Can I sue an engineer or architect for a design error in Ontario?
Yes. Engineers and architects are regulated professionals who owe a duty to design and review work to the standard of a reasonably competent member of their profession, and a genuine design error that causes damage or extra cost can support a professional negligence claim. As with other professional negligence cases, the comparison is against accepted practice at the time the work was done, not against a perfect result - engineering and design routinely involve judgment calls, and a reasonable choice that turns out to be imperfect isn't automatically negligent.
Because these disputes are technical, expert evidence from another engineer or architect is almost always required to show what the accepted standard was and how the actual design departed from it. Contribution from other parties is common in construction-related claims - a builder who deviated from approved drawings, or a contractor who ignored a specification, can share or bear the responsibility instead of, or alongside, the designer. Engagement agreements with engineers and architects often include limitation-of-liability clauses, so reviewing that contract early matters. Damages generally cover the cost to fix the defect and related consequential losses, supported by expert costing evidence.
Key takeaways
- Engineers and architects are judged against the standard of a reasonably competent professional at the time, not perfection.
- Technical claims like these almost always require expert evidence from another professional in the field.
- Contractors or builders who deviated from approved plans can share responsibility for the same defect.
- Contractual limitation-of-liability clauses in design agreements often affect what can be recovered.