Green façades on primary schools in Lisbon, Portugal

Both schools sit in Marvila, a highly urbanised residential parish in eastern Lisbon, and each combines kindergarten and pre-school (ages 3–6) with the first cycle of basic education (ages 6–11). EB1 & JI Manuel Teixeira Gomes was built in 1972 and extended in 2011, and comprises a main building of about 2,500 m² plus a 350 m² dining building on a plot of roughly 11,000 m², with two sports fields, two playgrounds and a small outdoor auditorium; 255 pupils were enrolled in 2017/2018. EB1 & JI Bairro do Armador has a first-cycle building of about 2,500 m² and a kindergarten building of about 1,000 m², with a playground, parks, covered areas and some green space; 274 pupils were enrolled in 2017/2018. Air quality and noise are concerns at both sites because of nearby high-traffic roads, and at the second school also railway and metro lines. Green and lawn areas are scarce at both, and the second school has few shaded areas, so indoor temperatures reach uncomfortable levels in summer. Portuguese pupils in the first cycle spend an average of 834 hours per year in school, above the EU average of 776 hours.

To develop a method for assessing the economic value of installing green roofs and green walls in public buildings, and to test it on two primary schools in order to establish whether such retrofits are financially, economically and socio-environmentally feasible.

Challenges addressed

The façade mainly targets socio-economic challenges, improving health and wellbeing for pupils and staff. It also helps manage air and noise pollution and supports climate change adaptation by reducing heat stress in the city.

Costs of NbS

The study assesses a planned 118 m² outdoor green façade on a primary school in Lisbon, one of five greening options tested for the school. Installation costs about EUR 138 per m² and maintenance about EUR 4 per m² per year. At the end of the 50-year life cycle, the system is replaced at about EUR 825 per m². Over the life cycle, total costs for the façade come to about EUR 27,100 (2023 prices, 6.67% discount rate).

The green façade improves the school’s appearance and reduces noise by about 2 dB, raising comfort for pupils and staff as well as the value of the building. It shields the wall from weathering, extending its lifespan by about 15 years, and absorbs CO₂ and NO₂ from the air. Most of the value comes from the higher property value; over the 50-year life cycle the benefits are worth about EUR 6,250 per m² (2023 prices). Wider benefits such as urban cooling were not counted, as a single façade has little effect at city scale.

Benefit–cost ratio

The façade reaches a BCR of 21.6, the highest of the five options tested for this school. Green façades outperformed green roofs and living walls, which cost more to install and maintain.

The researchers identified the main problems and needs at each school, designed fourteen greening scenarios and selected ten representative ones for full appraisal. They gathered cost data from Portuguese suppliers, contractors' budgets and published studies; collected local energy consumption and property market data; and ran questionnaires with school employees and teachers to help quantify inputs. They then carried out a discounted cost-benefit analysis for each scenario at financial, economic and socio-environmental levels, followed by a sensitivity analysis.

Inês Teotónio, CERIS, Instituto Superior Técnico, University of Lisbon — ines.teotonio@tecnico.ulisboa.pt

Study overview

Two primary schools in Marvila, in eastern Lisbon, were used to test whether greening the roofs and walls of public buildings makes financial sense. The study, by researchers at Instituto Superior Técnico, University of Lisbon, developed a cost-benefit method for green roofs and green walls in public buildings and applied it to EB1 & JI Manuel Teixeira Gomes School and EB1 & JI Bairro do Armador School.

Fourteen greening scenarios were designed around each school's particular problems: poor indoor and outdoor air quality and noise from nearby busy roads, railway and metro lines, a shortage of greenery and shade, and summer overheating. Ten were assessed in detail. They covered extensive green roofs (lightweight systems planted with low-growing species), green façades (climbing plants on the existing wall) and living walls (modular planted panels), installed either outdoors or indoors.

Each scenario was compared with the school's current condition over a 40-year life cycle for green roofs and 50 years for green walls, using a discount rate of 6.67%. Costs and benefits were grouped at three levels: financial (direct costs and returns to the building owner), economic (value added to the local economy) and socio-environmental (contribution to environment and society). Inputs came from Portuguese suppliers' prices, local energy consumption data for 2017, property values in the surrounding area, and published figures for noise reduction, pollutant uptake and rainwater retention.

All ten scenarios proved feasible once benefits beyond the owner's balance sheet were included, with benefit-cost ratios ranging from 3.01 to 34.99 and total discounted gains of between about €199,000 and €2.5 million. The most efficient option differed between the two schools: an outdoor green façade at the first (ratio 21.64) and an indoor green façade at the second (34.99). Several benefits to pupils' health and wellbeing could not be valued reliably, so the authors regard their estimates as conservative.