Reducing Thermal Bridging from Antenna Installations Using an External-Wall Mounting Block to Support Sustainable Development

Abstract

The aim of this study is to improve the energy efficiency of buildings by reducing the impact of point thermal bridges. A detailed analysis was carried out on an antenna holder mounted to the building partition. To limit heat transfer through the partition, a mounting block was applied. This element serves as an insulating function for the partition and as a load-bearing support for external components. In order to assess the effectiveness of the proposed solution, numerical simulations of heat transfer were conducted. Two types of models were analyzed: an idealized model, in which all layers (wall, insulation, and additional structural elements) are perfectly joined, and a more realistic model, which accounts for air gaps between different layers—especially between the insulation and additional structural elements—resulting from typical wear and usage. It was found that models with air gaps demonstrated the advantages of the proposed solution. In this case, the use of the mounting block retained twice as much heat inside the room compared to the configuration without the block. Thus, the applied mounting block effectively reduced the impact of point thermal bridges at the antenna holder by approximately 50%. This translates directly into reduced energy consumption during building operation, which aligns with the concept of sustainable environmental development.

1. Introduction

Building envelopes serve as a barrier that separates the indoor microclimate from the changing outdoor atmospheric conditions. Understanding heat transfer phenomena in buildings is essential from the perspective of both energy efficiency and structural durability. Analyzing these processes allows for the optimization of construction techniques and insulation strategies for new buildings, as well as the improvement of retrofitting methods for existing structures [1]. According to the directive of the European Parliament on the energy performance of buildings from December 2021, buildings are responsible for 36% of greenhouse gas emissions and consume 40% of the total energy in the European Union. Moreover, 75% of buildings in the EU are characterized by low energy efficiency, consuming two-thirds of the energy required for heating (Directive No. 2021/2077(INI) [2]). An important factor in maintaining high energy efficiency is the presence of point thermal bridges, which in modern structures often result from discontinuities in thermal insulation caused by the attachment of external elements to the building’s load-bearing structure. These include balconies and terraces, staircases, air conditioners and ventilation units, gutters and downspouts, railings, window and sunshades, facade panels, flag holders, antennas, lamps, and various types of awnings and coverings. Heat losses due to thermal bridges can lead to increased heating demand, as well as moisture condensation and mold growth within the building. According to the literature, the total impact of thermal bridges on heating energy demand can be significant, ranging from 5% to 42% [3,4,5,6]. This influence depends on various factors such as climate conditions, insulation thickness, thermal bridge geometry, the building type (its function and shape), and how these elements are accounted for in energy performance calculations [7]. Experimental studies are commonly conducted using infrared thermography techniques [8,9]. While the topic of point thermal bridges has been addressed in various publications, most focus on linear thermal bridges, such as: floor-to-ground wall junctions [10,11], floor-to-wall junctions [10,12], roof-to-wall junctions [10,13,14], window and door openings [15,16,17], balconies [18,19] and wall corners [20,21]. In the study by Qi [22], the authors investigated the influence of thermal bridges in Lightweight Steel-Framed (LSF) buildings, analyzing thermal bridges at locations such as external wall-beam junctions, internal and external corners of external walls, and cornices. Numerical simulations using Therm software were carried out, followed by thermal retrofitting of critical areas to reduce heat losses. Ilomes et al. [23] focused on building renovation, showing that thermal bridges were responsible for up to 23% of heat losses. After renovation, the analyzed buildings became more airtight, with losses reduced to 10%. Notably, the authors found that in some cases, increasing insulation thickness did not reduce heat losses, as the presence of point thermal bridges could still dominate, regardless of the insulation layer’s thickness. In scenarios where external elements, such as antenna holders, must be mounted, the insulation layer is typically penetrated and the holder anchored into the load-bearing layer. Steel anchors are commonly used in such cases, acting as highly conductive thermal bridges. The effect of steel anchoring bolts on insulation systems was studied by Luo [24], who analyzed three insulation thicknesses (composite rock wool boards): 7 cm, 10 cm, and 14 cm. It was observed that the use of metal connectors and anchors degraded the thermal performance of the insulation system. The negative impact on the insulation system amounted to 8.5%, 10.9%, and 13.9%, respectively, for the increasing insulation thicknesses. Furthermore, the heat transfer coefficient of the insulation system increased with insulation thickness. The diameter and number of steel bolts had a greater influence on heat transfer than the length of the bolts. The influence of connectors made from different materials was also studied in works by Ru [25,26]. In the study by Sadauskiene [7], the authors investigated the point thermal transmittance of aluminum mounting components based on parameters such as the thickness and thermal conductivity of the insulation layer and the material of the supporting structure. The results showed that enhancing the thermal conductivity of the support material and increasing the insulation thickness could raise the overall wall U-value by as much as 35% due to point thermal bridges. One of the innovative solutions for mitigating thermal bridging in balconies was presented by Buday [27], who analyzed the Isokorb balcony system. The study evaluated the impact of this system on heating energy demand and economic performance in residential buildings. The system consists of insulating blocks (e.g., made of Neopor) integrated with special reinforcement bars or mounting bolts. The influence of these components on the natural frequency and vibration behavior of the balcony slab was explored by Müller [28]. Another promising idea involves the use of monolithic insulating blocks, made from advanced materials or featuring innovative structures, which simultaneously serve as both structural and insulating elements. Research by Sousa [29] estimated the thermal transmittance of such monolithic walls at approximately 0.5 W/mK. However, it is unfortunate that the influence of steel anchors in such systems was not considered.

