Among other things, Jerusalem is famous for its sunlight—its clarity, intensity, and shifts in color. So when Israel Museum director James Snyder set out to expand the museum in 2007, he wanted to showcase that environmental quality. He commissioned Olafur Eliasson to create an artwork representing the colors of Jerusalem light, and for the architecture, he hired James Carpenter Design Associates (JCDA), a New York firm that specializes in a material not often used in the city: glass.

Alfred Mansfeld designed the Israel Museum in the 1960s as a modernist take on an Arab village—essentially, a series of low-lying pavilions set on a hill and plugged into a geometric grid. Mansfeld clad them in local stone, glazing them only with a thin clerestory strip along the upper edges. The $100 million campus renewal and expansion, which opened in July, razed several ad hoc additions and added nearly 100,000 square feet of space, most of which organizes the visitor experience via three new pavilions (ticketing area, bookstore, café), a new volume to anchor gallery circulation, and an axial campus-circulation spine.

Whereas Mansfeld’s buildings are hermetic exhibition spaces, JCDA’s are glazed from floor to ceiling. The light in Jersusalem is delightful, to be sure, but it also presents significant architectural problems in the form of unforgiving heat gain and blistering glare. “The intensity is severe,” Carpenter notes. So it fell to his firm to reconcile the desire for transparency with the environmental reality. The result is a series of glass pavilions, each set within an envelope of custom-designed louvers. This outer surface bounces the sunlight upward to the spaces’ ceilings, where it reflects down, creating a crisp, ambient natural light.

The architects used plaster models to develop the shape and curvature of the louvers, testing their performance through the energy-analysis software Ecotect. Then, using Radiance software, JCDA visualized interior light conditions and glare. “The museum’s building committee was concerned we didn’t understand Israel’s climate when we showed them renderings of glass pavilions,” says JCDA senior associate Reid Freeman, who oversaw the project. “We really had to demonstrate these buildings would perform.”

To fine-tune the analysis, Carpenter Norris Consulting, a daylighting and glazing consultancy headed by JCDA’s namesake and Davidson Norris, wrote software to introduce even greater specificity for Jerusalem’s conditions, allowing the designers to understand the precise performance of each elevation every day over the course of a year. They learned, for example, that the glass in the retail pavilion’s west elevation—the surface with the most direct sun exposure—received 454 watts per square meter of solar exposure without the louvers on Aug. 21. With the louvers, this value dropped to 5 watts per square meter. “We were really able to scale down the mechanical systems,” says Carpenter.

Compiling their findings, the architects determined the louver shapes required to create interior spaces flooded with diffused natural light and to minimize heat gain. Working with Moeding, a cladding manufacturer based in Munich, JCDA developed extruded terra-cotta louvers with an integral color that corresponds with the color palette of the local stone used throughout the campus. The material has an organic appearance, which JCDA liked, plus the reflectivity to redirect sunlight and a robust tensile strength. Set into custom aluminum clips, the louvers accomplish specific tasks. JCDA came up with two sets—one set for the east and west elevations and another for north and south. Each louver profile has a vertical surface to block direct light. A curved surface on top redirects light upward to the ceilings, while the slope underneath registers the light from the louver below, creating subtle ribbons of luminescence.

For the east and west elevations, which receive the most intense sun exposure, JCDA used louvers with an expanded profile and tightened the interval between them to eliminate direct sun penetration. For the north and south elevations, the architects opted for slenderer profiles and opened the gaps. In order to unify the pavilions, they locked all four elevations into a verticle module: one louver and a gap on the east and west sides, and two louvers plus two gaps on the north and south sides, equal 22.4 centimeters—the grid Mansfeld used to lay out the campus.

For the corridor connecting the campus entry with the gallery entrance, the architects had to negotiate a change in topography. They called for stacked axial paths: one outdoor and at grade, the other indoor and directly beneath it. To introduce natural light into the underground space, along the western edge of the upper path, JCDA introduced an in-grade cast-glass surface that serves as a ribbon of skylight glazing for the subterranean space, spanning a double-glass wall below. The surface of the wall running along the corridor is lightly acid-etched glass, which catches the light filtered through the cast glass above. Light is also brought into the subterranean space by a series of drilled-down courtyards, also along the western edge of the in-grade path, that house plants and sculpture.

“The way that the landscape and the museum architecture merge is an unbelievably powerful statement,” says Snyder. With JCDA’s additions, this merger takes on added significance. “Carpenter’s translucent volumes allow for a resonance with the opacity of the existing buildings,” Snyder adds. “He starts with glass, but it’s really about light. It’s about working with light, manipulating light.”