Customized Insulation Strategies for Türkiye: Life Cycle Cost Analysis and Impact on Business Competitiveness

Abstract

A significant portion of energy consumption in buildings is allocated to heating, with substantial losses resulting from inadequate insulation, poor sealing, and thermal bridging. While proper insulation plays a crucial role in mitigating these losses, determining its optimal thickness is essential to reduce energy consumption and increase energy efficiency. This study employs life cycle cost analysis and average heating degree day values to calculate the optimum insulation thickness for 81 provinces in Türkiye. The findings highlight the absence of a one-fits-all insulation solution, emphasizing the need for customized approaches tailored to specific conditions that consider specific factors, such as environmental conditions, heating sources, costs, economic parameters and the materials used. Proper insulation application is projected to reduce carbon emissions by 90% and lower annual heating costs by approximately 65%. These energy efficiency improvements are particularly significant for both households and businesses, enhancing profitability and competitiveness. Collaborative efforts to promote proper insulation solutions are anticipated to reallocate financial resources toward innovation and contribute to long-term business sustainability. This study provides an important framework for guiding the adoption of proper insulation practices in building design and construction.

1. Introduction

As the world grapples with the urgency of climate change, many private sector companies, particularly countries, are searching for new sustainable technologies and applications that will reduce energy consumption and carbon footprint. In this context, relevant laws, implementation incentives and restrictions are applied globally and locally in countries. The energy consumed by buildings, 30% of the total final energy consumption, is second highest after industry. With the use of appropriate insulation and high-efficiency equipment, this demand can be reduced by 15%, a reduction that surpasses the total electricity generation of several countries, including the Netherlands [1]. Therefore, thermal insulation stands as a cornerstone among factors that exert the most influence on the energy consumption of a building for sustainable practices.

Liu et al. (2021) [2] listed the importance of the 10 factors that exert the most influence on the energy consumption of a building, from high to low: roof heat transfer coefficient (HTC) > thermal insulation thickness > internal wall HTC > solar HTC throughout window > ratio of window to wall > floor HTC > energy efficiency of air conditioning > interior temperature > fresh air volume > temperature of natural ventilation. Among these 10 parameters, the HTC value primarily hinges on the thickness of the thermal insulation and its inherent properties. Yet, its efficacy hinges not only on its presence but also on its optimal thickness, striking a balance between thermal performance and economic viability.

In Türkiye, a standard called TS825 “Thermal Insulation Rules in Buildings” exists, which outlines the minimum insulation requirements for buildings to minimize heat loss and establishes the legal framework for energy efficiency, similar to the European EN 12831 standard. However, since this standard was published in 2008, its relevance to current conditions is frequently debated, and there are many calls for its update. Kon and Caner (2021) [3] determined the energy consumption for heating and cooling and CO₂ and SO₂ emissions of buildings in 20 capitals of Europe, including Ankara, according to TS825. It was observed that the recommended and/or legally required total heat transfer values listed for developed European countries were lower for Ankara. As mentioned above, this indicates the need for updating and improving the TS825 standard [3]. Aydın and Bıyıklıoğlu (2020) [4] determined the optimal insulation thicknesses for Türkiye by using life cycle cost analysis (LCCA) and compared them with the U-values recommended by the standard. The authors discussed the discrepancies and emphasized the need for an update to the TS825 standard.

Furthermore, TS825 determines the minimum insulation requirements for buildings solely based on thermal loss and gain calculations, without considering economic and environmental factors. This singular approach can lead to errors in the decision making and implementation processes. In this context, understanding the interplay between insulation thickness, annual energy efficiency gains, carbon emission reduction, and sustainable applications, along with long-term economic implications, has increased interest in sustainability and led to the development of LCCA. This analysis involves assessing expenses across all stages of a product’s lifespan, from creation to disposal, with the goal of reducing overall costs and providing economic advantages to both producers and users [5]. Complementing LCC, competitive cost analysis identifies crucial operational cost factors to aid in strategic decision making. The correlation between globalization, competitiveness, and improved industrial performance underscores the importance of cost management across the production and operational process [6,7].

