What are NZIB buildings?

While the concept of reducing energy consumption in buildings has been regulated by law in our country since 2018 [note], the term for reducing the ecological impact of buildings is a concept yet to be regulated in most countries, but it is extremely relevant in a scenario of climate emergency and the struggle for planetary sustainability.

The fact is that energy consumption is just one of the indicators to consider from a long list of impacts when discussing the life cycle of any built environment.

Beyond energy, all construction generates an impact on its direct surroundings that encompasses multiple factors capable of altering the balance and sustainability of ecosystems. If we want to maintain any chance of success in climate change mitigation and adaptation, it will undoubtedly be necessary to evaluate a building’s impact globally.

Thus, the concept of NZIB – Nearly Zero Impact Buildings was born, a term still without a specific definition within the regulatory framework of the construction sector, but one that has undergone years of evolution within the most internationally recognized independent certifications. The NZIB concept does not only consider energy consumption; it integrates a holistic view of the impact of a built environment on the natural surroundings and on people.

Preliminary concepts

To understand the framework in which the NZIB building designation appears, it is necessary to be clear on two key references that help us better understand its definition.

The first reference is the document The Limits to Growth, published in 1971, which discussed for the first time the impact of human beings and the goods or services they generate on the planet. This study, revised in 2012, is a key reference for understanding the impact of each of our actions on planetary sustainability and, in this case, on buildings, understood as complex machinery interrelated with their environment.

The second reference relates to the term Ecological Footprint, a tool that allows for the quantification of human consumption of the Earth’s productive resources in relation to their availability.

Limits to growth

In 1971, a group of scientists led by Donella Meadows from MIT drafted a report warning that population growth, combined with the constant increase in the consumption of planetary resources, was about to reach a breaking point.

This study was revised in 2012 by the same authors, stating that the physical limits of the planet had already been reached; for this, they used the ecological footprint tool that had first appeared in 1996. [1]

The ecological footprint

In general terms, the ecological footprint quantifies how much nature we have and how much we use. It is a tool that evaluates the human impact on nature and is expressed in global hectares.

The ecological footprint measures the impact of human activities on: grazing land, forest products, built-up land, cropland, fishing grounds, and carbon compared to their biocapacity. [2]

Based on these parameters, the area of biologically productive land necessary to maintain a good or service is measured, taking into account the resources required for its realization as well as the waste it generates.

Grazing and croplands provide us with food and fibers, forest products provide wood and paper, fishing grounds provide fish, built-up areas host the built environment, and carbon consumption provides energy. [3]

If we understand a building or built environment as a good or a service—and in practice, it could well be considered both—it will have an impact on the planet to the extent that it consumes resources and generates waste throughout all phases of its life cycle.

In this sense, the NZIB concept assesses a building’s impact based on its ecological footprint but also takes into account the people who inhabit it, understanding that any building must safeguard the health and well-being of its occupants, generating a positive impact.

From NZEB to NZIB

The NZIB building concept stands for Nearly Zero Impact Building. It is a concept complementary to NZEB buildings, or Nearly Zero Energy Buildings.

Unlike the NZEB concept, which refers to or quantifies only the energy consumption of a building, NZIB expands toward a more global vision and refers to the impact on the planet—closely related to the ecological footprint—and on people.

The fact is that the term NZEB, by referring only to the energy consumption of buildings, is focused exclusively on the impact of carbon emissions, a partial view of the total ecological footprint. [4]

For this reason, it is necessary to move toward the integration of the NZIB concept, a much more comprehensive model for analyzing the life cycle of a building and the elements that compose it.

CONSTRUCTION CRITERIA FOR AN NZIB BUILDING

In 2005, Professors Kibert and Grosskopf from the University of Florida’s Powell Center for Construction and Environment published a document [5] analyzing the new generation of green buildings, which they call Radical Sustainable Construction, and listed the five factors a green building must fulfill:

1. Integration with ecosystems and the environment.

According to Kibert and Grosskopf, one of the strategies that can yield the greatest long-term benefit in a green building is the extensive integration of ecosystems and landscape with the buildings.

The ecosystem surrounding a building has the potential to impact climatic conditions, well-being, water supply, production and waste generation, or environmental quality.

2. Construction with circular economy criteria.

One of the main challenges of sustainable construction is achieving high degrees of circularity. Today, only about 30% of a building’s construction materials are recovered at the end of its life cycle.

