Optimizando la renovación y demolición desde una perspectiva sostenible

The decision between renovating an existing building and demolishing it to build a new one is among the most consequential in terms of environmental impact. A comparative life-cycle analysis must consider the embodied carbon of the existing building (already emitted and irrecoverable), the carbon from demolition and waste management, the embodied carbon of the new construction, and the differential operational carbon over the remaining useful life. According to Preservation Green Lab (2016), a study commissioned by the National Trust for Historic Preservation of the United States that analyzed 6 building typologies across 4 climate zones, renovating an existing building produces between 25% and 75% fewer life-cycle emissions than an equivalent new construction over a 50-year horizon, even when the new building achieves nZEB standards. The reason is that the embodied carbon of new construction (300-800 kg CO2eq/m2 depending on typology and materials) takes between 20 and 80 years to be offset by the new building's operational carbon savings relative to the renovated one. In a more recent study by Marsh et al. (2022), published in Building and Environment, the analysis of 46 cases in Denmark confirmed that deep renovation was preferable to demolition-reconstruction in 78% of the cases analyzed when a 50-year horizon was applied.

The critical factor is the level of renovation required. A light renovation (envelope improvement and system replacement) consumes 50-150 kg CO2eq/m2 of embodied carbon, a deep renovation (with structural intervention) 150-350 kg CO2eq/m2, and new construction 300-800 kg CO2eq/m2. For demolition-reconstruction to be environmentally preferable, the existing building must present structural deficiencies that prevent safe renovation, contamination by asbestos or other hazardous materials whose removal exceeds 15% of the new construction cost, or a spatial configuration so incompatible with the intended use that renovation would generate more carbon than reconstruction. In Spain, 43% of the residential stock (approximately 11 million dwellings) was built between 1960 and 1990 with variable quality standards (MITMA, 2023), and individual assessment through the ITE (Technical Building Inspection) is mandatory for buildings over 50 years old in most autonomous communities, providing the diagnosis needed for the renovate/demolish decision.

The pre-demolition audit is the mandatory preliminary step in 18 EU Member States (including Spain since Law 7/2022) for buildings exceeding 1,000 m2. It consists of a quantitative inventory of all building materials, their conservation status, their reuse and recycling potential, and the identification of hazardous materials (asbestos, PCBs, lead). The audit is carried out through visual inspection, selective destructive testing, analysis of original project documentation, and increasingly through LiDAR 3D scanning that generates an as-built model of the building with a precision of plus or minus 5 mm. According to a CEN TC 350 study (2020), a well-executed pre-demolition audit increases material recovery rates from 40-50% (without audit) to 70-90% (with audit), at a cost of 0.5-1.5% of the demolition budget. European standard prEN 17901 (in the approval phase in 2024) will standardize for the first time the content and methodology of the pre-demolition audit, facilitating comparability across Member States.

Selective deconstruction, as opposed to conventional mechanical wrecking, proceeds in reverse order to construction: first furniture and equipment are removed, then services (wiring, pipes, ducts), followed by interior finishes (partitions, flooring, suspended ceilings), facade cladding, windows, roofing, and finally the structure. This process requires 30-60% more time than conventional demolition (ADEME, 2021), but allows the recovery of materials with a market value that partially or fully offsets the additional cost. A study from the European FISSAC project (2019) documented that the selective deconstruction of a 6,000 m2 office building in Madrid generated 4,200 tonnes of materials with the following distribution: concrete and masonry 68% (destined for recycled aggregate), steel 12% (steelworks recycling), timber 8% (particleboard recycling), glass 3% (glass plant recycling), aluminum and other metals 2% (recycling), and non-recyclable mixed waste 7%. The value of recovered materials was 85,000 EUR, against the deconstruction overcost compared to conventional demolition of 62,000 EUR, resulting in a net benefit of 23,000 EUR.

Deep renovation reduces energy consumption by 60-90% relative to the prior state, reaching nZEB or near-Passivhaus levels in existing buildings. The Energiesprong strategy, developed in the Netherlands and adopted in 7 European countries, industrializes renovation through the prefabrication of insulated facade panels, roof modules with integrated photovoltaic panels, and compact HVAC units with heat pump and heat recovery ventilation, which are installed in 1-2 weeks with occupants remaining in the dwelling. In the Netherlands, 6,500 dwellings have been renovated using this methodology since 2013, achieving net energy consumption of 0 kWh/m2/year (annual balance) at a cost of 60,000-80,000 EUR per dwelling financed through 30-year energy performance contracts. In Spain, the EuroPACE program piloted in Olot (Girona, 2020) adapted the model to Mediterranean single-family homes with budgets of 25,000-45,000 EUR and energy savings of 55-70%.

Prefabricated ventilated facades constitute the highest-impact solution for the renovation of residential blocks. The system comprises sandwich panels of 100-200 mm insulation (mineral wool or graphite EPS) with an exterior finish of composite, fiber cement, or ceramic, mechanically fixed to the existing facade without the need to demolish the original enclosure. The cost ranges from 120 to 250 EUR/m2 of facade, with heating energy savings of 40-65% and acoustic comfort improvements of 8-15 dB. A study by the IETcc-CSIC (2022) evaluated the deep renovation of 12 social housing blocks from the 1960s-1970s in the Txomin Enea neighborhood (San Sebastian), with a ventilated facade of 120 mm mineral wool, roof insulated with 200 mm of XPS, PVC windows with triple glazing, and centralized air-source heat pump. Heating demand dropped from 145 kWh/m2/year to 22 kWh/m2/year, an 85% reduction, at a cost of 38,000 EUR per dwelling subsidized at 65% by PREE funds with a payback period for the owner of 9 years. The embodied carbon of the renovation was 95 kg CO2eq/m2, compared to the 450-550 kg CO2eq/m2 that demolition and equivalent new construction would have entailed.

The Spanish regulatory framework for sustainable management of demolition waste has advanced significantly. Law 7/2022 on waste and contaminated soil transposes the Waste Framework Directive with CDW recovery targets of 70% by weight for 2025, and establishes the obligation of a pre-demolition audit for buildings exceeding 1,000 m2. The State Waste Management Plan 2023-2035 includes specific measures for construction: a landfill tax of 40 EUR/tonne for unrecycled CDW (compared to the current zero or symbolic rate in most autonomous communities), an obligation to incorporate at least 5% recycled aggregate in concrete for public works from 2027, and the creation of a national registry of reused construction materials. However, implementation is lagging: as of the end of 2024, only 5 autonomous communities (Catalonia, Basque Country, Madrid, Valencia, and Andalusia) have developed complementary regulations for the pre-demolition audit.

Sector prospects point to an accelerated transformation. The revised EPBD (2024) requires Member States to establish national renovation roadmaps to achieve a decarbonized building stock by 2050, with intermediate milestones of renovating 16% of the worst-performing non-residential buildings before 2030 and 26% before 2033. In Spain, this implies renovating 1.2 million non-residential buildings and 5-6 million dwellings over the next two decades. The Existing Building Logbook, regulated by Royal Decree 853/2021, establishes the obligation to document the conservation status, accessibility, and energy efficiency of buildings through the ITE and Energy Performance Certificate, creating the information base needed to plan renovations. The investment required to meet renovation targets is estimated at 150 billion EUR over 25 years (GBCe, 2023), but it generates quantifiable returns: 45 billion EUR in cumulative energy savings, 400,000 sustained direct and indirect jobs, and an emissions reduction of 25 million tonnes of CO2/year, 10% of Spain's total emissions.