They are legal for industrial use in the USA, under international codes for mezzanines, in Canada as "secondary stairs for convenience purposes" and in the UK for access to lofts and bedrooms that do not have the only bathroom. Another source says "codes do not require stairs to unoccupied attics and lofts, so it's up to the local code inspector a ladder or stair that does not meet rise and run requirements."
It is a real shame that Lapayre won't sell their stairs to anyone, because they have a really elegant aluminum one where with a center rail and very elegant casting that ties together with the handrail. This would look great anywhere. (more pictures here)
"The Karina modular space saver stairkit is a unique and stylish solution for narrow access areas, such as lofts or attics. The Karina's ingenious supporting structure allows complete flexibility in the application, and the Beachwood alternating style treads are appropriately shaped and staggered to guarantee maximum utilization of space, without compromising functionality."
Martin John Brown got an alternating tread stair approved for his wonderful tiny house in Seattle after many battles with the inspectors, but even he notes that "There’s a few caveats, though. Falls on this steep pitch could be serious, so the handrail is important. Using the handrail means you will only have one hand to carry things. And since people aren’t used to these stairs, they require PRACTICE. It might take just two or three uses to get that practice, but practice is essential. Several times I have observed a physically unfit and uncoordinated person taking their first trip down these stairs (you come down forwards just like on a regular stair), misjudging the second or third step, then stumbling a bit. They catch themselves with a hand on the handrail and then get down fine. After two or three uses they have no problem anymore. A physically coordinated person often has no stumbles at all."
So while they are a lovely space-saving idea and even legal in certain places, they are not for everyone. Still, I wish the authorities would give architects in North America a bit more leeway like they do in the UK.
See earlier Treehugger posts on the Bookcase stair (shown above) and a Czech version.. Gabriella Gustafson and Mattias Ståhlbom designed a stunning alternating tread stair that looks a little less safe and needs a handrail. See also Justin's roundup of great stairs at ::Materialicious