There are studies all over the world on thermal insulation to reduce the energy consumption of a building by using the LCCA method. Muddu et al. (2021) [8] proposed optimum insulation thickness (OIT) for typical walls in twenty-five locations in Ireland for the renovation of existing buildings. The material payback period (PP), CO₂ emissions, and annual heat energy consumption are all taken into account when calculating OIT. The strategy used is based on the LCCA method and heating degree day (HDD) for various combinations of insulation material, type of heat energy, and wall configuration. The findings show that the potential yearly cost savings (up to 170 EUR/m²) and carbon emissions (up to 50 kg/m²) are significantly influenced by the type of configuration, heat energy, wall materials, and insulation. Ali et al. (2024) [9] discussed various thermal insulation materials, emphasizing their properties, performance and environmental impacts. The authors researched recent trends that can enhance energy efficiency and sustainability in buildings. Additionally, the authors stated that different conditions require different applications and that the commonly accepted insulation materials, which have been in use for many years, are not suitable for all conditions and bring about several drawbacks. Deshmukh and Madhura (2025) [10] analyzed key factors in optimizing thermal efficiency, environmental impacts, and the economic viability of buildings by utilizing sustainable composite materials. The authors aimed to identify the most sustainable material choice by analyzing their thermal performance and associated costs. Ziapour et al. (2020) [11] determined the OIT using LCCA and the HDD method when the composite prefabricated wall block was used as an external wall member in three provinces of Iran. These provinces are chosen from the warm, cold and semi-arid climate areas. A special integration of polystyrene, polyurethane, and air gap was used as the insulation material. The findings, based on cooling and heating, demonstrated that when air conditions warm, the OIT rises, resulting in increased cost savings and a shorter PP. The OIT for cooling and heating varied between 10.6 cm and 16.35 cm, and the PP changed between 0.33 and 0.57 years. Further, 19% of power consumption is used for climate control systems in the residential sector (6% for rural and 13% for urban households), and 95% of homes in Mexico do not keep thermal insulation. Shrestha et al. (2014) [12] proposed a protocol for assessing the lifetime energy and environmental impacts of insulation materials, which considers all life cycle stages, such as raw material acquisition, manufacturing, installation and use, disposal treatment. Through this protocol, the authors delineated standardized calculation methodologies for avoided operational energy (AOE) and avoided environmental impact (AEI), which typically wield significant influence over the total environmental impact of insulation materials but have historically lacked precise definition. AOE expresses the difference between the energy consumed by the optimal insulation application following the prescribed protocol and that of the current insulation or non-insulated application over its lifetime. With higher AOE values, in accordance with the proposed protocol, it was stated that there is a potential to reduce total energy consumption for heating and cooling applications. Seo and Foliente (2021) [13] investigated the reduction potential of the carbon footprint through residential buildings in Australia with economically and environmentally sustainable retrofit methods. According to the findings, when structures are renovated with insulation and double-glazed windows, the environmental benefits increase over the course of a home’s life cycle more quickly than the economic benefits. The city has the potential to reduce 0.372 million tons of life cycle greenhouse gas emissions and save 3937 TJ of life cycle energy annually. Climate control systems are thought to consume 4.5-times as much electricity as the whole residential sector. The power consumption of air conditioner control systems (such as electric heaters, fans, and air conditioners) in all locations in Mexico (4525 urban and 187,719 rural locations) was determined by Rosas-Flores and Rosas-Flores (2020) [14]. Locations were divided into three climate regions: tropical, mild, and extremely hot. The OIT of the roofs and walls was calculated according to the different insulation stuffs, polyurethane, expanded polystyrene, glass-wool, rockwool, and extruded polystyrene. The repayment time for extremely hot zones changed between 6.1 and 7.5 years. By 2030, if the recommended adequate insulation system is applied to all current and future homes, it will potentially save 73.63 TWh in electricity, which equates to 38.66 tons of CO₂ emissions. It has been noted that, based on the reviewed studies, the OIT cannot be achieved through an engineering approach alone; a comprehensive evaluation of engineering, economic, and environmental factors is necessary. In addition to the studies carried out all over the world, a few studies have also been performed in Türkiye. The OIT of the building’s external wall surface and exergy cost savings in the provinces of Kars, Trabzon, Ankara, and Izmir were determined using thermo-economic analysis. Polyurethane and expanded polystyrene were used, and natural gas was selected. OIT values were 0.107, 0.06, 0.077, and 0.046 m in Kars, Trabzon, Ankara, and Izmir, respectively, for the expanded polystyrene material, as well as 0.055 m in Kars, 0.0304 m in Trabzon, 0.039 m in Ankara, and 0.023 m in Izmir for the polyurethane material. The minimum savings were seen in Izmir, whereas the maximum savings were seen in Kars. Exergy cost savings for the polyurethane and expanded polystyrene materials were 51% and 56.6% in Kars and 22% and 27% in Izmir, respectively [15]. Ekici et al. (2012) [16] computed OIT according to the wall types (concrete, brick, and stone), four cities from different climate zones (Kayseri, Elazıg, Istanbul, and Antalya), four different insulation materials (foamed polyurethane, extruded polystyrene, and expanded polystyrene). PP, energy savings, and OIT were calculated. It was indicated that PP, energy savings, and OIT changed between 0.714 and 9.104 years, 0.038 USD/m² and 250.415 USD/m², and 0.2 cm and 18.6 cm, respectively.

This study aims to fully underline the expression ‘optimum’ by examining insulation thickness from both economic and engineering perspectives by combining the TS825 engineering approach with LCCA. It is conducted in cooperation with the Silifke Chamber of Commerce and Industry to explore its pivotal role in curbing carbon emissions and reducing energy consumption while maximizing financial benefits and to raise the social awareness of end users and productivity and competitiveness for businesses. Within this study, the OIT was calculated for 81 provinces in Türkiye according to five various insulation materials and five different heating sources. EPS, XPS, PUR, glasswool, and rockwool are used as insulation materials. Electricity, LPG, fuel oil, coal, and natural gas are chosen as heating sources. A brick wall model that is open to the ambient air was chosen. Based on TS825, the HDD method and LCCA were used. The heat loss from the wall was computed, and OITs and energy savings were determined according to the LCCA. The effect of the heating source, location, insulation material, fuel and insulation price, interest and inflation rate, and project lifetime on OIT was considered for 81 provinces in Türkiye.

