The Kimbell Art Museum was cramped.Although it wasn’t obvious — the galleries always looked lovely — the successes over the past 41 years had led to problems. The good kind, but problems nonetheless.There was not enough room to display traveling exhibitions and the magnificent permanent collection at the same time. This often disappointed visitors who had come specifically to view the Fort Worth museum’s renowned holdings. Whenever a special exhibit was mounted, the permanent collection had to go into storage.There were issues behind the gallery walls, as well. The growing education department worked out of a closet, and offices were being partitioned or crammed into whatever space could be claimed.The art was being squeezed, and so was the staff.The remedy to the Kimbell’s space constrictions has been solved. The new expansion building, the Piano Pavilion, opens to the public Wednesday. The time between recognizing the problems and creating the fix was fraught with obstacles. The architecturally significant Louis Kahn building from 1972 was considered sacrosanct. There would have to be a separate structure built on the property. Where to put it, and who should design it, were delicate issues.There was a vocal resistance to any change. Architects worried that the existing building and site would be compromised by any modifications, and locals who used the expansive grounds of the Kimbell feared the loss of the parklike setting. The Kimbell board eventually chose Italian architect Renzo Piano and the Renzo Piano Building Workshop to alleviate the squeeze.It was a good choice.The Genoa, Italy-based Piano has become the go-to architect for museums, because he is quite sensitive to the demands of exhibiting artworks. Over the course of his nearly 50-year career, he has completed 21 museum projects, and four more are under construction.Plus, Piano, who is 76, had worked with the late Kahn and likely would be sympathetic to the older architect’s aesthetic.Still, there were grumblings — when the Kimbell announced that Piano had been chosen, when he presented his earliest design, and even after he produced a model that addressed the needs of the museums and the concerns of the detractors.Three years after breaking ground, the building is finished. If there are any doubters left, they should have few complaints.The Piano Pavilion is spectacular, and it successfully addresses the need for more galleries and an education center. And it plays very nicely with the Kahn building. They face each other across what Piano calls a lawn for conversation.No doubt they will share the incoming kudos.Piano was exceedingly gracious to Louis Kahn in designing a building that echoes many of the spatial allocations and proportions of the original.Each has a tripartite facade that has two long galleries flanking an entrance lobby.The buildings have a compatible symmetry but different personalities.While the Kahn building is musclebound and grounded, the Piano Pavilion seems airy enough to levitate.The Kahn is solid; the Piano, transparent.There is a sexual tension between the two. They look like a pair of ballet dancers mirroring each other’s moves — one male, one female; one strong, one sinuous; one grounded, one taking flight.It is an architectural pas de deux.The Piano Pavilion is visually lighter. The walls of glass give it a transparency, and the silky titanium-infused concrete is less weighty in appearance than the travertine walls of the Kahn building.While the original Kimbell has a procession of cycloid vaults, the Piano Pavilion has a flat roof with only the suggestion of curved roof panels, a slight nod to the cycloid vaults across the lawn.The large beams that support the glass roof seem to hover as if they are separate from the walls. Often, the intersections of materials are invisible.There are separations throughout the building, between interior walls and floors, between the window walls and the roof. This seeming lack of solidity makes the parts look as if they are about to float away. There is a significant common denominator, and that is the deft handling of wall-washing light. Piano uses a clerestory and many window walls that have a double layer of shades to control the amount of light that is admitted.The glass ceiling has louvers, and both the louvers and shades are controlled electronically to respond to the sun’s arc across the sky and to constantly adjust to the ambient brightness.There are light wells and interior gardens walled by glass that also wash the galleries in an abundance of light. Piano manipulates visitors’ experiences by forcing their first view of the campus on Kahn’s structure — something few people appreciated. Kahn underestimated Texans’ primal urge to park as close to the door as possible and then scurry inside.He expected visitors to park in the lot, walk around the building, take in the gardens and landscaping, walk across the lawn, then cross a graveled plaza (death to high heels) and enter the front door.It rarely happened.Most people entered through what was considered the back door.So Piano forces the visitors to gaze upon what was seldom appreciated. Entering Piano’s building from the new underground parking structure, whether by the glass-enclosed elevator or the stairs, the first thing the visitor sees is the front of the Kahn building.It’s a great view. The expansive lobby will multitask for receptions, educational events and parties.Eventually, a small cafe or coffee shop will be added when the crush of the opening crowds has passed.A gift shop just inside the African and pre-Columbian gallery will offer a more expensive mix of merchandise than that of the larger gift shop in the Kahn building. The building includes three large galleries in the Piano Pavilion, an auditorium that seats 298, and a four-room education center. Not open to the public are offices, a library with Kimbell archives and storage facilities.There is also an underground parking garage for 135 cars; access to it is from the south end of the old parking lot behind the Kahn building. The Piano Pavilion has a little more than 100,000 square feet of space, compared with Kahn’s 120,000, but each square foot in the pavilion will use half the energy. New energy-efficient construction techniques, such as the photovoltaic cells on the glass roof, 36 geothermal wells, low-energy LEDs and a breathable floor that emits low-velocity cooled or heated air, should provide substantial energy savings. For the opening celebrations, the Kimbell’s permanent collection is hung in the gallery that will display the special traveling exhibits. This was necessitated by the special exhibit from the Chicago Institute of Art that is on display in the Kahn building.No one expected the old masters’ works to shine on the pavilion’s walls, but many pieces look better here than they ever looked across the lawn. The concrete walls have a 2 percent solution of titanium, and this silky suedelike finish makes them a more neutral background than the pitted travertine.The Kimbell has installed its best pieces from the 16th, 17th and 18th centuries against these smooth, spartan gray walls.“We’ve seen it with modern pieces but never old master works,” says Kimbell director Eric M. Lee. “This may be the first time this has ever been done — putting old master works on concrete. And the paintings look fantastic.”He points to four enormous 18th-century paintings by Francois Boucher.“We’ve had these since 1972, and they are rarely seen together. We just didn’t have room,” says Lee, who pauses and slowly walks by the 9-foot-tall riotous mythologies swirling with gods and goddesses. They always looked a little much in the Kimbell — too big, too busy, too saccharine. Now, with room to breathe, they look very different.“They have never looked better,” Lee says. “They are among the highlights of the collection.” Having the space to pull out rarely seen works and putting the Asian, African and pre-Columbian pieces on semipermanent display will give new life to many of the Kimbell’s treasures.“With the Piano Pavilion, we can have almost the entire permanent collection on display and host special exhibitions at the same time,” Lee says.And now that the pavilion has shown it is a good venue for artworks of any age, it gives the museum great flexibility in mounting its collection, as well as special exhibitions. Problem solved.