A Biophilic Design Approach for Improved Energy Performance in Retrofitting Residential Projects

Abstract

The existing building stock is recognised as a major contributor to total energy consumption and related carbon emissions around the globe. There is increased attention on the retrofit of existing building stock, especially residential buildings, as a way of curbing energy consumption and carbon emissions. Within this context, human nature connectedness (HNC) has the potential of further amplifying the benefits of sustainable buildings both from an energy conservation practice and tangible improvements to users’ satisfaction, health, and wellbeing. This study attempts to show a case study of the potential of using HNC through the adoption of biophilic design principles to improve a residential building performance. A terrace house located in Sydney, NSW, was used as a case study and proposed retrofit scenarios were simulated with DesignBuilder^® and Rhinoceros/Grasshopper with a view of improved daylighting, thermal comfort, and energy consumption. The building performance is improved in terms of daylighting, thermal comfort, and reduced energy consumption, additionally enhancing HNC.

1. Introduction

In current practice, an increasing amount of attention is paid to improving energy performance in existing buildings by minimising energy consumption, which requires strategies beyond mere technical advancements [1]. A well-structured retrofitting strategy in existing buildings can offer a practical solution to reduce emissions, along with the associated cost, comfort, and environmental benefits [2]. The use of technological advancements in retrofitting overlooks additional benefits [3] such as improving building quality, providing opportunities to enhance occupant’s wellbeing [4] by nurturing for human nature connectedness (HNC). In addition, the outbreak of the COVID-19 pandemic and stay-at-home mandates increased people’s attention to mental and psychological wellbeing [5] and highlighted the role of the building design on people’s health and wellbeing [6], especially for residential buildings. Under strict lockdown, as people could leave home only for very limited tasks, the positive effects of nature exposure from home in mental health have been heightened [7]. The rising issues with the COVID-19 pandemic (such as contact with nature, improved indoor air quality, and comfort) call for urgent advocacy to seize the opportunity to link with nature instead of focusing only on improving energy efficiency in retrofitting projects. Further, biophilia, the human affinity to connect to nature, elevates pro-environmental behaviour and contributes towards energy conservation behaviours in the built environment [8].

Numerous recent studies have positioned biophilic design (BD) as a design approach that could fulfil the human inherent desire to contact nature [9,10,11]. BD principles are based on the use of natural elements and processes within the built environment, elevating a sensory connection to nature. The BD frameworks proposed by Kellert [12], Browning et al. [13], and Kellert and Calabrese [14] are the ones widely used in design [15]. However, these frameworks are focused on health and wellbeing associated with human performance, while less emphasis is given to addressing building performance. Majority of BD studies have demonstrated the benefits of its use within the sustainable built environment for enhanced human performance [16]. However, the potential to use BD strategies to achieve building performance are discussed within anecdotal studies [17,18] providing promising evidence for its use beyond human comfort including integrating nature for enhanced energy performance.

Hence, there is a lack of research studies to evaluate the biophilic design strategies in terms of maximising energy performance, especially in the retrofitting of existing buildings. The current design strategies for improving energy related building performance relies heavily on technological solutions. The potentials to use BD elements are overlooked. Therefore, the aim of this research is to present a BD approach to fill this gap that can achieve energy efficiency in a retrofit design. This design approach is premised on using natural elements and processes contributing to both energy efficiency and BD. The proposed approach was applied to an urban terrace house in Sydney, Australia. The terrace house was redesigned to improve its performance using BD elements where computational simulations were conducted with DesignBuilder^® and isovists were obtained with Rhinoceros/Grasshopper to compare before and after scenarios. The results are discussed with limitations in applicability and directing towards further developments.

2. Biophilic Design Approach for Retrofitting Projects

The BD approach for retrofitting projects has been explained in the following subsections regarding two main contributors, which are BD elements and energy efficient design strategies, in the designing of building components for improved energy performance.

