How Assembly-Line Innovation Can Shape the Future of Sustainable Housing

A variety of environmentally conscious products, from cars to solar modules, are made in factories. Could housing be next?

Clint Shireman
Habitat X Journal
7 min readJun 27, 2018


Blown fiberglass ceiling insulation installed in a controlled environment at a modular homebuilding factory in Alabama.

When I work with insulation contractors and I ask them how often they do Grade III work (insulation installed with “substantial defects,” according to RESNET standards), they always reply “never.” Whenever I am a part of or hear these conversations, my mind moves to another conversation, where someone told me that the difference between an apprentice and a master is that a master knows how to mask their mistakes. This makes me wonder, with so many masters of their respective crafts, what is being covered up?

If you ask if a home or building is built to code, you should get a “yes” from the builder. However, if you think about what it means to build to code — specifically the energy code — it’s a minimum standard. That means the builder gets a D instead of an A. Do they still build the best house now?

A quick search through any homebuilder’s website or brochure will reveal all the buzzwords the average homebuyer wants to hear, like “granite,” “tile,” or “hardwood.” It’s easy to know when words like this are a reality — you can see it. A few builders have ventured into using terms like “sustainable” (what does that word mean, anyway?), or “efficient,” but then don’t mention how they plan to be any more sustainable than the next builder. Fewer still are actually sustainable or efficient, and if they are, even fewer will be able to market those features. Of course, it’s tough to make what building science nerds love marketable. You can’t see those features once the house is finished, and some of the most important parts of a house — and trades responsible for that work — are rushed and undercut. Our focus seems to be finish rather than durability or comfort.

Someone told me that the difference between an apprentice and a master is that a master knows how to mask their mistakes. This makes me wonder, with so many masters of their respective crafts, what is being covered up?

I’m not saying that homes today aren’t completely durable. There are millions of old houses across the United States still standing that will stand for decades more. But most of those homes aren’t what they could be. The construction industry seems reluctant to change. We’ve built the exact same way for generations. Sure, we have new tools and new building products, but the actual process remains unchanged. The majority of builders I work with seem hesitant to work with new energy codes, not because they don’t want to build a great house, but because it means that their process has to change to accommodate it. Despite the science and economics behind the code (the requirements of which are the only part of the house that pays for itself), it forces change, and therefore a dismissal of that change and its importance.

Why the hesitation from builders, though? Are they afraid of adding extra cost and not being able to sell those efficiencies down the road when the house is finished? Are they afraid we’ll see a huge increase in time it takes to build? We’ve seen success with affordable multi-family projects in Philadelphia built to Passive House standards for roughly the same cost of a conventional code-built project. All it took was changing the process and how it was built.

Can you imagine building anything else the way that we build homes?

I’m going to build you a car. When you buy a lot in a subdivision where other “cars” are being built, and you pick the design and type of car you want, I’ll go to work on your site: a muddy field. For the next couple of months, I’ve got different contractors in and out. They’re masters of their craft, I’m told, so there is nothing to worry about.

But then there’s an accidental scheduling conflict, so one contractor has to undo and then redo another contractor’s work — but we are still moving forward. My contractor who does exterior finishing hit a delay, so the shell of the car is left exposed to ultraviolet rays and rain for three weeks longer than the manufacturer’s recommendation, but it eventually gets covered and looks good. Everything leading up to this point is just to satisfy code anyway before we get to what really brings in the money: leather seats and a cool touchscreen in the dash.

Sounds pretty ridiculous, doesn’t it?

Several people have drawn comparisons between homebuilding and automotive manufacturing, including building forensics expert — and Habitat X alumnus — Corbett Lunsford in this popular and informative video.

Of course it does. Cars are built on an assembly line in a factory, like many other consumer goods we use every day: pens, televisions, ovens, and those Yeti coolers that everyone goes on and on about.

Enter production building

No, not the type we’re used to seeing. I mean in a factory. Call it panelized, modular, pre-fab, site-assembled, or whatever else you want, there has been an uptick in interest in the last couple of years and we are starting to see more and more of it in the market. Just last year, Marriott Hotels increased their use of modular builds by 13%. Along with Marriott, other players, such as Katerra and Phoenix Haus, have entered this market segment, and some established builders, like Vermod, have been given new life.

This type of building has major benefits: in a controlled factory environment, you can have greater quality control. Building assemblies can be built with fewer people, and if they don’t pass the manufacturing standards, they don’t leave the facility. With an in-line and repeatable manufacturing process, companies can reduce material usage and thereby reduce their overall waste, reducing the need for on-site dumpsters emptied every week during a build. Since a lot of the actual construction work is done inside, it ultimately takes less time to construct the building in the field.

Poorly installed wall insulation is common in production homebuilding. Building sections assembled by well-trained factory workers could reduce such defects and increase the durability of newly constructed homes.

Panelized construction is one reason the Passive House projects in Philadelphia were able to reduce cost. Wall assemblies that already had utilities, mechanicals, and insulation in place showed up on site and were put together with fewer workers — in days instead of weeks. Once in place, they were ready to install the roof — a portion of a home that has been built in factories for years now — and begin finish work. Just like that, one project showed a scalable example of changing the way we build for greater efficiencies, and did so in a faster timeframe, despite the current labor shortage.

Shipping these pre-finished panelized assemblies, however, can be expensive. The thicker the wall, for example, the more insulation you can add, but since most insulation works by trapping air, you would be paying to ship more air in those assemblies. So there could be geographical cost-effectiveness limitations.

There is also the potential issue of grading the building. RESNET, LEED, the International Living Future Institute and many others certify the efficiency of homes and buildings based on several criteria in the field. But despite regional limitations, pre-fab construction could benefit production builders in major metropolitan areas, and with a certification for production — e.g., knowing what is in the walls — field verification could actually be sped up over conventionally built homes.

If pre-fab construction begins to take off in the US, what will our tradespeople do?

The construction industry doesn’t really like change, so these shifts could take years. There is still plenty of room to grow our skilled labor numbers, though, and advance the industry to be on the forefront of positive change. The new “starter home” is still unaffordable to many in my generation, and fewer buyers are willing to “trade-up” to a new home. Because of that, there has been steady growth for the last several years in remodel and DIY spending, and those numbers are expected to grow.

There are approximately 137 million existing homes in the US built to yesterday’s standards that could use a little more than a facelift. My generation (Y) and the one coming up next (Z) are beginning to care more and more about indoor air quality, efficiency, and sustainability. If I were a contractor or a builder, I would look at expanding my remodel portfolio by educating myself on how the house works as an entire system. Beyond air-sealing attics and dense-packing walls, there is tremendous opportunity for education and sales in remodels: removing dropped soffits and recirculating range hoods for exhausting hoods in kitchen remodels, moisture removal in bath remodels, and rainwater management for deck, patio, landscaping or roof work. The list goes on. We are on the front of a perfect storm for retrofit and remodel contractors to expand their business and be MVPs in their respective markets.

Pre-fab and site-assembled construction can greatly reduce waste, energy consumption, and alleviate several construction woes, but it will be a long time before it takes over the ever-expanding US housing market — if ever. Even if pre-fab were to start taking chunks out of our housing market, custom and regional builders will still have a presence. No matter how this all shakes out, we still need to advocate for tradespeople, and champion proper building science and construction education to move our industry forward. There is no magic bullet for products or process just yet. The best ideas and products are useless if they are not installed or executed properly by tradespeople who are willing to not only do the right thing, but to continue to learn and grow in their career as new information and technologies become available.