Why build modular residential buildings? Can they save time and money?
August 31, 2020
August 31, 2020
Ask an expert: Boston architect Larry Grossman explains the benefits and challenges of using prefabricated “boxes” for multifamily dwellings
This article first appeared as “Ask an Expert: Why build modular residential buildings?” in the Stantec Design Quarterly, Issue 09.
How does a modular construction approach for multifamily residential buildings influence design? Larry Grossman, senior principal in our Boston Summer Street office, talked with John Dugan, editor of the Stantec Design Quarterly, about how modular design and construction can increase speed and impact quality. And what that means for the industry.
Larry: I’ve been practicing architecture since 1985, and the multifamily practice at our firm was established some 15 years ago when we started designing a whole range of residential project types. Our residential design work was an outgrowth of our well-established commercial practice. And this modular project—28 Austin in Newton, Massachusetts—though it was on the smaller side at 68 units, was an opportunity to learn something new with the goal of finding a better way to economically satisfy our clients.
Larry: This was the first time I had an opportunity to work on a modular project, and what interested me is that we’ve been trying for years to crack the nut on the economics of multifamily. We have been challenged to build more economically because construction in Boston is expensive, and prices are continuing to escalate.
Affordability has always been the challenge. We’ve designed buildings with micro-units, which my colleague Aeron Hodges has written about extensively.
This project was a bit unique. It was wood on top of a concrete podium but everything on top of the podium was to be built in a factory in Canada. The “boxes,” as they’re referred to, are almost entirely completed on the interior in the factory. Everything right down to the paint and the tiles on the wall and the carpet on the floor.
Larry: For the region that we work in, New England, one benefit is that you’re not building in the middle of the winter. Instead, you have a controlled environment and workforce. We visited the factory in Canada in the middle of winter to see how they do it. It’s almost like the old Ford Model T plant that’s building the units. There is literally an assembly line where the boxes are built. They’re moved across the floor on a pulley system to the different trades on site. It was interesting.
We found the quality to be quite high and they benefit from working in shop conditions, not in rain and snow. I was intrigued because I thought this could be leveraged up with more practice, more sophistication to really save money. In this case, it saved us time and we got a superior product because of the controlled environment. But there are unique added costs.
Larry: Each box is loaded on a flatbed truck and shipped one at a time. Transportation and storage must be synchronized so that when you start to place the boxes, they are all ready. They need to all be stored at some location close to the site because each day the construction team is putting 6 to 10 in place. There must be a stockpile ready for installation. And because the boxes are transported outside, they must be tightly wrapped and able to withstand the elements—rain, snow, sleet. Each modular box must be watertight. It requires additional costs and logistics.
In terms of design, there’s a certain duplicity in the materials. Typically, when we build with wood, a floor becomes a roof, and then a roof becomes a floor. But with modular, because you’re building a box, each is complete with a roof and a floor in addition to duplicate walls for each unit. This duplication adds some cost but has tangible benefits such as better acoustical separation.
We need to build tens of thousands of housing units in the New England area over the next several years just to meet demand.
Larry: I think there’s a great deal of potential in building modular for residential projects. From a design perspective, we’re usually very site-specific, we’re always trying to improve upon our work, and we rarely use what we’ve done before. But in cases where we want to minimize costs, we may be able to simplify, we could reuse some of our unit designs for a modular project. That encourages us as designers to come up with a kit of parts of standard modules. There are some real benefits to this approach, for example, to a developer.
A manufacturer could put a package together, for say a hundred units of various types, and price that quickly. That can reduce the developer’s risk. If you can determine prices early on, that’s an advantage. Predictability of costs is very attractive as is predictability for project duration. If you know it takes 6 months to build a 50-unit project and that can be replicated, that’s good.
Larry: The rules are different. The boxes are all plumbed and wired, panel boards and light fixtures are in, everything’s in its final location. Each box has these stubs—wires and pipes—that project out into the corridor. A crew comes through and connects everything up. But everything’s there to be connected. It’s plug-in.
The rules are not onerous. It’s a kit of parts that we have learned how to manipulate and exploit. There are certain dimensional issues we must be aware of because we must design a module that can be shipped by flatbed truck. For this project, the module we came up with doesn’t vary much from 13 feet wide by 62 feet in length. You can’t tell by looking at a finished building that it’s modular construction and wouldn’t know that this was the methodology used to build it. Except for the module dimensions, there are no other design limitations. And it doesn’t need to be just an extruded form. The facades can step in and out, with balconies and bays. Some things are more cost effective, but otherwise the possibilities are limitless.
Larry: The backstory behind 28 Austin is interesting. It was a city-owned parcel, a municipal parking lot in an urban location next to a main shopping street just outside of Boston. The city put it out for development and its main stipulation for the program was that it had to retain the same number of public parking spaces.
A client asked us to join it on the competition. They brought in a partner, a husband and wife team of architects, who had some experience with doing modular construction. They suggested we propose a modular solution, so we could build it quicker, which would be less of an imposition to that community than traditional construction.
The community liked the idea that modular would take less time. We were the only ones who offered modularity and we won the work. Ultimately, we were able to accommodate residential parking in a below-grade garage. We lifted the building up and we were able to replace all the community parking by tucking it behind a small lobby and some retail space.
Larry: We need to build tens of thousands of housing units in the New England area over the next several years just to meet demand. And the construction process hasn’t changed that much over the course of my career. There are still men and women on the site nailing one piece of wood to another piece of wood. And a plumber comes in and attaches one piece of pipe to another piece of pipe and then electric puts the wire in.
They all drive, they bring their trucks in, the materials in. It’s very linear and slow. There’s an opportunity on the manufacturing side. This assembly-line approach offsite offers a lot of advantages.
I think it’s in its infancy. If there was a factory in the Boston area where they could build modular units close by, where we could inspect them locally and have local transportation and labor force, I think the program could take off.