2.1. Biophilic Design Elements

Although humans have lived within built environments for thousands of years, the human psyche possesses an inclination to form a connection with nature [11]. This connection can be experienced through a variety of human senses including sight, sound, touch, smell, taste, and movement from a direct or indirect experience with nature. Direct experience refers to actual contact with environmental features in the built environment including daylight, air, plants, water, etc., whereas indirect experience represents the characterisation of nature in particular forms and patterns [19].

This profound need of humans for nature has led researchers and practitioners to look for solutions that can define prominent aspects of the natural system to accomplish built environment living satisfaction [20]. To understand the scope of integrating nature into the built environment to ensure human comfort, for decades, many prominent frameworks have been developed to articulate the relationship between nature, humans, and the built environment. The primary concern of these frameworks is to ensure the human benefits of biophilia in design applications. Ryan et al. [21] developed a BD framework consisting of 14 patterns across 3 main categories that is inclusive of all human health and wellbeing aspects. The first category, ‘nature in the space’, is associated with the direct presence of nature, including daylight, air, plants, and water. The next category, ‘natural analogue’, addresses the organic, non-living, and indirect evocations of nature in the form of objects, materials, colour, shapes, and patterns that can be explored through artwork, furniture, décor, or textiles. Lastly, the ‘nature of the space’ prioritises spatial configuration in nature, which can be experienced through the creation of engaging arrangements to see beyond surroundings, in combination with nature in the space and natural analogue.

Figure 1 explores the design forms of biophilic elements, such as daylight, air, plants, and water used in buildings. For the present study, the main consideration is the direct experience of nature, which falls under the ‘nature in the space’ category.

2.2. Energy Efficient Design Strategies

The fundamental of energy efficiency in buildings is interconnected with the energy supply required to acquire the desired environmental goals with minimum energy consumption and conservation [23]. Heating, cooling, ventilation (HVAC) systems and artificial lighting are responsible for most of this energy demand [24], and by minimising this demand, significant reduction can be made towards energy consumption. Passive design strategies aid this purpose that include certain building design parameters to enhance energy performance of the building. One such key parameter is the building envelope which performs not only as a physical barrier between the external environment and the internal space [25] but also creates comfortable interior space by vigorously responding to the exterior condition [26]. With design strategies including better thermal insulation and shading, thermal massing, and optimum sizing of window-to-wall ratio (WWR) and skylight can contribute to reducing energy consumption as much as 33% [27]. These design strategies can be executed during planning or construction or even in retrofitting. The main targets of these strategies are to optimise energy consumption through reducing heat transfer, artificial lighting, and electricity demand.

Responding to this demand, energy retrofitting has gained a lot of attention and become a subject of importance to the real estate sector in recent years [28]. One study has shown that, through the energy-related retrofitting of the building envelope, the energy consumption of a detached house dating from around 1900 in Belgium was reduced from 410 to 79 kWh/m², an improvement of about 80% [29]. However, this attitude is missing a collective approach that integrates these energy efficient renovation strategies with significant biophilic elements that eventually improve the biophilic quality of the building. An integrated strategy combining energy efficiency along with biophilia can be addressed for a more efficient retrofitting.

Moreover, since these buildings have poor conditions, it is important to ensure that indoor environmental quality (IEQ) goals are met alongside energy efficiency [30], so that a measure taken to improve one strategy does not lead to deteriorating others [31]. IEQ refers to the quality of a building’s environment concerning its occupants [32]. IEQ is proved to have impacts on energy efficiency along with productivity and the health of occupants as people spend most of their time indoors for work and living. As thermal comfort and visual comfort are the major areas of concern for IEQ, this paper investigates the deeper incorporation of design strategies interpreting biophilic elements to ensure thermal comfort and visual comfort. Furthermore, as IEQ is also associated with the energy design strategies of the building, this can be an ideal approach to create an integration between energy performance and BD.

2.3. The Integration of Biophilic Elements with Energy Efficient Retrofitting Strategies

The current practice in improving energy performance is highly dependent on technology [33] and the challenge in developing a biophilic-oriented approach is to use natural processes and elements as design strategies. Addressing a similar challenge, Wijesooriya et al. [34] propose to use natural processes to bridge between the two design approaches of BD and current environmentally sustainable design (ESD) practice. Using building components that could support design strategies in both BD and ESD association mapping could be used to link building components with BD and energy efficient design strategies. Further expanding this idea of associating these strategies, we used the following methodology given in Figure 2.

