Although houses are quite durable products, they do reach the end of their useful life at some point. Demolition or deconstruction releases numerous raw materials that might be recycled. This is even required by law, but in practice the potential is hardly used. In addition, many building materials are almost inseparable, such as thermal insulation composite systems or paints on wallpaper that is glued to walls. The result is an expensive and unsustainable use of resources.

To find out if houses can be recycled more efficiently, a team from Hochschule München led by Prof. Dr.-Ing. Natalie Essig and Prof. Dr.-Ing. Andrea Kustermann launched the Rural Mining project. “We wanted to know whether building materials might not be reused in terms of a true circular economy or recycled at the same level of quality,” says Sara Lindner, describing the idea behind the project. The idea of rebuilding rather than discarding is not yet very popular in the building industry, but Lindner believes that the recycling of a house should actually be taken into consideration during the planning stage.

The young architect has supervised the Rural Mining project for the past three years and has accompanied several prefabricated houses while they were deconstructed and moved to another location. Prefabricated wood houses have a great advantage over solid construction buildings: They can be relocated quite easily. Some customers will buy show houses from a manufacturer's exhibition at favourable conditions, have them deconstructed and reassemble them at their place of residence. The project team has used this circumstance for their research and analysed exactly how many parts and raw materials could be preserved for reconstruction.

Even prefabricated wood houses cannot be completely reused

At present, 23 percent of all one- or two-family houses in Germany are prefabricated houses. Thus, the so-called prefabs are firmly established in the market but still outnumbered by conventional construction methods. The results of the Rural Mining project, which has specifically focussed on prefabricated wood houses, are therefore unlikely to revolutionise the entire building industry straight away. But they do impressively demonstrate how much potential there is for improvement: Even buildings made of prefabricated elements leave many materials behind that are no longer used when the houses are rebuilt.

“The prefabricated wood components, such as wall and ceiling elements, can be reused pretty easily,” says Lindner. “But with the top layers, things become more difficult: Plasterboard cladding and floor coverings, for instance, often have to be destroyed when removing them in order to get to the screw connections of the components.” And when it comes to the floor slab, reuse is completely out of the question: The solid concrete can only be removed by demolition and is later often used as filling material for road construction.

A guideline for manufacturers and subcontractors

In addition to a detailed list of which material can be reused in construction and to what extent, the project team also examined samples of prefabricated wood houses in the laboratory. They tested various tools, including home-made utensils and special tools from the manufacturers. When asked to summarise the results of this work, Lindner says: “Actually, almost anything can be disassembled if you try hard enough. The question is whether the effort is worth it. You can, of course, pull every single nail or track down and remove even the last staple. But for a general guide to deconstructing and rebuilding a house, that procedure is probably much too elaborate.”

Those steps that can be executed with reasonable effort, however, the team is currently compiling in a guideline which is primarily intended to serve as a manual for manufacturing companies and their subcontractors. But the guideline might also raise awareness among house buyers by showing them how many recyclable raw materials their house contains.

The problem is: When you buy a house, the last thing you will probably want to think about is its deconstruction. Lindner adds that, although energy consumption during its lifetime is now taken into account when a house is built, resource consumption during its construction or deconstruction is not. Yet selective deconstruction can be quite profitable, considering the high disposal costs for mixed construction waste. Moreover, if it is carefully deconstructed, buyers of a prefabricated show house may save considerably on material costs. These are a lot of incentives in addition to the ecological aspect of reuse and recycling, says Lindner.

Sustainability in the building sector is becoming more of an issue

However, the architect does not believe that prefabricated houses will be deconstructed and rebuilt all over the country in future. “That's more of a niche phenomenon,” she says. “But it does highlight the issue of sustainability in the building sector, and things are actually starting to move here: For example, we see more and more component exchanges for used building materials, such as the so-called HarvestMaps.” This concept of online marketplaces for used building components was established in the Netherlands several years ago.

So, things are definitely changing, especially in the construction sector which is one of the largest CO2 producers due to its massive consumption of concrete. Lindner, who has been working on various questions of sustainability in the building industry for years – for instance, she helped to develop the “Evaluation system for sustainable small residential buildings” – is already thinking beyond prefabricated wood houses: Can similar ideas and concepts be implemented for solid construction? How can walls made of bricks and mortar be recycled? Are there alternatives to adhesives and glue so that components can later be separated more easily?

Meanwhile, her study objects in the Rural Mining project – the houses whose relocation she has so meticulously accompanied over the past years – have all been reassembled in their new location. Some of them look exactly as they did in the manufacturer's exhibition, and some were even moved with furniture. Their new owners can probably claim to have achieved one of the highest reuse rates of all the one- or two-family houses in Germany.