Study of Cost and Construction Speed of Cladding Wall for Lightweight Steel Frame (LSF)

Abstract

The strategic issue faced by the Ministry of Public Works and Housing, Republic of Indonesia (PUPR) is the large housing backlog, especially in the urban areas. Low-income communities earning less than 2 USD/day are found as the most vulnerable to lack of access to affordable housing. This experiment aims to find an alternative solution on building construction material in accordance with the Ministry of Public Housing regulation No. 11 of 2011 about affordable housing guidelines. The experiment was carried out on an LSF to compare four different wall cladding materials. The building area was 36 m² and the total wall cladding area was 95 m². The wall cladding materials used were metal sheet, lightweight concrete brick, gypsum reinforced cement (GRC) board, and unplasticized polyvinyl chloride (uPVC) fiber. The experiment collected data on purchases of materials to develop the S-curve and measure construction progress. Then, the work unit price analysis (WUPA) approach was carried out to simulate the labor coefficient of construction speed and its comparison to the material costs of the four wall cladding materials. The experiment on this 36 m² house found that metal sheet is the most efficient material, which took 22.7 h to cover a 95 m² wall. Later, it was followed by uPVC fiber with 46.6 h, GRC board with 59.7 h, and finally lightweight con-bricks with 85.7 h. Apparently, the metal sheet not only presented the most efficient construction time, but also provided the lowest construction cost with 115.960 IDR/m² (8.24 USD/m²). It was followed by uPVC fiber at 133.37 IDR/m² (9.48 USD/m²); GRC board at 146.91 IDR/m² (10.44 USD/m²) and finally lightweight con-bricks at 156.88 IDR/m² (11.15 USD/m²). Through WUPA, this study also found that efficient workmanship (construction speed) of the labor greatly affects construction costs.

1. Introduction

The basic infrastructure for settlements is built to meet the needs of the community equally, as well as to provide services to support programs to help the poor. Based on PUPR data, the housing backlog reached 7.64 million units as of early 2020. It consists of 6.48 million housing units for low-income people, 1.72 million housing units for non-fixed-income people, and 0.56 million housing units for fixed-income earners [1]. Based on these data, it is clear that low-income people make up the most vulnerable community in fulfilling affordable housing needs. For this reason, the concept of a micro-house has been proposed with a maximum of 36 m² of building area. A micro-house has only one bedroom, a kitchen, and a bathroom. A micro-house means more affordable construction and operational costs. The smaller the building area, the less material required, which also requires less energy.

In Indonesia, the micro-house is mentioned in PUPR regulation No. 25 of 2011 concerning guidelines for the provision of low-cost housing, which has a maximum floor area of 36 m² [2]. The criteria and requirements for affordable housing for low-income people are also mentioned in PUPR No. 10/PRT/M/2019 [3].

As a basic human need, housing requires careful planning, including socio-cultural design aspects. The physical potential is associated with consideration of geological conditions, materials of the building, and local climates. Urbanization causes population accumulation, which becomes a cluster of slum areas. It is noted that the capital city of Jakarta has the highest population density in Indonesia at 18,000 people/km², followed by Bandung with a density of 14,510 people/km². Apart from these two cities, it has been recorded that Banjarmasin, Makassar, Tasikmalaya, as well as Pontianak each have a population density of over 10,000 people/km². In some cities, this rapid urban expansion reflects a lack of planning, making service provisions such as housing more expensive and ineffective [4]. Rapid expansion certainly has an impact on the acceleration and quality of development. In addition, another aspect is utilizing different materials to preserve the designed efficiency compared to the reduction of the cost [5]. The house models are later converted into multiple single crowded rooms similar to the “capsule” settlements in the big cities. This is common in the Asian continent, where city populations are larger than two million people [6].

Generally, the project owner wants the project at the lowest cost, the highest quality, and completion at the fastest possible time. Completion of the project on time within the specified budget is an important aspect of any construction project, making construction time and speed a priority [7]. Nowadays, the crucial requirements for flexibility and simplicity of the construction process involve the main parts of the building, such as load-bearing systems, facades, interior walls, and supply systems. As the construction system developed from closed concrete to on-site cast structures, it progressed from fixed joints to “open” prefabrication. Through independent technology, the structural system configuration of a massive house could then be divided into load-bearing systems (primary construction) and facade systems (secondary construction). This system has grown with companies making prefabricated (prefab) and semi-prefabricated systems and components for on-site assembled housing [8].

