Reduction of Embodied Energy and Construction Cost of Affordable Houses through Efficient Architectural Design: A Case Study in Indian Scenario

Embodied energy and cost of construction of any building depends upon the consumption of resources, more specifically construction materials. In housing clusters, the spaces provided for horizontal and vertical circulation of occupants such as corridors and contribute in the built-up area of individual unit without any increase in the usable/carpet area. &us, an efficient architectural planning of common circulation spaces plays a major role in lowering the built-up-to-carpet area ratio of individual housing unit in clusters.&ismay, thus, result in lesser embodied energy andmaximum area availability for occupant usage. In the present study, 30 clusters of Indian affordable housing units (IAHUs) of similar typology and different architectural designs are analyzed. &e built-up and carpet area of each IAHU are estimated, and the ratio of the built-up to carpet area is calculated. Detailed estimates of construction materials for each IAHU is prepared, and cost of construction and embodied energy is calculated. &e calculations of embodied energy and construction cost are done for major construction materials, viz., cement, steel, bricks, sand, and coarse aggregate and compared with different built-up-to-carpet area ratio. &e study of IAHUs concludes that a variation of 1.30 to 1.62 in the built-up area-to-carpet area ratio results in variation in construction cost (INR 13,425.00 to 20,138.00 per m carpet area) and embodied energy (4–6.5GJ per m carpet area). Analysis suggests that the IAHU with a lower built-up-to-carpet area ratio exhibits reduction in the cost of construction and embodied energy simultaneously.&us, an efficient architectural design plays a major role in improving the sustainability of IAHUs and built-up-to-carpet area ratio is an important indicator of sustainability.


Introduction
Life cycle energy of buildings is associated with different phases of buildings, which includes embodied energy (EE), operating energy (OE), and energy required for demolition and disposal. Of these, major phases of energy consumption are construction or preoccupancy phase (EE) and operational or occupancy phase (OE) [1][2][3][4][5][6][7][8][9][10]. EE of the buildings is the sum of all energy incurred on sourcing, procession/ manufacturing of building materials, and transportation of building materials including construction equipment and labor, energy incurred for onsite construction, and all secondary and tertiary process. Life cycle energy of buildings due to demolition, disposal, and transportation of material and use of construction equipment is very less, that is, 1-2% [11][12][13][14] and 0.7% [15][16][17], respectively. e energy in construction activities is negligible due to the predominance of manual labor in Asia [12,13,16,18]. Furthermore, the energy usage pattern in buildings depends on many factors. Low-rise and high-rise buildings, load bearing, RCC framed structures or hybrid construction, building use, buildings with different construction materials/envelopes/typologies, and so on, have different patterns of energy consumption during its lifetime [16,19,20]. In conventional buildings, OE is more predominant, whereas in energy efficient buildings, EE becomes significant [2,15,[21][22][23][24][25][26][27][28][29]. ere are two approaches for reduction of EE of any building: first, using low embodied energy construction material and second, by material resource conservation. e material resource load can be expressed as quantity of material used per unit of area. In housing clusters, the built-up area of an individual house is the addition of its own carpet area, external wall area in plan, and proportionate built-up area derived from common spaces and utilities. e utilities may be lifts, staircases, corridors, and so on. e houses intended for economically weaker sections (EWSs) have a low built-up area, and thus, material resource conservation becomes crucial for reducing its EE. Construction materials, which have high embodied energy and high cost, are used minimally in housing for economically weaker sections [3,7,12,28,29], further reducing its embodied energy (EE), life cycle energy (LCE), and construction cost (CC).
In India, Pradhan Mantri Awas Yojna (PMAY) [30] is an ambitious social housing scheme carried out by Government of India and is being implemented by its Ministry of Housing and Urban Affairs (MoHUA) for providing affordable housing with basic amenities to the masses on pan-India basis. is mission addresses housing shortages among the economically weaker sections (EWS) including slum dwellers by ensuring a permanent house to all eligible households. e mission supports construction of houses of about 30-60 m 2 carpet area with basic civic infrastructure for the EWS population. e requirement of OE in IAHUs is limited due to the inability to afford heating and cooling systems due to financial issues of the stakeholders. In this scenario, EE becomes more significant for improving sustainability index of the Indian affordable housing [3,7,9,12,30,31]. Life cycle energy (LCE) of a building is expressed as energy consumed per unit area. In this expression, the denominator may be either the built-up area or carpet area. erefore, any building may have two boundary values of LCE: higher limiting value with carpet area and lower limiting value with built-up area, unless the built-up and carpet areas are equal. Since the carpet area is the actual usable area available to occupants, the LCE value with the carpet area in the denominator becomes significant.
us, the LCE values reported with the built-up area in the denominator may give a false interpretation of lower embodied energy or LCE of the buildings. In other words, the ratio of the built-up to carpet area is a major indicator in expressing the embodied energy and cost indexes in sustainable buildings.
is indicator becomes even crucial in buildings, where energy efficiency is defined by primarily construction material conservation, such as housing for EWS. Efficient architectural design and judicious planning of common circulation areas and other spaces in buildings help to reduce requirement of construction materials, thus reducing EE and CC. e present paper investigates the effect of the built-up-to-carpet area ratio on EE and CC by analyzing 30 case studies of housing for the EWS in the Indian scenario.

