*1.1. Background and Purpose*

The World Health Organization (WHO) has pointed out the aging generation problem, where the global population over the age of 60 is expected to increase from 900 million in 2015 to 2 billion in 2050 [1]. Korea has become an aging society, with an aging rate of 14% as of 2017, and it is expected to reach 20% by 2025, at which point it will become a super-aging society. Recently, Statistics Korea predicted that this trend of aging in Korea will be accelerated more and more [2]. Due to the global COVID-19 pandemic from the end of 2019, "untact", non-face-to-face society (business, education, shipping, etc.), and non-face-to-face services (food, goods, drive-thru shopping, etc.) have quickly been established in Korea as the New Normal [3]. These social changes increase the staying time of residents in buildings, and they emphasize the importance of indoor environment (temperature/humidity/ventilation) and air quality, which directly affect human health [4]. In this regard, the housing condition of an aged house is affected by the indoor environment and air quality, and it is closely related to the health of the residents [5]. For example, high or low temperature indoors (summer/winter) causes cardiovascular diseases, high blood pressure, and respiratory problems [6]. Specifically, an imbalance in room temperature or humidity leads to mold growth, which may cause respiratory disease and lung cancer [7]. In addition, the problem of noise from the outside intruding into the house may also cause cardiovascular diseases, sleep problems, and cognitive impairment [8]. Improving the energy efficiency of old houses is known to be a good strategy for enhancing the

**Citation:** Kim, J.; Nam, S.; Lee, D. Current Status of Old Housing for Low-Income Elderly Households in Seoul and Green Remodeling Support Plan: Economic Analysis Considering the Social Cost of Green Remodeling. *Buildings* **2022**, *12*, 29. https://doi.org/10.3390/ buildings12010029

Academic Editors: Roberto Alonso González Lezcano, Francesco Nocera and Rosa Giuseppina Caponetto

Received: 22 November 2021 Accepted: 28 December 2021 Published: 31 December 2021

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

housing condition of a house in the long term [9]. For example, improving building envelope insulation, windows, and heating-cooling equipment may enhance the indoor thermal environment, and making high-performance window improvements using sealing materials (airtight tape, etc.) may reduce the external noise problem [10]. The total heat exchange ventilation system improves the indoor air quality by introducing purified outside air [11]. Insulation, windows, high-efficiency air conditioning systems (boiler/EHP), and total heat exchange ventilation systems are actively used as the elementary technologies of GR (Green Remodeling) for improving the energy performance of old buildings. These measures for improving the energy efficiency of old buildings are referred to using various terms such as energy retrofit and green renovation, but in this paper, the term 'GR' is used. Further, 'GR' in this paper includes deep energy retrofitting, such as improving insulation, windows, air condition, ventilation, etc., rather than a single measurement for performance improvement.

In April 2019, in a report on the perspective of the clean energy transition, the IEA highlighted the importance of energy transition through GR of old buildings [12]. The GR is used as a core energy saving policy in the building sector for energy conversion and greenhouse gas reduction. However, there are several barriers to applying GR policy for reducing greenhouse gas emissions, so many countries are using various measures to overcome these barriers [13,14].

The most representative barriers are economic feasibility, such as high initial construction cost and low subsidy. Technical skill level, information imbalance, uncertainty, and rebound effect have also been mentioned as barriers [13–15]. To alleviate these barriers and implement GR, many countries are using construction cost support, low-interest loans, technical support, and various types of promotional support according to the energy improvement performance of old buildings as auxiliary policies [13,14]. Many other research papers involving GR suggest an optimal GR planning direction by approving the energy effect of GR and analyzing economic feasibility to alleviate the aforementioned policy barriers. First, simple remodeling action (insulation replacement, windows replacement or air conditioning replacement) can bring about lower results than expected in terms of energy and cost effectiveness as compared to GR (insulation + windows + HVAC + ventilation) [16]. These relationships can be confirmed from empirical GR analysis cases in Europe and the United States [17–19]. The cause of this is that using a simple measure that is not coordinated with other aging elements (such as walls, roofs, windows, ventilation, and air conditioning) can lead to a lower energy saving effect than expected, due to the deteriorated quality of thermal bridges and elements that were not improved after construction [20]. By contrast, the GR provides energy performance to new construction levels by examining the deterioration of the target building in advance and planning all elements that require improved consideration of the latest legislations (insulation, thermal bridges, air tightness and ventilation, and mechanical and electrical installations). Accordingly, the EU Commission also recommends GR in consideration of reliable energy efficiency improvement and economic feasibility for the owners and investors of old buildings [21].

