” we have identified a set of design conditions through which a housing unit can increase its value over time; this without having to increase the amount of money of the current subsidy. ….We had to achieve enough density, (but without overcrowding), in order to be able to pay for the site, which because of its location was very expensive. …….. In between the private and public space, we introduced the collective space, conformed by around 20 families. The collective space is an intermediate level of association that allows surviving fragile social conditions…..due to the fact that 50% of each unit’s volume, will eventually be self-built, the building had to be porous enough to allow each unit to expand within its structure”. the architects in archdaily