As housing becomes less and less affordable in major cities around the world, governments, developers and designers are looking for ever-more radical solutions. One area of focus is micro-apartments, and one architect has come up with one of the smallest solutions yet.

Earlier this year Hong Kong-based James Law Cybertecture unveiled designs for homes inside concrete water pipes, called OPods. And they are only 100 SF.

The homes include a bench that folds out into a bed and cooking and bathroom facilities, as well as space-saving furniture.

The inspiration came from the city’s notoriously small and expensive housing. Consumer trend analysis firm Trend Watching points out that they may be tiny, but these rooms are still about twice the size of the houses some people inhabit in Hong Kong. They may be small, but at least they are well-designed, the theory goes.

Designer James Law said the concrete tubes were cheap and could be stacked in odd spaces between buildings or under bridges where other kinds of housing could not be built. Because the pipes are so heavy they do not have to be bolted together when they are stacked, meaning their location can be moved.

"We are facing a tangible affordability problem in our cities," Law told Business Insider. "It is almost beyond the reach of most people to afford to live in a proper home in Hong Kong.

"Because of the pressure caused by the growth of cities, we have to get more out of a smaller space," he added. "We need to make architecture that is more responsive to the actual conditions and needs of people."

The firm has signed its first development agreement to produce a scheme in Shenzhen, China.