However, this GR is not a measure that can be adopted by all owners of old buildings, because of the high initial construction cost which requires about 10 years (relatively long term) to recover the construction cost [22]. This is particularly true for low-income elderly households who experience a relatively large impact on energy bill burden, indoor environment, and air pollution. Although elderly households desperately need GR, it will be difficult to improve energy, indoor environment, and air quality without government support.

This paper investigated the aging status of buildings as well as the energy performance and usage status of nine old houses for low-income elderly households in Seoul, Korea. Among them, one old house was selected, and the total construction cost required for GR and energy savings before and after GR were analyzed. Based on the results of these analyses, an economic analysis was conducted in consideration of social costs. Then, to activate GR for low-income elderly households, a GR support plan that links the current energy transition with the low-income old housing support policy was proposed by utilizing the

health, safety, and energy improvement effects of GR. This support plan is expected to contribute to an improved residential environment along with activation of the GR from the GR support for low-income elderly households who are vulnerable to COVID-19 and climate change.

The unique features of this study are that when planning the GR of old housing for low-income elderly households, energy, health, and safety factors that were considered as housing characteristics of elderly households were all reflected in the construction cost to analyze economic feasibility. Therefore, an effective housing stabilization plane was proposed by integrating the old housing support policy for low-income elderly households with the direct and indirect effect of GR.

#### *1.2. Procedure and Method*

The research procedure was divided into four stages: Section 2 describes the literature review, Section 3 details the target selection and GR plan, Section 4 discusses the economic analysis, and Section 5 presents the GR support concept proposal. In the literature review in Section 2, previous studies were reviewed to derive health problems and the causes for the residents of old houses, and architectural methods that could be used to improve these issues were summarized. Then, factors for safety improvement were investigated in consideration of the residential characteristics of elderly households, which may be the most vulnerable group among residents of old houses. Finally, the scope of energy elements and performance level of improvement for old houses were investigated, and the improvement scope and performance level of buildings and facilities that were suitable for the characteristics of old houses in Korea were summarized. The GR range of this study based on the review includes health, safety, and energy performance improvements in consideration of the residential characteristics of low-income elderly households.

In Section 3, the status of aging houses of low-income elderly households in Seoul, Korea was investigated, and target buildings were selected for GR analysis. First, the aging status of the houses in which the vulnerable class (such as elderly households) with less than 70% income reside among the old single houses and multi-family houses that have been in Seoul for more than 30 years was investigated and analyzed. Next, GR target buildings were selected, and the scope and methods for GR improvement were summarized based on the results of a literature review and on-site investigations. This GR plan includes building and facility elements applied in terms of health, safety, and energy. The performance level of these elements was planned in consideration of regulations and construction costs.

In Section 4, the economic analysis considering social costs was described. First, the total construction cost was derived by calculating the construction costs of each element in the GR plan. For energy analysis, the annual energy and reduced amounts of the greenhouse gas (CO2) for the target building before and after GR were calculated using ECO-2 (Korean Building Energy Efficiency Rating Program). To analyze the economic feasibility, the annual energy saving cost (benefit of residence) was calculated by converting the amount of the energy into the electricity rates for houses. The social cost was calculated by converting the reduction amount of greenhouse gas (Social Benefit-(1)) and the reduction effect of the air pollutant (Social Benefit-(2)) into cost [23]. For the economic feasibility analysis, the residence benefit and the social benefit according to the GR of the old house compared to the total construction cost of the GR were analyzed and compared using the Net Present Value (NPV) method. The NPV method was used to analyze economic feasibility, because it can suggest the present value of future accrued benefits, and the results of its analyses can be used for other analyses [24].