Since the literature lacks effective solutions to eliminate point thermal bridges in the mounting of external elements (e.g., antenna brackets), this study proposes a novel approach involving a specially designed mounting block. This component is intended to transfer the load from the bracket to the structural wall while simultaneously eliminating point thermal bridges caused by conventional steel fasteners. The proposed element is made of polyethylene. Numerical simulations of heat transfer were conducted for various configurations, taking into account the load-bearing wall, insulation layer, mounting component, antenna holder, and potential air gaps caused by wear or construction inaccuracies in real-world conditions. The proposed research on reducing thermal bridging caused by antenna installations on building facades introduces a new perspective within the fields of building physics and sustainable construction. Analyzing the impact of installation components on heat loss and developing a dedicated mounting block represent genuine material and structural innovation, as the literature contains virtually no studies addressing the energy-related consequences of antenna mounting. The results may contribute to the advancement of disciplines such as civil engineering, materials engineering, and telecommunication technologies, offering solutions that support building energy efficiency and broader sustainability goals.

2. Materials and Methods

To eliminate point thermal bridges occurring at the mounting locations of external elements on building walls, the use of a specialized installation block has been proposed. The analyzed configuration is presented in Figure 1, where all dimensions are given in millimeters. The system includes four mounting holes that enable secure attachment of the block to the load-bearing wall structure.

In the initial analysis, the mounting element was fabricated from synthetic material—100% high-density polyethylene (HDPE). The material properties used in the study are listed in

Table 1. Parameters of the materials used.

Parameter	HDPE	Steel	Styrofoam	Plaster	Concrete Block
Thermal conductivity [W/mK]	0.28	60.5	0.031	0.4	0.56
Heat constant pressure [J/kgK]	2300	434	1200	1000	860

.

In the next stage, numerical models of the analyzed structures were developed. The numerical models were based on SOLID279 volumetric elements. These are 20-node, second-order hexahedral elements equipped with corner nodes as well as mid-edge nodes, which allows for accurate representation of both the geometry and the spatial gradients of the physical field. Moreover, these elements support coupled physical fields, including thermo-electrical processes. A total of 10 different configurations were considered, each comprising various structural components, including concrete blocks forming the load-bearing wall, cement-lime plaster, expanded polystyrene insulation of varying thicknesses, the proposed installation block, and an external antenna bracket attached to the main structure. The thicknesses of the individual elements were as follows: plaster—15 mm; concrete block—240 mm; polystyrene S1—90 mm; installation block—90 mm; polystyrene S2—60 mm; air gap between the holder and the polystyrene—2 mm.