Achieving good management of material reuse, keeping material in circulation for as long as possible and recovering or recycling it at the end of its useful life, requires planning from the start of the project.

Furthermore, the life cycle of the material itself and its local origin must also be assessed, as it can generate a high impact on its direct environment throughout its useful life.

3. Application of passive design strategies and renewable energy.

While regulations are beginning to require standards for the efficient operational control of buildings, passive design—in which energy demand is reduced to a minimum and the rest is generated through renewable sources—is a field where much progress and awareness are still needed.

Basic strategies of bioclimatic architecture, such as proper orientation and solar gain, solar protection and cross ventilation, or the use of construction systems that guarantee thermal inertia (temperature accumulation) and good insulation and airtightness, are basic premises to be respected.

4. Water resource management.

Water management is an issue of increasing importance in the design of built environments. There is now a real risk that both climate change and the stress placed on water resources due to population growth will threaten the constant, low-cost supply we are accustomed to in industrialized countries and further complicate the survival of developing countries due to the scarcity of drinking water.

Furthermore, sewage networks are overloaded and must manage not only domestic wastewater but also rainwater that cannot filter into increasingly over-paved ground.

It is for this reason that the need to include water resource management within the project itself becomes clear, assessing options for total or partial self-sufficiency, greywater recovery, wastewater management, and rainwater harvesting or filtration.

This is a part of the project that must be addressed holistically, linked to the approach of the implementation strategy, bioclimatics, and the design itself, understanding the consumption and wastewater that will be generated and including vegetation consumption as a key factor.

5. Implementation of environmental quality management measures.

Indoor Environmental Quality (IEQ) is a very important indicator when designing spaces that guarantee the health of their occupants.

It is surely one of the factors that has gained the most relevance in the field of space design following the COVID-19 pandemic, during which the entire planet was forced to understand the quality of the spaces they inhabited and the well-being they generated.

Indoor Environmental Quality is determined by multiple factors, such as humidity, temperature, electro-climate, or pollutants released into the air (chemical and biological).

This quality can be affected by factors of the design and construction itself (orientation, solar gain, openings, quality of construction systems and their execution, HVAC systems, etc.) as well as by external factors such as the environment where the building is located or the elements and finishes installed by the occupants themselves.

These basic criteria are included in one way or another in most current building certifications, and all of them stem from their analysis throughout the building’s life cycle.

Once we have defined the five design criteria to reduce a building’s impact to zero, we must evaluate the success of the strategies applied. This is where a multitude of independent construction certifications appear. Certifications such as LEED, BREEAM, VERDE, or Passivhaus, among others, are created by private entities that audit built environments, granting a qualification based on the achievement of certain criteria.

Although each establishes its own methodology, it is possible to group the evaluation criteria into categories according to the impact they measure.

Factors defining the impact of an NZIB building:

1. LAND USE

2. BIODIVERSITY

3. Water Resource Management

4. POLLUTION AND WASTE

5. GREENHOUSE GAS EMISSIONS

6. INDOOR ENVIRONMENTAL QUALITY

7. HEALTH AND WELL-BEING

1 LAND USE

When we talk about land use in architecture, we should not confuse it with its urban planning definition, in which territorial planning instruments define the different land uses that can be adopted in each zone.

In climate terms, land use refers to the utilization of the surface of all urbanized and vacant land in a specific place, at a given time and space.

This use defines human activities that are directly related to the land, taking advantage of its resources and inevitably having an impact on them. Implicitly, both built environments and fields, pastures, and settlements involve the management and modification of the natural environment and nearby wildlife.

The reduction of impact derived from land use is included in numerous European regulations and laws and is, in fact, one of the critical points mentioned in the latest IPCC reports.

A building has a direct impact on the land through a) the mere existence of the project that transforms the landscape and environment; b) the use of available natural resources; and c) the emission of pollutants and waste in its immediate surroundings.

The land, understood as the base support of humanity, provides us with food, water, and sustains our ecosystems. Today, around 70% of the non-frozen land surface is affected in one way or another by human activities that, on average, have raised the temperature of the land surface by 1.5 degrees since the last industrial revolution.

