Look up this project on the website of its architects, ACXT, and you will find that it goes by the rather understated name of 242 Affordable Housing Units in Salburúa (Salburúa being a neighborhood in the Basque city of Vitoria-Gasteiz). In many ways the downplaying of the name is in keeping with ACXT's quiet approaches to sustainable design. Though there may be no obvious green bells and whistles such as wind turbines or photovoltaics, passive architectural methods combined with on-site generation contribute to what ACXT claims is a "considerable reduction" in the building's carbon dioxide emissions.

Though largely a residential development the building, completed in 2011, incorporates nine shops at ground level. From there, it's social housing all the way up: between four and seven stories for the horseshoe-shaped block that forms the building's footprint, rising to 21 stories for the tower that rises above one end of that horseshoe.

Why the variation in height in the main block of the building? It's all to do with daylight, or specifically sunlight - the two being subtly different things. By limiting the height of the development to the south (we're in the northern hemisphere, needless to say), more apartments are granted a direct view of the sun. It's an arrangement the building appears to have borrowed from its closest neighbors, and though the tower, being located at the building's south-western corner, inevitably casts a shadow, the photographs suggest that an impressive proportion of the building's facades are bathed in sunlight at any given time. In any case, the positioning of the tower to the south inevitably means that more apartments are granted a south-facing aspect, and though direct sunlight can be problematic, it's also a very nice thing to have - especially at home.

Daylight to the apartments is further increased by ensuring that every single one is, as ACXT puts it, "double fronted." This means that the apartments occupy the full depth of the building, with windows into all of the apartment's key living areas (bedrooms, kitchens and living rooms).

More central to the building's sustainable efforts is the cogeneration system which produces 70 kW of electricity and 109 kW of heating on site. A relatively unglamorous technology, cogeneration (also known as combined heat and power, or CHP) is nevertheless a tremendously important weapon in a building designer's arsenal. In this case, effectively an on-site gas-fired power station (there's no reason why CHP cannot use biofuel), it's the proximity of the power generation to end use that sees CHP offering significant energy savings over grid-scale gas fired power, because a vast amount of the heat generated as a by-product can be put to use very near to where it is generated. Plus it's heat that doesn't have to be generated by other means, as would otherwise be the case. In a triumph of localism, cogeneration can almost be seen as putting the fuel to work twice in one go.

ACXT reports that the building is able to produce electricity to sell back to the grid, which suggests that, for some of the time at least, the cogeneration system is producing more electricity than the building needs: a good thing. Though it would be nice to have numbers to report (such as carbon dioxide emissions prevented by the use of cogeneration), such data is seldom released. In an ideal world every building would be wired to the 'net, publishing data in realtime on energy production, consumption, occupancy and everything else you can think of, but that is a much much broader issue and not a particular fault to be picked upon here.

Further design touches are aimed at making the building a more pleasant place to live. Because much of the building's roof is visible from the various towers in the vicinity (including its own), the architects chose to view the roof as the building's "fifth facade." So, the building's plant has been hidden away, with the necessary ventilation provided by subtle, continuous grilles rather than chimneys. In this way the building's "fifth facade" remains unsullied.

A final word on the building's color, which by now you have probably identified. Standing out and yet complimenting its white and gray neighbors, the choice of red feels like a risk that has paid off in spades. Standing second in line of a row of four siblings, it's 242 Units that stands out, but in a way that enhances them all (and more so than if all were red, or brightly colored). As an illustration of just how eye-catching the building is, search Salburúa, Vitoria-Gasteiz on Google Maps. It's not at all hard to spot.

It'd be nice to discuss the greenness of the building in more objective terms, but then that is nearly always the case.

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