Short answer
A basis of design document liability question starts when a system underperforms and someone says “design error.” The first issue is whether the design was wrong or the conditions exceeded what it was designed for. The documented basis of design answers that: the standard you designed to, the outdoor and indoor design conditions, and any owner requirements above the minimum. If it is written down and the owner approved it, you are in a much stronger position. Whether a policy responds depends on its wording and the facts.
Error vs. conditions
A design error is a mistake. Examples include a missed load, a math error or a wrong code reference. The design fails because someone got something wrong.
A condition beyond the design is different. The engineer designs to a recognized standard and a stated set of conditions. Later, the system faces weather or use that exceeds those conditions. The design may perform exactly as intended and still fall short of what the owner expected.
Owners and contractors often use one word, “error,” for both situations. The distinction matters because it shapes who pays for a fix and how an insurer views the dispute. Whether a design met the standard of care depends on the facts and the contract.
Our article on when the client says the HVAC does not work shows how a comfort complaint can escalate.
What a basis of design document should state
A basis of design records the criteria behind the design. It gives anyone reviewing the project a clear reference. A useful document usually states:
- The standard or code the design follows
- Indoor design conditions, such as temperature and humidity targets
- Outdoor design conditions, such as the weather data used
- Key assumptions about use, occupancy and equipment
- Owner requirements, especially those above the minimum
- Known limitations of the design
The ASHRAE site offers guidance on commissioning and owner’s project requirements, which often feed into this document. Keep it short and specific. A document that states numbers and sources is more useful than one that states general intentions.
Have the owner review and approve it in writing. Approval turns the document from an internal note into a shared reference.
Owner expectations above the minimum
Some owners want more margin than the standard requires. They may prefer tighter temperature control or extra capacity for extreme days. That preference is reasonable, but it should appear in writing.
If an owner asks for more, record the request and design to it. Price the added work and say so in the agreement. An owner who never asked for extra capacity may later argue the design should have included it. A written record shows what the owner requested and approved.
When an owner wants more than was originally designed, the added cost raises a separate question about betterment. Our article on betterment explains how those costs are usually treated.
Staff turnover on long projects
Long projects often outlast the team that started them. The engineer of record may leave, and someone new takes over. Assumptions can get lost in that handoff.
Make sure the basis of design carries over. The new engineer should review it, confirm it and record any changes. Note the date and the reviewer. If the new engineer changes the criteria, update the document and tell the owner.
A clear handoff record helps everyone reconstruct what the design was meant to do. Tell your insurer about key personnel changes when your policy or application asks for them.
Careful words during a dispute
Everyone in a dispute tends to use the word “error.” Once it appears in an email, it can follow the firm into later discussions. Keep your own written communication factual.
Describe what the system is doing and what the design conditions were. Leave conclusions about fault to the process. Talk to your insurer before you reply to a formal complaint. Our article on voluntary payments explains why offers and admissions deserve care.
Questions to ask your agent
These questions can start the conversation:
- Does my contract define the standard of care?
- Is my basis of design approved by the owner?
- Should I report this complaint as a potential claim now?
- How should I describe the facts in writing while the insurer reviews them?
What we see at Hardcover
On a surgical center project, a third-party engineer later sized a larger unit for more extreme rooftop conditions than the original design assumed. The owner and contractor called the problem a design error.
The architect’s position was that the original design met the recognized standard. The change reflected a new basis of design, not a correction of an error. That position depended on what the original documents said.
Related questions
Is it a design flaw if the engineer designed to the standard of care?
Not by itself. A design error is a mistake, such as a missed load or a math error. Whether a design met the standard of care depends on the facts and the contract. Keep your written communication factual and talk to your insurer.
What is a basis of design?
A document that records the criteria, standards and assumptions a design is based on.
Is designing to a code minimum a design error?
Not by itself. Whether a design meets the standard of care depends on the facts and the contract.
What if the owner wanted more capacity than the standard?
Document it and design to it. If the owner did not request it, the added capacity may be an upgrade rather than a correction.
General education, not legal advice. Hardcover is an insurance agency, not a law firm.