What Does a Structural Engineer Do? (And How They Differ From Architects)

Most projects need both a structural engineer and an architect, but they do very different work. Here's what each one is responsible for, and when you need each.

If you've never hired either before, the line between a structural engineer and an architect can be blurry. Both are involved in designing buildings. Both produce drawings. Both are licensed professionals. But they do fundamentally different work, and most projects need both.

Here's a practical breakdown of what each one does, when you need them, and how they work together.

What does a structural engineer do?

A structural engineer designs the systems that keep a building standing. Their work focuses on the physics of how the building handles loads, gravity, wind, snow, seismic forces, and the dynamic loads of people and equipment moving through the space.

Specifically, a structural engineer is responsible for:

• Foundation design: footings, slabs, retaining walls, and how the building transfers its weight to the soil below
• Framing design: the beams, columns, joists, rafters, headers, and connections that make up the skeleton of the building
• Lateral system design: shear walls, braced frames, moment frames, and diaphragms that resist wind and seismic loads
• Specialty structures: trusses, cantilevers, large open spans, mezzanines, and any unusual structural conditions
• Existing structure evaluation: assessing whether an existing building can support new loads (additions, renovations, change of use)

A structural engineer holds a Professional Engineer (PE) license, which means they can stamp drawings, taking professional responsibility for the safety of the structural design. In Washington, structural engineering for commercial and most multifamily projects requires this stamp.

What does an architect do?

An architect designs the building from the perspective of how people will use it and how it will look. Their work centers on space, function, aesthetics, and the experience of being in the building.

Specifically, an architect is responsible for:

• Floor plans and layouts: arranging rooms, circulation, and how spaces relate to each other
• Building envelope design: walls, roofs, windows, doors, and how the building interfaces with weather and climate
• Aesthetic design: materials, finishes, proportions, exterior appearance, and interior atmosphere
• Code compliance for occupancy and life safety: egress paths, fire ratings, accessibility, occupancy classifications, ventilation, daylighting
• Project coordination: bringing together engineers, contractors, and consultants into a cohesive design
• Construction administration: reviewing contractor submittals, answering RFIs, and confirming the building gets built per the design

An architect holds an architectural license, which authorizes them to stamp architectural drawings and submit them for permit.

The key difference, in plain terms

Think of it this way: the architect designs what the building is. The structural engineer designs what holds it up.

An architect can tell you how big the rooms should be, where the windows go, and what the kitchen will look like. A structural engineer tells you how thick the foundation has to be, what size the floor joists need to be, and how the building will withstand the next earthquake or windstorm.

When do you need both?

Most non-trivial buildings need both an architect and a structural engineer. This includes:

• Commercial buildings of almost any size
• Multifamily housing (apartments, townhomes, condos)
• Custom homes with non-standard geometry or features
• Major remodels that change the building footprint or structure
• Hillside, waterfront, or other challenging sites
• Any project with significant code or zoning complexity

When can you skip one?

Simpler projects may not need both:

• You may not need an architect for: a structural-only project like adding a load-bearing beam, a small addition that doesn't change layout significantly, or a basic shed or detached garage.
• You may not need a structural engineer for: an interior remodel with no structural changes, basic finish work, or a small project that falls within the IRC prescriptive paths.

For most commercial and multifamily work, however, you need both.

How do they work together?

On a typical project, the architect develops the design first, site planning, floor plans, elevations, sections, and material choices. As the architectural design takes shape, the structural engineer reviews it and develops the framing and foundation systems that support the architect's design.

This is an iterative process. The structural engineer may identify constraints that affect the architecture (a column needs to land in a certain place, a span requires a deeper beam than expected). The architect adjusts. The engineer responds. The result is a design that's both beautiful and structurally sound.

At JSL Engineering, we work directly with architects, builders, and owners every day. We can help coordinate the right team if you're not sure where to start.

What about civil engineers, mechanical engineers, and other consultants?

Larger projects often involve additional consultants:

• Civil engineers handle the site itself, grading, drainage, utilities, stormwater management. JSL provides civil engineering in-house alongside structural.
• Mechanical, electrical, and plumbing (MEP) engineers design the building systems.
• Geotechnical engineers investigate soil conditions for foundation design.
• Landscape architects design exterior site features and plantings.

The architect typically leads the team and coordinates between specialists.