Why do unoccupied houses age so quickly?

I don’t know if you have ever seen those vacant old houses in the countryside. If no one lives in them for a long time, the houses will deteriorate very quickly. Some old houses may even collapse within a few years.

This seems to contradict our usual thinking. Why do occupied houses last longer, while unoccupied houses break down first? Is this true for all houses?

Image from: www.pixabay.com

If a house is not maintained, it will age quickly.

I guess the thing you think of most is the daily maintenance of houses. Yes, many old houses in rural areas are built with natural materials such as soil, wood, and stone, and the tiles on the roof are often small and not firmly fixed, such as small green tiles. If such a construction system is to be durable, daily maintenance is essential.

For example, the Tibetan rammed earth dwellings in Aba County, Aba Prefecture, Sichuan Province, have yellow mud paving on the rooftops, which need to be repaired every year to ensure that the roofs are waterproof and flat. The earthen walls are covered with a protective layer of fine mud, which needs to be repaired once every ten years. During the repair, the villagers will come to help, which has become an important public activity and a bond for keeping in touch in rural settlements.

In Dabaiyi Village in Kunming, Yunnan, most traditional buildings are adobe or rammed earth houses. In the past, villagers would use mud or lime to protect the earth walls, and with the well-maintained small green tile roofs to shelter from wind and rain, the earth houses can be used for 100 years without any problems. However, the wall plastering needs maintenance and renovation every few years, and if the small green tiles on the roof are damaged by wind, rain or small animals, they must be repaired in time. Otherwise , if rain continues to wash along the earth wall for a long time, the wall will be seriously damaged, which may endanger the safety of the house.

In cold regions, a large amount of snow may be the last straw that breaks the camel's back. Although most buildings are designed according to local meteorological data to ensure that they can withstand the weight of snow, if the building itself is uninhabited and in disrepair, coupled with the increasing extreme weather caused by climate change, the risk of vacant houses being damaged or even collapsed by snow will be greatly increased.

In addition, many old houses now have water and electricity, and the water pipes, circuits and other system equipment inside the building also need daily maintenance. If they are not used and repaired for a long time, they may be damaged or even cause safety accidents such as fires, destroying the house, whether it is an old house or a modern building.

The Yunnan earthen house has fallen into disrepair and the plaster on the exterior wall has fallen off. Photo: Wan Li

In traditional society, people carefully organized craftsmen to repair houses, treating it as a way of life or even a ritual. This process is not only about the creation of living space, but also about the spiritual construction of a sense of belonging, dignity, and honor. However, the impact of modern society and urbanization has changed the traditional way of life and people's values. The building repair work that was full of rituals in the past has become troublesome, expensive, and thankless in the eyes of modern people who pursue efficiency. In the gradually hollowed-out villages, houses are also aging rapidly as people leave.

Over time, the power of living things

Organisms can adapt to the environment and can also change the environment. The same is true for buildings. The aging of many buildings is caused by organisms.

If the building is made of organic materials such as bamboo, wood, and animal fur, then mildew and corrosion prevention are important. Many traditional wooden buildings have fire pits or stoves. People light fires indoors to keep warm, and the smoke produced by roasting food will continue to roast the internal components of the building, keeping them dry while forming a black protective layer to prevent the components from getting moldy and worm-eaten. If no one lives in or uses it for a long time, there will naturally be no such "smoky air", and the building components will decay faster.

In addition, the harm of termites is well known. If there is no human inspection and timely intervention, the consequences will be disastrous. In North America, cute raccoons have become rampant. They invade homes, destroy walls, ceilings and roofs, and their ability to destroy homes is several times stronger than that of Huskies. People need to check the environment around their homes from time to time, trim branches, seal garbage, and prevent raccoons from invading. If you can no longer handle it yourself, you can only pay a professional company to drive it away (by the way, raccoons are not suitable pets for most people).

Raccoons damaging the roof of a building (Image source: www.nationalgeographic.com)

Plant seeds can also easily fall into the cracks of the roof or wall with the wind and take root and sprout. If there is no cleaning and maintenance by humans, the dust, bird droppings and garbage in the atmosphere will become the substrate, providing growth conditions for plants. Over time, the roots of plants will destroy the roof and walls, causing damage to the building.

