**4. Discussion**

*4.1. Coherent Building System*

Construction is improved with a complete and coherent building system that integrates: design, project and execution.

As described at the beginning, through the analysis of construction design, integrating design and execution, opportunities have been found to improve productivity in building, justified in lean construction.

In small-scale projects, single-family or block dwellings, small office and commercial buildings, the only technician to develop the design is the architect, whose work usually ends with the basic level of the project, which is specified in the premises of the habitat, developed according to concepts of space organisation, and respecting the legal ordinances and regulations that affect it.

The detailed project for the execution remains in two contributions—the structure and the installations—without going deeper into the constructive analysis, which is taken for granted according to the traditional rules of construction.

In larger projects, the work is complemented by detailed engineering, developed by engineering specialists, outside the architect's organisation, with no other relationship than that of external professional collaboration, normally occasional and without continuity.

However, frequently, even in these cases, either the engineering does not understand the architect's design orientation, or the object of the architect's design is far removed from the parameters of the technical project.

In any case, the execution is not usually developed in-depth, analysing techniques, products and components, which rationalise the construction.

#### *4.2. Economic Parameters*

An analysis of the economic parameters was carried out where it was possible to identify cost and time reductions, based on the criteria of the construction itself, without including other disciplines:

	- - Delays due to waiting times between trades, which are reduced or eliminated altogether.
		- - Avoid drying and setting times for hydraulic materials.
		- - Transferring time from site to "workshop".

New architectural optimization arguments have also been included to eliminate components of the habitat programme, which can be grouped into two categories:

1. Simplification of components:


These components define the functional programme of the habitat, which we have seen above, and are basic architectural elements at this level of design, principal elements, and involve both spatial and structural functions.

	- • Furniture, in the compartmentalization with cupboards and shelving.
	- • Reduction of cladding and transit spaces: walls and ceilings and cladding: structural elements: concrete and steel, leaving their qualities visible.
	- • Exposed installations, elimination of installation aids: chases and skirting boards.

On the other hand, these components are of more secondary application for a design level of definition of shapes and textures, more definitions for style than as a functional program.

Performance improvement, towards a lean construction process technology, is summarized:

	- • Decrease the impact of manpower on materials.
	- •Lower repercussion of auxiliary means: lower indirect cost.
	- • Shortening of time due to reduced times.

However, it would be necessary to quantify all these strategic lines, both those of an architectural nature and those of an economic nature, according to the cost and time of construction.

It would also be necessary to obtain a design basis combining the two strategies mentioned, a new method that would allow, in a systemic way, to align with these proposals and which justify a cost reduction on the final construction.

It is difficult to determine the reduction; it depends on the solution adopted, and it is not possible to give a general reduction parameter.

#### *4.3. 3C System: Compatible Components in Construction*

As a possible continuation of this article, we propose a design method that allows, within the discipline of design, to integrate the contemporary building into the current industrial environment.

This methodology is developed within systems engineering, adopting concepts and laws from its epistemological field.

Successful implementation of the lean concept as a sustainable approach in the construction industry depends on the identification of critical factors [34].

A system that focuses on industrialized components to obtain the two properties that we have obtained from the previous analysis. (Figure 9).

**Figure 9.** 3C system composition mock-up. J Guardiola A.

To this end, we will seek application in the discipline of systems theory, specifically systems engineering, to find design arguments that achieve the objectives along the lines outlined above.

The model shows how strategic implementation facilitates the integration of lean construction and sustainable construction from the design phase to the finishing phase of a project [35].

A system that we call the 3c system: Compatible Components in Construction.

This proposal brings together these improvement objectives, using the criteria of sustainable construction through the so-called "3C system: Compatible Construction Components". This system involves the use of prefabricated modules, factory materials and assembly using standardised joints. (Figure 10).

**Figure 10.** CAD model of the façade component of 3C system composition. J Guardiola A.

A design solution that will seek, first, to formalise its application principles, and then to contrast with traditional solutions, its optimisation operability, as a defined tool of lean construction [36]. (Figure 11).

#### *4.4. Lean Construction*

Finally, the lean construction methodology is confirmed as a tool that contributes to the sustainability of buildings [37] for the following reasons based on ISO 20887 [38]. This standard specifies aspects of sustainability in the field of recycling, dismantling and reuse in the field of construction.

**Figure 11.** Drawing of the façade component of 3C system composition and connections to other components. J Guardiola A.

The following arguments stand out for the sustainability of the construction:


• Cyclical economy: buildings, components and materials must be used for continuous reuse.

The first two are included in the analysis of cost elements, carried out previously, the third one is considered below, using the above-mentioned ISO 20887 standard as a reference.

This standard, ISO 20887: Design for disassembly and adaptability of buildings and civil engineering works, is structured on specific contents that determine design aspects to be applied to construction assets, of which we highlight the following.

Lean practices show the reduction of environmental, economic, and social impacts during the construction phase, and increase sustainability parameters in the development of projects [39].

Standardisation (seiketsu standardize) facilitates transport, storage, and reuse. It makes it possible to include the aspects of adaptability and simplicity.

Standardisation avoids waste, adapts to logistical, ergonomic, and functional requirements.

The constructive design is favoured by standardisation aspects such as: components, dimensions, and modules.

Simplicity, as a design principle, reduces the number of elements, components and materials to the minimum required to perform the intended function.

This includes limiting the use of decorative details, minimising the number and diversity of materials.

