3.1. Definitions of Categories and Attributes
In total, 23 attributes were identified from previous studies (as shown in
Table 1), and they were summarized into six categories. The six categories were energy conservation and environmental protection (
C1), construction efficiency (
C2), economic intensity (
C3), space intensity (
C4), people-orientation (
C5), and total process control (
C6). Category
C1 is concerned with environmental stewardship and category
C5 is focused on social inclusion. The remaining categories, i.e.,
C2,
C3,
C4, and
C6 are related to financial viability, which is linked to the economic aspect of the site layout. The six categories and the attributes they covered are explained in detail as follows:
Category 1 (C1): Energy Conservation and Environmental Protection
The green construction site layout should be arranged in accordance with the requirements of energy conservation and environmental protection [
59]. The site manager should design the construction site with goals of preventing soil erosion, avoiding water pollution, decreasing air pollution, adopting effective disposal measures for construction demolition waste, and conserving energy.
Lu and Cai [
57] and Xu and Song [
58] discussed the characteristics of construction site layouts and the arrangement of temporary facilities, then proposed a list of the relevant attributes. This involved an energy optimization ratio (
A11), utilization ratio of resource saving facilities (
A12), effectiveness of sewage disposal and solid waste collection (
A13), green coverage ratio (
A14), and effectiveness of dust control (
A15), which are explained as follows:
A11: Energy optimization ratio
This ratio is used to evaluate the utilization of cleaner energy and renewable energy, as shown in Equation (1).
A12: Utilization ratio of resource saving facilities
Facilities for resource saving, e.g., water and electricity saving, need to be set up within the construction site. Equation (2) is used to calculate the proportion of facilities devoted to resource saving to all temporary facilities needed during the process of construction.
A13: Effectiveness of sewage disposal and solid waste collection
As pointed out by Huo et al. [
51], adequate measures to reduce water pollution should be undertaken on construction sites. Controlling water pollution was also identified by Tam et al. [
60] as a requirement for green buildings. There are sewage disposal facilities and solid waste collection facilities on a construction site to prevent on-site pollution. In addition, some facilities are needed for the centralized treatment of solid waste. This attribute is to monitor whether there are appropriate sewage disposal measures, facilities, and solid waste collection procedures on the construction site, which can be calculated by Equation (3).
A14: Green coverage ratio
Green coverage ratio is the green area occupied to the total area of the construction site, which can be calculated by Equation (4).
Sufficient green space was one of the five most important factors in the site layout planning of green buildings identified by Huo et al. [
51]. However, their research did not provide any quantified standard to measure what “sufficient” means. The green coverage ratio can provide a quantified measure for this attribute.
A15: Effectiveness of dust control
Dust and air emission mitigation was the third most important item identified by Huo et al. [
51] in the site layout planning of green buildings. The attribute of dust control effectiveness monitors whether the particulate matter generated is in closed storage, and whether there are appropriate facilities for reducing dust. Dust may also be controlled by setting up hoarding surrounding a construction site or arranging a water spray device on the dust-generating area of the site.
Category 2 (C2): Construction Efficiency
A green construction site layout needs to satisfy many requirements for increasing construction efficiency, including producing construction outputs in a timely manner, placing temporary facilities at appropriate locations, avoiding material re-handling, and shortening on-site transportation distances [
61]. According to the research on optimizing construction site facilities’ layout to improve construction efficiency [
62,
63], the following attributes were considered:
A21: Effectiveness of temporary road layout
This attribute is used to measure whether a circumferential road has been installed at the construction site to prevent internal traffic congestion. A good road layout allows relevant temporary facilities to be directly linked together, such as storage buildings and yards.
A22: Layout integration of facilities
Using a similar principle as for road layout, related facilities such as the material storage yard and workshop, or rebar bending yard and rebar laydown area, should be placed close to each other. A well-integrated facility layout can provide efficient space usage.
A23: Effectiveness of temporary drainage facilities
Effective temporary drainage facilities are vital to construction efficiency, as the ponding area in the rainy season may block vehicle access to and circulation within the construction site. It is necessary to set up drainage facilities on both sides of the traffic road.
A24: Location rationality of machinery
All construction machinery should be arranged to have easy access to other machinery and satisfy its functional requirements. For example, the service radius for the tower crane should cover the entire construction area.
Category 3 (C3): Economic Intensity Degree
Being economically intensive is an important requirement for construction management and a basic element of sustainable development. In order to reduce transportation costs, temporary facilities should be placed in appropriate locations for the effective movement of personnel, materials, and equipment [
64]. According to the principle of systematic layout planning [
65] and more recent research by Li and Liu [
66], Aboutaleb et al. [
16], and Wu et al. [
67], the following attributes can be used to measure the degree of economic intensity:
A31: The ratio of existing resource utilization
Installation, re-establishment, and removal of facilities will lead to greater construction expenditure. In order to reduce construction cost, existing buildings and roads on the site should be reused to avoid additional expenditure during various stages of the construction. This dynamic attribute can be evaluated by Equation (5).
A32: The cost saving of temporary facilities
In order to reduce the construction cost of temporary facilities, it is beneficial to take the whole project into account when assigning temporary facilities. It would be best to meet the basic standard of the mandatory national standard and requirements of construction quality and safety.
A33: Total transportation cost saving
Total transportation cost saving is the sum of transportation cost savings in different project stages. The dynamic attribute is the ratio of cost saving for resource transportation in comparison with the budgeted cost, as shown in Equation (6).