Although some plants do not grow directly on buildings, their roots, branches, and leaves may affect buildings if they are too close to them. If the fallen branches and leaves of plants accumulate on the roof for a long time, they may cause excessive weight. Some chemicals produced by plant roots may even damage and decompose the foundation of the building.

For example, Japanese knotweed, which was introduced to Europe in the 19th century, is a horticultural plant that produces clusters of small milky white flowers. However, due to its suitable soil, climate and lack of natural enemies, it was listed as an invasive species by the UK Environment Agency and even earned the nickname "house killer."

Because the root system of Japanese knotweed is very strong, it can penetrate asphalt, concrete, hollow bricks and other materials. Any gap can become a growth space for it. Once it drills in, it will expand the cracks while growing. If it is not handled in time, it will easily cause house leaks, pipeline damage, and even affect structural safety. In areas where Japanese knotweed is rampant, house prices will also fall, and people need to spend a lot of manpower and material resources to remove it through physical, chemical, and biological methods.

Japanese knotweed growing through a wall (Image source: www.environetuk.com)

Can reinforced concrete just sit back and relax?

Old houses in rural areas are like people. They are bound to have bumps and minor ailments, and need careful care. It is easy to understand that houses that are taken care of last longer, while houses that are not taken care of deteriorate faster. Modern buildings in cities have long been updated and use industrialized materials. So will urban buildings still deteriorate quickly if no one lives in them?

Indeed, the stability and durability of industrialized materials have been greatly improved, and they no longer require frequent maintenance and renovation like old rural houses. However, if no one lives in them for a long time, there will still be many problems.

At this point, I remembered that a few years ago, my parents moved to my city, and the commercial house in my hometown was empty. One time, my mother went back to work, and when she came home, she saw that the kitchen cabinets were already shaky and the countertops were cracked. What was the reason?

In fact, in addition to the inspection and maintenance of houses, human habitation also has an important function - to maintain the temperature and humidity in the house within a relatively comfortable range.

Although the house itself does not "feel" comfortable or uncomfortable, if no one lives in it for a long time, the indoor environment will fluctuate greatly with the changes in the external climate. Summer is hot and humid, winter is cold and dry, and repeated dry and wet cycles, thermal expansion and contraction, will cause indoor furniture, decoration materials, electrical equipment, and pipes to mold, crack, deform, and fall off.

That’s not all! Alan Weisman, a famous American science writer and journalist, wrote a book called The World Without Us, which discusses what the world would be like if humans suddenly disappeared. He believes that without humans, water and fire would slowly destroy a modern city.

Heavy rains can clog pipes, flooding low-lying areas such as subways and underground parking lots, corroding the city's foundations. Asphalt roads and concrete can crack from repeated freezing and thawing. As water seeps in, the steel bars in the concrete will rust and expand, eventually breaking the concrete and causing the building to collapse. Gas and other flammable materials may leak and cause fires, and without firefighting measures, the fires may spread to entire blocks.

We never expected that the "concrete forest" that we thought was indestructible would be so fragile without human use and maintenance, while seemingly insignificant things like plastic waste could continue to exist for hundreds of thousands of years after humans disappear. Even more dangerous are the containers that store crude oil, toxic chemicals, and radioactive materials. If they are not maintained by humans, they may break and leak, causing massive pollution and even disasters to the ecological environment.

For thousands of years, humans and buildings have formed a mutually dependent relationship. In traditional society, building and repairing houses are very important parts of human production and life. Through division of labor, coordination, and mutual assistance, people have inherited skills and wisdom in the construction and maintenance of their homes, and also maintained cohesion and a sense of belonging. Now, while pursuing development, we must also think about how to take care of these man-made behemoths that provide shelter for millions of people and be a responsible user.

Planning and production

Author: Wan Li, Associate Researcher, School of Architecture, The Chinese University of Hong Kong

Review丨Zhu Xuanxuan, Senior Engineer, Beijing Municipal Engineering Design and Research Institute Co., Ltd.

Planning | Xu Lai

Editor: Ding Zong