Elements Reviewed

A revision of the programme allows a reduction of architectural components, which favours cost-cutting.

Identification of components that make up the functional and technical categories:


• Interior partitions: walls

•Fluid lines: pipelines (electrical, mechanical, gas, etc.)

A rational study of the design of the habitat facilitates its execution, towards economically optimised results, as many superfluous elements are eliminated.

Some components of functional space can be reduced: corridors and partitions for semi-private spaces, while compatible spaces can be unified.

On the other hand, the free plan, as Le Corbusier's paradigm, achieves the simplicity ofrelationsbetweenusesofthebuilding,not conditionedbytherigidstructuralfunctions.

A well-coordinated structural choice can simplify internal partitioning conditions and eliminate redundant elements. (Figure 5).

**Figure 5.** Housing plan: rehearsal of the organisation of a living space–J. Guardiola.

The application of the lean methodology in construction allows for the elimination of components that do not add value to the user, which is achieved by reviewing the needs of the habitat programme in the stages from the beginning of the project [31].

#### *2.4. Construction Engineering: Price Decomposition Analysis*

The analysis of productivity improvement in construction focuses on cost elements, not including other aspects such as management, organisation or quality.

The aim of systems engineering [32] is to formalise new ways of approaching the execution of the building, with which we will understand better the advantages of industrial approaches, using its own internal logic in the design.

However, it is not only necessary to industrialise the components for their industrial manufacture but also to go further, thinking about assembly and maintenance, summarized by contemplating the full 360◦ cycle of the complete exploitation of the building asset.

Cost optimisation is studied based on the price decomposition of the construction components, following the elementary cost analytics known in construction.

As far as execution concerns, including material and assembly, the material execution cost is established, which is broken down into three elementary prices:


When analysing the construction timings for the execution process, different types of construction timings are found:


The deadline is reduced, with the shortening of work times, in each of its modalities. Therefore, the cost—through its impact of manpower and auxiliary resources—the deadline and the design will be the scope dimensions of this study.

The Elements of the Material Execution Cost: Current Situation

Current construction uses old methods and materials, and the execution is highly conditioned by manpower and weather conditions and is very dependent on auxiliary resources.

The price of a construction element consists of: manpower, materials and auxiliary resources.


On the other hand, execution times are aggravated by current on-site construction methods, affected by weathering and by a linear sequence of jobs, which accumulate their times.

More extensively, these observations are further elaborated by differentiating for the three cost elements:


Means charged directly on items, in which repercussion, according to companies, is in the range from 1 to 2% and refer to tools applied for internal finishing works, not applicable for installation works.

Special external means for lifting and external platforms and mixing and storing hydraulic materials, through which repercussion is a direct price and varies depending on the construction. These means are normally applied as a temporary rate, either as a rental or as amortisation, and are charged for the time employed, so that the term acts directly against these units.

• Material considerations:

Material adjustments to the geometry are necessary, resulting in waste: shrinkage and trimming.

Traditional materials without technological evolution, natural materials with few possibilities for development.

End caps, overlaps: special pieces to cover up or cover unavoidable defects.

Auxiliary resources required for their work: Moulds, formwork, scaffolding, platforms and cranes, etc.

They require drying and setting times due to the use of hydraulic materials, usually binders and finishing materials.

• Timeframe considerations:

> Semi-finished products, which require time for shaping, setting or drying.

Semi-finished products, which require a large amount of manpower to be produced on-site and therefore time consumed.

It is of interest to shift the manpower time from on-site to off-site production: workshop, factory or industrial factory.

Linear construction: chained times in traditional construction, with waiting times between them due to the difficulty of coordination between different trades.

## **3. Results**

In summary, the following results can be deduced from the optimisation of the lean methodology in construction.

Firstly, in the same methodological order, through the results obtained from the analysis of the combination of technologies and products used in construction (Section 2.1.1), it can be determined that incoherent construction occurs when mixing craft technologies with factory-produced materials or industrial technologies using materials made on site.

According to the analysis of technologies and design (Section 2.1.2), there are four possibilities, distinguished between the design of the habitat and the construction technology provided.


From the stages of the project, studied in the methodology (Section 2.2), there are two areas in a construction project: The design and the execution.

Of the four design stages listed in the UNE-EN 15643-3-2012, conceptual design and preliminary design would be in the architecture project group, while technical design and detail design would be in the engineering execution group.