To begin with, a thorough study needs to be performed on the existing situation through the collection of information and site analysis of the selected context. This step leads the way to figure out if there is an opportunity for energy improvements. The next step follows a retrofit scenario where design strategies for energy efficiency and BD are explored to implement in the designing of building components based on the analysis. This is the most crucial part of the study where elements of biophilia and energy efficient design criteria are finally put together to come up with the strategies for improved performance of the building. After the implementation, computer-based simulations are performed to understand the improvement in energy consumption for pre- and post-retrofit scenarios. The proposed approach with the integrated BD elements is compared to investigate the energy performance and HNC. The study concludes by presenting a quantitative analysis of the improved building performance while evaluating proposed BD approaches simultaneously.

To find out the interrelation between biophilia and energy efficiency criteria, it is important to understand their associative link. Figure 3 represents the association map that serves the purpose. First biophilic elements and integrated energy design strategies are listed and then connected through the building design elements to establish their link.

The map includes elements of biophilia, such as daylight, air, plants, and water used in buildings in the form of window, skylight, clerestory, green wall, vegetation, water wall, and constructed water body. The next step is to identify the affiliated energy design strategy. Lighting, space heating, cooling, and ventilation are responsible for the majority of energy consumption in a building. For this specific research, from an ample amount of available energy efficient design strategies, those which reduce the HVAC load along with ensuring an optimised consumption of energy are considered. The strategies include WWR, optimum use of skylight, thermal massing, and insulation. The map summarises the possibility of biophilic elements being able to serve the dual purpose of being an energy efficient element as well as fulfilling the specific targets. The strategic approach incorporates all these elements, such as how daylight availability can be incorporated into a building through window, skylight, or clerestory design and its consequences on energy design strategy, how natural air can have an impact on a building design that enhances both human health and the overall impact on energy consumption. For the present study, in the case of selecting biophilic elements, the main consideration is the direct experience of nature, which falls under the ‘nature in the space’ category.

3. Implementation of the Biophilic Design Approach

3.1. Case Study

For the case study, a two-storey urban terrace house located in Sydney (Figure 4), Australia, was selected. These houses comprise 12.9% of the national building stock and 12.2% of the housing stock in New South Wales [35], so it makes this case study highly representative of a bigger cohort of buildings. The general layout of the plan does vary a little but generally involves a long and narrow floorplan with two bedrooms upstairs and two rooms at street level, extending out behind, containing a kitchen, laundry, and bathroom. The size of the house is about 5 m in width and 15 m in depth. The spaces are divided into 6 zones: foyer, bed-1, living, kitchen and dining, toilet-1 and laundry, and the backyard and courtyard. This house is not considered to be a part of the heritage conservation program, listed by the City of Sydney [36], so changing the plan to some extent with some space alteration would be permitted.

3.2. Retrofitting Scenarios

The general problems arising in these buildings are summarised below and represented in

Table 1. General problem statement of existing terrace houses in Sydney (Source: Authors).

	Brief Explanation	Current Situation
Daylight: Limited access of daylight throughout the day	Most of the spaces in the house do not receive enough daylight throughout the day Terraces facing east–west will receive sunlight during the mornings and evenings, whereas north facing houses tend to become too hot during summer Window-to-wall ratio (WWR) on average 4–5%	Skylight above the stair provides insufficient daylight in the lobby area. Artificial lighting is required most of the time.
Natural Ventilation: Poor IAQ	Insufficient WWR obstructs natural ventilation Each room has a single window leaving no option for cross ventilation	Typical layout of bedrooms. No provision for cross ventilation.
Damp: Formation of mould in the damp wall	Lack of ventilation and heat circulation causes damp which leads to mould Termites and woodborers are often attracted to the house	Damp can enter from the ground up or from the roof down.
Noise: Unwanted noise intrusion	Because of the shared walls, terraced houses come with an increased risk of unwanted noise from neighbours and nearby roads	Shared wall often becomes the reason of compromised privacy.
Connection to outdoor space (backyard/courtyard): Unintegrated backyard/courtyard	A terrace house has a considerably smaller backyard/courtyard than most property types They are not integrated with the existing floor layout to provide natural daylight or ventilation to the house Therefore, a missed opportunity on such a small site The ground is covered with impermeable concrete surface	Typical layout of backyard.