In Indonesia, bricks are the most common building material [9]. There is still no standard for building walls other than brick material (clay and concrete), especially for affordable housing modules [10]. On the other hand, the development of metal prefab known as LSF has become more popular now in Indonesia because of its durability, even though the construction cost for LSF is relatively high compared to wood or concrete frame. The other benefits of LSF are (1) favorable stress and strain transfer, (2) resistance to high temperatures, (3) a lack of moisture absorption, (4) non-flammability, (5) good compressive and shear strength, and (6) better wear resistance and thermal expansion. The development of materials and construction is certainly growing rapidly [11].

With the advantages of this metal material, this study then emphasizes the use of LSF in affordable housing design. This material must be able to meet the needs of an affordable house for a backlog reaching 7.64 million in 2020. For this reason, this research conducted experiments on wall cladding as a facade system and how much it could affect the speed of construction, which can reduce construction costs. One of the significant factors that affects the increase in construction speed is the technology used in the building, aside from managerial strategies [12]. The other consideration of LSF and cladding systems for the affordable housing per unit is the limitation of IDR 150,500,000 million (USD 10,726.45) according to the regulation of the Minister of Finance of the Republic of Indonesia No. 81/PMK.010/2019 [13].

Several studies on the selection of low-cost material of wall cladding as a facade system have been carried out recently. According to comparative cost analysis by Mac-Barango (2017), buildings constructed of timber are more expensive that those constructed of sand concrete block [14]. On the other hand, Tushar et al. (2022) have investigated several different materials such as concrete, clay tiles, corrugated steel sheets, or timber coverings [15]. This research tries to ensure the lowest reasonable cost material selection. However, the method used is still from an investment perspective, which is technically inaccurate. In an investigation of brick walls in South Sulawesi, the use of traditional wall materials has a higher energy cost than using innovative wall materials. The study of innovative and different materials is therefore crucial [16]. Another study on low-cost housing found that prefabricated bamboo reinforced wall panels are cost-effective and lighter in weight as compared to traditional brick walls [17]. Previous studies indicate that some materials are cost-efficient for wall cladding. However, there are still limited studies that have examined the selection of wall cladding materials based on their application to low-cost housing, relating costs to the speed of construction.

This study aimed to seek alternative wall cladding material highly available in the market, whether in the urban or rural areas, at an affordable price for the LSF. Four different cladding wall materials (metal sheet, uPVC sheet, GRC, and brick, which is still widely used as wall material) were chosen. Brick at a U-value of 2.33 W/m² for a hot and humid climate results in inefficient energy use [18]. The comparison between those four materials later focused on the cost and construction speed in the 36 m² house model area with 95 m² of total wall cladding area. Construction costs and duration were necessary factors for decision making in the early stages of the project, including the construction of cladding walls for LSFs [19].

2. Materials and Methods

2.1. Framework of the Research

The wall cladding experiments on the model house were carried out simultaneously with four different materials, ZINCALUME^®, Hebel^®, KalsiClad^®, and Alderon RS^®. Each material was built in a different building orientation to determine the level of construction speed and cost of each cladding material. After measuring the experimental results of the four materials, the study continued by multiplying the total area of the facade to see the cladding installation duration and cost for the entire surface of the LSF. Furthermore, a simulation was carried out to compare the real measurement results with the WUPA coefficient system approach based on government regulations and the Indonesian National Standard (SNI).

The data were taken from workflow and construction cost per m² that is equivalent to the total wall area of 95 m². The materials were placed on the model house with an area of 27 m². The house model is seen in Figure 1.

Figure 2 below explains the assembly details for the whole side, the connection between the wall and the door, the wall and the window, as well as the wall bracket as a supporting structure.

2.2. S-Curve

The S-curve is a tool that can be used to work on projects and work progress by offering a picture of the relationship or the sum of the progress of the cumulative work implementation. The curve can change depending on whether the work is going according to plan or progressing faster than expected [20].

