Barcelona is already one of the most densely-populated cities in Europe, at about 74,000 people per square mile. That’s because the city is trapped between the mountains on one side and the Mediterranean Sea on the other. To increase living space, the only way to go is up. But how do you do that without knocking down the city’s beautiful buildings?

La casa por el tejado (the house on the roof), or LCT, is a project to drop penthouses onto the flat tops of buildings in Barcelona’s Eixample district. Billed as a way to solve the problem of limited space, it has several advantages.





For starters, it uses a resource that’s not exactly scarce in Barcelona–roof terraces. While some are used regularly as places to hang out, the truth is that most are given over to satellite dishes, clothes-drying lines, and junk. And in the summer, it’s too hot to go up there during the day. I lived in Barcelona for almost 10 years, and the only folks who use their terraces regularly are those whose apartments open straight onto one.

Prefabricated homes are also relatively painless for the neighbors. Instead of months of building work–which is particularly agonizing in a city where you’re stacked in such close proximity to everyone else–you just have to drop the thing in on a crane, then spend a while connecting utilities and finishing up.

Environmentally, putting prefabs on top of existing buildings looks fantastic. It’s fast, it doesn’t require demolishing old buildings, and it taps into existing infrastructure.





But there are downsides. First bear in mind that the housing shortage in Barcelona isn’t due to a lack of housing. It’s due to a lot of empty apartments, either because property was bought on speculation or family-owned buildings lie empty instead of being rented. In fact, the local government has considered a plan to force renting these properties if they’re left empty for too long.

Let’s look at the website of the project. The plan works like this: building owners agree to have a prefab penthouse dropped on the roof, and in turn the company (LCT) pays the owner. The suggestion is the the building owner can use the cash to improve the rest of the building, renovating it in accordance with building regulations. It’s just like selling off a plot of spare land to a developer. The penthouse is then sold by LCT.