Literature Review
In literature, life cycle energy analysis (LCEA) for different types of buildings has been carried out and values of LCE, EE, OE, and CC are reported for per unit area of the buildings [2-9, 16, 19, 20, 32-37]. e prescribed LCA/ LCEA values in the literature may vary too much due to different system boundaries and typologies of the buildings, and thus, it is reflected in the energy footprint per m 2 of area [8,13,23,26,37]. e type of structures (framed/load bearing/hybrid) [28], height [29], occupancy type (Apartment/individual/population), circulation spaces, built-up area [38], etc., have different requirement of construction materials. Reducing wall thickness and designing circulation spaces efficiently will not only increase the carpet area of the building but also reduce demand of construction materials, which, in turn, reduces CC and EE of the buildings. It has been observed in literature that while reporting LCE values, the ratio of the built-up area and carpet area varies from 1 to 1.45.
Pacheco-Torres et al. [39] analyzed a three-storey house in Spain with a built-up area of 313.13 m 2 and total carpet area as 260.86 m 2 . e results were reported on an energy per unit area basis taking the built-up area in the denominator. Paulsen and Sposto [4] analyzed houses with mass in Brazil for an area of 48 m 2 ; however, as per available drawings, the carpet area is 43.40 m 2 . is is 1.10 times higher than the carpet area. Das [32] have analyzed housing complexes in India for energy conservation, with apartments of different built-up areas. However, the author assumed that the same set of staircases and lifts can be fitted into any design, which may not be correct. Pinky Devi and Palaniappan [3] have analyzed an affordable, single-storey house in India with an area of 32.5 m 2 , but as per architectural drawings, the carpet area is 22.32 m 2 , resulting in a ratio of 1.45. Oyarzo and Peuportier [33] have analyzed houses in Chile, with an area of 32 m 2 , a carpet area of 32 m 2 as per drawings, and the ratio as 1. Embodied energy values of low-rise Indian affordable housing have been compiled by Bansal et al., [20] as 1.6-5.0 GJ/sqm of plinth area. EE can also be reduced using alternative construction materials and physical planning. Bansal et al. [7] & Stephan and Athanassiadis, [40]. Antonín et al. [41] have studied strategies for reducing embodied energy and CO 2 emission through efficient designing building elements, structural system, and passive systems of houses. Vukotic et al., [42] have presented ways for optimization of energy in different stages of building, primarily by construction materials. Worth et al. [43] have optimized a roofing system based on EE and cost.
From the literature, it has been observed that as the height of buildings increases, the circulation space requirement increases, thus increasing the built-up-to-carpet 2 Advances in Civil Engineering area ratio. Bansal et al., [44] carried out a study to find the variation in the carpet area and built-up area for different heights of buildings from single storied to 30 storied and found that for the same carpet area, built-up areas increased from 32% to 148% as the height of the building increases [20,44]. e results are presented in Figures 1(a) and 1(b) below. e increase is visualized due to the increase in provision of floor area for circulation spaces for staircases, lifts, elevator, and so on in high-rise buildings.
However, in the studied literature, the discussion on change in LCE, EE, and CC values due to difference in the built-up-to-carpet area ratio is not highlighted.
us, an integrated approach toward reducing EE and CC of a building design efficiency in terms of the built-up area-tocarpet area ratio is not addressed in past studies. In the present study, authors investigate the effect of the built-upto-carpet area ratio on EE and CC of buildings specifically for EWS housing projects.
irty buildings from Indian affordable housing units (IAHU) are identified and analyzed. Buildings are analyzed for their architectural designbased design efficiency in terms of the built-up area-tocarpet area ratio. EE and CCs have been calculated per m 2 of built-up and carpet areas to choose the optimum architectural design with the least EE and CC. is will provide an integrated approach to designers about the design efficiency of architectural designs, in terms of EE and CC, based on the ratio of the built-up to carpet area. e design efficiency of architectural design will help in analyzing sustainable buildings by the finding optimum range of ratio of builtup-carpet area that will result in minimum construction cost and embodied energy.

