In construction, BOD stands for Basis of Design. It’s a document that records the principles, assumptions, calculations, and decisions behind a building’s design. Think of it as the “why and how” behind every technical choice made on a project, from the type of heating system selected to the indoor temperature a building is designed to maintain.
What a Basis of Design Document Contains
A BOD captures the technical approach for a project and explains how each design decision connects back to the owner’s goals. It includes both written narratives describing the overall design strategy and specific technical parameters that engineers and architects used to size equipment, select products, and configure building systems.
For mechanical systems alone, a typical BOD spells out indoor temperature and humidity targets (often 74°F for cooling, 70°F for heating in occupied spaces), hours of operation, noise criteria for different room types, equipment sizing, connected loads, operating pressures, and flow rates. It also addresses how much spare capacity the design includes for future needs. Brown University’s facilities standards, for example, call for 20% additional capacity built into all systems to accommodate future renovations.
Beyond mechanical systems, the BOD covers structural assumptions, electrical design criteria, plumbing parameters, fire protection strategies, and any other system that requires engineering judgment. Each section documents which building codes and industry standards governed the decisions.
Who Creates It and When
The design team, typically architects and engineers, is responsible for developing the BOD. It starts taking shape during the earliest design phases and grows more detailed with each submission as the project moves from concept through construction documents. By the time construction begins, the BOD should be a comprehensive record of every significant design choice on the project.
ASHRAE Guideline 0, a widely referenced standard for the commissioning process, requires the BOD to be submitted and updated with each design milestone. This ensures the document stays current as the design evolves rather than becoming a snapshot of early assumptions that no longer apply.
How BOD Differs From the Owner’s Project Requirements
The BOD is often discussed alongside another document called the OPR, or Owner’s Project Requirements. These two documents work as a pair, but they serve very different purposes. The OPR describes what the owner wants: their goals, how they plan to use and operate the building, energy performance targets, budget constraints, and any specific expectations. The BOD is the design team’s technical response explaining how they plan to deliver on those requirements.
As the University of Michigan’s project procedures describe it, the OPR is the owner’s detailed description of goals and expectations, while the BOD is the design team’s detailed description of concepts, assumptions, calculations, and product selections made to meet those goals. The BOD is formatted to directly coordinate with and respond to each item in the OPR, creating a clear line from “what the owner asked for” to “how the design delivers it.”
Why the BOD Matters During Construction
During construction, the BOD serves as a reference point for the commissioning process. Commissioning is the systematic verification that installed systems actually perform the way they were designed to. The BOD provides the acceptance criteria needed to test mechanical, electrical, and plumbing systems, including sequences of operation, setpoints, and minimum performance thresholds. Without these benchmarks written down, there’s no objective standard to test against.
Commissioning agents use the BOD to check that what’s being built matches the original design intent. If a contractor installs equipment that differs from what was specified, the BOD is the document that flags the discrepancy and provides the technical justification for why a particular choice was made in the first place.
Its Role After the Building Opens
The BOD doesn’t lose relevance once construction wraps up. It evolves into a reference document for building operations and maintenance staff. When a facility manager needs to understand why a system was designed a certain way, or what conditions it was sized to handle, the BOD provides that context. It’s especially valuable during recommissioning, when existing systems are retested and retuned years after the building opens. Having the original design assumptions documented means maintenance teams aren’t guessing at intent.
For anyone managing or maintaining a building long-term, the BOD is one of the most useful documents in the project file. It bridges the gap between the design team’s knowledge and the operations team’s daily reality, preserving institutional memory that would otherwise walk out the door when the design professionals move on to their next project.