A black box built from oriented strand board houses the kitchen and bathrooms of this converted barn home in Portugal, and also integrates a staircase leading to the mezzanine floor above (+ slideshow).

Lisbon-based architect Inês Brandão renovated a 50-year-old barn in Leiria, Portugal to create the family home.

"The aim was to maintain existing memories from a space that was once the stage to such varied experiences," said Brandão. "We chose to protect it and elect it as the protagonist of the new home of a young growing family."

Limited budget meant the architects chose affordable materials to complete the project. This included oriented strand board (OSB) – a type of engineered panel made up of wooden strands.

The material was also recently used to build a giant camera obscura and an adaptable Madrid apartment.

The black-painted OSB box occupies a space within the main living space. It provides a kitchen on one side, storage on the other, and encloses bathrooms at its centre. It also include a staircase to a new mezzanine floor.

"With a very small budget, it was essential to create a compact element bringing together all the new functions," said the architects. "This 'furniture' is fundamental in the compartmentalisation of the social area."

A dining-cum-living area is located towards the front of the space. Here, an L-shaped grey sofa faces a wood-burning hearth.

A long wooden table offers enough space to seat eight diners, illuminated by a sculptural pendant light.

The upper level, which once functioned as an area for drying grain, overlooks the living space. It offers residents a quiet retreat that doubles as a workspace.

Walls and ceilings throughout the entire property are painted white, offering a stark contrast to the black volume. Floors are wooden throughout, but the master bedroom features parquet.

Other agricultural buildings that have been converted for residential use include an Alpine cattle shed that is now a holiday cabin and a former barn in England featuring a staircase hidden behind a cupboard door.

Photography is by João Morgado.