Methodology
In the present study, 30 representative Indian affordable housing units (IAHU) from PMAY have been selected for this case study. ese buildings have been designed according to the guidelines of PMAY and the technical specifications of National Building Code of India (NBC) [45] and are located in different parts of country. ese 30 IAHUs have ground plus two storeys with a load-bearing structure. Each IHAU is designed as cluster consisting of 2 to 12 apartments per storey. e service life of buildings in India is about 50 years [28,31]. e plan for a typical IAHU is presented in Figure 2. Table 1 presents specifications of IAHU. While designing the IAHU, the safe bearing capacity of soil is taken as 11 MT/m 2 at 1.0 metre depth from natural ground level, seismic zone III, and basic wind speed 47 m/s as per the NBC. e architectural plan in terms of length of walls, openings, arrangement of rooms, and provision of common spaces in a cluster play a major role in building construction. For the same built-up area, if the number of internal walls or the area of staircases, corridors, and so on increases, the effective or usable area (carpet area) will reduce and vice versa. is change is reflected in the consumption of construction materials or bills of quantity as well. e quantity of construction material thus varies per unit of the built-up/ carpet area in different architectural designs due to the different arrangement of walls and spaces. Since reinforcing steel, cement, fired clay bricks, sand, and coarse aggregates are the main contributors in construction cost (CC) and embodied energy (EE) [46][47][48]; any change in the quantities of these construction materials is reflected positively or negatively in CC and EE. us, an efficient design may lead to reduction in CC and EE, and the built-up area-to-carpet area ratio plays a significant role in the overall CC and EE of buildings. Figure 3 indicates the interrelation of these parameters. e present study investigates and quantifies effect of the built-up area-to-carpet area ratio on CC and EE of 30 case study IAHUs. e IAHUs are designated as A1 to A30 and arranged in the ascending order of the built-up area in Table 2, which presents the built-up area and carpet area values of the selected IAHU. As evident, the built-up area-tocarpet area ratio changes from 1.30 to 1.62 due to the change in architectural design. e bill of quantities for the IAHU in this study has been prepared. Since cost estimates prepared by government agencies are based on the schedule of rates published by the Central Public Works Department (CPWD) and Delhi scheduled Rates (DSRs) 2016 [49], the cost of construction materials is adopted from these publications and presented in Table 3.
Similarly, the EE value for 30 IAHUs based on major construction material consumption was calculated. Since the embodied energy of a material depends on a variety of factors such as raw material (local/imported), processing (manual/mechanical), transportation, and so on [50][51][52], the embodied energy values have been taken from the Indian scenario [9,50,52,53] as well as international sources [54]. ese values are presented and compared in Table 4. ese values show large variations, which is primarily due to the factors discussed earlier. To represent the local condition, in this study, the EE values from the Indian scenario are considered for the calculation of EE of the case study IAHU.