2.3. Wall Cladding Materials

2.3.1. Metal Cladding

Metal cladding wall here refers to an aluminum–zinc alloy. ZINCALUME^® is a trademark of Bluescope Steel Ltd., the largest armored steel producer in the world. In Indonesia, the company name is PT NS BlueScope Lysaght Indonesia (NSBI). The coated steel is an alloy-coated steel sheet with a composition of 55% aluminum and 45% zinc offering excellent protection, so that the steel is suitable for various building and manufacturing applications. At the same cost, ZINCALUME^® coated steel provides two to six times longer service life compared to galvanized coated steel in the same application. ZINCALUME^® coated steel has a clear resin finish that makes the surface easy to paint, preventing scratches and hand spots. At the same time, the layer of passivation ensures that its silvery surface is maintained. Its glossy appearance provides high light and heat reflectivity [21]. In this experiment, we used Lysaght Spandek^® that made from ZINCALUME^® high tensile strength steel and clean Colorbond^®. The profile of Spandek^® ZINCALUME^® from PT NSBI is shown in

Table 1. Spandek^® specification.

Profile	Lysaght Spandek®
Grade of steel	G550 (550 N/mm2 yield strength)
Effective coverage width	70 cm
Total coated thickness	0.47 mm
Base metal thickness	0.42 mm
Custom cut length	Each measurement, together with the maximum length and tolerance
Packing	In the bundle, I tone has the maximum mass of the note
Tolerances	Width + 1–2 mm, length + 1–15 mm

[22].

2.3.2. Lightweight Concrete Brick

Lightweight concrete brick has a lighter specific gravity than concrete in general, which is made from aggregate sand, cement, gypsum, water, and aluminum paste or foam agent as a developer and for the hardness of the concrete. The lightweight concrete brick used in the experiment is Hebel^®, with the following specification [23]:

• Dry specific gravity of 520 kg/m³.
• Normal density of 650 kg/m³.
• Pressure strength of more than 4.0 N/mm².
• Thermal conductivity of 0.14 W/mK.
• Species thickness of 3 mm.
• Resistance to fire of 4 h.
• The amount of light brick required per 1 m² is 8–9 pieces without construction waste.

2.3.3. Glass fiber Reinforced Cement (GRC) Boards

GRC was introduced as a new composite material, based on a cement or cement matrix and a fine filler reinforced together by adding relatively small strands of alkaline resistant glass [24]. In this experiment, the GRC refers to KalsiClad^®, a board designed for external wall cladding. The benefit of this material is its light weight and versatility that complements design flexibility for modern and contemporary solutions. KalsiClad^® 12 with a thickness of 12 mm is preferably mounted on a suitable steel frame (recommended design, dimensions, thickness, and spacing). Parameters such as wind load, dead load, building height, and earthquake risk level need to be calculated carefully. When installing the outer wallboard, the joint can be left open (visible) or closed (flush joint) by using a special sealant to withstand weather changes and moisture movement. It is recommended to use a polyurethane sealant with UV protection and a paintable sealant [16,25].

2.3.4. uPVC Fiber

This experiment used Alderon RS^®, a single-ply uPVC roof, as a wall cladding. Alderon RS^® is known for high performance at a lower life cycle cost. In addition, it is lightweight and practically opaque. There are three kinds of Alderon RS^® single ply, as seen in Figure 3 [26], with 8–9 pieces of light brick required per 1 m² without construction waste.

2.4. Budget Plan

There was a comparative measurement of the price and speed of installing wall coverings, followed by a development plan that included other requirements such as mechanical and electrical, plumbing, frames, and doors. The total budget plan for ongoing development can be seen in

Table 2. Budget plan for prefab building.

