QA vs QC in Construction

These two terms get collapsed into "QA/QC" so often that people use them interchangeably, but they describe two different things happening at two different points in a project.

The One-Line Version

QA prevents problems. QC finds them. That's the whole distinction, though it's worth unpacking what each looks like in practice.

Quality Assurance

QA is process-focused and forward-looking. It's the set of standards, procedures, and review steps a firm puts in place before work happens, meant to reduce the chance of errors occurring at all. On a design team, this includes things like documentation standards, coordination meeting cadence, and constructability review built into the schedule. QA doesn't check finished work, it shapes how the work gets produced in the first place.

Quality Control

QC is verification-focused and backward-looking, in the sense that it checks work that's already been produced against a standard. In design, that's reviewing drawings and specs for accuracy and coordination. Once construction starts, QC becomes physical: concrete testing, welding inspections, envelope water testing, and confirming installed work matches the design.

A Concrete Example of the Difference

Say a firm has a QA standard requiring every mechanical drawing to be cross-checked against structural drawings before issue. That standard is QA, it's a process meant to prevent coordination errors. If a reviewer actually goes through and checks a specific set of mechanical drawings against structural drawings and finds three conflicts, that checking activity is QC, it's verifying whether the work meets the standard the QA process set up.

Where Breakdowns Actually Happen

A lot of expensive construction problems trace back to a QA process that either didn't exist for a particular risk or wasn't followed carefully, combined with a QC check that also missed it. One documented example: incomplete performance specifications that weren't caught during a documentation QC review led to a cascade of submittal revisions, schedule delays, and eventually water infiltration issues requiring costly remediation. A stronger QA process up front, or a QC review that caught the specification gap, would have prevented the entire chain.

Shared Responsibility, Not One Owner

Neither QA nor QC belongs to a single role. Architects and engineers set quality standards in contract documents and review submittals. Contractors are generally responsible for quality control once construction starts, supervising work and coordinating inspections. Owners set overall quality goals and sometimes bring in independent special inspectors. A construction manager, where one exists, often coordinates the QA/QC program across all of these parties rather than owning it outright.

Where AI Review Fits

AI-assisted drawing review, like Structured AI's QA/QC Compliance Checks, sits mostly on the QA side: catching coordination and code issues before a set goes out, which is a preventive step rather than a field verification step. It doesn't replace QC activities like site inspection or material testing, which happen once work is physically underway. It's meant to strengthen the QA layer so fewer issues reach the QC and construction stages in the first place.

FAQ

Can a project have good QA but still fail QC? Yes. A strong process doesn't guarantee every individual piece of work meets the standard, which is exactly why QC verification still matters even with a solid QA process in place.

Is QA/QC only relevant to large commercial projects? No, though the formality typically scales with project size. Smaller projects still benefit from basic QA steps like coordination checks, even without a fully documented program.

Does automated drawing review count as QA or QC? It's generally QA, since it happens before construction and is meant to prevent issues from reaching the field, rather than verifying installed work, which is a QC activity.