Results and Discussion
Construction materials are major contributors to CC and EE in any building construction. In the present study, the bill of quantity for each IAHU is tabulated and the cost of construction is calculated based on consumption of construction materials. Cost of construction includes materials, labor, electrical, plumbing, and so on completely. As per the CPWD 2016 [55], the cost of construction materials is about 36%, cost of labor is 30%, PHE/electrical works is 7%, hire charges of tool and plants, consumables and miscellaneous is 12%, and contractor profit is taken as 15%, making a total of 100%. Table 5 presents a summary of cost of construction for 30 IAHUs and indicates that the cost of construction varies between INR 13,425.00 to 20,138.00 per m 2 of carpet area. It is seen from Table 4 that the built-up area varies from 1.30 to 1.62 of carpet area due to different architectural designs with the same specifications and the same functional requirements. is is reflected in the construction cost of the IAHU. e total cost of major construction materials such as fired clay bricks, cement, steel, sand, and aggregates is Advances in Civil Engineering 3 calculated from the bill of quantities for each IAHU and is tabulated in Table 6 with the per unit carpet area. It is also observed that cement, sand, aggregate, steel, and brick together account for 35%-38% of the total cost of construction that varies from INR 4,697.00 to 7,433.00 per m 2 on the carpet area basis with brick as the major contributor. It is evident from Table 6 that in the load-bearing structure, brick, cement, and steel contribution is in the descending order of the total cost of building. us, reducing consumption of these construction materials reduces the overall cost of construction.
Similarly, EE of major construction materials has been calculated and presented in Table 7. For calculation of embodied energy, the average values of EE indicated in Table 4, for respective construction materials has been used. It is observed that fired clay bricks are major contributors in the total EE of IAHUs. us, a good architectural design with lesser volume of main and interior walls plays a major role in reducing EE of the IAHU.
From the results, it is observed that the minimum cost of construction and EE is corresponding to built-up-to-carpet area ratio 1.31 for IAHU, which is design no. A22 and the            is study shows that the construction cost, cost of major construction materials, and EE are directly proportional to the built-up-to-carpet area ratio. e more the ratio, the more inefficient design would be. e cost of construction materials varies from INR 4,697.00 to 7,433.00 per m 2 of carpet area, which is about 35%-37% of construction cost per sqm of carpet area. It is seen from this study that architectural designs have a major bearing on construction cost and embodied energy of the buildings; as in an architectural design, spaces are arranged in a particular way, which results in different placement of walls and    circulation areas. is results in different built-up areas for the same carpet areas in different architectural designs. To reduce the overall cost and EE of any building, its architectural design must be efficiently planned so that the builtup-to-carpet area ratio is at the minimum.

Conclusion
As per the norms of the Government of India, a carpet area of 30 m 2 to 60 m 2 is proposed for economically weaker sections and low-income groups. e total usable area (carpet area) per IAHU is calculated by subtracting the area consumed in the circulation spaces plus the area occupied by external walls from built-up areas. Increasing the area in common or circulation spaces reduces effective usable or carpet area per IAHU in a cluster, which increases consumption of construction materials. is results in an increase in construction cost and embodied energy of IAHUs.
us, the built-up-to-carpet area ratio plays a major role in the sustainable and affordable design of IAHUs. is can be achieved by an efficient architectural design having more carpet area in a given built-up area, keeping the built-up-tocarpet area ratio minimum. e embodied energy of these houses is estimated as varying from 4 to 6.5 GJ/sqm of carpet area and with the built-up-to-carpet area ratio varying from 1.3 to 1.62; these values are 30%-62% higher on built-up area's basis, which is in line with embodied energy of lowrise Indian affordable houses (1.6-5.0 GJ/sqm) calculated by many researchers. is study is based on the analysis of 30 numbers of low-rise load-bearing designs of IAHUs of the most common typologies. In designing sustainable and affordable housing, it is essential to choose an efficient architectural design, which has the least variation in the ratio of the built-up and carpet area so that its CC and EE are minimized. Much information is available on construction materials about their cost and embodied energy, but very few researchers have worked on the efficiency of architectural design to design sustainable buildings. Efficient architectural designs are essential as 30% to 62% of the carpet area goes into external walls and circulation spaces, resulting in variation in embodied energy by 62.5% and construction cost by 50%, which can be optimized in sustainable affordable housing. e built-up-to-carpet area ratio can give a true picture of the efficiency of affordable housing.

Abbreviations
Carpet area: Floor area of a building within external walls Load-bearing construction: System of building construction, in which masonry/walls are the main load transferring members RCC: Reinforced cement concrete RCC framed construction: System of building construction, in which RCC columns and beams are the main load transferring members M25: Cement concrete, whose 28

Data Availability
All the data used in this work are available from the corresponding author upon reasonable request.

Conflicts of Interest
e authors declare that they have no conflicts of interest.