No.	Materials	Vol.	Unit	Cost/Unit (IDR)	Total (IDR)
1	Elephant GRC Board 6 mm	15	sheet	192,000	2,880,000
2	Elephant GRC Plank 20 t = 8 mm	16	sheet	69,300	1,800,000
3	Alderon RS®	30	m2	60,000	1,800,000
4	Lightweight Concrete Brick	3	m3	750,000	2,250,000
5	Spandek® 0.3	7	sheet	276,000	1,932,000
6	Aluminum Glass Door	1	unit	1,828,400	1,828,400
7	Casement Windows	3	unit	2,048,000	6,144,000
8	Big Jalousie	1	unit	5,000,000	5,000,000
9	Small Jalousie	1	unit	2,500,000	2,500,000
10	Machine Stand	1	ls	850,000	850,000
11	Dual Socket Outlet	4	pcs	29,000	116,000
12	Dual Socket	2	pcs	33,000	66,000
13	Single Socket	1	pcs	14,000	14,000
14	Electrical Installation	10	pcs	340,000	3,400,000
15	Assistive Tools:
	a. Scaffolding	2	set	75,000	150,000
	b. Artisan tools	1	ls	2,500,000	2,500,000
	c. Laburan tools	1	ls	3,500,000	3,500,000
	d. Cement	4	sack	70,000	280,000
	e. Mortar	12	sack	150,000	1,800,000
	f. Gravel	1	m3	250,000	250,000
	g. Sand	1	m3	275,000	275,000
	h. Frame Bracket	48	pcs	18,000	864,000
	i. Formwork Planks	1	m2	725,000	725,000
	j. Nuts and Bolts	1	ls	1,650,000	1,650,000
16	Wage Labor	1	ls	6,000,000	6,000,000
Total				47,883,200.00
USD 1 = IDR 14,500				USD 3394.37

.

2.5. WUPA

In this research, the calculation of the material approach was based on the Indonesian WUPA. WUPA offers guidelines for analyzing unit prices for public works in PUPR regulations [27,28]. A WUPA estimates working hours for completion of work. In addition to material prices, this analysis can also identify the impact of labor costs that are influenced by the coefficient of construction time.

The number of hours worked is represented by the coefficient of labor or the quantity of hours worked per unit of measurement [29]. This coefficient is a factor that shows the duration of the implementation of the labor required to complete one unit of work volume. Factors that affect the labor coefficient include the number of laborers and the level of workforce expertise. Therefore, labor skills have been included in this analysis. Determination of the amount and expertise of the labor follows the productivity of the main equipment. The amount of labor is relatively dependent on the main workload of the product being analyzed. The total amount of time was used as the basis for calculating the number of laborers employed [30].

3. Results and Discussion

The construction process lasted for 15 days with the installation of four different types of materials on each facade in the LSF by three laborers. The implementation was carried out at the development stage with a daily development monitoring process for accuracy to the schedule and purchase of materials. The construction started on 6 July 2020, and finished on 21 July 2020. Figure 4 below shows the S-curve for construction progress. As seen in Figure 5, the west facade was covered with Hebel^® lightweight brick, while the east facade was covered with Spandek^® ZINCALUME^® wall metal. The other facade was covered with GRC KalsiClad^® in the north orientation, and uPVC Alderon RS^® covered the south orientation.

The data collection of house construction was carried out every day, and recorded based on its development progress. The material installation for each building orientation was recorded. Hebel^® took the longest period of cladding construction of four working days, followed by GRC KalsiClad^® with three working days of installation. The uPVC Alderon RS^® and Spandek^® finished in the same duration of two days of installation. These data were later refined into detail as the S-curve based on the duration of work construction.

Table 3. The construction speed of cladding wall materials.

Materials	Surface Areas (Per m2)—A	Construction Speed (Hours)—B	m2/h = (A/B)	Labor (Person)
Hebel®	20	18	1.11	3
GRC KalsiClad®	22.361	14	1.59	3
Spandek®	30.44	7.25	4.19	3
uPVC Alderon RS®	22.4845	11	2.04	3

explains the construction speed of installing the cladding wall material.

