How Sustainable Is Modular Construction?

Modular construction, a type of prefab, is leading the way in eco-conscious building practices by slashing the industry's waste problem and maximizing recycled materials.

A modular is a portable home or commercial building that is built at an off-site facility and transported to a more permanent plot for assembly. The product can be of higher quality because it's made in a controlled environment. For all its environmental advantages, the global modular market is thriving, expected to grow by an impressive 50% from 2021 to 2028.

Here, learn more about factory-made modular builds and their environmental impact—from the materials used to the emissions generated to their longevity compared with traditional site builds.

History of Modular Construction

Though modular construction is still considered to be disruptive to the industry today, the concept is thousands of years old. A period of expansion took place following World War II, when prefab trailers were set up to provide fast, low-cost housing. These trailers were officially rebranded later on as "modular housing."

Modular construction looks a little different today: Portions of the structure are built separately—from bottom to top—in a factory setting, wrapped with a weather-resistant membrane where they are open, then transported to the property by truck, and, finally, connected.

A certain kind of prefab called volumetric is even more simplistic. Entire six-sided structures with finished interiors are built in the factory and then merely bolted together at the building site.

Modulars have experienced a few popularity surges over the past century, from the quick-build trends of the '70s to the design boom of the early aughts to now, fueled by a modern-day housing crisis.

How Common Are Modulars Today?

A report by Dodge Data and Analytics said modular construction made up only 4% of the U.S. housing market in 2020. Other data shows that off-site projects account for a slightly higher and ever-growing portion of North American commercial builds—5.52% in 2021. Still, these numbers are minuscule compared to the modular market share in countries like Sweden (45%) and Japan (15%).

It's no coincidence that two countries known for their forward-thinking, green-minded architecture are also leading the charge on modular construction. This building style is believed by many pros to be the most sustainable.

Modular Construction Means Less Waste

One of the biggest draws of modular construction is that it's far less wasteful than on-site construction. When the European Union surveyed construction and demolition waste in 2008, it found that C&D materials, as they're often called, accounted for an astounding third of all waste generated in the region. In the U.S., C&D waste is twice the amount of municipal solid waste.

The controlled manufacturing environment of modular construction makes it easier to be precise in material usage. Any materials that aren't used for one project can be stowed away for the next without even leaving the facility. Factory building also eliminates waste associated with weather damage (inevitable when building on-site), therefore reducing the need for demolition and keeping materials nice enough to recycle at the end of their lives.

What's more, because modular buildings are virtually portable, they can be easily moved off a site to deconstruct and discard materials responsibly or to continue being used on another site—no need for demolition.

Overall, this method has been shown to reduce the weight of C&D waste by up to 83.2%.

Emissions From Modulars vs. Traditional Site Builds

Another big environmental advantage of modular construction is the reduction in emissions from frequent site deliveries. In fact, a 2021 study of new builds in Pakistan found that modular construction generated almost half the greenhouse gas emissions of conventional site-built building (about 3,450 kgCO₂-equivalent versus 6,500).

Site deliveries make up a colossal portion of emissions generated from construction, but one must also consider the embodied carbon of building materials. When a building is constructed outside, weatherproof materials like concrete and steel are often used in place of wood because wood is prone to water damage (from rain or just general humidity). Research shows that using sustainable timber instead of manmade materials can reduce construction-phase emissions by 69%.

Drawbacks of Modular Construction

In the early days of modular construction as we now know it, this style might have had its limitations with regards to building size, style, and shape (the original modular designs were very modern and primarily rectangular). This would have restricted the creativity and uniqueness of the design, plus it would have meant finding a plot to suit the standard rectangular shapes.

Nowadays, almost any style of home can be made modular. Clayton Homes, one of the largest modular home builders in the U.S., makes very conventional-looking houses nobody would look at and say, "That's modular." Because the modules are constructed in a factory, there are still some limitations with regard to room sizes, ceiling heights, and the like.

Moreover, the transport of the modular home is expensive. Building sites should be close to the manufacturer in order to minimize costs and hassle. (Still, even with the manufacturer close by, back orders can occur and delay delivery.)

Another problem with this technique is that it can lack flexibility—meaning one can't usually make changes to the design once it's been finalized and the building starts. With a site build, designs can be updated during construction.