The Tondela-based practices added two brightly coloured modules to each of the apartments to help define specific areas for sleeping and dining within the open-plan space.
This cabinetry forms a golden-yellow niche for a kitchenette and a blue nook for a bedroom in each home.
To help make the most of the limited floor space, Waataa also integrated several pieces of fold-out furniture into the modules.
A dining table can be pulled down from a wall adjacent to the cooking area, while a bed extends from the back panel of the sleeping area. Drawers and cupboards are also slotted into these nooks to provide plenty of storage space.
"The incorporation of fold-away furniture in the design is both a rational space-saving mechanism and an opportunity of interaction with one's own house, favouring the overlapping and intertwining of spatial functions according to the moment's necessity," architect Lucas Diz told Dezeen.
"Due to the nature of its pre-existence, the housing core to be generated could not and should not follow conventional patterns."
The trio of apartments known as the BY Studios benefit from the high ceilings, large windows and bathroom facilities of their former use as offices, but Waataa introduced the accents of bright colour to give the spaces a more residential feel.
The architects used blue for the bedrooms to evoke a sense of calm and rest, while a vibrant yellow provides the backdrop for the kitchen.
These brightly coloured areas are emphasised by the neutral decor of the rest of the space, with each apartment finished with white walls and a slate-grey bathroom.
Simple materials have been implemented throughout, with Waataa choosing plain ceramic tiles, vinyl and painted plasterboard for surfaces.
A mezzanine level was also added to each apartment to provide a "space of refuge and quiet" from the open-planned areas below.
The upstairs of the largest studio is fitted with a long table, offering an alternative place to work or entertain guests.
The architects have chosen to use alternate-tread steps to save further space. French architects Schemaa created a similar staircase to double as storage for a tiny Paris apartment.
Architecture: Waataa Architects
Design team: Rita Cantisano Diz, Lucas Cantisano Diz, Miguel de Gouveia André