In Section 5, a GR support plan was proposed in which the housing stability policy and the energy conversion policy for low-income elderly households were mixed based on the analysis results. Figure 1 shows a flowchart of the research contents according to the research procedure.

**Figure 1.** Research flowchart.

#### **2. Literature Review**

In the literature review of previous studies, three aspects of old housing were investigated. First, the causes of health problems in old houses and architectural methods to improve them were investigated; second, using the 2017 Seoul housing situation survey data, factors for improving the safety aspect of the elderly households who are vulnerable groups were derived; and third, GR factors and performance levels in terms of energy were summarized. The results of this survey will be used as basic data when planning the GR of old housing for low-income elderly households.

#### *2.1. Causes of Health Problems in Old Houses and Methods of Architectural Improvement*

Sick Building Syndrome refers to a phenomenon wherein the indoor air quality and indoor environment can adversely affect the health of the residents [25]. Outside air polluted by PM2.5 and PM10 enters the room without being purified, which can cause respiratory diseases in the residents [26,27]. In addition, various damages may be caused to residents due to damp wallpaper and mold growing inside the wall, various harmful gases leaking from the grain pipe, and VOCs (volatile organic compounds) that may be present after interior construction [8,25,28].

First, the unexpected inflow of polluted outdoor air by particle materials (PM2.5, PM10) into the room is largely affected by the quality of the aged windows [27]. The inflow of polluted outdoor air can be reduced by replacing old windows and sealing window edges. Mold growing indoors mainly occurs on the side walls (where the outside and the wall come into contact) according to the temperature difference between the inside and outside, and this difference worsens when the indoor air is not ventilated. The vulnerable areas to indoor dewing and mold are mainly the space between furniture (closets, etc.) and the wall and/or in the space between the wallpaper and the wall. The main cause of this problem may be the wall heat bridging and lack of indoor ventilation. For an architectural method to improve this problem, an insulation construction without thermal bridges (external insulation) and a total heat exchange ventilation system suitable for the purpose may be applied [29,30]. The leakage of methane gas, ammonia gas, carbon monoxide, and carbon dioxide from old drains or gas pipes may cause headaches or dizziness. To solve these problems, old pipes should be regularly cleaned and replaced [30]. Specifically, it is necessary to properly manage and replace the trap protecting the water seal which can block the backflow of odors to facilitate drainage and manage aging vent pipes to protect the water seal. There is a possibility of causing chronic diseases such as headaches and

allergies due to organic compounds such as acetone, benzene, and formaldehyde generated from materials and furniture that is newly installed due to repair activities, such as interior construction and furniture replacement, while maintaining the building. This problem may be improved by regular ventilation and the use of environment friendly materials [31,32].

According to the Health and Home Upgrades research report by DOE (U.S. Department of Energy) in February 2017, housing environment has a significant impact on resident health, and improving the energy performance and ventilation facilities of old buildings also enhances the energy and health of residents [28]. As an empirical case of health improvement by GR, Beysse et al. analyzed the health improvement effect of 40 elderly households after GR in the US. As a result, respiratory diseases, overall health problems, indoor environment (temperature/humidity), indoor air quality, and musty smell from pipes were all improved [33]. Ahrentzen et al. performed GR (including eco-friendly finishing material and furniture) for 57 aged houses of low-income elderly citizens in the United States. As a result, the indoor environment (temperature/humidity) and indoor air quality (formaldehyde, particle matter, etc.) were improved, and the overall health of residents was enhanced as well [34]. In addition, in the analysis of a number of GR empirical cases, the resident health was enhanced from the improvement of the indoor environment and indoor air quality after GR [35–37].

