Following in the footsteps of the top-scoring entrant from the 2012 Solar Decathlon Europe, a handful of the teams participating in the 2014 edition of the collegiate solar home design/build/perform showdown — now winding to a close at its new home at Cité du Soleil in Versailles, France — have unveiled projects that address the need for innovative yet affordable modes of housing in increasingly cramped urban areas.

In a departure from past Solar Decathlons, European or otherwise, the 20 competiting teams were actually encouraged by event organizers to think beyond the creation of individual houses and address the density issue with "collective housing projects." While there's been a smattering of past Solar Decathlon entrants that have broached the subject of housing and urban population growth, this year's turnout is quite exceptional when it comes to city centricity.

And you truly can’t get anymore city-centric than the Rooftop Project from Germany’s Team Rooftop, a team comprised of students from the Berlin University of the Arts and the Berlin Institute of Technology. An urban housing solution conceived in direct response to the “aggressive” gentrification occurring across Berlin, the Rooftop Project involves plopping down high-performance modular dwellings atop the city’s sizable stock of Altbau buildings — large and highly inefficient prewar apartment blocks (literally: “old-build”) with a decent amount of rooftop real estate to spare.

Explains the team:

… instead of promoting urban sprawl or taking away the city’s soul with the standard apartment-investment complexes for expats, we want to use and revalue this prime living space: densifying and not displacing the people who lived in their neigbourhoods for years. Our concept is to create living space on top of the Altbau and to improve its overall energy balance — thus finding one solution to two pressing challenges. The Rooftop House replaces the makeshift inefficient roof truss and gives energy back to the building below.

This isn’t a strictly one-way relationship, however, and the Altbau doesn't reap all the benefits of hosting a sleek, energy-producing rooftop tiny house on its roof. It’s a polite and highly symbiotic arrangement as Team Rooftop describes “on one hand the rooftop house’s water is supplied via the Altbau; on the other hand, the electricity generated by our solar panels is transferred to and shared with the host building.” Furthermore, Team Rooftop views the roof-bound dwelling, crowdfunded by the existing residents of an Altbau, as being a “catalyst to galvanize a local movement encouraging and supporting the owners to bear responsibility for their homes.”

Post-competition, the prototype dwelling will be installed on the rooftop of a building at Berlin University of the Arts or Berlin Institute of Technology (the two schools share a Charlottenburg campus) and used as a joint research facility. However, a vacant Altbau rooftop located within one of Berlin’s most housing-strapped neighborhoods, not an educational institution, remains the ultimate goal.

Another German team, Team OnTop, is also eyeing the disused urban rooftop as a place in which to perch the plus-energy house of the future. Composed of students and faculty from the University of Applied Sciences Frankfurt am Main, the OnTop concept, like the Rooftop House concept, envisions a completely symbiotic relationship between the new rooftop structure and its host which, in this instance, would involveFrankfurt’s abundance of post-war buildings.

The main idea is increased density in the inner city with the help of a build-up on top of an existing building. Thereby additional living space is created, where increased density at the ground level is not possible due to densely built-up areas. At the same time the build-up is able to produce an energy surplus by building integrated solar energy technique, because it elevated and ideally unshaded. This surplus is transferred to the existing building stock, on which it is built and provides energy for itself and partly for the old building. At this point of intersection a symbiosis comes into existence. Our prototype for the SD Europe features significant characteristics of a symbiont. The new resulting unit and the benefit that it takes and returns from its surroundings we describe as symbiogenesis. This is an innovative and intelligent node which blends in with the energy, mobility and social networks of the city.

While Team OnTop's official Solar Decathlon homepage doesn't offer all that much info on the engineering or design fronts, the concept itself seems to be a winning one.

In addition to rooftop urban infill projects, the humble rowhouse, a staple of cities across the globe, is also being treated to a reimagining at the 2014 Solar Decathlon Europe. From Team Réciprocité, a partnership between seassoned Solar Decathlon vets Appalachian State University and France’s Université d’Angers, comes Maison Reciprocity, a low-rise multi-family housing unit that's described as “an answer to the lack of affordable, healthy, high-quality, durable, sustainable, and adaptable housing" in existing rowhouse neighborhoods.

