There are a few ineluctable facts about buildings. They are expensive, time consuming and labor intensive to make. They are strongest if built from the sturdiest materials. Well, no, on all counts. Japanese architect Shigeru Ban has built homes, pavilions and churches, some of them permanent, using little more than cardboard tubes. I was interested in weak materials, says Ban, 42. Whenever we invent a new material or new structural system, a new architecture comes out of it. Ironically, Ban may be closer to the old modernist ideals than many who build today in glass and steel. He wants beauty to be attainable by the masses, even the poorest.Ban first began to use the tubes in the '80s, in exhibitions. Impressed by the material's load-bearing capacity (he calls cardboard improved wood), he thought of them again in 1995, after the Kobe earthquake, and used donated 34-ply tubes to build a community hall and houses. Working with the United Nations, Ban has shipped paper log houses to Turkey and Rwanda. Refugee shelter has to be beautiful, he says. Psychologically, refugees are damaged. They have to stay in nice places. But it's not all about utility. Ban has managed to turn ugly-duckling cardboard into some gorgeous swans. The Japanese pavilion he created for this year's EXPO 2000 in Hannover, Germany, is a huge undulating grid of paper tubes enclosed, like a covered wagon, with a paper canopy. An eight-ton, 27-m-long lattice arch of tubes currently swoops over the garden at the Museum of Modern Art in New York City, casting a thatch of ever changing shadows. Ban's designs touch the earth lightly in more ways than one. After EXPO 2000, his pavilion will be shipped to a recycling center to be returned to the pulp from whence it came. Just try that with bricks.