Traditional on-site construction vs off-site construction: What’s the difference?

The concept of off-site (aka modular, pre-engineered or prefabricated) construction has been around for years now, enabling entire structures to be pre-built off-site before being transported to their final location for assembly.  

New tech advances have enabled off-site construction to evolve far beyond its infancy stage and become a viable (and in some cases superior) alternative to the traditional brick-by-brick, on-site construction used in most cases. Some of the most notable benefits include increased efficiency, quality control and environmental performance. 

In fact, the method is already being widely used across the globe with stellar results, most notably in infrastructure development and house building. So how does off-site construction actually compare with the traditional, on-site method? 

Widely used in house building

To answer this question, we’ll walk you through some of the pros and cons of each, providing insight into how off-site construction is transforming the industry. But first, let’s start with some basics. 

What is off-site construction? 

Off-site construction involves designing, planning and pre-fabricating different construction elements in a separate location (e.g. factory) and bringing them together for rapid on-site assembly. 

Off-site structures are manufactured in controlled environments, making it possible to monitor the quality of every module or component. This makes it easier to plan ahead and add some much-needed speed and accuracy to the construction process. 

Off-site construction in a controlled environment

What are the benefits of off-site construction?

Here are just a few of the benefits the off-site construction method provides:


Off-site projects enable off-site (e.g. at the factory) and on-site teams to work in parallel tracks, making timelines faster and more streamlined. 

An additional benefit of having each model pre-built in a factory setting is that the process is unaffected by weather conditions like rain or snow. This can significantly reduce any weather-related delays that would normally slow the on-site construction process. 

Increased quality control, reliability and precision

Each structural unit or model is produced in a controlled factory setting, making it easier to monitor every step and produce more reliable results. 

Precision cut / quality control

Increased cost-effectiveness

Prefabrication in a factory setting enables more precise budget, materials and labour planning. This decreases waste and saves on unnecessary costs. 

Increased safety for workers

Controlled factory environments offer a more predictable and safe setting than construction sites, which can be affected by weather and decreased visibility. These conditions make it less likely that a worker will be hurt or injured.

Less disruption to clients and neighbours

Pre-fabricating a structure off-site decreases the noise, air pollution and disturbance from moving construction vehicles and machinery in the surrounding area. 

Energy efficiency, minimal waste and increased sustainability

In off-site construction, most of the pre-fabrication is computer-aided, enabling a more accurate calculation and usage of materials. CO2 emissions are also reduced in off-site projects because there is less need for machinery, transport and commutes than on-site construction. This minimises waste and decreases the project’s overall carbon footprint.

Accurate fit, less wastage & reduced use of machinery

What are the cons of off-site construction?  

Now that we’ve gone through some of the benefits of off-site construction, let’s look at some of the cons:

Not every site is suitable

The site needs to be able to handle the delivery of large modules. Unfortunately, not all sites have this capability.

Late changes are a challenge

The modular nature of off-site construction involves set planning, making it difficult to change things later on in the process.

It demands detailed planning and coordination

Off-site construction requires a high degree of planning before the building process begins. This is understandable, considering each piece has to fit perfectly together like a puzzle.  There is also an increased need for coordination and communication between the on and off-site teams. A lack thereof can affect the successful completion of the project.

Detailed planning and drawing

Customisation options can be limited

The modular nature of off-site construction can make customisation options more challenging when compared to the traditional method.  

What is on-site construction?

On-site construction refers to the traditional construction method in which structures are built sequentially in their permanent location. The process consists mainly of a design phase and a build phase.

On-site construction

What are the benefits of on-site construction?

Let’s take a look at some of the main benefits of the on-site construction method:

Customisation is limitless

On-site construction offers more options for customisation in terms of design and details. 

Late design changes are possible

Due to its sequential nature, it’s possible to make design and structure changes later in the process. 

No need to move large modules

The traditional on-site method builds structures on-site, brick-by-brick, so there is no need to transport large modules. This makes it the preferred method in urban areas where sites are smaller. 

Easy to renovate and expand

It’s easier to tailor and blend renovations and expansions to your existing structure using the on-site method. 

What are some of the cons of on-site construction?

These are the main cons of working with the onsite construction method:

Weather delays

On-site projects are vulnerable to weather delays like heavy rain, snow or flooding. These delays can be unpredictable, lasting from a few hours to a few days.

Delay caused due to flooding: on-site construction

Increased safety risk for workers

In general, traditional construction sites pose a higher safety risk for workers when compared to operating in a controlled factory environment.  

Why off-site construction is the future.

There’s plenty of anecdotal and study based evidence making a case for the off-site construction method - and it’s easy to see why. As explained in a study by KPMG, it addresses many of the challenges facing the construction industry today by delivering:

  • Increased productivity
  • Reliable budgets and completion dates
  • Providing better monitoring and increased transparency
  • Addressing the construction labour shortage by including profiles with factory skills

Examples of innovative providers in this space include companies like Kingspan and Entekra, boasting benefits like 500% increased productivity and 40 to 50% decreased labour needs. The sheer number of benefits delivered by this innovative construction method begs the question: Why isn’t off-site construction a more widely adopted practice? 

Well, according to a survey by the National Institute of Building Sciences, some of the barriers include:

  • A fixed construction culture
  • Trouble making late design changes
  • Lack of awareness among decision-makers and owners

Although these barriers have delayed the wider adoption of off-site construction, the benefits are already changing the culture, making the practice of off-site building more popular than ever.  

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Keith Cotter
Sales Manager