In all the analyzed models, two identical layers were present, i.e., interior plaster (layer 1) + concrete block (layer 2). The next layer contained the installation mounting block, whose application is examined in this study. It was included in models M2, M3, M6, and M10. The mounting element occupied an area of 540 cm², while the remaining area of that layer was filled with polystyrene of a thickness corresponding to that of the mounting element (in other words, the polystyrene surrounded the mounting block).

In models M4, M5, M7, and M9, the third layer consisted of a steel antenna holder mounted to the wall. The remaining models served as reference cases: in model M1, the third layer contained only polystyrene with a thickness of 9 cm, whereas model M8 contained polystyrene with a total thickness of 15 cm (9 cm in layer 3 + 6 cm in layer 4).

Model M3 differed from model M2 by the presence of an antenna holder mounted to the mounting block. Model M6, in addition to the layers in model M3, include an extra 5 cm layer of polystyrene placed around the antenna holder rod. The last model containing the mounting element, M10, had the same layers as model M6, but with an added air gap between the antenna holder and the polystyrene. The width of the gap was assumed as a model value of 2 mm. Under real conditions, a gap will appear between the antenna and the polystyrene due to imprecise installation and vibrations of the structure. Its size is usually not constant and may vary across the polystyrene thickness. However, the value of 2 mm was adopted as an example model parameter to observe interactions in this type of mounting.

In model M4, besides the antenna holder, a 9 cm layer of polystyrene was included. In model M7, two polystyrene layers (9 cm + 6 cm) were added around the antenna bracket. In models M5 and M9, an additional gap was introduced between the polystyrene and the antenna holder. Detailed specifications of the individual models are presented in

Table 2. Analyzed structures.

Configuration	Layer 1	Layer 2	Layer 3	Layer 4	Layer 5	GAP
Model 1 (M1)	Plaster	CB	S1
Model 2 (M2)	Plaster	CB	AB + S1
Model 3 (M3)	Plaster	CB	AB + S1	AH
Model 4 (M4)	Plaster	CB	AH	S1
Model 5 (M5)	Plaster	CB	AH	S1		AH − S1
Model 6 (M6)	Plaster	CB	AB + S1	AH	S2
Model 7 (M7)	Plaster	CB	AH	S1	S2
Model 8 (M8)	Plaster	CB	S1	S2
Model 9 (M9)	Plaster	CB	AH	S1	S2	AH − S1 + S2
Model 10 (M10)	Plaster	CB	AB + S1	AH	S2	AH − S2

CB—Concrete Block, AB—Assembly block, AH—Antenna Holder, S1—Styrofoam 90 mm, S2—Styrofoam 60 mm.

.

The heat transfer phenomenon in the considered case can be described by the general energy balance equation, derived from the Kirchhoff–Fourier law, and expressed as [30]:

$${\displaystyle \frac{\partial T}{\partial t}}+(\overrightarrow{w} \nabla )T={\displaystyle \frac{1}{\rho c_p}}[\nabla (\lambda \nabla T)+q_v,$$

(1)

where

T—temperature field [K];

t—time [s];

$\overrightarrow{w}$—velocity wector of the fluid [m/s];

c_p—specific heat capacity at constant pressure [J/(kg·K)];

λ—thermal conductivity [W/(mK)];

q_v—volumetric heat source [W/m³].

The solution to the problem is determined using numerical methods, in particular computer simulations. However, it was assumed that the temperature field does not depend on time and there is no internal heat source. Therefore these components are equal zero: ∂T/∂t = 0; q_v = 0.

Numerical investigations were carried out using the Ansys Workbench environment(2025 R1), employing a Steady-State Thermal simulation approach. In the initial phase of the numerical study, a model of the investigated structure was developed, and an appropriate mesh was generated based on the PN-EN ISO 10211 standard [31]. According to the guidelines specified in the standard, the minimum distance between the boundary of the computational domain and the analyzed component should be 1 m, and at least three times the thickness of the analyzed element (i.e., the mounting component). Preliminary calculations were performed using two mesh variants, where the second mesh contained twice as many elements as the first. To determine the number of elements in the base model, the principle was also applied that a minimum of three mesh elements must be present across the thickness of each component. The base model used in this analysis was Model 2 (M2), the schematic of which is shown in Figure 2.

