Published in 4/2023 - Forest


Erat, Still a Role Model

Pekka Hänninen

Bruno Erat designed almost all of his ecological houses using the principles of his own home, Villa Solbranten. There are more than 40 plant species growing on the green roof.

Bruno Erat’s ideas on sustainable construction from half a century ago are still, according to Pekka Hänninen, the best Finnish examples of ecological architecture.

Curbing climate change and adapting to it, as well as stopping biodiversity loss, are currently the biggest challenges facing architecture – and humanity as a whole. Architect, licentiate of technology Bruno Erat (1936–2023) was already searching for solutions to these issues half a century ago, and the relevance of his buildings and ideas only increases as the years pass.

Erat’s own home Villa Solbranten (1978) is, in my opinion, still the best example in Finland of how architecture can promote ecological sustainability. The building’s architecture stems from the site, the placement of spaces in thermal zones, and the passive and active utilization of solar energy. It also supports local biodiversity and practicing a sustainable lifestyle. I don’t think an equally comprehensive ecological building has appeared in Finland since Villa Solbranten – in the later, so-called ecological building the focus has often been narrowly on energy efficiency and low carbon energy.

The model for Villa Sobranten was a Finnish farmhouse, where the main living space and bedroom are grouped either side of a spine wall. In Villa Solbranten, the living areas are placed on the south side, and the bedrooms, which need less heat, as well as the kitchen and utility rooms, are on the north side, acting as a buffer zone against the cold. The house is comprised of, so to say, two houses, one inside the other: the outer “house” can be left unheated when the spaces are not needed. Erat designed almost all of his later ecological houses using the principles of Villa Solbranten.

Villa Solbranten

The utilization of solar energy is the starting point for the architecture of Erat’s own home: the living spaces are gathered around the fireplace and the hot-water heater. The spaces requiring heat are placed on the south side, whereas on the north side, the house is sheltered under the roof eaves. The green roof imitates endangered fields and meadows, and there are more than 40 plant species growing there.

The Swiss-born Erat moved to Finland in the 1960s, attracted by Alvar Aalto and good skiing terrains. In 1968-1970 he was a visiting professor in the United States and experienced an environmental awakening after seeing the poor state of cities and reading the books that formed the basis of the general environmental awakening of the 1970s, such as Rachel Carson’s Silent Spring, Wesley Marx’s Frail Ocean, and Paul and Anne Ehrlich’s Population Bomb. Erat was instilled with a strong feeling that something needed to be done.

After returning to Finland, Erat’s thinking came to fruition. At that time, there was no teaching on ecologically sustainable construction in Finland – in fact, there was very little information overall. One had to learn and figure things out for oneself. Villa Solbranten and its identical neighbouring house turned out to be a significant learning experience. Erat shared his experiences for 25 years at various universities as well as in his book Ekologia, ihminen, ympäristö (“Ecology, Human Being, Environment”, 1994).

The type house utilizes ideas from Villa Solbranten – cloaked in the consumer fashion trends of the era. The rooms are grouped around the hearth and spine wall.
Tapanila ecohouse

The house is placed on a narrow urban plot in such a way that the existing beautiful lilies were spared. Long overhanging eaves and vegetation protect the interior from the sun in summertime, yet allow it to warm the spine wall during wintertime, where the heat radiates into the rooms at night.

The central idea in Erat’s architecture is to reduce energy needs as much as possible through the means of architecture, and only afterwards make use of technical devices. Erat explored the utilization of solar energy in almost all of his projects. In the wintertime, the sun’s rays are allowed to penetrate into the house, where they warm the spine wall that stores heat, but in the summertime, the long eaves and deciduous trees protect the interior from overheating. Structural sun protection becomes more important as the climate gets warmer.

Erat used organic materials, that is, minimally processed and additive-free. The structure of the outer envelope must be breathable, without any plastic vapour barrier. Erat’s eco-houses incorporate natural ventilation. Simple technology is more fail-safe.

According to Erat, individuals should always feel that they can influence their environment. That is why he considered a dense and low urban fabric to be ecologically and socially sustainable. According to him, the over-intensification of land use reduces the pleasantness of the environment, which in turn means that many sustainable development goals would go unrealised. When it came to the placement of buildings, Erat said that he admired Alvar Aalto, in whose office he worked in 1966–68. Erat’s own buildings have been carefully placed on their plots, utilizing the resources of the site and respecting nature. For Erat, ecological sustainability formed the comprehensive starting point of design.

Two houses in Vihti ecovillage
Erat designed two houses in the Vihti ecovillage, where the goal was a low need for heating energy, a small carbon footprint and an affordable price. The 140 m2 houses have an almost square-shaped floor plan with two storeys, so that the heat-dissipating surface of the outer envelope is as small as possible in relation to the floor area.
Tämän kuvan alt-attribuutti on tyhjä; Tiedoston nimi on erat_bromarv.jpg
Bromarv ecovillage

The aim of the project initiated by the local Martha organisation was to produce ecologically sustainable housing in the countryside and to secure the maintenance of the rural village’s services by attracting new residents there. The village is heated with its own wood-chip and solar-power plant. Wastewater is separated into grey and black and purified locally.

How have Erat’s buildings and ideas withstood the test of time? I studied and compared some of his single-family houses for my book Ekologisesti kestävä pientalo (“The Ecologically Sustainable Single-family House”, 2022). For example, Villa Solbranten’s delivered energy consumption is 60 kWh per square metre per year, which is reasonable even by current standards. The carbon footprint of living in the two small houses built in Vihti in the 2000s is 375 kilograms of carbon dioxide per inhabitant per year, while the corresponding footprint of the average Finn is 1,200 kilograms per year. The eco houses in Vihti can be seen as the culmination of Erat’s long development work.

Besides the technical features, Erat’s buildings strongly exude an ease of practicing a sustainable lifestyle and an understanding of nature. In his teaching, Erat called for an understanding of nature and hoped that the education of architects would include more on the natural sciences. In Erat’s thinking, buildings, residential areas and communities had to be seen as entities where materials and energy circulate and no waste is generated – that is, the circular economy. ↙

An architect specializing in ecologically sustainable building, and a freelance writer.

The text is based on the author’s interviews with Bruno Erat, the numerous discussions they had about ecological construction, as well as visits to the buildings designed by Erat.