One of the objectives is the elimination of waste in disassembly, aided by the simplification of tools and techniques required for disassembly. This directly improves the appearance of cleanliness (seiso shine), eliminating debris and debris and keeping the workspace tidy.

Lean methodology seeks the reduction of "waste". This "waste" can also be assumed in construction in different categories [40]:


By increasing the functions that material provides, it contributes to dematerialisation in construction, thus reducing the problem of material layering.

Order and systematisation in construction is a fundamental aspect of the work. Seiton, set in order, organises, and places the necessary materials according to the order of use by zones on the construction site and establishes the areas where these stockpiles, auxiliary resources, reusable material, and rubble, etc. are to be made.

Independence is particularly important for the "levels" of the construction, related to the temporal prediction of the function of each component.

The main levels that can be identified are:


The challenge is to achieve independence without compromising the functionality of systems and materials in their integration.

Independence facilitates the separation and disconnection of building systems, favouring spatial and functional adaptation and the reuse of systems. In addition, disassembly shall allow materials and components to be removed without disrupting other components or materials.

The levels of a building shall be differentiated to facilitate adaptation and dismantling. Separating levels of long-life components from those of shorter life facilitates retrofitting and reduces the complexity of dismantling.

Durability is defined for an asset or component as the ability to perform as required for its specified period of time without the need for repair or modification.

Durability and adaptability are close concepts.

To minimise maintenance or repair, materials with a long service life should be used. In other cases, shorter life designs are required, with easy disassembly and consequent re-use of components and materials.

The accessibility of components, especially connecting elements with a shorter service life, facilitates replacement and avoids damage to adjacent elements of the assembly. Another advantage is that disassembly of these components from the building sometimes does not require special equipment.

The requirement for easy access to connectors can have an aesthetic impact on the building design.

The discipline of improvement is necessary; shitsuke sustain propose maintenance, sustaining process to create the habit, explaining to the team how it works and how it is maintained.

An open construction, where parts are interchangeable, allows for modifications in the implementation without significant repercussions.

All in all, these reasons contribute to the fact that "Lean Construction not only contributes to creating the economic value to the construction process but can also contribute to promoting the environmental and social issues" [41] and meets several points of the objectives for sustainable development (OSD):

With the development of new building techniques [10], lower consumption of material and energy resources and the planning of the building life cycle, more sustainable cities and population centres can be achieved [12].

Controlling resources and reducing waste through Lean techniques will lead to responsible production and consumption [13].

## **5. Conclusions**

In order to improve productivity, in the current situation of construction, the transfer to industrialisation is essential.

With a complete building system, integrated by design, project and execution, the construction is improved and more sustainable.

It can be determined that incoherent construction occurs when mixing craft technologies with factory-produced materials or industrial technologies using materials made on site. (Figure 1).

Incoherent construction is also made when advanced technologies are used with a traditional design or when traditional techniques are combined with a rational design. (Figure 2).

A lean analysis in construction must be based on the order of stages established in construction projects, as set out in the UNE-EN 15643-3-2012. Of the four design stages, conceptual design and preliminary design would be in the project architecture group, while technical design and detail design would be in the execution engineering group.

The habitat system must correspond to new modes of construction, which respect the arguments obtained by the new type of buildings.

Reducing the cost of construction is of grea<sup>t</sup> importance, both from an economic and a social point of view.

Attempts to reduce the cost of traditional manual labour methods by introducing more rigorous organisational techniques have so far produced only a little progress.

On the other hand, numerous studies, both technical and sociological, have reviewed the human habitat, looking for more rational solutions, which have an impact on space-saving.

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

The new objective, uniting both trends, is to seek construction by means of industrial production methods with spaces that meet the real needs of the habitat.

Industrial production must necessarily go through a manufacturing process at the ground level, using components that can be assembled "in situ". Modern technology is already prepared to take this step, but today's construction still uses archaic manual methods, in which the machine plays only an auxiliary role.

From the project phases of architectural design, reviewing the habitat and the defining components of the spaces to the execution phases of engineering and analysing process improvements from the analytical decomposition of the prices of building components, opportunities have been found to improve the construction process.

A new methodology should bring together these improvement objectives, using the criteria of construction sustainability, through the so-called "3C system: Compatible Building Components". This system involves the use of prefabricated modules, factory materials and assembly by means of standardised joints.

The application of the BIM methodology in the building's life cycle can go from the beginning of the design to its demolition. This building life can be programmed efficiently, if, during the design process and its execution, the lean methodology is applied, seeking to reduce waste, saving time and materials.

As a final conclusion, it is established that the elements that must integrate a complete and coherent building project require the incorporation of industrial manufacturing and lean methodology in the construction processes in order to achieve sustainable architecture.

**Author Contributions:** Conceptualization, T.A. and J.G.; methodology, T.A. and J.G.; software, D.F.; validation, T.A. and D.F.; formal analysis, T.A. and J.G.; investigation, T.A. and J.G.; resources, J.G.; data curation, T.A. and D.F.; writing—original draft preparation, J.G. and T.A.; writing—review and editing, T.A.; visualization, T.A. and D.F.; supervision, J.G. and D.F.; project administration, T.A. and D.F.; funding acquisition, T.A., J.G. and D.F. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Acknowledgments:** Thanks to all the organizations and people who participated in the project, particularly to professors who have a spirit of continuous improvement.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