The main calculations were carried out based on the PN-EN 12831 standard [32], according to which the selected location—Lublin—was assigned to the third climatic zone. For this zone, the design outdoor temperature is −20 °C, while the design indoor temperature (for residential spaces) is 20 °C. The model with the applied thermal load is shown in Figure 3.

In this study, the SOLID279 elements were employed in the static thermal configuration, in which temperature is the only active degree of freedom, while the remaining degrees of freedom were deactivated. This approach enables the use of advanced second-order interpolation and the enhanced accuracy of the element, while maintaining the physical consistency of the thermal problem. As a result, the obtained model provides reliable mapping of temperature distributions in objects with complex geometries and varying material properties. After applying the temperature load, the sum of the absolute values of the heat fluxes entering the object was calculated (using the Reaction Probe option in the Ansys simulation package). According to the standard, the difference between models with two different mesh densities should not exceed 1%. The initial model M2 consisted of 66,788 mesh elements and yielded a heat flux value of 68.885 W. The second model contained 142,257 mesh elements and resulted in a heat flux of 68.878 W. The difference between these results is 0.007 W, which represents only 0.0001%. Therefore, the model with fewer elements (66,788—see Figure 4) was used for further analysis, as it meets the requirements of the PN-EN ISO 10211 standard. In other variants, this model was extended with additional components, such as the antenna holder.

3. Results and Discussion

Based on the numerical model validated in the previous step, a series of simulations was conducted for all the analyzed models (Table 2). The analyses were carried out using the finite element method in the Ansys environment in accordance with the PN-EN 12831 [32] and PN-EN ISO6946 standard [33]. The simulated temperature conditions for the exterior and interior matched those of the third climatic zone (city of Lublin): −20 °C outside and 20 °C inside. The heat transfer coefficient (convection) on the external surface was assumed to be 25 W/(m² K). The numerical studies focused on the temperature distribution within the considered models. The resulting temperature maps are presented in Figure 5.

The temperature gradient follows the expected direction of heat flow, from the interior (higher temperature) toward the exterior (lower temperature). In the baseline models M1 and M8, the isotherms remain regular within the homogeneous wall layers, whereas in the region of the mounting block/antenna holder, noticeable curvature and local distortions appear, indicating the presence of a point thermal bridge. Overall, the generated contour maps clearly highlight zones of increased thermal sensitivity.

The analysis of heat flux through building envelopes, such as external walls, constitutes an important aspect of evaluating the energy performance of buildings. Determining the value of the heat flux allows for a quantitative assessment of energy losses, which is crucial both in the design of new buildings and in the modernization of existing ones. Therefore, in this study, it was decided to calculate the heat flux Q (Equation (2)), which defines the amount of heat transferred per unit of time through a given surface due to a temperature difference [34].

$$Q=U ∆T,$$

(2)

where U—heat transfer coefficient through a building envelope; and ΔT—temperature difference between the wall inside and outside the facility.

The heat transfer coefficient is a measure of a building envelope’s ability to conduct heat. It represents the amount of heat (in watts) that passes through 1 square meter of the envelope in one second when there is a temperature difference of 1 kelvin (K) between its two sides. This coefficient takes into account the thermal conductivity of all layers of materials constituting the partition, and it can be determined by the inverse of the total thermal resistance (R), which is presented in Equation (3) [34]:

$$U = {\displaystyle \frac{1 }{R }},$$

(3)

The total thermal resistance of a building envelope is the sum of the thermal resistances of all material layers that make up the envelope, including the internal (R_si) and external (R_se) surface thermal resistances [34]. The thermal resistance of each individual layer depends on its thickness and the thermal conductivity of the material, as expressed in Equation (4):

$$R = R_{si}+{\sum }_{i=1}^n{\displaystyle \frac{h_i}{{\lambda }_i}}+R_{se},$$

(4)

where h_i—thickness of the i-th layer; λ_i—thermal conductivity of the i-th layer; R_si—heat transfer resistance from the inside; and R_se—heat transfer resistance from the outside. However, in our calculations the heat transfer resistance from the outside and inside were equal to zero.