The findings of this comprehensive study provide valuable insights into the optimal insulation thickness for 81 provinces in Türkiye, considering different factors, such as climatic conditions, energy sources, insulation materials and economic parameters. This study sheds light on the importance of energy-efficient building practices and their impact on our environment and economy, and it serves as a guide to inform decision makers, industry professionals, and the public alike.

2. Materials and Methods

In this study, Türkiye’s recent fuel consumption patterns as a heating source and production data for insulation materials, HDD values over the last 10 years, fuel prices, insulation material prices, inflation rates, interest rates, and general external wall application in the construction sector were used. The external wall model commonly preferred for building in Türkiye, along with the calculation of the thermal resistance of the uninsulated wall, is given in

Table 1. Calculation of uninsulated thermal resistance of wall model.

Wall Structure Elements	Structural Element Thickness (m)	Thermal Conductivity Value λ (W/mK)	Thermal Conductivity Resistance R (m2K/W)
1/αi	-		0.13
Lime mortar, lime–cement mortar	0.01	0.87	0.0115
Full or vertical perforated brick	0.2	0.5	0.4
Cement mortar	0.01	1.4	0.0071
1/αe	-		0.04
		TOTAL	0.589

.

2.1. Optimization of Heat Load and Insulation Thickness for the External Wall

The degree day method is a widely used and practical approach for estimating energy requirements. Basically, this method estimates the building’s energy needs by utilizing the difference between indoor and outdoor temperatures. On the other hand, LCCA is an economic evaluation technique that calculates the cost of a system or component over its lifetime. This analysis is significantly impacted by factors, such as insulation material, insulation thickness, heating source price, insulation price, inflation rate, interest rate, and the system’s lifetime. LCCA can enhance productivity and competitiveness within businesses by providing a thorough economic assessment of different systems, while customer engagement and effective cost management significantly contribute to firms gaining a competitive edge, emphasizing the need for further research in management accounting focusing on these areas [17].

The inflation rate, interest rate and lifetime influence the present worth factor (PWF) of the system (insulation in this case), which is crucial for cost evaluation. PWF represents a financial concept used in engineering economics and to evaluate the economic viability of a project by comparing the present value of a series of cash flows to the present value of an equivalent annuity. The equivalent value of future cash flows in terms of their present value, considering interest and inflation rates, can be determined by PWF. Particularly in OECD countries, with significant annual changes in interest and inflation rates, the PWF value fluctuates, and its contribution can vary depending on the application’s lifetime. Necessary parameters are given in Table 3 to calculate PWF.

2.2. Heat Losses and Energy Calculations

Heat losses in buildings usually occur from external wall surfaces, windows, ceilings, and air infiltration. In this study, it was assumed that heat losses only occur on the external wall surface.

The heat loss per unit area of the external wall is as follows:

$$q=U·∆T$$

(1)

The annual total heat loss per unit area of the external wall is as follows:

$$q_A=\mathrm{86,400}·HDD·U$$

(2)

The annual energy needs due to heat losses are as follows:

$$E_A=\mathrm{86,400}·HDD·U/\mathrm{ƞ}$$

(3)

where $\mathrm{ƞ}$ is the efficiency of the heating system, given in Table 2. The total heat transfer coefficient for the external wall is as follows:

$$U=1/(R_{w,t}+{\displaystyle \frac{x}{k}})$$

(4)

where $R_{w,t}$ is the total thermal resistance for the non-insulated wall, x is insulation thickness and k is thermal conductivity of insulation material, which are given in Table 2 and Table 3. Annual heating energy cost per unit area of external wall is as follows:

$$C_A={\displaystyle \frac{\mathrm{86,400}·HDD·C_y·U}{H_u·\mathrm{ƞ}}}$$

(5)

2.3. LCCA Calculations

In this study, total heating costs were evaluated together with LCCA, which performs a cost analysis of a system. With LCCA, net value factor (r) and present worth factor (PWF) are calculated as follows:

$$PWF={\displaystyle \frac{{(1+r)}^N-1}{r·{(1+r)}^N}}$$

(6)

If i > g:

$$r={\displaystyle \frac{i-g}{1+g}}$$

(7)

If i < g:

$$r={\displaystyle \frac{g-i}{1+i}}$$

(8)

where $i$ is interest rate, g is inflation rate and N is lifetime. Total insulation cost can be calculated as follows:

$$C_{y,t}=C_y·x$$

(9)

where $C_{y,t}$ is total insulation cost and $C_y$ is fuel price. Total heating cost of insulated building is as follows:

$$C_{t,y}=C_A·PWF+C_y·x$$

(10)

Optimum insulation thickness to minimize total cost is as follows:

$$OIT=293.94·{({\displaystyle \frac{HDD·C_y·PWF·k}{H_u·C_y·\mathrm{ƞ}}})}^{0.5}-k·R_{w,t}$$

(11)

If the OIT is preferred, the net saving per unit area according to uninsulated condition is as follows:

$$A_y=C_t-C_{t,y}$$

(12)

Payback period is as follows:

$$pp={\displaystyle \frac{C_{y,t}}{C_{y,1}-C_{y,2}}}$$

(13)

Fuels and insulation material properties, which are taken from manufacturers in Türkiye, are given in Table 2.