The construction speed to install Hebel^® in the LSF took 18 h with a facade area of 20 m², averaging around 1.11 m²/h. Then, the north facade that used GRC KalsiClad^® required an installation duration of 14 h covering an area of 22.361 m², with an average of about 1.59 m²/h. The east facade, where the cladding wall used Spandek^® material with an area of 30.44 m², showed the shortest installation duration of about 7 h 25 min, with an average of 4.19 m²/h. Finally, the southern facade that used uPVC Alderon RS^® took 11 h and resulted in installation work of 22.494 m² at an average of about 2.04 m²/h. The duration of house construction indicates that Hebel^® was the material that needed the most time for installation at 1.11 m²/h. Lightweight concrete has the desired strength to be an alternative construction material for industrial building systems [31], but the construction speed was relatively longer compared to the other three construction materials. Spandek^® was the fastest cladding material to install in the LSF with a speed of 4.19 m²/h. This shows that metal wall cladding is fast track construction, especially when compared to other construction processes [32].

After obtaining the value of construction duration per m² for each cladding material, the cladding installation duration for each material could be simulated to determine the installation speed for the entire wall in the whole house with a wall surface area of 95 m². The result of cladding installation duration is shown in

Table 4. Cladding installation duration for the entire LSF surface.

Materials	m2/h—A	Simulation: Total Surface Facade Areas (m2)—B	Speed of Completion of All Facades (in Hours)—B/A	Day Assumption (if 8 h/Day) = (Speed of Completion/8 h)
Hebel®	1.11	95	85.76	10.72
GRC KalsiClad®	1.59	95	59.66	7.46
Spandek®	4.19	95	22.70	2.84
uPVC Alderon RS®	2.04	95	46.62	5.83

.

Table 4 explains that Hebel^® was the most time-consuming work, taking 85.76 h, or about 10.7 days, with working hours as much as eight hours per day. The use of GRC KalsiClad^® needed 59.66 h or about 7.45 working days to install on each facade. The uPVC Alderon RS^® required 46.62 h, equivalent to 5.8 working days. The fastest cladding installation was with Spandek^® with a working time of 22.70 h, or the equivalent of 2.8 days, to cover each building facade.

The obtained data from construction speed can be used to find the unit construction cost shown in

Table 5. Materials cost construction.

Material	Tools	Unit	Coef.	Cost of Material and Tools/m2 (IDR)	Total Cost of Material and Tool (IDR) = (Total Surface 95 m2 × Cost of Material and Tool/Unit)	Cost Labor/Day (IDR)	Total Cost of Labor (IDR) = (3 × Cost of Labor/Day × Day Assumption)	In Dollars
Hebel®		m2		75,000.00	7,125,000.00	166,985.64	5,370,258.18
	Cement	sack	0.531	15,306.5	1,454,117.5
	Sand	m3	0.081	10,041.79	953,895.00
Total					9,533,012.5		5,370,258.18
Total Budget Hebel® Material for 95 m2 Surface Simulation				14,903,270.68				USD 1050.62
GRC KalsiClad®		m2		66,666.67	6,333,333.67	133,583.22	2,989,592.46
	Nuts and Bolts	pcs	8	40,000.00	3,800,000.00
	Artisan Tools	ls	1	833,333.33	833,333.33
Total					10,966,667.00		2,989,592.46
Total Budget GRC KalsiClad® Material for 95 m2 Surface Simulation				13,956,259.46				USD 983.86
Spandek®		m2	95	55.200.00	5,244,000.00	133,583.22	1,138,129.03
	Nuts and Bolts	pcs	8	40,000.00	3,800,000.00
	Artisan Tools	ls	1	833,333.33	833,333.33
Total					9,877,333.33		1,138,129.03
Total Budget Spandek® Material for 95 m2 Surface Simulation					11,015,462.36			USD 776.55
uPvc Alderon RS®		m2	95	60,000.00	5,700,00.00	133,583.22	2,336,370.52
	Nuts and Bolts	pcs	8	40,000.00	3,800,000.00
	Artisan Tools	ls	1	833,333.33	833,333.33
Total					10,333,333.33		2,336,370.52
Total Budget uPVC Alderon RS® Material for 95 m2 Surface Simulation					12,669,703.85			USD 893.16

.

Table 5 shows the cost of cladding wall materials compared to the total budget. Spandek^® was found as the cheapest material to install in the LSF for the area of 95 m² that cost as much as IDR 11,015,462.36, followed by uPVC Alderon RS^® with IDR 12,669,703.85, and GRC KalsiClad^® with IDR 13,956,259.46. This experiment indicates that the most expensive cladding material in this research test was Hebel^® at IDR 14,903,270.68. Consideration of cost-efficiency is one of the potential factors that can influence the choice of alternative materials for wall cladding [14].

