-Fir-L, SPF, SYP, WRC, Hem-Fir) or $b$ is 0.75 (for PSL);

$d$ is the diameter of galvanized cement nail, mm;

$l_{ef}$ is the depth of the specimen embedded in the wood structure, mm;

$K_D$ is the loading duration factor, 1.0;

$K_{SF}$ is the service condition factor, 1.0;

$\alpha$ is the angle between the screw axis and the wood grain, 90°;

$\delta$ is the material adjustment factor ($\rho$ ≥ 440 kg/m³, $\delta$ is 82; $\rho$ < 440 kg/m³, $\delta$ is 85);

$\rho$ is the drying relative density, g/cm³;

$\phi$ is the coefficient, 0.9;

0.8 is the adjustment of standard load;

0.84 is adjusted to the 5th percentile for drying relative density.

$$P_a={\displaystyle \frac{F_a·n}{S_a}}÷1000$$

(2)

In Formula (2):

$P_a$ is the total bond strength of nails, MPa;

$F_a$ is the pull-out force per nail, N;

$n$ is the total number of nails;

$S_a$ is the bond area for calculating bond strength, m².

According to <Technical Specification for Interior Thermal Insulation on External Walls> (JGJ/T 261-2011) [28], the bond strength of interior insulation systems must meet a minimum requirement of ≥0.03 MPa, with an effective bond area of mortar ≥ 20%. Based on Equation (3) specified in the standard, the calculated bond strength for traditional interior insulation applied to 1 m² of spruce wood is 0.006 MPa.

$$P_b=\eta ·\alpha ·S_b$$

(3)

In Formula (3):

$P_b$ is the mortar bond strength, MPa;

$\eta$ is the bond strength, MPa;

$\alpha$ is the effective bond coefficient;

$S_b$ is the bond area, m².

Under identical conditions, the encapsulation of wooden columns using cement nails demonstrates superior performance compared to traditional internal insulation methods, exhibiting 1.225 times greater structural strength. This study employs 1.8 × 20 mm galvanized cement nails, spaced at 200 mm intervals with washers, to secure the wire mesh layer, subsequently overlaid with curved vacuum-insulated panels and finished with wood-grain coating. The implementation of 1.8 mm galvanized cement nails embedded in 300–400 mm diameter wooden columns achieves minimal invasiveness to the original wooden structure while enhancing structural integrity and aesthetic appeal. The external cladding consists of 30 mm thick insulated decorative material, providing comprehensive fire resistance and anti-corrosion properties alongside improved visual continuity (Figure 6).

The refined design of nail dimensions establishes a physical foundation for subsequent non-destructive disassembly. The galvanized cement nails, fabricated from high-strength steel, balance localized reinforcement requirements with controlled penetration through precise dimensional specifications (φ1.8 mm diameter × 20 mm length). This configuration prevents excessive stress concentration within the wooden columns while maintaining structural efficacy. The fixation mechanism relies solely on mechanical interlocking between nails and the wood substrate, deliberately avoiding irreversible adhesives. This design enables future removal using specialized tools (e.g., nail extractors), achieving complete nail extraction with controllable micro-perforations. In this heritage timber column restoration project, the reversible application of galvanized cement nails operationalizes a “limited intervention—dynamic maintenance—nondestructive withdrawal” technical framework. By synergizing traditional craftsmanship’s physical reversibility with modern material science’s controllability, the methodology extends structural lifespan while preserving compatibility interfaces for future technological iterations. This practice fundamentally embodies the conservation philosophy of reversibility, ensuring minimal intervention depth and maximum adaptability for evolving preservation paradigms.

4.2. Micro-Realignment

4.2.1. High-Precision Door and Window Replacement

The renovation addresses the severe deterioration of building fenestration through high-fidelity replication. Laser scanning technology digitally captures original window/door parameters, including geometric configurations, structural joints, and ornamental characteristics, establishing a BIM database that archives critical features such as profile sections, mortise-tenon connections, and decorative pattern ratios. This data-driven approach enables specialized manufacturers to precisely customize energy-efficient fenestration units that replicate traditional wooden window profiles (including molding proportions and carved motifs) while incorporating modern thermal break frameworks. The exterior surfaces maintain architectural authenticity preservation through wood-grain cladding with artificially weathered finishes, achieving both historical accuracy and visual coherence with adjacent architectural elements.

