Will is concerned. He and Charlie have been meaning to expand the house for a while now, but with the imminent arrival of their mates for a fortnight, space is suddenly essential, and he's having great difficulty finding a room. He's wandered around a few candidates on Vbay (a virtual peer-to-peer auction site), and although one of the options is a second-hand double bedroom available close by it's not the master suite they were hoping for.

Charlie was one of the first residents of the Hackney Reef - a modular housing complex built around a communal square and facilities (a couple of bars and a gym in this case given the predominantly young professional demographic of the occupants).

When they decided to move in together, Will brought a couple of his rooms with him from the Cambridge Reef, selling the duplicate core facilities to his neighbours who were looking to bud-off a small self-contained flat from their larger family dwelling.

Once his rooms were attached to Charlie's it became clear that they still had more space than they needed, so after a bit of haggling they swapped one of the reception rooms for a nano-solar roof conservatory to provide food and additional power. What with the Reef geothermal, they're now entirely self-sufficient in energy.

Now it's time to grow their house again. Will is toying with the idea of ordering a new customised module, but it's not the added carbon expense (in comparison to a recycled one) that's putting him off, more the fear that it might not be delivered in time. He's beginning to lose faith in the search, but decides on one last visit to the LifePlus second-hand market and is amazed to spot precisely what they are looking for arriving as he does.

A quick look around confirms that not only is it the right size, but it's relatively local and has the intelligent wall surfaces upgrade - no need to spend time decorating, they can simply download the colour, patterns or images they want to display.

Plus, it is the same make as their current rooms, so all the power, entertainment and building control services will plug directly in to the house with no need for an adaptor kit. Best of all, it's available immediately and could be delivered and installed at the weekend - panic over.