Category 4 (C4): Space Intensity
The space intensity category measures the efficient use of space. Ideally, the smaller the construction area occupied by temporary facilities, the more space is left for facility movement and layout changes [
29]. Li and Liu [
66], Abotaleb et al. [
16], and Chakraborty and Banik [
68] studied the optimal layout design and presented attributes for space intensity. The attributes are explained as follows:
A41: The flexibility of site space
The construction site layout needs to respond to the construction process. In order to facilitate efficient construction operations, there should be unused or lightly used space left to allow adaptation to any changes made on the construction site.
A42: Degree of space utilized
This attribute measures whether site space is used in efficient manner, which is a dynamic attribute that changes with different project stages.
A43: Average proportion of site occupied by site facilities
The average proportion can be expressed by Equation (7), where i represents different stages and n is the total number of construction stages.
Category 5 (C5): People-Oriented Principles
The people-oriented category for green construction layout considers the degree of satisfaction labor and staff display while on site, and includes attention to the arrangement of fire facilities for the health and safety of the employees [
69]. Human health protection and construction noise mitigation have also been identified by Huo et al. [
51] as two out of the five most important items in site planning of green buildings. Health protection and noise mitigation are related items, as noise has detrimental impacts on health. The five attributes identified by Chakraborty and Banik [
68], Sjøbakk and Skjelstad [
62], and Cambron and Evans [
70] under the people-oriented category were considered appropriate and are listed below:
A51: Noise emissions
Noise pollution on site cannot be ignored during construction, as it is usually the main reason for neighbor complaints and has an impact on human health. The evaluation of noise emissions is confined to the main structure stage, owing to the operation of a great quantity of construction equipment. The structure stage accounts for a large proportion of the whole construction project. This attribute measures the difference in decibels between actual construction site noise and the national standard of environmental noise.
A52: Effectiveness of noise reduction measures
This attribute measures whether low-noise and -vibration equipment used in the construction operations and whether there actions have been taken for sound insulation and vibration isolation.
Noise not only causes hearing damage, but also leads to high blood pressure, heart disease, and other diseases [
71]. More seriously, noise distracts workers, and this can lead to a variety of safety concerns [
72]. Thus, the attributes of
A51 and
A52 are included in category
C5.
A53: Employee satisfaction
Welfare facilities, such as canteens and labor huts, must be properly placed to bring convenience and satisfaction to the employees.
A54: Separation of living area from construction area
Living areas should be separated adequately from construction areas to guarantee the health and safety of construction workers.
A55: Status of safety management measures
The construction site layout should be designed according to the requirements in the safety regulations or safety standards, such as installing safety warning signs and fire hydrants, and inflammable and explosive material storage areas should be separated from the boiler room. This attribute is used to evaluate the status of safety management on construction site in compliance with the safety regulations and standards.
Category 6 (C6): Total Control of Process
The construction site layout varies with the stages of the construction process, since different site facilities and construction methods are needed for different construction stages. A green construction site layout plan should consider the dynamic nature of site activities and prepare a balanced plan for different construction stages to guarantee smooth transitions across the entire construction project period [
73].
In order to measure how adaptive a green construction site layout can be to the different construction stages, Abotaleb et al. [
16] and Chakraborty and Banik [
68] proposed the following attributes.
A61: The ability of the site layout to respond to the construction process
This attribute evaluates whether the site layout is capable of adjusting the location of facilities in a timely manner in order to satisfy the requirements of a particular stage. Professional construction experts could evaluate this attribute using their own experience, since they are familiar with the whole construction process.
A62: The effectiveness of the resource schedule plans
The labor plan, material laydown area, and equipment should be arranged bearing in mind the different construction stages to avoid congestion in the construction area and ensure adequate space to store and process construction material.
A63: The efficiency of the transition of operational equipment
A good site layout plan can ensure efficient equipment transitions between different construction operations and stages and minimize the transition time.
3.2. Hierarchy Structure for a Green Performance Evaluation System
Six categories cover the three dimensions of sustainability: environmental, economic, and social aspects. Energy conservation and environmental protection (C1) are clearly related to environmental sustainability, and category C5 is focused on social inclusion. The four remaining categories, i.e., C2, C3, C4, and C6, are related to financial viability. The construction site layout plan involves the effective utilization of space (category C4) to smooth and facilitate construction operations (category C2 and C6) and satisfy management goals. In this case, construction cost reduction (category C3) is a critical requirement for construction management.
Twenty-three attributes were developed for the six categories, and the hierarchy in the green performance evaluation system is shown in
Figure 1.
In the following section, the requirements of categories and the definition of attributes are introduced to clarify the classification of attributes.
3.3. Attributes Classification
The attributes in the green performance evaluation system were divided into qualitative and quantitative categories and are summarized in
Table 2.
The quantitative attributes can be determined by an actual value, which are calculated using records and data in the construction site layout; they are objective attributes. However, the qualitative factors can only be evaluated in a subjective way according to personnel knowledge, experience, and preferences. In order to establish the caliber of green performance of the construction site layout, a standard evaluation rule for the qualitative and quantitative attributes should be established.
As the construction site layout evolves with construction progress, some attributes, such as the flexibility of site space (A41), the degree of utilization of site space (A42), and the effectiveness of the resources schedule (A61) are dynamic and will need to be evaluated with the changing construction site layout plan in different construction stages. Therefore, in the case study, more than one site layout plan was adopted to show the impact of these attributes on the green performance of the layout.