:

• Limited access of daylight
  • Most spaces of the house do not receive enough daylight throughout the day.
  • Terraces facing east–west receive sunlight during the mornings and afternoons, whereas north-facing houses tend to become too hot during summer.
  • WWR on average is 4–5%.
• Poor interior air quality (IAQ)
  • Insufficient WWR reduces the effectiveness of natural ventilation.
  • One sided window, leaving no option for cross ventilation.
  • Potential mould formation due to dampness in the walls, caused by insufficient ventilation and heat circulation.
  • Due to the dampness, termites and woodborers are often attracted to the house.
• Unwanted noise intrusion
  • Because of the shared walls, terraced houses come with an increased risk of unwanted noise from neighbours and nearby roads.
• Unintegrated backyard/courtyard
  • A terrace house has a considerably smaller backyard/courtyard with impermeable concrete surface which is not integrated with the existing spatial layout.

While the major focus in retrofitting terrace houses has been given to spatial configuration, the list also illustrates the demand for more access to daylight and a connection with nature. However, the relevancy of these strategies to the overall energy consumption of the houses has not been documented or considered in most cases, let alone their relevancy to HNC. The concept of BD and its association with energy performance and occupant comfort is missing in the current retrofitting practice.

As mentioned previously, the typical ground floor layouts are designed in such a way that the indoor spaces are not connected well enough with the outdoors. Moreover, the inadequate WWR causes non-uniform and limited daylight distribution throughout the day that eventually leads to an increasing application of artificial light. Moreover, the existing WWR restricts the opportunity for cross ventilation. To reduce the use of artificial light, a skylight is provided over the stair area, but the size of the skylight is insufficient to be effective.

Above all, the backyard and courtyard of the terrace house are covered with concrete surfaces and are not well integrated with the building function. Issues identified in

Table 2. Summary of problem statement of the selected terrace house and retrofitting scenarios (Authors, 2021).

Problem	Issues	Current Scenario	Retrofit Scenario
Poor thermal resistance	Thermal resistance of the building envelope is not adequate to fulfill the compliance criteria of Section-J of the National Construction Code [37]		Potential energy efficient strategy Potential BD elements	Air
Poor space layout	Misconfiguration of spaces and poor organisation of spatial interrelations	Ground floor–indoor–outdoor connection in the current scenario of terrace house		Daylight, Air
Limited daylight availability and natural ventilation	Low WWR (current ratio: 5%) Limited daylight access Limited cross ventilation	First floor—typical layout of bedrooms. No provision for daylight access and cross ventilation		Daylight, Air
	Skylight Inefficient size of area to provide enough daylight	Long section—typical size of current skylight over stair lobby		Daylight
Limited indoor and outdoor connection	Not integrated with the existing space layout Impermeable ground cover	Ground floor—impermeable ground cover on backyard and courtyard		Air, Plant

are focused on the indoor–outdoor connection which affects both HNC and energy efficiency. For the retrofit scenario, design approaches are proposed based on the studies mentioned in Section 2. As Figure 3 represents the relationship between energy efficient design strategy and BD elements, the issues found in the existing scenario are considered to explore the potential energy design strategy and their associated BD elements.

After going through the existing scenario, in terms of energy efficiency and biophilia, the retrofitting strategy can be organised into five phases (Figure 5):

• Improving R-values—Phase 01: Improving thermal resistance of the building’s external walls and roof to meet the minimum requirements of Section-J of the National Construction Code [37] (

  Table 3. U-value of the building envelope.