Emissions from the global food system and land use contribute 21-37% of global Greenhouse Gas (GHG) emissions today, and although agriculture and livestock are the main impacts, land use and waste generated by the built environment are also impacts that alter the balance of ecosystems. [6] In fact, the reduction of emissions as a consequence of activities that use land is included in the Paris Agreement declaration. Agriculture, livestock, and forestry, among other activities with an impact on fertile soil, represent around 20% of greenhouse gas emissions. [7]

The 2019 IPCC report highlights the need to reduce emissions from the sector by taking urgent action to reduce emissions and achieve resilient land use that does not degrade land and improves biodiversity. [8]

Furthermore, the report warns of the role of climate change on desertification, land degradation, sustainable management, food security, and greenhouse gas flows in terrestrial ecosystems. This is why the European Commission declared land as the planet’s first scarce resource as early as 2005, delving into the implications of this fact on environmental diversity. [9]

Buildings affect ecosystems in various ways and consume agricultural land and wetlands or bodies of water, compromising existing wildlife. The solution involves integrating buildings into the surrounding context, both biotic and abiotic, and conserving material and land resources through optimized land use.

At the European level, the existing regulation on land use is called LULUCF, regulation for land use and forestry for 2021-2030, with the implicit objective of achieving climate neutrality by 2050. This document establishes a binding commitment for each European Union country to ensure that emissions from land use are offset by an equivalent removal of CO₂ from the atmosphere through actions in the sector, known as the “no debit” rule. [10]

2 BIODIVERSITY

Biodiversity is defined as the interaction between human beings, fauna, and flora; soil, water, air, climate, and landscape; and material goods and cultural heritage.

The Earth Summit held by the United Nations in Rio de Janeiro in 1992 recognized the global need to reconcile future preservation of biodiversity with human progress according to sustainability criteria.

From this meeting emerged the Convention on Biodiversity, conceived as a practical tool to turn these principles into reality and signed by 150 political leaders. [11]

Construction projects have the potential to impact natural habitats, affecting wildlife and plant species. The sector itself is also a major consumer of resources, many of which are produced or derived in processes that in turn have an impact on biodiversity. Therefore, it is necessary to raise awareness so that construction plays an important role in protecting sensitive sites and minimizing damage to ecology. Furthermore, there are opportunities not only to avoid impact but to improve biodiversity by creating habitats for native species as part of the project.

Thus, it is important to assess how a building transforms its environment or is integrated into it, and how its life cycle affects the environment with consequences for nature conservation, depletion of the water table and modification of river flows, air and water pollution, changes in fauna and flora, among others.

The impact of all these phenomena is not restricted to the building site but can extend over a larger area due to the chain of cause and effect produced by the intrinsic interrelation and interdependence between living beings, known as external effects.

3 Water Resource Management

The focus is usually placed on the use of water resources during the useful life of a building, neglecting that water is also used during its construction and in the manufacture of the materials that compose it.

A project can seriously affect the natural water resources of the site. Water extraction also has an impact on energy consumption, thus also contributing to carbon emissions into the atmosphere.

The path toward sustainable water management, which uses but does not deplete or impoverish its quality and returns it to its environment in the same or better quality than it receives, is a key factor in adapting urban construction toward climate change resilience. [13]

4 POLLUTION AND WASTE

POLLUTION

Pollution is a concept related to the urban scale in which the processes generated in buildings, especially industrial ones, are the main problem.

At the urban scale, pollution is a form of contamination originating from waste from biological or industrial processes. It is damage that not only affects the environment but can also have serious effects on the health of the population.

It is for this reason that the WHO reports that 91% of the world’s population lives in places where pollution levels exceed the established limits.

Most industrial buildings are especially involved in the release of these harmful substances, which can generate pollutants beyond greenhouse gases. These can be both other polluting gases such as CO or nitrogen derivatives such as NO₂, an atmospheric pollutant whose main sources are emissions from certain industries, but also road traffic and combustion from coal heating, currently in disuse.

On the other hand, we find particulate matter, which we inhale when breathing and whose composition is very varied and can accumulate all kinds of pollutants, some very dangerous to health. However, given the difficulty of knowing what substances they contain, experts classify them according to their size and how they behave once incorporated into our body through respiration, being more harmful the smaller they are.

