The Short Answer
You need a structural engineer whenever a project affects a building's load-carrying system, requires a PE-stamped set for permit, or involves conditions that could put people or property at risk. That's a broad definition — and intentionally so, because the consequences of structural failure are irreversible.
Common Situations That Require Structural Engineering
Removing or Modifying Load-Bearing Walls
Any wall that carries loads from above — floor joists, roof framing, or upper-story walls — is load-bearing. Removing it without engineering can cause progressive collapse. A structural engineer determines whether the wall is load-bearing, sizes the replacement beam, designs the post and footing below it, and stamps the drawings for permit. This applies to residential remodels, commercial tenant improvements, and restaurant build-outs alike.
Additions and New Construction
Any new structure that will be occupied requires structural engineering under virtually every building code in the US. Foundations, framing systems, lateral resistance (shear walls, braced frames), and connections all need to be designed and documented by a licensed professional engineer.
Seismic Retrofits and Upgrades
Older buildings — particularly those built before modern seismic codes — often have soft stories, inadequate connections, or unreinforced masonry that creates risk in an earthquake. Retrofits require a structural engineer to evaluate existing conditions and design the strengthening measures. California, Washington, Oregon, Nevada, Utah, and other high-seismic states have mandatory retrofit programs for certain building types.
Equipment Installation on Roofs or Floors
Replacing an HVAC unit, adding a generator, installing solar panels, or mounting heavy equipment on a roof or mezzanine all impose loads on the structure. If those loads weren't accounted for in the original design, you need a structural engineer to verify capacity or design reinforcement. Many cities require PE-stamped structural calculations for rooftop mechanical permits.
Tenant Improvements with Structural Scope
Commercial TIs often involve new wall openings, ceiling support for heavy equipment, RTU replacement, kitchen equipment mounting, or modifications to the structural frame. When structural elements are touched, permit authorities require engineering documents.
Signs of Structural Distress
Diagonal cracks at window or door corners, stair-step cracking in masonry, sagging floors or ceilings, doors and windows that no longer operate correctly, or foundation movement are all signs that a structural engineer should evaluate the building. These symptoms don't always indicate danger, but they need professional assessment to determine cause and appropriate response.
Change of Occupancy
Moving from a warehouse to a fitness center, an office to a medical clinic, or a restaurant to an assembly use changes the live load design requirements. A structural engineer reviews whether the existing structure can support the new occupancy loads — and if not, designs the necessary upgrades.
When a Permit Requires It
Even if you're not sure whether your project has structural implications, the permitting authority may require structural documents. Most jurisdictions require PE-stamped structural drawings and calculations for any scope that touches the building's structural system. When in doubt, check with the local building department before starting.
What Happens If You Skip It?
Unpermitted structural work creates multiple risks: the work may be unsafe, the building may not pass inspection, the property may fail sale due diligence, insurance claims related to the work may be denied, and liability for any resulting injury falls to the owner. In some jurisdictions, unpermitted work must be demolished and redone.
How to Work With a Structural Engineer
The process starts with a scope description and, ideally, existing architectural drawings. The engineer will review what you have, identify what additional information is needed (field measurements, photos, geotechnical data), and provide a fee proposal. Most firms can turn around a proposal within 24–48 hours of receiving project information.