Renzo Piano never wanted to build a house. With a portfolio of museums, towers, and other award-winning buildings across the world, his mind was elsewhere. But in 2005 a friend approached the architect asking if he would design a home for his family in Colorado's Rocky Mountains. Piano was resolute: he had never done residential work and had no intention of starting now. Hoping to entice the architect, the friend invited him to visit the site—a 183-acre ranch on a mountainside along a breathtaking valley veiled with aspen and scrub oak—via Google Earth. “That was the end,” says Piano. “I went flying in a little spaceship and then landed on that mountain with a light touch, floating a bit above the ground—then we started to dream together.”

Piano became intrigued by the potential of a project outside the large, institutional realm. While the programmatic needs of a house are straightforward, “Everything about it is more subtle, more personal,” he says. “It's about the culture and desires of the specific person. The clients have to tell you about the emotion they want to communicate. Then you have to translate this into a building.”

The husband and wife, who have grown children, had a straightforward brief: “Please build us a house where we live outside but don't get wet when it rains.” And they hoped to capture the essence and simplicity of traditional Japanese design. But Piano spoke in terms of rhythm, of music and poetry, which at first threw them off. “But he was right,” acknowledges the husband. “In the end, it was a more holistic experience we were after—that of quiet and vibration. The millions of details achieve that objective.”

Through a gate and past the caretaker's residence and a large barn, the drive meanders below the house's decks shooting out toward the valley, and then winds up to the entrance on the east. Except for the emphatic red metal roofs—which Piano painted his trademark ruby red to inject color as well as highlight the fragmentation of the house—the glass and wood forms nestle quietly into the slope. And, in winter, the roofs disappear under a blanket of snow.

The architects say they were drawn to timber by the fact that the west was built out of lumber. “America has had a tradition of building beautifully with wood,” says Piano. “This house is a little homage to that.” Honey-colored Douglas fir, which flows from the exterior to the interior walls, ceilings, and floors in a silken veneer grade is hardly the stuff of pioneer days, but it imbues the house with a glowing warmth. Using one primary material gives the building integrity and a sense of coherence, notes Piano. Another goal was to show how the house was made “without being too exhibitionistic,” he says, referring to the wood and steel structure, which is expressed—with restraint—both inside and out.

Not wanting a single monolithic building, the architects conceived the 13,800-square-foot house as a composition of seven volumes that correspond with the programmatic elements and are articulated by the separate roofs. “The form took shape as we maximized the views out to the south,” says Bianchi. Initially, the team envisioned the roofs as a system of wings lifting out toward both the north and south. But local building-height limitations prevented them from using steep pitches on the valley-facing side. So, instead, they designed flat roofs there, and used steeply pitched ones for the two upper-level guest suites, emphasizing the views toward the slope. The plan is simple and rational. A broad 130-foot-long central corridor runs east to west, connecting the various elements: the “kids' ” wing and guest rooms, the living spaces, and the master bedroom, whose acutely angled facade directs the gaze from the living room out to a dramatic mountain bookending the dale. At its center, this main “street” widens into a “piazza” that functions as a dining room, setting an informal tone and marking the heart of the house. The organization, points out Piano, is like a little village, with the central spine connecting the pieces. The journey along this path is punctuated by glimpses into jewel-box courtyards and through the house's multiple layers, and then the surprise as the tableau of the valley gloriously comes into view through the long south-facing facade.

“We're not talking about anything too cerebral or complicated. We're talking about compression and expansion of the space, about transparency and intimacy,” says Piano. When the house is not bustling with the activity of family and friends, a penetrating silence inside breeds introspection. At the same time, you are linked to the outside world through a sequence of planes that begins with the facade—a sublime Italian custom stainless-steel window system that forms the walls. The next layer is the stand of aspen, which shifts moods as it crosses the seasons with sprightly greens, flaming autumnal displays, and, in winter, lacy scrims. The final plane is the majestic peaks beyond.

The desire for this layered effect helped determine the house's 18-inch grid (a three-month discussion, say the architects), which is reflected in the mullion spacing. With too much glass, the first plane would be lost. And 18 inches granted more freedom than, say, 16 inches. The rigor of the dimensional grid and the tightness of the tolerances are mind-blowing. The centerlines between the deck boards align with the centerlines of the mullions, which align with the centerlines between floor planks, which align with the centerlines of the glue-laminated wood beams, which align with the standing seams on the metal roof. “When you try to have the world line up, it answers the questions but presents a lot of problems,” says Patrick Leeds, formerly with the executive architect Harry Teague, sounding a pragmatic note. “Where it comes to bear is in construction and whether we have contractors who are OCD enough.” They did. The result is that the connections and component pieces fade and you are left with an essence, which is the emotion—a calming frisson—that rings through the house.

With its museum projects, RPBW is known for understated design and “putting the art first.” Here, too, the architects have deferred to the program: the owners wanted an open, warm environment that matched their outlook and lifestyle. After all, notes Piano, “a house is not a mirror of the architect. It is a portrait of a family.”