WASTE

Among all the environmental impacts produced by a building throughout its life cycle, one of the main ones is the generation of construction waste during the material manufacturing process, which is concentrated right at the end of its useful life, during its demolition. [14]

This situation makes it easier to tackle the problem by concentrating all efforts at a specific moment. Thus, the management of demolition waste is essential, for which there is a Protocol for the management of construction and demolition waste in the EU from 2016. [15]

One of the greatest difficulties in recycling and reusing construction and demolition waste in Europe is the lack of confidence in the quality of recycled materials from these activities, a conceptual error that the European Commission intends to resolve.

The proposed measures aim to achieve the goal of recycling 70% of construction and demolition waste by 2020, thus closing the life cycle of a large part of products by increasing recycling and reuse. At the Spanish level, work is underway on a law that discourages landfill disposal, making it more expensive to do it wrong than right, that is, to opt for comprehensive or selective demolition.

Focusing on the building use phase, it is also important to assess the waste generated by the users who live in it and their willingness to reduce it in relation to the principles of NZIB buildings. The philosophy of the zero-waste home establishes a pyramid of the 5 Rs that is carried out in hierarchical order with the aim of avoiding generating household waste. The points in order are as follows: refuse the unnecessary, reduce what we need and cannot refuse, reuse what we consume, recycle, and compost the rest.

In 2018, an update to the European Directive on waste management was established, which includes a very relevant point that sets a new municipal waste recycling target. With a deadline of 2025, it requires that at least 55% of municipal waste by weight be recycled. This target will rise to 60% by 2030 and 65% by 2035.

It previously analyzes that there are large differences between Member States in their waste management performance, especially with regard to municipal waste recycling. In light of the average annual progression rates of Member States over the past fifteen years, meeting these targets would require those Member States to increase their recycling capacity to levels well above their previous averages.

Furthermore, Member States must aim to achieve an indicative target of reducing food waste at the Union level by 30% by 2025 and 50% by 2030. On the other hand, by January 1, 2025 at the latest, separate collection of textile and hazardous household waste must be established. [16]

To achieve this goal, one of the actions included in the Climate Plan is the deployment of individualized collection systems for household and commercial waste in cities or municipalities. Door-to-door selective collection consists of delivering well-separated waste at the doorstep following a pre-established calendar for each fraction.

With a door-to-door model, all household fractions (residual, organic, glass, packaging, and paper and cardboard) can be collected, or only some fractions can be collected while maintaining some containers on public roads. Practice has shown that this is a system that improves selective collection results, reaching results of between 60% and 80%, encouraging users’ co-responsibility in management by avoiding the anonymity of waste delivery.

5 GREENHOUSE GAS EMISSIONS

With the appearance of the mandatory construction of NZEB (Nearly Zero Energy Buildings) in 2020, the aim is to regulate and reduce greenhouse gas emissions throughout the entire life cycle of a building.

EMISSIONS FROM MATERIALS

While the definition of NZEB only takes into account so-called operational carbon, that is, the carbon consumed during the building’s useful life, the NZIB concept adds the accounting of embodied carbon, coming from the life cycle of construction materials and present in practically the same percentage as operational carbon—derived from the use phase.

This is where Environmental Product Declarations (EPDs) come into play, a document whose purpose is to provide quantitative information on the environmental impacts of that product throughout its life cycle. In this sense, EPDs calculate the kg of CO₂ equivalent throughout the production chain of construction materials, that is, their carbon footprint. These are increasingly present among suppliers, but European regulations do not yet establish them as mandatory.

That is why we must pay special attention to the life cycle of these elements and their implications beyond their emissions, essential for construction that respects existing ecosystems. Following the principles of the circular economy, we must close the life cycle of materials, ceasing to distinguish between renewable and non-renewable by understanding materials as permanent, that is, circulating in a closed circuit that William McDonough calls the cradle-to-cradle philosophy.

All in all, it is necessary to opt for low environmental impact materials, especially local ones, since you never have to go very far to find varied and quality offerings. [17]

In fact, the only renewable and natural materials are materials such as wood or bamboo, and with the latter, care must be taken since at the moment it is produced very anecdotally in Europe, so it ends up coming almost entirely from Asia, with the consequent and unnecessary carbon footprint derived from transport. In the case of wood, there are PEFC and FSC certifications, which demonstrate that forest management is sustainable and a necessary chain of custody is carried out, in which for every tree cut down, a new one is planted.