Table 2. Fuel and insulation material properties.

Parameter		Natural Gas	Coal	Fuel Oil	LPG	Electricity
Hu	(TEO/unit)	0.000825	0.00061	0.00096	0.00270	0.00008
ƞ	%	93	65	80	90	99
Cy *	USD/unit	0.32	0.44	0.80	0.675	0.139
Parameter		XPS	EPS	Rockwool	Glasswool	PUR
k	W/mK	0.032	0.033	0.040	0.043	0.026
Cylt *	USD/m3	27.3	42	29.4	21	118.65

* sourced from the Silifke Chamber of Commerce and Industry.

Table 2. Fuel and insulation material properties.

Parameter		Natural Gas	Coal	Fuel Oil	LPG	Electricity
Hu	(TEO/unit)	0.000825	0.00061	0.00096	0.00270	0.00008
ƞ	%	93	65	80	90	99
Cy *	USD/unit	0.32	0.44	0.80	0.675	0.139
Parameter		XPS	EPS	Rockwool	Glasswool	PUR
k	W/mK	0.032	0.033	0.040	0.043	0.026
Cylt *	USD/m3	27.3	42	29.4	21	118.65

* sourced from the Silifke Chamber of Commerce and Industry.

Table 3. Parameters used in the calculation of insulation thickness.

Parameter	Value
Uninsulated thermal resistance of Model.1	0.589 m2K/W
Inflation rate, g *	10%
Interest rate, i *	14%
Lifetime, N	15 years
Net value factor, r	0.363
Present worth factor, PWF	2.723

* representing the average annual changes anticipated over the next 15 years, with calculations based on forecasts made by official institutions, considering the macroeconomic models that Türkiye is currently implementing and plans to adopt in the future.

Table 3. Parameters used in the calculation of insulation thickness.

Parameter	Value
Uninsulated thermal resistance of Model.1	0.589 m2K/W
Inflation rate, g *	10%
Interest rate, i *	14%
Lifetime, N	15 years
Net value factor, r	0.363
Present worth factor, PWF	2.723

* representing the average annual changes anticipated over the next 15 years, with calculations based on forecasts made by official institutions, considering the macroeconomic models that Türkiye is currently implementing and plans to adopt in the future.

Ten-year average HDDA values were used in this study. HDD values over the last 10 years, which were obtained from the Meteorological Service of the Turkish State, are given in

Table 4. Ten-year average heating degree days between 2013 and 2024.

No.	Province	HDDA	No.	Province	HDDA	No.	Province	HDDA
1	ADANA	741.00	28	GİRESUN	1400.09	55	SAMSUN	1444.09
2	ADIYAMAN	1448.55	29	GÜMÜŞHANE	2869.36	56	SİİRT	1717.27
3	AFYONKARAHİSAR	2482.82	30	HAKKARİ	2960.36	57	SİNOP	1508.55
4	AĞRI	4095.55	31	HATAY	1154.25	58	SİVAS	2990.82
5	AMASYA	1929.36	32	ISPARTA	2252.73	59	TEKİRDAĞ	1649.64
6	ANKARA	2292.18	33	MERSİN	563.91	60	TOKAT	2114.45
7	ANTALYA	801.27	34	İSTANBUL	1406.09	61	TRABZON	1368.55
8	ARTVİN	2083.45	35	İZMİR	942.91	62	TUNCELİ	2405.00
9	AYDIN	1043.27	36	KARS	4330.55	63	ŞANLIURFA	1226.45
10	BALIKESİR	1782.82	37	KASTAMONU	2882.18	64	UŞAK	2193.09
11	BİLECİK	2091.91	38	KAYSERİ	2684.91	65	VAN	3006.73
12	BİNGÖL	2515.18	39	KIRIKKALE	2286.55	66	YOZGAT	3008.18
13	BİTLİS	3556.27	40	KIRŞEHİR	2482.09	67	ZONGULDAK	1651.82
14	BOLU	2646.27	41	KOCAELİ	1391.00	68	AKSARAY	2258.27
15	BURDUR	2087.09	42	KONYA	2525.27	69	BAYBURT	3583.27
16	BURSA	1593.09	43	KÜTAHYA	2546.18	70	KARAMAN	2294.00
17	ÇANAKKALE	1386.73	44	MALATYA	2114.18	71	KIRKLARELİ	1920.73
18	ÇANKIRI	2589.45	45	MANİSA	1344.82	72	BATMAN	1836.27
19	ÇORUM	2597.73	46	KAHRAMANMARAŞ	1389.91	73	ŞIRNAK	1908.55
20	DENİZLİ	1358.73	47	MARDİN	1681.36	74	BARTIN	1979.27
21	DİYARBAKIR	1890.55	48	MUĞLA	1710.36	75	ARDAHAN	4623.91
22	EDİRNE	1836.82	49	MUŞ	3114.64	76	IĞDIR	2455.64
23	ELAZIĞ	2245.91	50	NEVŞEHİR	2607.00	77	YALOVA	1482.00
24	ERZİNCAN	2677.27	51	NİĞDE	2502.91	78	KARABÜK	2220.82
25	ERZURUM	4373.36	52	ORDU	1472.91	79	KİLİS	1286.09
26	ESKİŞEHİR	2398.91	53	RİZE	1522.82	80	OSMANİYE	871.45
27	GAZİANTEP	1696.82	54	SAKARYA	1429.64	81	DÜZCE	1842.82

.