The thermal performance enhancement implements a multi-tiered energy efficiency system, structural thermal bridges at critical junctions are mitigated through insulation gaskets, achieving over 60% reduction in linear heat transfer. Fenestration openings undergo triple-stage airtightness treatment, where structural gaps are sealed with thermal-resistant materials to minimize air infiltration. The primary glazing employs double silver Low-E coated insulating glass units, integrating 12A argon-filled cavities and warm-edge spacer systems. Laboratory tests confirm stabilized window U-values at 1.5 W/(m²·K), representing 83% thermal improvement over traditional wooden windows while meeting Grade 8 energy efficiency criteria per GB/T 8484-2020 [29] (Figure 7).

This research establishes a technical framework of “3D digital repository—traditional craftsmanship reinterpretation—contemporary performance optimization”. Historical construction features are meticulously preserved in operational mechanisms and hardware configurations, ensuring the renovated fenestration system simultaneously complies with modern energy codes and perpetuates architectural heritage through the unbroken transmission of historical narratives and artistic values. The methodology demonstrates synergistic advancement in both cultural heritage conservation and building performance enhancement.

4.2.2. Spatial Energy Compartmentalization

This study proposes a compartmentalized spatial unit-based thermal bridge control and airtightness collaborative optimization strategy for brick–timber composite structures, establishing a progressive retrofitting system (Figure 8):

(1)

Spatial thermal boundary control: Modular spatial micro-reshaping technology deconstructs buildings into independent energy-saving units with closed thermal boundaries. A dual-layer interface system is embedded in the first- through third-floor masonry structures. The interior insulation layer and vapor barrier membranes form an active defense system to block horizontal heat transfer. Horizontal compartmentalization in the upper timber structures (≥4th floor) achieves three-dimensional thermal bridge interruption through the use of silicone sealant and vapor barrier lamination. This system transforms heat conduction paths from disordered diffusion to closed-loop dissipation within units.

(2)

Graded airtightness optimization: A triple-aspect airtightness protection system integrates material, construction, and spatial components. ① Interface layers employ weather-resistant silicone sealant for dynamic joint displacement compensation, with continuous molecular sieve structures formed by vapor barriers. ② Window systems integrate vacuum insulation panels and dual-sealing technology, achieving topological isomorphism between historic features and energy performance through high-fidelity replacement techniques. ③ Elastic buffer zones at unit junctions establish gradient airtightness protection hierarchy.

(3)

Unitized energy management: Each energy-saving unit forms independent thermal circulation systems. Masonry zones adopt tri-directional insulation coupling (ground, wall, and roof), while timber zones create air cavities through secondary window systems. Differentiated regulation strategies between units enable precise local thermal environment control and global energy consumption optimization.

4.2.3. Device Covert Processing

The functional–aesthetic conflict between wall-penetrating sleeves and architectural appearance can be reconciled through cultural symbol reinterpretation and refined detailing. This project draws inspiration from the “Nine Dragons Spouting Water” stone carvings in Beijing’s Forbidden City (Figure 9). A BIM model (Figure 10) is developed based on exhaust vent airflow requirements, explicitly annotating sleeve–structural connections. This integrates mechanical exhaust ports with traditional decorative art, overcoming compatibility challenges between modern materials and historic architectural features. Digital technologies enable contemporary reinterpretation of traditional craftsmanship, establishing a paradigm for the symbiotic integration of electromechanical equipment and historical aesthetics in heritage-inspired architecture.

For the caisson ceiling as architectural focal points, this project implements suspended ceiling additions (Figure 11) to conceal equipment and piping within interstitial spaces, preserving visual integrity while maintaining functionality. Roof insulation is installed above suspended ceilings, with thermal insulation rock wool boards filling the cavities between wood furring strip. A 20 mm thick oriented strand board (OSB) treated with anticorrosive coating forms the lower layer. Vibration damping pads and flexible connections are employed to control equipment-induced vibrations and noise within acceptable thresholds, ensuring structural safety and meeting the fireproof/anticorrosive requirements for caisson ceilings.

4.3. Micro-Renewal

Intelligent management and long-term maintenance of equipment during renovation are achieved through embedded real-time building performance monitoring systems integrating photothermal sensing modules and adaptive adjustment devices. Smart windows automatically regulate their opening angles based on outdoor illumination intensity and indoor temperature, effectively reducing HVAC and lighting energy consumption. A preventive maintenance mechanism is established through envelope aging assessment models and energy efficiency decay prediction algorithms, enabling cost-effective life-cycle management.