If we talk about embodied carbon in a building, it remains stable throughout the useful life of the existing building stock, so reducing it becomes more important. That is why it makes sense that with each renovation, embodied carbon reduction strategies are implemented. Recently, so-called carbon sequestration technologies are emerging, which aim to offset the carbon footprint through CO₂ capture and storage. [18]

EMISSIONS FROM ENERGY DEMAND

Even so, these new technologies should not replace the urgent need to stop emitting carbon, reduce embodied carbon in rehabilitation and renovation operations, and pay attention to other greenhouse gas (GHG) pollutants such as methane, which is 28 times more polluting than CO₂.

Therefore, it is necessary to minimize as much as possible the need for energy input in the built environment, first reducing demand, which helps reduce the energy produced, as well as emissions. This is carried out through passive strategies, such as solar orientation, thermal insulation, absence of thermal bridges, thermal inertia, ventilation, and airtightness.

The choice of certain construction systems also has direct implications on the ecological impact and greenhouse gas emissions of a building. Prefabrication processes are usually more efficient: they manage to minimize waste—material waste generated during construction—and are usually dry systems, allowing greater ease of disassembly and reuse and better resolution of construction details—important when avoiding thermal bridges to reduce the building’s energy demand.

Once this is reduced, we must think about the best way to obtain energy for the building, which will be transformed from natural resources. Therefore, the minimum remaining energy input must be the most efficient and come from renewable energy, responding to the definition of an NZEB building. The important thing is to understand that this use of renewable energy sources would not have sufficient power if the previous steps had not been taken to reduce demand as much as possible. The solution is to reduce before contributing, following old consumption logic.

For all these reasons, the EU regulatory framework put into force in 2010 a Directive on the energy efficiency of buildings, under the title Energy Performance of Buildings Directive, which establishes the end of 2020 as the deadline for all new construction to be NZEB. A long-term goal is also established in which all buildings will be Net Zero Energy Buildings, that is, zero consumption, by 2050. [19]

The underlying question is how each country quantifies its criteria for considering a building under the NZEB label, which in the case of Spain are determined by the Technical Building Code (CTE), specifically the Energy Saving section. [20]

Due to its close relationship with carbon emissions, reducing energy demand is one of the fields on which the European community has placed the most emphasis. This is verified by reviewing the current legislation on NZEB buildings, which is not only mandatory but specifically requires quantification that is so useful when comparing, unlike when we base ourselves on abstract objectives or concepts.

EMISSIONS FROM TRANSPORT

On the other hand, as in the case of pollution, the reduction of greenhouse gas emissions derived from transport can be avoided not only in the material manufacturing or building construction phase but during the use stage by the users of the NZIB building, whose lifestyle and habits are also part of its operating cost.

The world’s dependence on fossil fuels for transport is enormous, including freight transport and private transport. As users, it is in our hands to minimize the latter. In 2010, more than 53% of global primary oil consumption was used for 94% of total energy demand for transport. In 2014, approximately one-quarter of total GHG emissions in the EU originated from transport. Private vehicles contributed 44% to emissions in the transport sector, and heavy vehicles and buses represented an additional 18%. [21]

It is true that, as with other polluting phenomena, transport will become increasingly efficient and allow greater use of energy from renewable sources. However, the initial objective must be to reduce its need as much as possible, completely avoiding dependence on private transport. And this involves generating more accessible cities by prioritizing the value of the local, which will imply less need for travel but also provides added value in terms of rootedness in the environment and sense of belonging. Combating the lack of public services or public transport networks in neighborhoods or municipalities, promoting green mobility such as bike lanes, shared mobility or car-sharing, implementing the possibility of teleworking or having a coworking space in the same building where we live, are some measures of local revaluation.

In fact, there are four potential mitigation options to reduce GHG emissions from personal transport. The first is to avoid unnecessary trips through densification and mixed zoning of cities. The second is the choice of more efficient modes of transport, such as switching from private cars to public transport, walking, or cycling. It is also possible to improve the efficiency of aircraft, train, ship, road vehicle, and engine performance by manufacturers or result in lower fuel demand. Ultimately, the inevitable use of fuels can be based on sustainable biofuels or electricity produced from renewable energy.

Decarbonizing the transport sector is a challenge for many countries, but if well-designed policies are developed that incorporate a combination of infrastructure design and modification, technological advances, and behavioral measures, joint benefits and a cost-effective strategy can be obtained. [22]