Casa SPI was designed for the Spinelli family in San José de la Montaña, Heredia, at over 1600 meters above sea level, on a densely vegetated property in a cold mountain climate. The project is the culmination of Beer’s geometric field strategy — the work in which his decade-long research into field geometry as a design tool reached its fullest expression, and the one he considered closest to answering the shortcomings of the Modern Movement on his own terms.

The design derives from the rotation of seven squares, drawn from Beer’s study of Greek theatre geometry. Two squares of equal size, each rotated forty-five degrees from one another, establish the foundational field — the pauta — that governs the entire composition. The living and dining areas occupy the intersection of these rotated squares, and from their sides, vertices and intersections, the rest of the house is projected. The geometric order does not merely organize the plan; it generates spatial tension between elements — between the fireplace and the adjacent wall, between structure and light — tensions that Beer orchestrated to produce unexpected spatial effects that the geometry alone could not anticipate.

Brick, timber, and glass are the three predominant materials, deployed with compositional clarity that keeps the interior language legible despite the complexity of the underlying geometric system. Light works alongside them as an active design element: Beer calculated that sunlight entering through the roof opening and firelight at night would behave differently against the irregular pyramidal surfaces, producing constant change across the day and the seasons. Form, texture, and illumination work together toward a single architectural intention: permutation — a house that continues to surprise space by space, hour by hour, season by season.

Casa SPI has been the subject of academic research, most recently analyzed in a peer-reviewed article published in Academia XXII by UNAM (2024), examining its role in the development of Costa Rican architectural practice.