The results of heat flux calculations for selected cases from Table 2, which were compared with numerical results obtained using the Ansys environment were presented in

Table 3. Heat flux through building envelopes [W/m²].

	Model 1 (M1)	Model 8 (M8)
Analytical	11.87	7.54
Ansys	11.87	7.48
Error [%]	0.00	0.80

. Detailed calculations were performed for models M1 and M8. Comparing the obtained results, very good agreement was found for the two analyzed models. A relative error of less than 1% was achieved.

For all analyzed cases, curves representing the temperature distribution through the center of the cross-section of the mounting element were generated. In each variant, the same location was analyzed—along a straight path from point 1 to point 2—as illustrated in Figure 6. The selected points referred to the wall with plaster, i.e., point 1 was located on the inner side of the partition, while point 2 was situated at the end of the concrete block wall (thickness of 25.5 cm). Moreover, the resulting temperature profiles along the wall thickness are presented in Figure 7.

To conduct a more detailed analysis, the models were additionally grouped into series, for which graphs illustrating the relationship between temperature and the thickness of the partition were prepared. In the first series, models M1, M2, and M8 were presented (Figure 8). The graphs cover the entire wall thickness, including the insulation, because these models do not contain an antenna mount. By comparing the obtained curves, it was found that the initial M2 model with a mounting element had 49% poorer insulation performance than model M1, which did not have a mount but had a continuous layer of polystyrene without any interruptions. Moreover, as expected, model M8, equipped with a double layer of polystyrene, exhibited the highest partition insulation performance (a temperature drop on the external surface of the load-bearing wall of approximately 17% compared to the temperature inside the room), significantly outperforming particularly the model with a mounting block (M2)—better insulation performance by about 60%. The difference in the external surface temperature of the wall between these models was approximately 12 °C. Additionally, it can be observed that the extra 6 cm layer of polystyrene (S2) slightly (by 2 °C) increases the temperature within the load-bearing wall. Thus, the insulation performance of the partition with two layers of polystyrene (M8) differs by 10% from that with a single polystyrene layer (M1).

In the second series, models with an insulation layer thickness of 9 cm were compared (Figure 9). Model M1 (pure Styrofoam) was used as a reference point for the other cases. Analyzing the graph shown in the figure, it can be observed that in an ideal scenario, where the materials forming the individual layers of the model are tightly adhered to each other without any gaps, the use of a mounting block (M3) does not provide advantages over the case of installing the antenna handle directly on the wall and weakening it with a layer of Styrofoam (M4). The difference in temperature on the outside of the load-bearing wall was 1 °C in favor of the mounting block. Only when a more realistic scenario is considered (M5)—where a gap forms between the Styrofoam layer and the antenna handle during usage—does model M3 demonstrate its superiority. In this case, the temperature difference between the M3 and M5 models was about 4.5 °C. Therefore, the wall insulation increases by approximately 25%. A comparison between the actual model and the reference model indicates that the installation of the wall-mounted bracket induces a thermal bridge, manifested by a temperature differential of approximately 16 °C. Accordingly, the insulation performance of the partition with a single layer of polystyrene and an antenna holder, along with an operational gap (M5), deteriorates by 82% compared with the reference model (M1).

