Structural Engineer vs Architect — Two Different Professionals, Often Both Needed
One of the most common questions homeowners ask before starting a renovation, ADU, or addition in Orange County is whether they need a structural engineer, an architect, or both. The confusion is understandable — both professionals work on building projects, both produce drawings, and both are licensed by the state of California. But their roles are fundamentally different, and understanding the distinction will save you time, money, and a significant amount of frustration.
This guide explains what each professional does, when you need one versus the other, when you need both, and how the two disciplines work together on a typical residential project in Orange County.
What Does an Architect Do?
An architect designs how a building looks, feels, and functions. Their work focuses on the spatial experience — how rooms connect, how natural light enters, how people move through the space, and how the building relates to its site and surroundings.
Architect Responsibilities
On a typical residential project, the architect produces floor plans that show room layouts, dimensions, and spatial flow, exterior elevations showing what the building looks like from outside, interior elevations for kitchens, bathrooms, and detailed spaces, a site plan showing the building's position on the lot relative to setbacks, easements, and other structures, door and window schedules specifying sizes, types, and locations, finish schedules specifying materials, colors, and specifications, and code compliance documentation for zoning, egress, accessibility, and energy requirements (Title 24 in California).
The architect is responsible for the design intent — the vision for what the building should be. They coordinate with the structural engineer, MEP engineer, and other consultants to ensure that vision can be built safely and legally.
When You Need an Architect
You typically need an architect when you are designing a new building or a significant addition that changes the building footprint or layout, when the project involves complex spatial design decisions like room configurations, window placement, or aesthetic details, when your city requires architectural plans for permit submission (most cities require them for new construction and major remodels), or when you want professional design guidance on how to use your space most effectively.
What Does a Structural Engineer Do?
A structural engineer designs the load-bearing system that keeps the building standing. If the architect designs what the building looks like, the structural engineer designs what holds it up.
Structural Engineer Responsibilities
On a typical residential project, the structural engineer designs and specifies the foundation system (slab-on-grade, raised foundation, or modifications to existing foundations), the framing system (wall studs, floor joists, roof rafters or trusses, beams, headers, and columns), the lateral force-resisting system (shear walls, hold-downs, anchor bolts, and drag struts that resist earthquake and wind forces), connection details (how every structural element attaches to the next — beam-to-column, wall-to-foundation, floor-to-wall), and structural calculations showing that every element meets California Building Code and ASCE 7 requirements for gravity, seismic, and wind loads.
The structural engineer's work is about safety and code compliance. The structure must resist all loads it will experience over its lifetime — including the weight of the building itself, the weight of people and furniture, and the forces generated by California earthquakes and wind.
When You Need a Structural Engineer
California requires a licensed PE for any project that modifies or creates load-bearing elements. Specifically, you need a structural engineer for ADUs and garage conversions (California requires PE-stamped structural plans for all ADU permits), room additions and second-story additions (new structural systems must be designed and existing systems must be verified), load-bearing wall removals (the replacement beam, columns, and connections must be engineered), seismic retrofits (foundation bolting, shear wall upgrades, and soft-story reinforcement require PE design), structural inspections and PE letters (real estate transactions, insurance claims, and permit compliance often require a PE evaluation), and any project where the building department requests structural calculations.
When You Need Both an Architect and a Structural Engineer
Most residential addition, ADU, and major remodel projects in Orange County require both an architect and a structural engineer. The two disciplines serve different functions, and a complete permit submission typically requires both sets of drawings.
How They Work Together
The typical workflow looks like this. The architect creates the design — the floor plan, the layout, the window and door locations, the overall building form. The structural engineer then takes the architectural design and engineers the structure to support it. This means sizing the beams that span the rooms the architect designed, designing the foundation that supports the building the architect drew, specifying the shear walls that resist earthquakes without conflicting with the architect's window and door layout, and detailing the connections that hold everything together.
The two disciplines need to coordinate. The architect's design drives the structural requirements — a wide open floor plan requires bigger beams than a compartmentalized layout. The structural requirements sometimes influence the architectural design — a shear wall might need to go where the architect wanted a window, or a beam depth might affect the ceiling height the architect envisioned.
When this coordination works well, the result is a building that looks the way the architect intended, is structurally sound, and passes plan check without corrections from either discipline.
When Coordination Fails
When the architect and structural engineer do not coordinate effectively, the results are predictable. Drawings conflict at plan check — the architectural plans show a window where the structural plans show a shear wall. Plan check corrections are issued that neither firm takes responsibility for. The GC receives two sets of drawings that do not align and has to make field decisions that should have been resolved during design.
This coordination failure is the single most common source of plan check corrections and construction delays on residential projects in Orange County. It is also entirely preventable when the two disciplines communicate during the design phase rather than working in isolation.
When You Only Need a Structural Engineer (No Architect)
Some projects require only structural engineering without architectural plans. These are projects where the structure is being modified or evaluated but the spatial layout and design are not changing.
Load-bearing wall removals are the most common structural-only scope. The homeowner already knows what they want — an open floor plan — and the engineer designs the beam and column system that makes it possible. No architectural redesign is needed.
Structural inspection letters are another structural-only engagement. The engineer evaluates the existing structure and provides a PE-stamped letter with findings. No design work is involved.
Seismic retrofits, foundation repairs, and structural repairs are also typically structural-only scopes. The engineer evaluates the existing condition and designs the fix without changing the building's layout or appearance.
When You Only Need an Architect (No Structural Engineer)
Purely cosmetic or non-structural renovations may require only an architect. Interior remodels that do not move or modify any load-bearing walls, kitchen and bathroom renovations that do not change the structural layout, finish upgrades, and space planning within existing walls are examples of projects that might only need architectural plans.
However, if there is any doubt about whether a wall is load-bearing or whether the project involves structural elements, it is safer to have a structural engineer evaluate before work begins. The cost of a brief PE consultation is always less than the cost of discovering structural problems mid-construction.
Cost Comparison
Architectural fees and structural engineering fees are separate line items. For a typical ADU or addition project in Orange County, architectural plans range from $3,000 to $10,000 depending on design complexity and scope. Structural engineering ranges from $1,200 to $6,000 depending on project type and complexity.
Structural-only scopes like wall removals ($1,200 to $3,500) and inspection letters ($400 to $1,200) do not require architectural plans, so the total professional fee is lower.
How to Choose the Right Professionals
When hiring an architect, look for someone with experience in your project type and your local jurisdiction. Ask to see examples of permitted projects similar to yours. Confirm that they coordinate with structural engineers regularly and understand the structural implications of their design decisions.
When hiring a structural engineer, ask five questions. Will you work directly with the PE who stamps the plans? What is your typical response time? How detailed are your drawings? Do you review against my city's plan check standards? Are you available during construction?
The answers to those questions will tell you more about the quality of the engagement than the fee alone.
How Affinity Design Group Works with Architects
At Affinity, we work alongside architects regularly. If you already have an architect, we plug in as the structural engineering team and coordinate directly with your architect to ensure the plans align before submission. If you do not have an architect and your project requires one, we can recommend architects we have worked with successfully on past projects.
For structural-only scopes — wall removals, inspections, seismic retrofits — you work directly with us without needing an architect at all.
Ready to Start?
Not sure whether you need a structural engineer, an architect, or both? Call (714) 215-7413. We will tell you exactly what your project requires in 5 minutes — no obligation, no charge for the initial conversation.