In summary, energy saving and improvements in both indoor environment and indoor air quality are some of the expected benefits of reforming insulation, windows, heating and cooling, and ventilation facilities which are general elements of GR. Further, the results showed that it can help improve the indoor environment to enhance the health of residents by applying eco-friendly materials and furniture, as well as proper management and replacement of old pipes when improving the interior space.

### *2.2. Review of Housing Improvement Factors for Elderly Households among the Vulnerable Classes*

To capture the housing situation survey in Seoul in 2017, the factors necessary for housing improvement were investigated by reflecting the characteristics of elderly households [38]. A survey was conducted that covered a total of 10 items, as shown in Figure 2. In the results of a study comparing owned houses to rented houses, 'Nonslip Floor Materials', 'Indoor Emergency Bell', 'Door Knobs', and 'Support Knobs' appeared at high proportions. Among 10 items, except for the 'Indoor Emergency Bell' and 'Safety Knobs', these items are optional items which can be reflected in a GR plan without affecting the cost and the plan. Therefore, when planning a GR improvement model in this study, the items of 'Indoor Emergency Bell' and 'Safety Knobs' were included in consideration of the characteristics of elderly households of aged houses, and they were reflected in the construction cost.

**Figure 2.** Ratio of items required for rebuilding houses of elderly households.

#### *2.3. Investigation of Energy Performance Improvement (GR) Factors and Performance Level of Aged Houses*

Recently, the research on energy performance improvements of aged buildings has mainly focused on energy saving by total GR or the cost efficiency of zero-energy GR, rather than the energy efficiency of individual items. In particular, to increase the utilization of GR research, various studies have examined GR strategies for apartment houses, school facilities, and business facilities, which are in high demand [10,39–41]. The improvement scopes and performances of these precedent studies have differences in climate by region, technology level, and residential environment, so care should be taken when adopting the applied technology for use in various settings. Accordingly, in this study, the performance of the improvement scope was considered by referring to the GR guidelines issued by the Korean government.

In 'Guidelines for the Establishment and Implementation of Urban Renewal Revitalization Plan for Urban Renewal New Deal Projects' published in August 2018, the Korean government disclosed GR cases, scope of technical elements, and recommended performance of aged houses [41]. The scope of improvement in the guidelines includes the replacement of roof/exterior wall insulation, windows (including entrance doors), air conditioning equipment, indoor LED lightening, and renewal of façade design. These need to be additionally reflected when planning the GR improvement model, because the literature review does not include the consideration of a ventilation system or sealing system for resident's health. This guideline provides performance improvement standards for each GR item, and it can be used to determine the performance level. Table 1 presents the improvement in factors and performance for each item. 'Bad' refers to the performance of the aged building, 'Good' refers to the performance of a passive house in Germany, and 'Recommended' refers to the performance level of each item of the GR plan considered in this study.


**Table 1.** Improvement in factors and performance in terms of energy consumption [41].

Finally, the use of IoT-based smart home technology for small elderly households is spreading [29]; however, the GR plan described in this study minimizes the automatic control facilities and applies only the items related to safety (emergency bell linked to mobile phone) while considering the cost aspect.

Figure 3 summarizes the problems in health, safety, and energy aspects and the direction of architectural improvement considering the characteristics of residents of aged houses from the literature research. Figure 3 shows that the architectural method for enhancing the health problems of aged houses and the method for improving the building energy performance have many items in common. Based on this, it is clear that performing the GR described in the literature review has the effect of enhancing the health problems of residents. However, the GR scope of this study considering the health and safety of elderly households should be additionally applied to the material selection and replacement of sanitary piping, and the additional installation of various knobs, non-slip pads, and emergency bells, along with the removal of faulting should be considered based on the fact that the residents are elderly people. The results of this survey will be used in a GR plan considering health, safety, and energy after investigating the status of aged houses of low-income elderly households.

