By Dvir Atias
“Basis of design” means two different things in construction. In a specification it is the product the design was built around, which other manufacturers can sometimes match. In commissioning it is a document that records the design team’s assumptions. Here is what each one means, how to read them, and why manufacturers should care.
Search for “basis of design” and you will find two different things. Architects and spec writers use it for a product: the one a design was built around, named in the specification. Engineers and commissioning agents use it for a document: the record of the design team’s assumptions. Both matter on the same project, so here is each one in turn.
Basis-of-design product in a specification
In a spec, the basis-of-design product is the product the architect or engineer designed around: its dimensions, performance and appearance shaped the drawings. It is named in Part 2 of the section, usually in the article on manufacturers or products, in language like:
“Basis-of-Design Product: Subject to compliance with requirements, provide Manufacturer A; Product X, or a comparable product by one of the following…”
Naming a basis of design does not always lock the project. What follows it decides how open the door is:
- Basis of design plus listed manufacturers. Other named manufacturers can bid if they match the basis-of-design product.
- Basis of design plus “or approved equal.” Any manufacturer can propose a product, if the design team accepts it as equal. See what “or approved equal” means.
- Proprietary. Only the named product is acceptable. On publicly funded work this is generally the exception.
Basis of Design document in commissioning
In building commissioning, the Basis of Design (BOD) is a document written by the design team. It records the criteria, assumptions and design decisions behind building systems such as HVAC, lighting and controls, and explains how the design meets the owner’s goals, which are set out in a companion document called the Owner’s Project Requirements (OPR).
The commissioning process, described in ASHRAE Guideline 0, uses the OPR and the BOD as the yardsticks the finished building is checked against. Green-building programs such as LEED also require both documents for fundamental commissioning.
A typical BOD covers the design criteria for each system, the codes and standards applied, the assumptions about occupancy and loads, and a narrative of how each system works. It is updated as the design develops.
The two meanings, side by side
| Basis-of-design product | Basis of Design document | |
|---|---|---|
| What it is | The product a spec section is written around | A record of design criteria and assumptions |
| Who writes it | The architect or engineer, in the spec | The design team, for commissioning |
| Where you find it | Part 2 of a MasterFormat section | A separate commissioning document, paired with the OPR |
| Why it matters to a product rep | It tells you who is named and whether you can still compete | It sets the performance your product must support |
Why basis of design matters to manufacturers
Being the basis-of-design product is the strongest position a manufacturer can hold on a project. When a competitor holds it, the next question is whether the spec allows an equal and when substitution requests are due, which is set in Division 01, usually section 01 25 00 Substitution Procedures.
- Find the projects where a competitor is basis of design and equals are allowed.
- Note the substitution deadline, not just the bid date.
- Match the performance the spec, and the BOD document, require.
- Work with the design team early, so your product is the basis of design on the next project.
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