Furthermore, a BIM-based system is developed that integrates architectural physics perception, dynamic regulation, and preventive maintenance. This platform achieves multi-source data fusion and cross-system collaborative control, continuously monitoring operational status while conducting in-depth energy consumption analysis to evaluate equipment efficiency. By synthesizing building usage patterns and environmental variations, the intelligent system provides data-driven decision support. Through the automated adjustment of operational parameters (e.g., HVAC temperature setpoints and lighting intensity), it facilitates dynamic energy optimization, enhances operational efficiency, and reduces maintenance costs while supporting the formulation of rational energy conservation strategies.

5. Result Analysis

For various reasons, the project was stalled after the construction drawings had been completed. Unfortunately, the post-transformation measured data cannot be obtained at present. However, in accordance with drawing examination requirements, China Swire software PHES2025 was adopted for simulation analysis during the construction drawing stage, and the results, which meet the evaluation standards for ultra-low energy consumption buildings under <Design standard for energy efficiency of public buildings> (GB50189-2015) [30] and <Technical standard for nearly zero energy buildings> (GB/T51350-2019), are shown in

Table 2. Simulation of energy consumption based on PHES2025.

	Design Building	Reference Building
Energy consumption of building itself (kWh/m2)	61.03	146.97
Comprehensive energy consumption of building (kWh/m2)	18.28	146.97
	Value	Limiting value
Building energy efficiency improvement rate (%)	58.47	25.00
Building energy saving rate (%)	87.56	50.00
Standard basis	<Technical standard for nearly zero energy buildings > (GB/T51350-2019), Table 5.0.4
Standard requirement	Building energy saving rate (87.56%) ≥ 50%; building energy efficiency improvement rate meets the requirements of Table 5.0.4 [20].
Result	Satisfactory

. In order to ensure the reliability of the data, this paper also uses the industry’s common Design Builder for simulation verification.

Design Builder 6.1.0 is a comprehensive graphical user interface simulation software for EnergyPlus, a dynamic simulation program for modeling building energy consumption [31]. By providing performance data to optimize design and evaluation, complex buildings can be modeled to simulate energy use within buildings on a year-by-year, day-by-day, and hour-by-hour basis [32]. All parameters in the model (building orientation, body shape coefficient, window-to-wall ratio, and functional layout, etc.) are consistent with the measured buildings. The typical meteorological data of Shenyang city, sourced from the China Standard Meteorological Database (CSWD) and provided by the software, are used for outdoor climate. According to the parameters of the external protection structure, the room disturbance settings take into account heat dissipation, lighting, electrical equipment, and other conditions. The outputs include indoor air temperature, average radiation temperature, and other variables. The body shape coefficient of the building model is 0.29, and the window-to-wall ratios of the east, south, west, and north exterior walls are 0.04, 0.05, 0.04, and 0.05, respectively. The heat transfer coefficients of the roof, exterior walls, exterior doors, windows, and ground are 0.27, 0.23, 1.5, and 0.17, respectively. The simulation employed dynamic coupling algorithms incorporating time-varying thermal disturbance factors (including equipment heat dissipation, lighting loads, and occupant activities) to generate iterative solutions for both indoor air temperature and mean radiant temperature. The HVAC system integrated fresh air heat recovery with dual-dimensional time-temperature control strategies, ensuring spatiotemporal synchronization between heating/cooling compensation mechanisms and occupancy patterns (Figure 12).

Through the above parameter settings, DB energy consumption analysis software was used to simulate and analyze the annual cooling and heating energy consumption of the reference building, and it was concluded that the building also meets the requirements for ultra-low energy consumption (

Table 3. Simulation of energy consumption based on DB.

	Simulation Results of DB	Simulation Results of PHES2025	Error Control Objective
Energy consumption of building itself (kWh/m2)	61.05	61.03	≤±1%
Comprehensive energy consumption of building (kWh/m2)	18.60	18.28	≤±2%
Building energy efficiency improvement rate (%)	58.15	58.47	≤±0.5%
Building energy saving rate (%)	87.34	87.56	≤±0.3%

). At present, although the actual data of this project cannot be obtained, the simulations from the two software programs confirm the feasibility of energy-saving transformation measures guided by the theory of minimum intervention degree in the design stage, providing theoretical support and a direction for technical innovation for solving the energy-saving transformation of a large number of existing brick-and-wood antique buildings.