**Figure 3.** Issues associated with aged people in households of the old houses and the orientation of improvement in parts of the GR.

#### **3. Current Status Survey and GR Plan for Aged House of Elderly Households in Seoul, Korea (Scope of Improvement and Performance)**

To investigate the current status of aged houses of elderly households in Seoul, the sites were surveyed with the project implementer for about two months with the cooperation of the 'Hope home repair project' of Seodaemun-gu, Seoul and the 'Structural safety status survey project' of Dongjak-gu, Seoul. More than 20 aged houses were investigated, and nine households were found to be suitable for this study.

Accordingly, in this section, common characteristics were derived by summarizing the aging status and problems of nine buildings of low-income elderly households. Among them, buildings that could be used to analyze the improvement effect by GR were selected as the target sites.

#### *3.1. Survey on Current Status of Aged Houses for Elderly Households in Seoul*

Table 2 summarize the building status, resident information, and building energy performance of aged self-owned houses or aged multi-family houses in which elderly households reside. As shown in the survey results, most elderly households living in aged houses for around 30 years were women over 70 years old, and they often lived on the lower floors (1st floor) with inconvenient movement and relatively insufficient ventilation and light.


**Table 2.** Results of survey on sites of old houses of households

 of aged people.

Dewing and mold, both of which have substantial effects on the health of residents in terms of building function and age, were found in all except the two remodeled houses (No. 4 and 6). There was a household (No. 3) with a public restroom and a household (No. 1) with an indoor rest room that had thresholds higher than 500 mm, despite the inconvenience of mobility. In terms of building energy and indoor air quality, all households had very poor insulation. Regarding the windows, all except two households were equipped with a combination of wooden single windows and AL single windows, so the insulation performance was less than 1/3 of the current legal standard performance. As the window frames have been used for more than 20 years, the air tightness performance was very weak. In addition, the front doors of all households were not equipped with a windproof structure, and there were no ventilation facilities at all. This was expected to have a significant negative impact on the health of elderly people, who are relatively vulnerable to particle matters and indoor air pollutants. Finally, regarding the heating and cooling facilities, all households were equipped with wall mounted air conditioners for cooling and boilers for heating using urban gas. Some households had outdated cooling/heating equipment, but there was no problem in usage. Table 3 presents images of major defects such as dewing and mold, a restroom in need of improvement, old window sets, and household front doors.

**Table 3.** Survey cases of defects in aged houses.


#### *3.2. Selection and Status of Target Sites for GR Effect Analysis*

According to the site survey, the low-income elderly households were living on the lower floors of single-family or multi-family houses with monthly rent or that they owned themselves. Among them, residents of multi-family houses that were paying monthly rent requested relocation to a public rental apartment or housing cost support rather than facility improvement. By contrast, residents in their own aged house wanted subsidies for facility improvement or full facility improvement. In the case of owned single-family households, there was a problem in new construction and sale because the site area was small (less than 33 m2) and it was located in a dead-end alley. To solve this problem, it may be an option to proceed with the remodeling by consulting with the neighbor of the adjacent site, but this is not easy.

Although all households surveyed require housing stability by facility improvement, by considering problems such as (1) self-ownership or rental, (2) relocation of residential households after facility remodeling, and (3) the scope of facility remodeling, the houses with clear land and architectural boundaries among self-owned houses were selected as the target buildings for GR analysis of aged houses. From the households surveyed, three households were single-family houses, and among them, No. 4 and 5 were candidates. No. 4, which has a relatively clear boundary of the building area on the site, was selected for analysis. Even though No. 4 was renewed by some facility improvements such as a window renewal and interior-exterior finishing renewal project in July 2019, there were no improvements in building energy, indoor air quality, or safety, except for windows. Table 4 presents the status of No. 4 after facility improvement.

**Table 4.** Cases of the survey on defects of old houses.