We summarize the review of the design definition of the programme (Section 2.3) followed by the results of the economic analysis of the price in construction. It is necessary to reduce architectural elements and resources, materials, and execution time.

#### *3.1. Reduction of Architectural Elements*

The results are obtained from the analysis of the construction systems and technologies used in relation to the design.

A rationalised design of the habitats' conditions, programme, space and uses, using arguments of the original design and fundamentally detached from traditional and conservative typologies can lead to innovative solutions along the lines of the savings sought in lean construction.

The rationalisation of construction is favoured on the defining elements of the architectural space, according to three differentiated modes:

	- - Reduction of interior partitions
	- - Elimination of doors, passages between partitions.

•


• Integration of:



The rationalised design also facilitates the simplification of superfluous elements, simultaneously reducing costs and timescales.


Rational building design makes it possible to favour cost reduction by reducing the elements of architectural composition.

Rational architecture optimises spaces and construction elements.

These architectural conditions lead to saving in material resources, in the definition of habitat programs, in line with lean methodology.

Later, optimisation of construction can be completed, obtaining better production costs and further reductions in execution times.

As a specific result, applying what is analysed in the article and as an example that materialises industrialisation in housing in an experimental way, one of the authors brought together all the parameters analysed in his Guardiola–Babecka single-family house in Madrid, which has been awarded for its innovative proposal.

Figure 6 shows the interior environment of the house, in which elements of the space have been reduced to define different functions of the habitat.

#### *3.2. Cost Cutting: Resources, Materials and Execution Time*

From the construction price decomposition studied in Section 2.4, construction prices are composed of three components:


From these, the following options have been obtained within the framework of cutting and saving time and resources, along the lines of lean construction.

With industrial manufacturing, we reduce the impact of material costs; however, in order to reduce the manpower and auxiliary resources, it is necessary to think about the execution method, simplifying the deadlines.

As far as the construction method is concerned, a mechanised technical assembly allows not only less qualified manpower, with the consequent cost savings (the assemblers could be the users themselves, suitably directed and with assembly instructions), but also independence from climatic conditions, as no materials that have to set in dry weather, are involved.

The repercussion of manpower and auxiliary resources is directly related to the time used for assembly; if the period decreases, these cost components will decrease.

On the other hand, when comparing the prices of traditional materials with those of industrial origin, the price of industrial components shows a downward trend.

**Figure 6.** Interior of Guardiola–Babecka single-family house in Madrid.

They also serve to guide mechanised construction using the contents of "open industrialisation" applied to construction. In summary, the following arguments are the key to sustainable construction.


#### *3.3. Streamlined Design: Transfer to Implementation (Productivity Improvement)*

A revised design over implementation, through industrialised construction, will improve the evaluation of the final cost.

Based on the above analysis, three strategies for change are observed, for the optimisation of the cost of implementation.

#### 3.3.1. Decrease the Impact of Manpower on the Materials

The trend of the material cost for industrial products is downward, in contrast to the manpower, which is upward.

Consequently, a low manpower impact on the price of the material and a material of industrial origin with a negative trend: decreasing cost, generate a doubly decreasing total cost. (Figure 7).

**Figure 7.** Industrialisation trend (own source).

Two aspects are therefore of interest:


3.3.2. Lower Impact of Auxiliary Resources: Lower Indirect Costs

Execution based on a design with a low impact of auxiliary resources generates a decreasing cost for two reasons: the elimination of auxiliary resources with a direct impact and the shorter time charged for those of external implementation.

#### 3.3.3. Shortening the Deadline by Shortened Times

Time cuts should be sought in activities that overlap with finished products [33].



In summary, the improvement of performance towards a lean process technology in construction would be stated with the following arguments:


• Shortening of time due to reduced times. Grouping into the three defined categories of the price under construction decomposition:


The prioritisation of material costs over manpower, by means of industrialised components specialised in their function and prepared for rapid assembly on site is characteristic of industrialised construction.

Likewise, the reduction of lead times is an objective of the application of the tried and tested methods of industry in construction.

Both strategies, with the cost of resources and time, add up to the cuts that are characteristic of the application of lean construction.

As a summary of the results obtained in relation to the methodology used, the table in Figure 8 is shown.

**Figure 8.** Methodology and results obtained (own source).