  Building Elements		Material Description	Thermal Properties of Building Elements/U Value (W/m2K)
  			Existing Values	Proposed Values
  Floor		150 mm thick concrete floor	0.78	0.78
  Wall	External	250 mm brick with 10 mm plaster either side	1.7	0.36
  	Internal	125 mm gypsum board with 10 mm plaster either side	1.2	1.2
  Roof		15 mm thick zinc metal deck roof with 150 mm airgap	0.31	0.25
  Door		50 mm thickness plywood door	2.98	2.98
  Window		Single panel of glass with wooden frame	5.89	2.60

  ).
• Modifying space layout—Phase 02: In the existing scenario, the position of the toilet on the ground floor creates a visual barrier between the existing backyard and the living area. To improve the biophilic quality and HNC of this existing scenario, a new space layout is suggested, changing the toilet position on the ground floor from the rear to the middle between the living and kitchen–dining areas to let the kitchen connect directly to the rear courtyard. The indoor of the house is now more open to the backyard and courtyard both visually and physically. As the living area is the space where the family spends most of their time together, to make the existing area more spacious and connected to the outdoor, bed-1 has been removed and the whole area is considered as a single space that allows an adequate amount of daylight and air to enter. Compared with other typical terrace house plans, it was observed that this bedroom was not included in the original plan. Rather, it was a much later addition. Moreover, balconies have been added to the living, kitchen and dining, and bed-2 and bed-3 for ensuring visual connection with the outdoors.
• Improving skylight—Phase 04: A skylight that is of a larger area is proposed to let enough daylight to enter the staircase. The area of the skylight is enlarged from 0.5 to 2 m² in the proposed scenario. To make the skylight more efficient, micro louvers, the smallest and most efficient solar shading system that can reduce solar heat gain by 86% [38], were added on the surface, to be positioned on the exterior face of the skylight.
• Courtyard integration–permeable ground cover—Phase 05: The backyard and the courtyard are not well integrated with building function and the ground cover is not permeable in the existing condition. To improve this situation, the proposed layout would create a visual connection between indoor and outdoor. Introduction of greenery is proposed to increase the biophilic quality of the courtyard. By changing the ground layer of the courtyard and the roof over the kitchen, an improvement in energy efficiency along with biophilic quality can be achieved. Australian native plants can be introduced to serve the purpose through a combination of grasses, desert plants, shrubs, ground cover, succulents, herbs, food plants, fruit, and berries. Among many benefits of native plants, the most vital ones are they support local ecology by providing food and shelter which attract birds, butterflies, and lizards. They also require minimum maintenance and are better resistant to local weather.

3.3. Energy Simulation Model

3.3.1. Building Model

DesignBuilder^® has been used to run energy consumption simulations in terms of daylight factor (DF), thermal comfort, and energy consumption. DesignBuilder^® is the interface of simulation engine EnergyPlus and is used to create the 3D modelling of the selected case study. The simulation model of the existing building has been given in Figure 4. Structural elements of the building envelope were selected based on the City of Sydney archive. The thermal properties of the building’s elements have been upgraded according to the compliance criteria of Section-J of the National Construction Code [37] (Table 3).

3.3.2. Weather Data

The study area is in Sydney, Australia, located in the southern hemisphere. Among 7 climate zones in Australia, Sydney is in climate zone 5, which has a warm summer and cold winter [39]. The mean annual temperature in Sydney is 17.6 °C and the annual percentage of humidity is 57%. Moreover, the monthly mean temperature ranges from 21 to 24 °C during the summer months of December to February, while the monthly mean temperature ranges from 12 to 13 °C during the winter months of June to August [40]. The weather data used for the simulation represent typical long-term meteorological weather conditions for Sydney, NSW (Australia). The weather analysis can be summed up in these points:

• Comfort temperature during summer and winter ranges from 20–26 °C;
• Winter months (June–August) have a relatively high amount of annual rainfall;
• Summer months (December–February) have a relatively low amount of annual rainfall with high humidity.