The third series of results compares cases where the insulation layer thickness is 15 cm (Figure 10). In this scenario, for idealized models (M6, M7—without gaps between structural elements caused by installation imperfections or wear over time), the use of a mounting block seems unnecessary. It is worth noting that the temperature maps were compared in a single cross-section. Slightly greater sensitivity may be observed in the cross-sections of the mounting screws, which will be verified in the next research step. However, in a realistic scenario (with gaps between structural elements—M9, M10), the advantage of solutions with a mounting block becomes clear. Models M6 and M7 demonstrated a high level of agreement, with a difference of less than 2%, which was attributed to the overly idealized model. This raised a pertinent question: what is the purpose of using a mounting element if a model without this element but with an external antenna achieves nearly identical results? To address this question, it was decided to simulate more realistic conditions. In models M6 and M7, ideal connection conditions between components were assumed, with no gaps or dilations. In these models, a temperature drop of approximately 5 °C was achieved compared to the M8 reference model. However, in reality, when an external antenna is attached to the wall structure, external forces, such as wind gusts, can impact the Styrofoam layer. As a result of contact between the adjoining elements, stress is generated on the Styrofoam, leading to minor deformations of the insulating material. This, in turn, creates a gap between the steel structure of the antenna and the Styrofoam. To investigate how this gap affects the temperature distribution, models M9 and M10 were developed. Model M10 includes a mounting element and a 2 mm gap between the antenna and the Styrofoam (Figure 11a). Meanwhile, in model M9, the antenna handle is attached directly to the supporting wall structure, with a 2 mm gap also included between the antenna and the insulation (Figure 11b).

After considering more realistic operating conditions of the system (M10), a significant advantage of the mounting elements was observed. This model achieved 50% better partition insulation compared to the M9 model without the mounting element. The temperature on the load-bearing wall of the partition was 10.23 °C higher in model M10 compared to model M9, which directly impacts the energy gains that can be achieved by using the mounting element.

4. Conclusions

This study presents a method for reducing point thermal bridges in building structures. The detailed analysis focused on attaching an antenna mount to the load-bearing structure of a building using an additional mounting element made of high-density polyethylene (HDPE). The purpose of the mounting element is to transfer the load to the load-bearing structure and increase the thermal resistance of the wall at the connection point with the antenna mount. As part of the research, ten variants of building partitions were tested. Numerical studies were conducted for all models, analyzing the temperature distribution in the load-bearing partition of the building.

Based on the conducted research, the following conclusions were developed:

• Under ideal conditions (M4 and M3), it was found that the temperature distribution in the load-bearing wall was nearly identical. A similar situation was observed with two layers of polystyrene, i.e., model M6 and M7. The temperature difference did not exceed 2%.
• A significant advantage of the mounting elements was observed in more realistic operating conditions (model M10). In this case, the use of the mounting block retained twice as much heat inside the room compared to the configuration without the block (M9). The temperature on the outer wall of the concrete block in the M10 model was 9.49 °C, while in the model without the mounting element (M9) the temperature in the same place reached −0.74 °C. Thus, the applied mounting block effectively reduced the impact of point thermal bridges at the antenna holder by approximately 50%.
• The analyses revealed that the presence or absence of gaps between the antenna mount and the insulation layers significantly affects the results obtained during simulations.
• Models with two (M9) and one layer of Styrofoam (M5) were compared, and it was found that an additional 6 cm thick layer of Styrofoam increases the temperature on the wall by only about 1 °C (when the gap is taken into account) or by about 2 °C (between the reference models M1 and M8).

The numerical model of the wall assembly with the mounting block was developed in strict accordance with PN-EN ISO 10211, which specifies steady-state thermal conditions. Although the standard does not explicitly incorporate airflow modeling, the simulation included convective heat-transfer boundary conditions on the exterior surface, corresponding to average winter wind speeds required by the normative approach. Consequently, the model is suitable for the assessment of stationary heat flows and the resulting thermal bridge effects. Moreover, the model can serve as a reliable basis for:

• Evaluating linear and point thermal transmittance values;
• Analyzing local temperature fields and identifying regions with increased surface-temperature risk (e.g., mold-growth risk);
• Comparing alternative material or installation configurations of mounting blocks;
• Providing boundary conditions for more advanced transient or 3D analyses in future work.

It seems necessary to examine more closely the impact of gaps at the boundaries of insulation layers and structural elements on the energy efficiency of the insulation. The authors believe that it would also be beneficial to use more advanced numerical models that include airflow (CFD), especially on the external side of the wall. This would allow testing the proposed solution under a wider range of scenarios (e.g., different wind directions and speeds) beyond those specified in the standards. Such studies are planned as a continuation of this work.