3. Results and Discussion

This study seeks to comprehensively explore the concept of the ‘optimum’ insulation thickness by evaluating it from both economic and engineering perspectives using life cycle cost analysis (LCCA). By incorporating LCCA and average heating degree day (HDD) values, this study calculates the ideal insulation thickness for 81 provinces in Türkiye. However, for a more focused analysis, tables are presented in this section for five representative cities: Istanbul (the largest city), Ankara (the second largest and the capital), Izmir (the third largest city), Mersin (hottest city and where Silifke Chamber of Commerce and Industry is located), and Ardahan (the coldest city). Due to the complexity of providing all figures for 81 provinces, figures are provided with a reference to the capital of Türkiye, Ankara, to aid understanding of the analysis. Additionally, the full analysis results (the OIT, the PP, annual savings and emission reduction for different insulation materials according to natural gas, coal, fuel oil, LPG and electricity as heating source) for all 81 provinces in Türkiye are given in the Supplementary Materials.

There are two parameters that affect the total heating cost of an insulated building. These are insulation and heating source costs. Heat loss is reduced due to the increase in insulation thickness in buildings. Therefore, the energy requirement for heating the unit area is reduced, and the total cost is reduced. However, as mentioned in the Materials and Methods, increasing the insulation thickness more than necessary could even lead to negative outcomes during its lifetime. When the initial investment cost is examined according to the PWF value throughout the application life, the economic viability of the project can be discussed. In this context, the value at which the total cost is minimal is expressed as the OIT.

When choosing the insulation material for a building, it is necessary to consider not only the type of material but also the type of heating source (fuel) used. Although the use of natural gas has become widespread in Türkiye, there are still regions where it cannot be delivered due to its location. For this reason, calculating the insulation thickness with a single fuel source will not reflect reality. In addition to that, insulation materials can be produced regionally as different types due to reasons, such as thermal conductivity, moisture retention, fire resistance, ease of production and material availability. For this reason, calculating the insulation thickness with a single insulation material will also not reflect reality. In this context, calculations were carried out with five different insulation materials: extruded polystyrene (XPS), expanded polystyrene (EPS), polyurethane foam (PUR), glasswool, and rockwool. There were also four different heating sources: natural gas, coal, fuel oil, LPG, and electricity.

The effects of heating source and insulation material on the OIT according to LCCA are given in

Table 5. Changing the OIT according to the heating source and insulation material types for 5 listed cities.

Optimum Insulation Thickness (mm)
Cities	XPS	EPS	PUR	Glasswool	Rockwool
Natural gas
İstanbul	43.64	31.72	11.70	57.26	43.76
Ankara	60.93	45.88	19.18	80.12	62.39
İzmir	32.32	22.46	6.81	42.30	31.57
Mersin	20.72	12.96	1.80	26.97	19.07
Ardahan	94.46	73.33	33.68	124.44	98.52
Coal
İstanbul	75.66	57.94	25.55	99.59	78.26
Ankara	101.82	79.36	36.86	134.16	106.44
İzmir	58.55	43.93	18.15	76.96	59.82
Mersin	41.00	29.57	10.56	53.78	40.92
Ardahan	152.54	120.88	58.79	201.19	161.09
Fuel oil
İstanbul	78.73	60.46	26.88	103.65	81.57
Ankara	105.74	82.57	38.56	139.35	110.67
İzmir	61.06	45.99	19.24	80.29	62.53
Mersin	42.95	31.16	11.41	56.35	43.02
Ardahan	158.11	125.44	61.20	208.56	167.09
LPG
İstanbul	60.15	45.24	18.84	79.09	61.55
Ankara	82.02	63.14	28.30	107.99	85.11
İzmir	45.84	33.53	12.66	60.18	46.14
Mersin	31.18	21.52	6.32	40.80	30.34
Ardahan	124.41	97.85	46.63	164.02	130.78
Electricity
İstanbul	103.95	81.10	37.78	136.98	108.74
Ankara	137.94	108.93	52.48	181.90	145.36
İzmir	81.71	62.90	28.17	107.58	84.78
Mersin	58.92	44.23	18.31	77.46	60.22
Ardahan	203.84	162.89	80.97	269.00	216.36

for the five listed cities. As can be seen in Table 5, OIT changes according to the insulation material and heating source as well. One of the factors affecting the OIT is the thermal resistance of the wall. As the thermal resistance of the wall increases, the required insulation thickness decreases. Therefore, the insulation thickness to be applied to walls with high thermal resistance can be lowered. The degree day values for Türkiye varied between 878 (for the province of Hatay and the city of Iskenderun) and 5443 (for Ardahan province) in the study of Bolattürk (2006) [18]. This shows that a building located in the province of Ardahan requires 6.2-times more energy for heating than the one in Iskenderun with the same characteristics. This serious change in energy demand also significantly affects the OIT.