3.3.3. Schedules

The building is naturally ventilated, no active cooling system has been utilised. There is one electric heater installed in each of the rooms. Fresh air is supplied only during occupancy hours. Heating, lighting, and occupancy schedules for the simulations are seen in Figure 6.

3.3.4. Comfort Criteria

Visual Comfort

To analyse the visual comfort level of the house, the DF is selected as a variable. DF is simply the ratio between exterior and interior illuminance under an overcast sky. DF is used in architecture and building design to assess the internal natural lighting levels as perceived on working planes or surfaces. It is one of the variables to determine if the light is enough for occupants to carry out normal activities. The higher the DF, the more daylight is available in the room. With 5% or more DF, a room is lit enough to avoid the need for artificial electric lighting during daytime [41]. Achieving a DF of 2% over at least 60% of the floor area is recommended within the Green Star rating system developed by the Green Building Council of Australia [42]. The Green Star recommendation has been considered as a benchmark for verifying the daylighting impact of the proposed design strategies.

Thermal Comfort

The comfort zone range for Sydney climate is between 20 and 25 °C for all seasons [43]. Assuming that a high comfort level is desired during the occupation hours, in the existing and the proposed, in both scenarios, the comfort temperature is maintained only during the occupied hours. To assess the thermal comfort scenario, annual hours within the temperature range of 20–25 °C are calculated based on the occupancy hours for the particular activity zones. The lower the percentage of discomfort hours in a specific zone, the higher the comfort is. ASHRAE standard 55-2004 [44] has been referred to define uncomfortable hours.

3.4. HNC Analysis

Isovist is used by researchers as a reliable method to analyse the visibility [45]. The method was applied on floor plans to compare existing building and retrofitting scenarios by using Rhinoceros and Grasshopper. The isovist approach helped to reveal the increase in HNC with the proposed model. Three-dimensional images of interior views have been created with the use of SketchUp to evaluate the level of connection to outdoors. In addition, isovists have been presented to show how the existing building has a limited indoor and outdoor connection due to misconfiguration of spaces and having exceptionally low WWR.

4. Results and Discussion

4.1. Influence of Retrofitting Opportunities on Energy Efficiency and Occupant Comfort

The simulation results for the existing model have been presented in terms of energy intensity, DF (of 2%), and uncomfortable hours based on ASHRAE standard 55-2004 [44] (

Table 4. The simulation results of existing model and retrofitting scenarios.

Biophilic Design Strategies	Performance Assessment Criteria	Model 1	Model 2	Model 3	Model 4	Model 5	Model 6
		Base Model	Improved Thermal Resistance	Modified Space Layout	Increased WWR	Increased Skylight Area	Courtyard Integration
Day light into room, larger windows for nature connectivity, access and connection to courtyard, space layout for connectivity with nature	Energy Intensity (kWh/m2)	158.25	120.85	172.11	138.49	149.96	152.31
	Uncomfortable hours 1	4420	4871	3552.5	5013.5	3451	3310
	DF (%2) 2	19.2	19.8	21	29.2	41.5	41.5

¹ Time not comfortable based on ASHRAE55-2004 (total building). ² % area meeting requirements of DF (%2) (total building).

and Figure 7, Figure 8 and Figure 9). All retrofitting scenarios were simulated along with the existing phase during the period of one year. It has been shown that (Table 4) by implementing biophilic elements—daylight, air, and plants—in particular retrofitting phases, the house performs better in terms of daylighting, thermal comfort, along with a slight improvement in overall energy consumption. The energy efficiency improvement has been marginal because most of the energy demand is for heating load, and there exist limited opportunities for reducing the heating load, due to the façade’s minimal external exposure.

The discussion focuses on the challenges of improving the overall built environment energy performance as well as occupant comfort by implementing biophilic elements using daylight, air, and plants in five phases. Each phase of the retrofitting design has been compared with base model and differences in building performance have been discussed in detail.

