House Lessans, which stands on the site of an old farmstead in County Down, was chosen over six other architect-designed homes vying for the annual Royal Institute of British Architects (RIBA) House of the Year prize.
It was named as this year's winner during the final episode of the Channel 4 television series Grand Designs: House of the Year.
Belfast studio McGonigle McGrath designed House Lessans to meet the needs of a semi-retired couple and their children, who have left home but occasionally visit and stay.
It is formed of two pared-back volumes with walls made from white-rendered concrete with pitched zinc roofs, designed to complement the neighbouring agricultural outbuildings.
McGonigle McGrath used deliberately simple details and construction methods that included cheap concrete blocks for the walls and huge openable windows, instead of bifold doors.
As a result, House Lessans cost just £335,000, equivalent to £1,425 per square metre.
RIBA president Alan Jones said the home was "executed with incredible clarity and restraint".
"House Lessans demonstrates that life enhancing architecture does not have to cost the earth" he said.
"McGonigle McGrath have used simple and cheap materials to create a truly bespoke home that resonates with its owners and its context. Even with the tightest of budgets, House Lessans shows that a dream home, designed by a talented architect, can be a reality."
One wing of the house contains a suite of three bedrooms, while the second hosts the communal living spaces that includes a double-height living room.
Like the exterior, all the rooms have simple finishes. The focus is on views out over the landscape that are framed through expanses of glass.
The house was chosen for RIBA House of the Year by a panel including Tom Miller of Haysom Ward Miller Architects, last year's winner of the award, and John Pardey as chair.