La importancia de considerar el ciclo completo en proyectos verdes

The first generation of green buildings focused on minimizing operational energy consumption, a necessary but insufficient goal for the genuine decarbonization of the sector. A building that achieves the nZEB standard with a primary energy demand of 30 kWh/m2/year has addressed the B6 module of its life cycle, but if to achieve this it uses 400 kg/m2 of conventional reinforced concrete, 50 kg/m2 of structural steel, 35 kg/m2 of aluminum in windows and facade, and 15 cm of extruded polystyrene insulation, its embodied carbon can reach 500-700 kg CO2eq/m2, a carbon debt that will take 30-50 years to offset through operational savings compared to a conventional building. According to Chastas et al. (2018), in a study published in Energy and Buildings that analyzed 95 nZEB and Passivhaus buildings, embodied carbon represented between 26% and 57% of the total life cycle over 50 years, with an average of 38%. For net zero energy buildings (which produce as much energy as they consume), embodied carbon can represent 70-90% of total impact, making material selection the most consequential environmental decision.

This reality generates documented paradoxes. A study by Pomponi and Moncaster (2016), published in the Journal of Cleaner Production, compared 4 emission reduction strategies for a 5,000 m2 office building in the United Kingdom: (a) envelope improvement to Passivhaus standard, (b) substitution of concrete structure with CLT timber, (c) combination of both, and (d) conventional building with 100% renewable electricity. Strategy (b) reduced life-cycle emissions by 42% against the baseline, (a) by 35%, (c) by 62%, and (d) by 38%. The result demonstrates that structural material selection has a greater impact than envelope thermal optimization when the electrical grid is decarbonizing, because module A1-A3 emissions are fixed and irreversible, while module B6 emissions automatically decrease with the penetration of renewables in the electricity mix. In Spain, where the grid emission factor dropped from 0.38 kg CO2/kWh in 2010 to 0.12 kg CO2/kWh in 2023, this trend reinforces the urgency of addressing embodied carbon.

The influence of design decisions on life-cycle environmental impact follows the MacLeamy curve: 80% of the impact is determined during the concept and schematic design phases, when only 5-10% of the total project cost has been invested. The most consequential decisions are the selection of the structural system (concrete, steel, timber, or hybrid), the ratio of gross to usable floor area (compactness factor), the glazing-to-opaque ratio on the facade, the floor plate depth (which determines dependence on artificial lighting), and the building's orientation. A study by Malmqvist et al. (2018), published in Energy and Buildings, evaluated 4 variants of the same functional brief (an 8-story residential building with 40 dwellings) with different structural systems and documented that the CLT structure variant emitted 310 kg CO2eq/m2 in A1-A5, compared to 420 kg CO2eq/m2 for the precast concrete structure and 520 kg CO2eq/m2 for the in-situ concrete structure, a 40% difference between the optimal and conventional options, with no impact on construction cost (deviation below 3%).

Whole-life integrated design requires the project team to include an LCA specialist from the concept phase onward who evaluates the impact of design decisions in real time. The LCAQuick methodology, developed by BRANZ in New Zealand, can estimate the life-cycle GWP of a building in 30 minutes from basic geometry and material data, with a margin of error of plus or minus 15% compared to a full LCA. In Spanish practice, the studio Batlle i Roig Arquitectura applied a whole-life approach in the 1,500-dwelling project for the Marina del Prat Vermell neighborhood in Barcelona (2019-2025), where early LCA evaluation led to substituting the planned reinforced concrete structure with a hybrid structure of recycled concrete (30% recycled aggregate) and CLT floor slabs, reducing embodied carbon by 28% (from 480 to 345 kg CO2eq/m2) with a cost premium of 1.5%. The One Click LCA tool reports that projects performing LCA at the concept phase achieve average reductions of 22% in embodied carbon compared to those performing it at the detailed design phase, and 35% compared to those that do not perform LCA at all.