This modular, two-story townhouse — perhaps one of the more commercially viable entrants in this year's competition — is composed of a trio of distinct prefabricated modules: CHORD (Container for High-Performance Operation, Recirculation, and Distribution), a module which houses the building’s mechanical core along with kitchen and bathrooms; the Urban Shell which serves as the structure’s highly insulated structural envelope; and the “Living” Brise-Soleil, a multi-tasking intelligent façade that sports photovoltaic panels, a rainwater collection system, and operable sun shades that prevent the interior of the building from becoming uncomfortably toasty during the summer months.

Team Réciprocité, first place winner in the all-important Energy Balance competition, is one of two joint Euro-American teams duking it out at this year's Solar Decathlon Europe. The other is Team Inside Out (Brown University, the Rhode Island School of Design, and Germany's the University of Applied Science - Erfurt).

Last but not least, there’s RhOME for denCity, an Active House project from Italy’s Universita Delgi Studi Di Roma Tre with a (cumbersome to type out) name that pretty much explains it all.

Unlike most Solar Decathlon entries that traditionally serve as standalone dwellings, the RhOME prototype concept is a 645-square-foot apartment geared to combat the strain on resources brought on by overcrowding in cities. Revolving around five “Rs” (Reuse, Reduce, Regeneration, Rapidity, and Relationship) and taking in numerous social, economic, and environmental considerations, the prototype apartment — “a home for Rome" —was designed to serve as the top floor of four-story apartment complex proposed for the Tor Fiscale district.

Rome, the eternal city full of beautiful ancient remains and roman heritage, shares the same aspect with other metropolis about urban degeneration. Our work try to give an answer to big city issues, through the elaboration of a replayable settlement method with recognisable values, that can bring to the regeneration of existing cities. The project designed for Rome urban areas is taken as an opportunity to deal with the global condition, that it’s easier to explain with the description of a local act. We want to convey people the idea of thinking globally by acting locally'.

The RhOME team presents a lot of big ideas (as evidenced above) and the design of the prototype unit isn't initially easy to comprehend. I still don't quite get it. However, the Solar Decathlon Europe judges have seemed to respond well to the concept, awarding it second prize in the Architecture contest and fifth in the Sustainability contest.

The final awards along with the grand winner of the 2014 Solar Decathlon Europe will be announced tomorrow, June 12, at Cité du Soleil — billed as a "temporary and sustainable micro-city" — in Versailles. The 18-day public exhibition period will conclude on July 14. As you might recall, the 2010 and 2012 editions of the event were held not in Versailles, but in Madrid.

As of publication, these four intriguing and urban-oriented entrants all currently rank on the top half of the SD Europe scoreboard with Maison Recoprocity in second place (645.34 points) overall followed by the Rooftop Project in third place with 644.01 points. RhOME for the denCity (637.29 points) and OnTop (618.96 points) trail in fifth and ninth place, respectively. These rankings, however, could very much change in the coming hours. I'm guessing, however, that the four projects profiled above will remain within the top 10.

Do take a moment to peruse the 2014 SD Europe website for up-to-date scoring and monitoring and to vote for your favorite solar-powered abode fighting for the title of most attractive, cost-effective, and energy-efficient solar-powered prototype home. As to be expected, European teams make up a bulk of the competition although there are also fierce contenders hailing from Mexico, Costa Rica, Japan, Thailand, Taiwan and India. In total, students and faculty from schools in 16 different countries are participating in this year's event.

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Matt Hickman ( @mattyhick ) writes about design, architecture and the intersection between the natural world and the built environment.

2014 Solar Decathlon Europe competitors tackle urban density
Sustainable city living is a focal point for a quartet of contenders at the 2014 Solar Decathlon Europe in Versailles.