It can be said that there is no practical application that can be used in every condition; it depends on various conditions. Even this can lead to an awareness to select the proper insulation material and even the proper heating source. As mentioned in the Materials and Methods section, the insulation applications are carried out in two ways after the construction of the structure. That means that the heating source was already selected. Therefore, proper insulation material must be selected according to these values. In addition to that, if there are two options as heat sources (electricity as air conditioner and natural gas, for example), the more suitable solution for heating can be selected according to Table 5.

As can be seen in Table 5, different OITs are obtained for different insulation materials and heating sources. For this reason, as mentioned in the third paragraph of the Results and Discussion section, it is very important to carry out this study with more than one heating source and insulation material. PUR insulation material seems to be the most suitable choice according to Table 5. However, not enough data were shared to say this. Any interpretation based solely on this table will be nothing more than misleading. As stated in the Materials and Methods section, examining the OIT with LCCA will provide accurate information about the economics and applicability of the project.

To better understand the results presented in Table 5 and to evaluate the findings from an economic perspective, the effects of the heating source and insulation material on the PP according to LCCA are given in

Table 6. Changing the PP according to the heating source and insulation material types for 5 listed cities.

Payback Period (Years)
Cities	XPS	EPS	PUR	Glasswool	Rockwool
Natural gas
İstanbul	2.05	2.60	5.34	2.08	2.37
Ankara	1.71	2.03	3.24	1.73	1.90
İzmir	2.51	3.48	10.58	2.56	3.05
Mersin	3.65	6.26	91.78	3.76	5.00
Ardahan	1.44	1.60	2.12	1.45	1.54
Coal
İstanbul	1.56	1.78	2.56	1.57	1.69
Ankara	1.40	1.55	2.00	1.41	1.49
İzmir	1.75	2.08	3.40	1.77	1.94
Mersin	2.13	2.75	6.01	2.16	2.48
Ardahan	1.26	1.35	1.59	1.27	1.31
Fuel oil
İstanbul	1.54	1.75	2.47	1.55	1.66
Ankara	1.39	1.53	1.95	1.40	1.47
İzmir	1.71	2.03	3.23	1.73	1.90
Mersin	2.07	2.64	5.50	2.10	2.40
Ardahan	1.25	1.33	1.56	1.26	1.30
LPG
İstanbul	1.73	2.04	3.29	1.74	1.91
Ankara	1.51	1.71	2.38	1.52	1.63
İzmir	1.99	2.50	4.89	2.02	2.28
Mersin	2.58	3.63	11.76	2.63	3.16
Ardahan	1.33	1.44	1.77	1.33	1.39
Electricity
İstanbul	1.40	1.54	1.98	1.40	1.48
Ankara	1.29	1.39	1.67	1.30	1.35
İzmir	1.51	1.71	2.38	1.53	1.63
Mersin	1.74	2.07	3.38	1.76	1.94
Ardahan	1.19	1.25	1.41	1.20	1.23

for the five listed cities. In light of the data presented in Table 5, PUR appears to be the most suitable choice; however, when both engineering and economic factors are considered together, it becomes evident that making a selection based solely on Table 5 would be a highly flawed decision. As can be seen in the table, PUR insulation material seems to be the worst choice. The reason for this is its cost. All other insulation materials presented values close to each other. It can be said that XPS insulation material seems the best for most locations. However, as previously mentioned, if the selection of insulation materials is made solely based on engineering and/or economic factors, a comprehensive approach would be compromised. A decision that takes into account not only engineering and economic factors but also environmental and production aspects will ensure both an integrated and sustainable solution in the long term. Insulation materials can be produced regionally as different types due to reasons, such as thermal conductivity, moisture retention, fire resistance, ease of production and material availability. In addition to that, global agreements signed by countries (The United Nations Framework Convention on Climate Change), laws passed to reduce carbon emissions, etc., play a major role in the selection of the insulation material to be used in applications. Shrestha et al. (2014) [12] examined the environmental effects of various insulation materials from the manufacturing stage to the disposal process in their study. They emphasized that the insulation material to be chosen should be recyclable, the waste rate during installation should be low, the materials used during production should be of recycled origin, etc. The ratio of carbon dioxide equivalent emission reduction compared to non-insulation for different insulation materials and heating sources is given in

Table 7. The ratio of emission reduction according to different insulation materials and fuels when OIT is applied.

