In slightly more than a week, a clever kit of parts can transform an old rental house into a net-zero energy home–one that creates as much renewable energy as it uses in a year–at no extra cost to tenants or building owners.

Net-zero homes are the kind of project that usually cost so much that only the richest, most environment-obsessed homeowners attempt it. But in the Netherlands, a group of innovators figured out how to create a system that could be used on the country’s huge inventory of low-income housing.

The mid-century rental houses, built in townhouse-like rows, all have a similar layout, so construction companies were able to design a system of prefab parts that pop easily on existing properties. A roof covered in solar panels can go directly on top of an old roof, minus tiles. New facades cover the old walls without any demolition. In the backyard, a new cube-shaped energy module holds everything needed for sustainable heat, hot water, power, and ventilation. It just needs to be plugged into the house.





The kit makes the retrofits fast enough that they barely disrupt the lives of the people living inside. “They don’t have to move out,” says Linda van Leeuwen, an engineer business developer for BAM Group, one of the construction companies behind the project. “For example, the same day we remove the window frames we are able to place the complete new front and back facade. We only need 20-40 inches of free space along the window frames inside the house, which means you just have to move your couch or television a little bit.”

The business model is as innovative as the actual design. A government team called Energiesprong realized that renters in the social housing projects were already paying a yearly energy bill of around $2,200. The retrofits eliminate that bill–and by asking tenants to pay the social housing corporations the same amount they would have paid a utility, it completely funds the construction process. Tenants don’t pay any extra, but they end up with a fully renovated house.

The building owners also save money. “These houses are about 50-60 years old,” says van Leeuwen. “Social housing corporations usually refurbish the bathroom, kitchen, and toilet every 15-20 years. Which means most bathrooms, kitchens and toilets need refurbishment anyway. By doing it now we can at the same time integrate new technologies, like ventilation, and new materials like glass that need less maintenance over the years.”





The cost of the retrofits is also quickly dropping. Two years ago, a single townhouse cost about $144,000 to retrofit, and now the cost is around $88,000. The development team is aiming to ultimately reach a cost as low as $45,000, so the retrofits could also be easily affordable for private homeowners.