The word “duplex” carries a certain connotation of budget-friendliness, whether it be in terms of its actual cost or the economy of its proportions, as it can easily slot into densely-populated urban areas. Typically consisting of two units contained side-by-side within a single structure, duplexes can be either humble and nondescript or grand and historic, like the classic Greystone buildings commonly found in Chicago. But rarely do these conjoined dwellings have the striking modern aesthetic of the Two-in-One House by Reiulf Ramstad Arkitekter, which was recently completed in Norway.

The Oslo-based firm, known for creating dramatic structures infused with Scandinavian minimalism, has designed a truly unique duplex that stands out for its crisp modernist aesthetic without striking a discordant note in a residential neighborhood dominated by homes built in the 1950s. Set into a steep snowy hillside, this narrow rectangular home marries two single-family residences within a glass volume perched atop a concrete base and clad in warm vertical slats of wood. The timber elements are meant to interplay with the straight, slender trunks of the broadleaf trees that surround the structure as the glass reflects the sky. The untreated cedar will weather with time, fading to a very similar shade as that of the living wood.

The rocky slope to the west embraces the building, which juts out over a patch of forest to the east. The small town of Ekerberglia, just outside Osl...