In the next stage, the WUPA simulation was carried out to see the comparison of the four materials using the labor coefficients that were determined following the guidelines for the analysis of unit prices for public works in PUPR regulation No. 28/PRT/M/2016 [27]. This simulation calculated the complete building construction of each material (each material directly calculated for the area of the entire building facade). The simulation was carried out to compare the experimental results with the multiplier coefficients that have been set by the government based on Indonesian national standards [30]. WUPA has been applied to most construction activities in Indonesia [29]. This simulation aimed to provide an overview of the relevance of its later application to low-cost housing in Indonesia.

WUPA divides the labor into four levels, namely general labor (laden in Indonesian), specialist labor, chief labor, and foremen. The price of wages for each type of labor adjusts to the level of expertise and type of specialty (masonry, carpenter, iron and steel labor, etc.).

The results of this WUPA are in line with the experimental results, thus strengthening this study’s conclusions. Hebel^® was the material with the longest construction duration, reaching 11.08 days. Spandek^® had the fastest construction speed, taking only 2.53 days to complete. uPVC Alderon RS^® was the second fastest with 4.43 days, followed by GRC KalsiClad^® which required 6.33 days (Figure 6). The results of this analysis indicate that the experimental results are relevant if applied to buildings with standard construction methods in Indonesia.

There are many factors that can affect the time and cost of a project [7]. In this wall cladding study, materials and workers were factors that could be identified. Through WUPA, costs can be divided into labor costs and material costs. According to the WUPA approach, the highest and lowest material costs correspond to the experimental results where Hebel^® was the most expensive (100.545 IDR/m²), while Spandek^® was the cheapest material (69.200 IDR/m²). In addition, uPVC Alderon RS^® was the second cheapest (93.600 IDR/m²), and GRC KalsiClad^® was the third (73.155 IDR/m²). In Figure 7, the difference in material costs did not really affect the difference in the total cost of wall cladding construction. Based on all wall cladding materials, material cost was the most expensive cost item when compared to labor cost.

The significant difference in the total price of the wall cladding work occurred due to the low labor costs of several materials. In Figure 7, the low cost of Spandek^® work was due to the low percentage of wages at only 20% (17.424 IDR/m²) of the total price of the work when compared to material costs of 69.200 IDR/m² (80%). Likewise, the labor wage for Alderon RS^®’s work was only 26% (32.930 IDR/m²) of the total price of the work when compared to material costs of 93.600 IDR/m² (74%). Hebel^® (40%) and KalsiClad^® wages (48%) were a fairly large percentage of the wage price, making the total price more expensive.

The wage coefficient for labor in WUPA is the duration of work per day multiplied by the general wage of each specialization. Therefore, it can be identified that efficient workmanship (construction speed) of the workforce greatly affects construction costs. In addition to using cheaper materials, choosing materials that are quickly built can also be an option for the government to solve housing backlog problems and provide low-cost housing [1,2]. Specific technological and managerial strategies to reduce the construction period can be another alternative solution to reduce the construction costs of residential projects, as mentioned in previous research [12]. This research opens further experiments for affordable housing building materials related to massive low-cost housing procurement strategies, the context of different locations and sources of materials, as well as health and safety aspects.

4. Conclusions

This research shows that the construction cost and workflow schedule depend on the decision of cladding wall material. Construction speed plays a key role in efficiently building an LSF home. This study found that the most efficient construction speed based on workmanship was Spandek^® with 4.19 m²/h, followed by uPVC Alderon RS^® with 2.04 m²/h, then GRC KalsiClad^® with 1.59 m²/h, and finally Hebel^® with 1.11 m²/h. The construction speed of Spandek^® was found to be five times faster than Hebel^®, which is generally still widely used for detached houses in Indonesia. The cost of construction of Spandek^® per m² is also 26% lower than Hebel^®. An LSF with Spandek^® cladding can be an alternative for affordable housing provision and a means of resolving the housing backlog for low-income people. This study also found that the speed of construction time of labor due to the selection of the type of cladding material can lower building costs.