The Architect’s Guide to Modular Construction (& Prefab!)

You’ve seen articles about shipping container houses

In some areas, hotels are shipped to the site as a kit and assembled like a toy. Editorials praise how quickly the structure went together and may suggest that every building will be constructed this way in a few years. As an architect, you know the truth: Modular building systems have been around for years and their design systems can be limiting.

Beyond the “wow” factor, why is there all of this buzz today and why is this relevant to you as an architect or designer?

This guide will get you up to speed on contemporary trends in offsite, modular, and pre-fab construction. Then we’ll explain how modular construction works from a process perspective. Let’s jump in.

Modular, Prefab, Off-site?

Isn’t prefab the same as modular? Modular is a type of prefabrication, but not all prefab is modular. To explain the difference, here is a list of common terms you may encounter:

• Modular Construction: A building method where sections, or "modules", are fabricated offsite in controlled environments, then transported and assembled on location.
• Prefab / Prefabrication: Often used interchangeably with offsite construction, pre-fab specifically refers to the production of components (like walls, floor systems, and trusses) in a controlled factory environment. These components are then shipped to the site for assembly.
• Restoration: Retaining materials from a particular time from the building’s history while removing materials from other time periods. 
• Volumetric Modular: A method of construction where entire rooms or sections of a building are pre-constructed off-site, complete with interior finishes, fixtures, and fittings. Once transported to the site, these modular units are assembled and connected to create a cohesive structure. The emphasis here is on complete units or rooms, as opposed to individual components.
• Offsite Construction: A broad term that encompasses any construction process or technique where a significant portion of a building's components — or even the whole building — is manufactured away from the final building site. This includes modular construction, prefab, and a kit of parts approach to building.
• Kit of Parts: A method mirroring industrial production, it standardizes building processes and components for efficiency and consistency. You can draw parallels to a famous Danish interlocking building toy. 
• Industrialized Construction: A method of building that mirrors industrial production. Industrialized Construction standardizes building processes and components for efficiency and consistency. This approach emphasizes mass customization, reduced waste, and technology integration, and in turn offers the potential for quicker and more cost-effective construction.

Each of these terms falls roughly under the category “modern methods of construction.” This is not a term you may not encounter much in the US. This term is commonly used in Europe, especially the UK. MMC may also include new building materials, the use of AI, and any other emerging construction technology. 

Why is prefabricated construction getting so much attention today?

High demand for infrastructure, housing, manufacturing facilities and more is driving record levels of construction. Installation of pre-manufactured components or entire units, modular and prefab typically leads to less construction time overall, especially time on site. For the construction industry this means they can build more projects, faster.

Other benefits to this type of construction include:

Efficiency

• Factory-made panels and prefabricated buildings ensure precision, minimizing waste.
• Resources such as manpower and equipment can be optimized in a factory environment.
• Factory environments are controlled which increases worker safety and there will never be weather delays.

Sustainability & Diversity

• Construction waste is more easily captured and recycled, particularly emissions from tasks such as painting.
• Less on-site work means limited land and ecosystem disturbance to the construction site.
• Factories attract a more diverse workforce due to better conditions and consistent hours.

Safety & Diversity

• Precise planning and scheduling limits cost overruns and wasted labor hours.
• Bulk buying allows a program to reduce materials cost overall.
• Modular designs typically allow cost-efficient upgrades.

It all sounds great. So why wouldn’t an architect want to employ these approaches?

There are many benefits to modular construction, but you can’t simply “slice up a design” any design and have it built in a factory. You’ll need to work within a defined design systems and with a larger team of stakeholders.

Modular construction requires a partnership approach between all stakeholders. 

Many of the benefits of modular construction rely on precise timing of deliverables as well as a design that’s easy to both manufacture and assemble. Offsite manufacturing is not yet a commodity like many traditional building materials so suppliers will often have a larger role in project fulfillment. For instance, a company such as Marriott may partner with an offsite builder on a modular or pre-fab initiative (or even implement program wide) along with their existing team of architects and general contractors. 

As an architect, you will need to work in a consortium to help the team balance your skills for translating client needs into drawings and models while working within a tighter set of design, engineering, and scheduling constraints. This will mean several differences in how you approach a modular project: 

1. Your will design with a different “set of tools”.
   To work within the bounds of the modular or off-site program you’ll essentially work with building blocks instead of lines. This content will typically be provided by the owner, but may be co-developed by the AOR or consultants. Each program differs in how they implement off-site construction
2. Proposed designs may have the additional constraints such as heavy equipment needed to install modules or panels. Do the site conditions support assembling your proposed configuration of prefabricated components?
3. The documentation generated to build the plan will differ.
   Depending on the contract structure, you may be responsible for producing additional documentation for offsite builders to follow along with the on-site team. 

You’re starting on your first Modular Construction Project, what should you know?

Your client will share their system and standards with you at the start of the project. Here are the four biggest things you should consider as you get started: 

• Design Flexibility: How customizable are the modules or panels you are required to use? 
• Transportation & Assembly: Pre-fabricated components will need to be transported then assembled on-site. Your design will need to take both of these factors into account. 
• Local Regulations and Standards: Are there any local codes or standards that dictate different requirements for portions built off-site vs. on-site?
• Sustainability: How do the materials and processes align with the client’s green building standards and sustainability goals? What information will you need to report during handover?

In Conclusion

As the construction landscape evolves, modular and prefab methods will become much more prevalent. As an architect, you may need to work within the boundaries of this construction process due to a client requirement. 

Learn More: If you want to learn more about the modular construction industry in the United States, the Modular Building Institute is an international non-profit trade association dedicated to the advancement of both permanent modular buildings and relocatable structures.