China’s prefabricated construction is gaining the world’s attention. A Chinese firm called Broad Sustainable Building (BSB) in Changsha built a 57-story building in 19 days. This building is called Mini Sky City. BSB is also planning to build a prefab tower called Sky City in Changsha. Once erected, Sky City will be the world’s tallest prefab skyscraper.
Chinese prefab construction seems like a promising solution to the housing shortage in the United Kingdom. The China National Building Material Company (CNBM) is working with U.K. housing association Your Housing Group and renewable energy company Welink to build six factories to produce prefab houses with pre-engineered wall panels, solar power and energy efficient designs in the U.K.
Prefabricated houses or buildings are constructed in a factory before shipping it and assembling on site. Compared to traditional house construction, the assembling requires less space and is completed at a faster rate. That is why you now see stunning state-of-the-art houses in the woods where it is deemed as a normally difficult environment for house construction, or jaw-dropping high-rise buildings completed in less than 20 days.
Not all the prefab houses or buildings are the same. To be more specific, they can be categorized into four main types:
1. Modular Homes/Buildings. Major work is done in the factory. Each module has a full finishing which includes plumbing, electrical, doors, stairs and closets. Very little on-site work is required for this prefab method. They used to be aesthetically boring because of its boxy look. However, it can now be combined with various panelized walls or roofing to make it stylish.
2. Panelized Homes/Buildings. These are built-in panels which are then shipped on site for assembling. Unlike modular homes/buildings, it requires more finishing work such as painting and installing floors. It is very versatile and can be of any style and look.
3. Pre-Cut Homes/Buildings. You can think them as an Ikea furniture kit. You can follow the instructions to assemble everything on your own, or with the help of contractors. These are designed for builders to put everything together themselves. This type of prefab house needs more on-site assembly time.
4. Shipping Container Homes. Made from industrial steel shipping containers, it can be a single dwelling, stacked or placed together. Originally not designed for residential use, it requires more design and modification work from its future occupants.
Reducing construction costs and time
Different construction projects feature different designs. Traditional construction needs more material preparation than what is really need for cutting. The leftover materials from cutting usually cannot fit the current project. However, prefab manufactures can fully utilize most materials. They have a wide range of projects which enable the manufacturer to fit leftover material for another project. As a result, prefabricated housing construction eliminates construction waste. The shipping cost of materials to the site can be reduced because less amount of materials are needed. The labor cost for final assembly is also reduced. Therefore, the overall savings bring down the construction cost, and this makes prefab construction more affordable and attractive to new clients.
Prefab manufacturers use uniform measurements for production. The pre-made parts are as standard as Lego pieces. As a result, the connection of the prefab homes or buildings are tighter than conventional construction. Tighter seams prevent air leakage between houses and the outside environment, and it also saves energy use. The modular design enables consumers to fit energy efficient appliances to the final package. For example, a low wattage refrigerator or air conditioner.
Arguable waste reduction and environmental savings
Prefab structures use 20 to 30 percent more raw materials than stick-built homes in order to withstand transportation. On a conventional construction site, 30 percent of the materials are wasted through theft, damage, or just being thrown away. Would you rather choose more of these materials into making your house stronger or being thrown away? The energy and water used for on-site construction are drastically reduced for a prefab home/building. The prefab sites can eliminate dust to a minimum level. However, the energy and water used and dust generated in the factory should also be taken into account in the life cycle of the project.
People are worried about the safety of prefab assembly. Theoretically, the assembly is very reliable. The actual concern is not only about the quality of off-site manufacturing, but also on-site assembly. The on-site assembly is more about “plug and play”, rather than quality control (QC). One single mistake can put the entire building in danger. Workers on a prefab site are expected to complete the project as quickly as possible. They work under immense pressure and tight deadlines which can lead to higher chances of mistakes made, as compared to traditional on-site construction which is typically not associated with fast completion times.
No streamlined processes
Since prefabricated homes or buildings are new to the market, the existing building code interpretations cannot be simply applied to prefab construction in many places. This might be the largest constraint in the development of prefab construction. The uncertainties have led to delays or halting of construction in some cases. The Mini Sky City was designed to be 97-stories tall, but it was cut to 57-stories due to the nearby airport. The big change was taken place after the company had already built 20 stories, rather than being informed in the beginning of the project or during the permit process.
The pre-construction activities for the world’s tallest prefab tower Sky City stopped in 2013 after the central government required additional approval. In the summer of 2016, the project had been dropped due to the damage to the Daze Lake wetland. The wetland is the location where the Sky City was originally planned to be built. It is surprising that regulators did not point out this issue during the permit phase.
In conclusion, prefabricated homes and buildings are suitable in many cases. For example, prefab housing is possibly the best economic solution in rural areas where transportation is not easy to reach, or places that have limited space to maneuver. Another example could be construction projects with time-sensitive schedules. The off-site prefabricated construction helps shorten the conventional building period.
I believe with the future regulations and industrial norm, the technical challenges and problems we face with prefab will be solved. The construction management industry is ready for this new movement. The next generation of professionals should make decisions based on systems thinking and life cycle analysis approach: do not only count the on-site savings or losses, but also trace back to upstream and downstream practices.
(Top photo from Pixabay)