Emission Reduction kg CO2e/m2 (%)
Cities	XPS	EPS	PUR	Glasswool	Rockwool
Natural gas
İstanbul	69.84	62.01	43.32	69.33	65.00
Ankara	76.38	70.24	55.61	75.98	72.59
İzmir	63.17	53.60	30.78	62.55	57.26
Mersin	52.37	40.01	10.49	51.57	44.74
Ardahan	83.37	79.05	68.74	83.09	80.70
Coal
İstanbul	80.06	74.88	62.52	79.72	76.86
Ankara	84.38	80.33	70.65	84.12	81.88
İzmir	75.65	69.32	54.24	75.24	71.74
Mersin	68.51	60.33	40.82	67.98	63.46
Ardahan	89.00	86.15	79.33	88.82	87.24
Fuel oil
İstanbul	80.69	75.67	63.70	80.36	77.59
Ankara	84.87	80.95	71.57	84.62	82.45
İzmir	76.41	70.29	55.68	76.02	72.63
Mersin	69.50	61.58	42.69	68.99	64.61
Ardahan	89.35	86.58	79.98	89.17	87.64
LPG
İstanbul	76.14	69.95	55.17	75.74	72.32
Ankara	81.31	76.46	64.89	81.00	78.32
İzmir	70.87	63.30	45.25	70.38	66.20
Mersin	62.33	52.55	29.20	61.70	56.29
Ardahan	86.84	83.43	75.28	86.62	84.74
Electricity
İstanbul	84.65	80.67	71.16	84.40	82.19
Ankara	87.98	84.86	77.41	87.78	86.05
İzmir	81.26	76.39	64.78	80.94	78.25
Mersin	75.76	69.47	54.46	75.36	71.88
Ardahan	91.54	89.34	84.10	91.39	90.18

. It should also be noted that the insulation material itself generates carbon emissions, both directly and indirectly, from the beginning of its production process throughout its entire lifespan. In a study conducted by Resalati (2022) [19], the embodied carbon emissions of insulation materials, such as EPS, XPS, PUR, rockwool, and glasswool, were examined from the beginning of their production processes, based on an estimated 15-year lifetime, considering both direct and indirect emissions. The results showed that the lowest embodied carbon values were determined for glasswool, rockwool, EPS, XPS, and PUR, respectively, with the primary factor for the lower values of glasswool and rockwool, as their production is from natural materials. Additionally, total emission values for different heating systems and insulation materials were also analyzed for 20 capitals of Europe, including Ankara [3]. Therefore, this environmental factor can be a crucial decision-making element when selecting insulation materials. This aspect must certainly be taken into account.

In light of the results obtained, it can be said that there is no “the suitable insulation material” for all locations and conditions; the OIT alone is not a sufficient and acceptable concept. All factors concerning energy and engineering economy, economic viability, environmental impacts, and producibility should be meticulously evaluated and calculated, tailored to the specific location determined with clarity. Only in this way will the expression ‘optimum’ insulation thickness be valid. This result is consistent with the interpretations provided by authors in similar studies previously conducted in the literature [20].

Based on the results obtained from Table 5, Table 6 and Table 7, EPS and XPS are found to be the most suitable insulation materials for the capital city of Türkiye. In addition to that, natural gas is very widely used in Ankara; therefore, to better understand the LCCA, individual analysis is given in Figure 1 and Figure 2 for Ankara with the insulation materials EPS and XPS and the heating source as natural gas.

OIT was calculated as 60.9 and 45.9 mm for Ankara with the heating source as natural gas and insulation materials as XPS and EPS, respectively. Under these conditions, the total heat transfer coefficient for the use of XPS and EPS insulation materials was calculated as 0.401 W/m²K and 0.505 W/m²K, respectively. The total heat transfer coefficient naturally varies depending on the type of fuel used, as the optimum insulation thickness calculated with LCCA differs for different heating systems, even for the same wall, leading to changes in the total U-value. For instance, when coal is used as the fuel, the total heat transfer coefficients for XPS and EPS are calculated to be 0.265 W/m²K and 0.334 W/m²K, respectively. In the previously mentioned TS825 standard, the recommended limit value for Ankara province is specified as 0.5 W/m²K, without varying based on the heating system or insulation material (no different value has been provided). Firstly, this can be quite confusing. When considering the selection of the heating system and insulation material, the availability of materials, and environmental factors for the relevant location, the TS825 standard alone does not provide sufficient guidance for determining the optimum solution for the different applications. The insulation thickness corresponding to the recommended total heat transfer coefficient of 0.5 W/m²K is defined by the TS825 standard for Ankara, using natural gas and XPS, alongside the optimum insulation thickness calculated through the LCCA presented in Figure 3. As can be seen in Figure 3, the insulation thickness calculated using a purely engineering approach results in a increase in total fuel costs, overall costs, and a reduction in annual savings. In addition to that, based on the LCCA, the payback period for the optimum insulation thickness is 1.715 years, while the payback period calculated using the TS825 reference is 1.75 years. At first glance, the thinner insulation thickness may seem more appealing, but from a holistic perspective, it falls short in every aspect. For this reason, the result of an analysis based solely on an engineering approach, which is labeled as “optimum”, is far from reality and inaccurate.

As can be seen in Figure 1 and Figure 2, as expected, increasing insulation thickness increases annual gain and decreases emission reduction and annual cost for fuel. However, there is a limit in terms of economic viability. With insulation, continuous annual gains will be achieved compared to no insulation. However, as can be seen in the figures, the peak of the annual gain will indicate the OIT. Although every thickness of insulation materials before this point provides annual gains, it is not fully suitable for the optimum. At every thickness after this point, although the annual gain remains positive up to a point, it offers less gain than the peak point. Similarly, it would not be correct to use the expression optimum for this region.

