On-site construction refers to the utilization of traditional construction methods in which all work is performed sequentially on-site. Off-site construction typically refers to modularization and off-site assembly as well as pre-fabrication prior to installation on-site.
Pre-fabrication can increase efficiency, mitigate safety risks, and reduce the cost and duration of the same work performed in the field by approximately 30%. However, there is a time and place for both off-site and on-site construction approaches.
Below we detail the pros and cons of on-site vs. offsite construction and situations in which each approach may be the most effective for project success.
On-Site vs. Off-Site Construction: Understanding the Pros and Cons
Let’s look at some of the pros and cons of on-site vs. off-site construction as well as well-suited situations in capital projects for each approach.
Pros of On-Site Construction
- Increased flexibility for changes after construction begins: While it is best practice to avoid making changes in design or to the project scope, on-site construction allows for the flexibility for changes to be made after construction begins.
- Renovation and add-on accessibility: On-site construction allows for renovations and additions to existing structures to be completed and installed more easily.
- Decreased logistical constraints: On-site construction requires less logistical planning efforts and reduces the level of communication and coordination required between a potential on-site and off-site crew to schedule and complete construction. Modular building off-site often comes with engineering constraints, as the module needs to fit specific criteria that enable it to be built, moved, and shipped to another location.
Cons of On-Site Construction
- Weather impacts: As each step in the sequencing of traditional construction techniques is primarily performed on-site, weather conditions can impact the speed of progress as well as construction sequencing—this can ultimately lead to schedule creep.
- Safety risks: By nature, on-site construction is more prone to safety issues compared to off-site construction, particularly in environments where hazardous operations, extreme weather conditions, heights, and neighboring construction activities may be involved.
- Decreased productivity and increased schedules: Due to site and personnel constraints, on-site construction does not offer the level of productivity and efficiency that accompanies off-site construction. This often results in longer schedules to complete work compared to off-site shop environments.
- Availability of labor: Workers have to be physically on-site wherever the project is located.
Situations Well-Suited for On-Site Construction
- Civil and concrete works, depending on characteristics
- Open work sites with few trades
- Existing facilities that are congested with little room for modules in the footprint
Pros of Off-Site Construction
- Reduced project duration: Parallel construction work in fabrication shops can aid in addressing constraints that impact the project schedule. For example, construction work can be de-sequenced to improve project schedule by pre-fabricating and assembling structural steel off-site while foundations are poured on-site.
- Mitigation of safety risks: Off-site construction provides safer working conditions through the reduction of worker exposure to hazardous operations, extreme weather conditions, heights, and neighboring construction activities.
- Reduced overall risk: Off-site fabrication and assembly work schedules contain fewer inherent risks that result from overlapping disciplines and crafts, permit delays, weather delays, environmental impacts, or intrusion on ongoing facility or site operations.
- Improved quality: The fabrication of components off-site allows for a higher degree of quality control because the work is being performed in a more controlled environment.
- Minimized waste: The carbon footprints of construction projects are reduced through technologies, such as computer-aided manufacturing of prefabricated construction, that minimize waste.
Cons of Off-Site Construction
- Site constraints: Not every construction site is suitable for accommodating the delivery and/or installation of large prefabricated or pre-assembled modules.
- Increased engineering, planning, and coordination requirements: Off-site construction often requires a greater degree of detailed planning before construction as well as strong communication and coordination with on-site and off-site crew.
- Decreased flexibility: After an off-site construction project begins, it may not be possible for changes to the design to be made.
- Potential higher cost: While off-site construction offers potential cost savings that are driven by field and shop labor rate and productivity differentials, there is a potential for a higher in-place cost.
Situations Well-Suited for Off-Site Construction
- Schedule-driven projects
- Remote projects
- Project sites with inherent labor constraints, extreme weather, or a lack of local infrastructure
- Projects with access for delivering off-site assemblies or modules
Look to H+M for Your On-Site and Off-Site Construction Needs
Whether you require on-site or off-site construction or want a professional opinion on determining your optimal choice, H+M Industrial EPC will help you make the right decision and drive your project to success.