4.1.1. Influence of Improving R-Values—Phase 01

The thermal performance of the external walls has been improved by increasing the R-value to R2.80 to meet the minimum requirements of Section-J of the National Construction Code [37]. This has resulted in an energy intensity reduction from 158.25 to 120.85 kWh/m². However, not much improvement has been observed in terms of daylight availability (Table 4).

4.1.2. Influence of Modified Space Layout—Phase 02

A comparison of the existing and proposed phases in the house to verify the extent of floor area receiving a DF of 2% indicates an increase to 21 from 19.2% for the existing condition. Significant improvement is observed in the “Time Not Comfortable Based on Simple ASHRAE standard 55-2004” [44], as the number of discomfort hours has been reduced from 4420 to 3552.5 (Table 4).

However, the annual energy consumption has increased from 158.25 to 172.11 kWh, for the existing and Phase 02 models, respectively, which is almost 8% higher than the existing. The reason for the increased energy consumption is the increased extent of the living area in the modified space layout, which improves the building functionality but causes a higher energy load due to increasing the daytime conditioning load, in comparison to being retained as the existing night-time conditioned bedroom zone. The performance results for the Phase 02 model, with a revised layout, have been considered as a reference benchmark against which the results of subsequent test options have been verified.

4.1.3. Influence of Increased WWR—Phase 03

WWR enhances the biophilic quality of the house in terms of connections to the natural environment in terms of access to daylight, ventilation, and views. Increased WWR allows more daylight to enter spaces while simultaneously providing an opportunity for optimising natural ventilation, which together would potentially improve the visual and thermal comfort of the occupants, respectively. In this process, WWR also simultaneously impacts the cooling, heating, and lighting demands of the house.

Phase 03 involves increasing the WWR from 5.10 to 12% via larger sized windows. The floor area that achieves an average DF of 2% increased to 29.2% compared to 19.2% at the existing phase (Table 4). However, a closer look at the DF map shows that all the studied areas except for the stair reach the threshold standard. The increased amount of window area may potentially lead to direct or reflected glare, but this issue is not covered in this specific research report.

The existing house has unprotected single glazed window panels with a U-value of 5.89 W/m²K (Table 3), which is lower than the walls. For this proposed scenario, double glazed window panels with a U-value of 2.60 W/m²K are selected. High-performance windows in combination with insulating blinds and other window improvement methods, such as special films and coatings, can reduce energy costs and improve thermal comfort.

As the windows are considered open during occupied hours outside of the winter season, they let an ample amount of air exchange within the house to release the internal energy along with the heat gained through the glazing.

While the selected house does not have any active cooling system installed, the proposed WWR reduces the average heating energy load, mostly during the winter months, by allowing external solar gain while concurrently allowing natural daylight to enter spaces resulting in reduced electric lighting use. At this phase of the retrofitting strategy, the annual energy consumption reduced from 172.11 to 138.49 kWh/m² (Table 4) in comparison to the energy consumption of the Phase 02 scenario. Increased WWR plays a significant role in reducing annual energy consumption by reducing the demand for heating energy and electric lighting. This proves that with every stage, the introduced biophilic elements are playing a role in improving the built environment energy performance. The results of the annual thermal comfort hours indicate that the time not comfortable has increased from 3552.5 h in Phase 02 to 5013.5 h, which is almost 29% higher than Phase 02. To reduce the extent of discomfort hours, further analysis has been conducted under Phases 04 and 05.

4.1.4. Influence of Skylight—Phase 04

The earlier phases show significant improvement in overall daylight availability within the house. To improve the daylighting to the stair area, the area of the existing skylight is enlarged, along with provision of operable shading, so that while letting the daylight in, the unwanted heat can be controlled. This addition increases the extent of floor area that meets the DF threshold of 2% to 41.5% in comparison with 21% of the Phase 02 model. This intervention also positively impacts on the annual thermal comfort hours, as the discomfort hours are reduced from 3552.5 in Phase 02 to 3451 h in Phase 04 (Table 4). This improvement is due to the operable opening installed with micro louvre solar shading and its capability to initiate ventilation via stack effect. At this phase of the retrofitting strategy, the annual energy consumption reduced from 172.11 to 149.96 kWh/m², in comparison to the energy consumption of the Phase 02 scenario, resulting in an improvement of around 13%.