6. Conclusions

This study takes the contradiction between the “preservation of architectural form” and the “improvement of energy efficiency”, which has long hindered the energy-saving renovation of the envelope structures of existing brick–wood ancient-style buildings, as its core. Based on the theory of minimum intervention, it proposes the principles of micro-intervention for the energy-saving renovation of ancient-style buildings. The investigation reveals that there is very little relevant research in the field of this type of buildings (especially those with wooden structures). Occasionally, only theoretical overviews are available, and no specific construction designs and strategic plans have been found yet. Therefore, this study has a certain degree of innovation and mainly achieves the following breakthroughs:

(1)

Based on the spatial and structural characteristics of ancient buildings, a compartmentalized energy-saving space model has been creatively proposed. One the one hand, through the model of breaking the whole into parts and under the premise of ensuring that the architectural form of the ancient-style building remains unchanged or undergoes minimal changes, the enclosure of the thermal insulation structure and the airtight unit layer is achieved, providing fundamental support for the energy-saving renovation of ancient-style buildings. On the other hand, through the refined compartmentalized energy-saving settings, the traditional extensive energy-saving model, which treats the entire building as the unit, is disrupted. As a result, it is possible to achieve the subdivided energy-saving treatment of “different structures in the same building” (in terms of construction) and “different energy consumptions in the same building” (in terms of energy consumption), and a better cost-effectiveness ratio can be achieved across multiple aspects, such as investment and operation.

(2)

Based on the principle of minimum intervention, the technical strategies of “Three-Micro” (micro-intervention, micro-realignment, and micro-renewal) have been proposed. An innovative technical concept has been put forward: “micro intervention implantation-micro realignment regulation-micro renewal iteration.” Ranging from material selection to structural design, and from the integration of component forms to system renewal and replacement, traditional structures are combined with modern energy-saving technologies through the use of modular node design. From the aspects of components and structures, a systematic energy-saving structural renovation plan for existing brick–wood ancient-style buildings has been proposed.

(3)

The technical concept of low invasiveness and reversibility has been proposed. Based on the realization of low invasiveness through the technical strategies of “Three-Micro”, this study further puts forward the technical concept of reversibility. Different from the energy-saving renovation of ordinary buildings, which can be carried out with relatively large-scale renovation, repair, and maintenance, the renovation of existing brick–wood ancient-style buildings or non-core ancient buildings requires the use of low-invasive structural solutions during the renovation stage. This is an important measure to ensure the improvement of energy efficiency while maintaining the architectural form. However, during the repair and later renovation stages, the proposed concept of protective and reversible design for pre-installed energy-saving structures is an extremely plays a crucial role in the protective renovation of brick–wood ancient-style buildings or non-core ancient buildings, whose service life is longer than that of ordinary buildings.

At the same time, this technical system has a wide range of adaptability: the construction parameters are adjusted through micro-intervention technology to meet the requirements of different climate zones; for heritage structures other than brick–wood structures, such as stone structures and brick–concrete structures, the language translation between modern energy-saving technologies and traditional construction logics is achieved with the help of the micro-realignment regulation strategy, solving the problem of material system compatibility; in response to the differentiated functional requirements, the energy consumption zoning management across different functional spaces is achieved through the micro-renewal iteration mechanism without changing the architectural form, reflecting the dynamic coupling between the technical strategy and usage scenarios.

Moreover, the micro-renewal iteration strategy introduces the concept of reversible design thinking, endowing the energy-saving structure with the capability for dynamic upgrading. It allows for partial replacement as materials age and technologies advance, avoiding the irreversible losses associated with traditional renovation methods. By integrating the advantages of precise regulation in the compartmentalized energy-saving model, this system forms a virtuous cycle of “progressive optimization—sustainable maintenance” throughout the entire life cycle of the building. This not only meets the current needs for energy efficiency improvement but also reserves technical interfaces for future repairs. In doing so, it theoretically resolves the contradiction between heritage protection and performance enhancement across the dimension of time.

In summary, this study proposes the concept of a gradient technical system of “compartment unit-Three Micro technology-reversible structure”. By reconstructing the energy-saving dimension through the compartment model, breaking through the intervention scale with the “Three-Micro” technology, and extending the protection cycle through the reversible system, a technical path has been established for the coordinated improvement of the authenticity of the architectural form and the advancement of energy efficiency. This provides a solution with both theoretical value and practical significance for the energy-saving renovation of the envelope structures of existing brick–wood ancient-style buildings.