Moreover, a comparison between EPS and XPS for Ankara with the use of natural gas in terms of PP is given in Figure 4. As can be seen in the figure, OIT with the use of EPS is less than with the use of XPS. However, the PPs were calculated as 1.71 and 2.03 for XPS and EPS, respectively. When considering environmental factors, XPS stands out with a greater reduction in emissions (Table 7). As mentioned before, the OIT by itself is not a sufficient determinant. Other factors, according to LCCA, should be examined to achieve the optimum value.

As mentioned in the first paragraph of the Results and Discussion section, it is not feasible to present all figures for the 81 provinces. However, the results of all analyses conducted for the five selected cities, as well as for Ankara, chosen for individual analysis, are provided in the Supplementary Materials with full details.

As a result, the effective implementation of building insulation strategies in Türkiye requires collaboration between policymakers, the private sector, and consumers. First, government regulations should focus on updating the existing TS825 standard to align with the European EN 12831 standard. In this regard, minimum insulation requirements should be tightened, and region-specific insulation policies should be developed based on Türkiye’s diverse climate conditions. Moreover, tax incentives and subsidies should be introduced to encourage insulation investments. For example, Germany’s “KfW Energy Efficiency Program” provides low-interest loans and grants to promote insulation applications. A similar model in Türkiye could significantly enhance the competitiveness of SMEs and large industrial enterprises. However, certain barriers hinder the implementation of these strategies, including high initial investment costs, lack of awareness, and price fluctuations in locally produced insulation materials. Therefore, these challenges should be addressed through awareness campaigns and long-term financing models to ensure the widespread adoption of insulation practices.

4. Conclusions

In this collaborative study, the primary goal was to raise awareness among end-users, practitioners, and producers by calculating the optimum insulation thickness (OIT) for 81 provinces in Türkiye using life cycle cost analysis (LCCA). Five different insulation materials (EPS, XPS, PUR, glasswool, and rockwool) and five distinct heating sources (electricity, LPG, fuel oil, coal, and natural gas) were considered. The results underscore the significant influence of variables, such as the chosen heating source, insulation material, inflation and interest rates, fuel price, and insulation cost, in determining the OIT.

The key findings of this study include the following:

• There is no single “optimum insulation application” that is suitable for all conditions.
• The OIT alone is not a sufficient determinant; its efficacy depends on finding an optimal thickness that balances economic viability. Factors, such as the heating source, insulation material, inflation and interest rates, project lifetime, and carbon emissions, must be considered through LCCA to determine the optimum value.
• Insulation should not be regarded solely as an investment cost, with doubts about its profitability dispelled. This study demonstrates that a well-executed insulation project can recoup its costs within an average of 2 years.
• Proper insulation implementation can lead to a reduction in carbon emissions by approximately 90% and an annual cost reduction of around 65%, resulting in short payback periods.
• Despite PUR appearing as the optimal choice for thermal insulation, its economic viability is hindered by higher payback periods and lower carbon emission reductions.
• XPS and EPS insulation materials emerge as potentially suitable choices for various conditions in terms of both thermal engineering and economic viability, although a preliminary assessment is necessary based on the heating source and engineering economics.

This study aims to bridge the gaps in the literature and serve as a guiding resource for businesses and end-users to adopt energy-efficient building practices, with a particular focus on proper insulation application. Beyond its environmental and economic benefits, proper insulation contributes significantly to business competitiveness by improving operational efficiency and reducing energy expenses, which can free up resources for innovation, expansion and other strategic investments. In today’s socially aware marketplace, businesses that prioritize sustainability gain a significant advantage by attracting environmentally mindful consumers, who increasingly favor companies that demonstrate a commitment to reducing carbon emissions and energy consumption. This not only improves brand perception and consumer trust but also ensures long-term success.

Furthermore, investing in energy-efficient building practices can future-proof businesses against rising energy costs and regulatory pressures. As energy prices continue to fluctuate and governments implement stricter environmental regulations, businesses that have already implemented energy-efficient solutions, including proper insulation, will be better positioned to adapt. Fostering societal awareness of these advantages is crucial for reducing overall energy consumption and emissions. By spreading knowledge and empowering the public to advocate for and incentivize improved standards in business practices, productivity, competitiveness, and sustainability across industries can be enhanced. Possible future developments and limitations include the following:

• For developing countries like Türkiye, which have a high dependence on foreign sources for energy and raw materials and consequently experience periodic economic fluctuations in fuel and insulation material prices, as well as variations in interest and inflation rates, it is crucial to periodically repeat such studies.
• The consideration of microclimatic conditions can be crucial in the results obtained from calculations conducted for a specific location and/or application.
• A specific study that includes the embodied carbon emissions of the insulation materials used and calculates the total carbon emissions over the entire building lifetime would be highly insightful.
• A study that analyzes the gains and losses of applying the insulation thickness corresponding to the recommended U-value specified in the TS825 standard, which forms the legal framework for insulation applications in Türkiye, compared to the optimum insulation thickness across the entire country would be highly insightful (as exemplified in Figure 3).
• The primary factor driving the need for a revision of this nearly 17-year-old standard is the findings of this and similar academic studies. In this context, conducting comparative analyses with equivalent studies from developed countries could provide valuable insights for establishing the foundations of a future revised standard.