4.1.5. Influence of Courtyard Integration–Permeable Ground Cover—Phase 05

Changing the outdoor ground cover from hard to permeable increases the water efficiency and enhances the built environment performance of the terrace house. The use of porous surface to purify groundwater is an example of the former, while heat reduction is an example of the latter. Water usage as a strategy to reduce heat is constantly being researched [46]. A green landscaped ground cover has been modelled; however, the implementation of water strategy requires specific tools to measure the impact of water in this phase in terms of the selected simulation variables. So, although it has been proposed as a design strategy, only the greenery has been modelled. The highest impact of this strategy has been observed in the decrease in time that had not met the thermal comfort criteria of the ASHRAE standard 55-2004, as the hours decreased from 3552.5 in Phase 02 to 3310 h (Figure 8). Overall energy consumption of the residence has also improved in comparison with the Phase 02 scenario by around 11.5% (Table 4, Figure 7).

4.2. Influence of Retrofitting Opportunities on HNC

The proposed BD approach offers a green courtyard with a combination of layers of plants, vegetation, and green surfaces. While an increase in WWR enhances contact by viewing, the proposed balcony and roof terrace on the first floor and green covered courtyard help to support contact by touching and entering. The impacts of this retrofitting scenario have been discussed from the aspects of energy efficiency and occupant comfort. While the problems of limited daylight availability and poor natural ventilation were solved, HNC has been increased (Figure 10).

Encouraging the use of BD elements in retrofitting projects allows for exposure to nature, and in turn, this design approach improves occupants’ health and wellbeing. Although empirical evidence of user experience to understand the health outcomes of the BD approach has not been investigated within the scope of this study, the findings of existing literature could be useful to make assumptions on its benefits. There are several possible benefits of green environments; physical and mental health, particularly through stress reduction and attention restoration [47], improved self-perceived wellbeing and quality of life [48], and personal wellbeing [49] have already been approved by several researchers. Houses with building-integrated vegetation are more preferred and found to be more beautiful and they evoke more positive emotions and are more restorative [50]. A survey study conducted by Kaplan [51] with the communities of six low-rise apartments provides considerable support for the premise that contacting with nature by viewing through windows contributes substantially to residents’ satisfaction with their neighbourhood and with diverse aspects of their sense of wellbeing. It is obvious that, beyond viewing, experiencing nature via touching and entering throughout a courtyard would bring people into closer relation with one another [52]. Luck et al. [49] have assessed the personal wellbeing and level of connection to nature of over 1000 residents in 36 residential neighbourhoods in south-eastern Australia and concluded that vegetation cover had the strongest positive relations with personal wellbeing.

5. Conclusions

There is a growing consensus that bringing nature into interiors via the key design elements including extensive daylighting, natural ventilation, connection to outdoors with views of nature, as well as green walls, plants, and other forms of living nature can help to create much healthier, more stimulating, and psychologically restorative environments. For the present research, daylight, air, and plants have been selected as the primary biophilic elements to renovate the urban terrace house. These three elements lean more towards a direct experience of nature, while other patterns of biophilia such as the indirect experience of nature or spatial configuration of nature should be addressed. The study focused on improving energy efficiency and HNC with a BD approach which was useful in introducing BD as a retrofitting strategy; however, further studies are needed to show empirical assessments of occupants’ mental health and wellbeing. Although the research concludes by summing up the quantitative analysis of these three biophilic elements and their impact on energy consumption, their potential influence on human health and wellbeing extends far beyond that. The findings of this study encourage to take further steps to work on exploring user experience to measure the health outcomes of this approach including stress reduction, improved cognitive performance, and enhancements. As the research context is based on an urban Sydney terrace house, another potential use of this research is as a reference for upgrades to the existing terrace housing stock in Australia and throughout the world. The upcoming further step for this research team will be including other parameters of BD for investigating both energy efficiency in these houses and their impact on occupants’ health and wellbeing.