A dwelling should be a place for families to conduct activities to meet their needs. The actually needed space is often greater than that available on the existing. The family’s need of space grows with the passage of time. Rusunawa is a type of shelter for the poor. It usually includes a multifunctional space, a kitchen, a bathroom/WC, and a balcony. The space to live in, the multifunctional space, should serve for living, sleeping, studying, TV watching, eating, storing, child-caring, and sometimes home-based business. Additional space that must occur in the multifunctional space may be done by occupying the corridor and extending or changing the function of the balcony which are illegal. The appropriate way for meeting the additional space demand is by adapting vertically. This study observes how much space is actually needed by the families and what these families did when they experiencing space shortage. 100 families living in Rusunawa Surabaya spreading across 14 locations are taken as respondents. The outcome is a recommendation of which type of space could be created by installing a mezzanine.