Life Cycle Costing (LCC) is the economic dimension complementary to environmental LCA and reveals that whole-life green buildings are also the most profitable in the long term. Standard ISO 15686-5:2017 establishes the LCC calculation methodology for buildings, including investment costs, operation, maintenance, component replacement, end of life, and residual value, discounted to present value with a rate of 2-4%. According to RICS data (2022), the construction cost represents only 15-20% of the total cost of ownership over 50 years for an office building, while energy costs represent 25-35%, maintenance 20-30%, and component replacement 15-25%. A study by Kneifel (2010), published in Energy and Buildings, analyzed 228 design variants of an office building across 16 climate zones in the United States and found that energy efficiency investments that increased construction cost by 5-10% generated LCC savings of 10-25% over 40 years, with payback periods of 4-12 years.

Integrating LCC with LCA allows the identification of solutions that simultaneously minimize environmental impact and total cost. A ground-source heat pump, for example, has an investment cost 2-3 times higher than a condensing gas boiler, but an operating cost 60-75% lower and a useful life of 25-30 years compared to 15-20 years. The 30-year LCC of geothermal is 15-25% lower than that of a gas boiler for buildings exceeding 2,000 m2, while also eliminating direct CO2 emissions (module B6). In Spain, an LCC analysis conducted by IDAE (2022) for the energy renovation of multi-family housing demonstrated that nZEB solutions (ETICS insulation of 12 cm, PVC windows with low-e double glazing, air-source heat pump, and rooftop photovoltaics) present a 30-year LCC that is 8-15% lower than that of minimum CTE renovation, when energy savings, lower maintenance requirements, and the higher resale value of the property are factored in (a 10-15% premium for an A rating according to Idealista, 2023). The cost of inaction is also quantifiable: exposure to projected carbon costs (EU ETS2, estimated at 45-80 EUR/tonne CO2 for 2027-2030) will increase the energy cost of unrenovated buildings by an additional 15-30%.

The concept of Net Zero Whole Life Carbon (NZWLC) represents the ultimate evolution of the green building: a building whose total life-cycle emissions (modules A1-A5, B1-B7, and C1-C4) are reduced to the minimum that is technically and economically feasible, with the remainder offset through verified carbon credits or biogenic carbon storage in materials such as timber. The UKGBC (2019) defined the reference framework with thresholds of 300 kg CO2eq/m2 of embodied carbon (A1-C4 excluding B6-B7) for housing and 500 kg CO2eq/m2 for offices, and 0 kg CO2eq/m2/year of net operational carbon (B6). The WGBC (2021) estimates that only 1% of new buildings constructed in 2024 globally meet NZWLC criteria, but the forecast is to reach 10% by 2030 and 100% by 2050. Documented NZWLC buildings include the Enterprise Centre at the University of East Anglia (Norwich, 2015), with 180 kg CO2eq/m2 of embodied carbon (CLT and straw structure) and net zero energy consumption thanks to 300 m2 of photovoltaic panels.

In Spain, the whole-life approach is gaining regulatory and professional traction. GBCe published in 2023 the first Spanish whole life carbon guide for buildings, with benchmark values adapted to the national construction and climate context. The VERDE 2024 certification increased the LCA weighting from 10% to 18% of total points, and requires the LCA to mandatorily cover modules A1-A5, B4, B6, and C1-C4. BREEAM ES 2024 awards up to 9 credits (up from a maximum of 5 in the previous version) for performing a whole life-cycle LCA with reduction targets relative to the reference building. According to a CSCAE survey (2024), 42% of Spanish architecture firms with more than 10 staff have performed at least one building LCA in the last 3 years, compared to 8% in 2019, indicating accelerated but still concentrated adoption among medium and large firms. The main barrier is the cost and time of LCA (estimated at 3,000-12,000 EUR and 40-120 hours of work for a typical residential building), which professionals consider disproportionate when it is not mandatory. The regulatory mandate anticipated for 2026-2027 and the simplification of tools such as LCAQuick and integrated BIM-LCA modules are expected to resolve this barrier within the next 3-5 years.