Called Very Tiny Palazzo, the 40-square-metre annexe provides a studio or guest room nestled in a lush garden, which it overlooks through fully-glazed elevations.
Small, simply finished and largely transparent, the structure is topped by a concrete roof that spans the width of the garden, inlaid with a pink circle of Estremoz marble and small black squares of Marquita marble.
"This is the smallest house we ever built," Fala Atelier told Dezeen. "Calling it a palazzo refers to the main building nearby – a palace-like house – and provides a certain ambition to the otherwise very discrete piece."
"The luxuriant environment suggested an ambivalent approach to the architectural object," added the practice.
"At human height, the palace is transparent, but its crown is proud, adorned with precious stones and spanning across the perimeter walls."
Inside, a set change in the level of the concrete floor creates two distinct areas that can be used as living, bedroom or studio areas, with a bathroom and storage area tucked behind a full-height white cabinet.
Metal-framed sliding glass doors at either end allow this interior to be completely opened to the landscape, enabling the structure to function either as a more intimate residence or an open, pavilion-style space.
"In an [Adolf] Loos-like manner, two representative areas are defined by the different floors, with different degrees of intimacy," said the practice.
"The bathroom and storage room are hidden behind a unitary cabinet of lacquered wood, whose scale deliberately sits somewhere between architecture and furniture. A palace shouldn't be too simple after all," it continued.
Taking inspiration from French artist Henri Rousseau's painting "The Dream", the narrow garden, designed by landscape architects Oh!land studio, is filled with lush vegetation, surrounded by a wall of stone and metal fencing.
An informal path of wooden planks and stones cuts through this garden, connecting the main home and the rear of the plot to the Very Tiny Palazzo at its centre.
Fala Atelier was founded in 2013 by Filipe Magalhães, Ana Luisa Soares and Ahmed Belkhodja, and is known for the often colourful, geometric aesthetic used in its designs across Porto.
Previous projects by the practice include a home in Porto finished with candy-coloured accents, and a series of micro-apartments around a communal courtyard created by renovating two granite buildings.
The photography is by Ivo Tavares.
Architect: Fala Atelier
Project team: Filipe Magalhães, Ana Luisa Soares, Ahmed Belkhodja, Lera Samovich, Ana Lima, Rute Peixoto, Paulo Sousa
Landscape architect: Oh Land