Solar Structural Engineering: A Code-Level Guide for Developers, EPCs and Installers

Every solar permit set makes the same structural promise: the roof, the racking connections and the foundations can carry the dead, wind, snow and seismic loads the system adds, for the life of the system. A solar structural engineer backs that promise with calculations and a professional stamp that the authority having jurisdiction (AHJ) will accept.

This guide explains how solar structural engineering works at code level, from a single-family rooftop to a multi-megawatt tracker field. It is written for the people who buy engineering: developers, EPCs and installers who need approvals without redesigns. Dynamo Structures has 10 years in solar structural work across 100s of AHJs, with PE licenses in CA, NY, NJ, PA, FL, IL, HI and TX, and SE licenses in Illinois and Hawaii.

What a Solar Structural Engineer Does

The work changes by market, but the question is always the same: does the structure have the capacity for the new loads, and if not, what is the most efficient fix?

See how this works by market: residential solar structural engineering, commercial solar structural engineering and utility-scale solar structural engineering.

In all three, the engineer of record is responsible for the structure that supports the array. Racking manufacturers certify their own components. They do not certify your roof or your soil.

Not sure whether your project needs a structural report at all? See do I need a structural engineer for solar panels.

The Codes That Govern Solar Structures

ASCE 7: The Load Standard

ASCE 7, Minimum Design Loads and Associated Criteria for Buildings and Other Structures, defines how wind, snow, seismic and other loads are calculated. Two editions are in use across the country:

• ASCE 7-16 was the first edition to address rooftop solar wind loads directly, in Sections 29.4.3 and 29.4.4. It is referenced by the 2018 and 2021 IBC.
• ASCE 7-22 added wind provisions for ground-mounted fixed-tilt solar (Section 29.4.5), moved to reliability-targeted snow loads, and tightened the seismic rule for rooftop arrays in Section 13.6.12. It is referenced by the 2024 IBC.

The adopted building code, not the latest standard, decides which edition applies. Two projects in neighboring jurisdictions can legitimately use different editions. Every Dynamo calculation package states the edition on the cover sheet.

Risk Category, Exposure and Site Parameters

Before any load is calculated, the engineer sets the inputs that drive every number downstream: the building's Risk Category (most solar sits on Risk Category II buildings, but hospitals, schools and emergency facilities are higher), wind exposure category from surrounding terrain, topographic effects on hills and escarpments, and site-specific ground snow and seismic values. ASCE's Hazard Tool provides the mapped values. Getting exposure wrong is one of the fastest ways to under- or over-design an array.

IBC Chapter 16: Structural Design

The International Building Code sets roof live loads, load combinations and structural requirements. Its photovoltaic live load provisions have moved with each edition, which trips up plan reviewers and designers alike:

Two provisions matter on almost every rooftop job. Roof live load need not be applied under the panels where the clear space between panels and roof is small enough that people and materials cannot be stored there (the IBC sets that limit at 24 in.). And the roof must still be checked for full roof live load with no panels present, because arrays are removed and replaced over a building's life.

IEBC: Alterations to Existing Buildings

Most solar goes on buildings that already exist. The International Existing Building Code decides how much of the existing structure must be brought up to current code. Its 5% gravity and 10% lateral thresholds are covered in Adding solar to existing buildings below.

IRC R324: One- and Two-Family Dwellings

For houses built under the International Residential Code, Section R324 covers solar energy systems. R324.4 requires the roof to be checked for two cases: dead load including the PV system plus snow load, and dead load without the PV system plus roof live load or snow load, whichever is greater. Areas of the roof not covered by panels are designed for the normal roof loads.

Load Calculations for Solar

Dead Load and Concentrated Loads

Modules and racking typically add 3 to 4 psf on a flush-mounted residential array. Ballasted commercial arrays can add far more, depending on wind exposure and the ballast layout. The distributed number is only half the check. Each attachment or ballast tray puts a concentrated load into a rafter, purlin or joist chord, and that local effect often governs on light framing.

Wind Loads on Rooftop Arrays

ASCE 7-16 and 7-22 provide two rooftop methods:

• Section 29.4.3 covers panels on flat roofs or roofs sloped 7 degrees or less. Design pressure is p = q_h(GC_rn), where (GC_rn) is a nominal coefficient adjusted by a parapet factor (γ_p), a panel chord factor (γ_c) and an array edge factor (γ_E). Geometric limits apply, including a panel chord of 6.7 ft or less and gaps of at least 0.25 in. between panels.
• Section 29.4.4 covers panels installed close to and parallel with the roof surface on any slope. It starts from the roof's component and cladding pressures and applies the array edge factor and a pressure equalization factor (γ_a).

The array edge factor is where many designs go wrong. γ_E = 1.5 applies to uplift on exposed panels within 1.5 times the panel chord of the end of a row at an exposed edge. Elsewhere, and for downward loads, it is 1.0. Getting the exposure classification right can change attachment spacing or ballast by a meaningful amount, in either direction.

For low-profile arrays on flat roofs, the SEAOC PV2-2017 report, Wind Design for Solar Arrays, and manufacturer wind tunnel testing per ASCE 49 are common alternatives. AHJs vary in what they accept. See commercial ballasted rooftop systems for how this plays out in ballast design.

Wind Loads on Ground-Mounted Arrays

Before ASCE 7-22, there was no ground-mount solar method in the standard. Engineers adapted open-building or sign provisions. ASCE 7-22 Section 29.4.5 now covers ground-mounted fixed-tilt systems within defined limits, including a panel chord between 6 and 14 ft, tilt between 0 and 60 degrees, and a minimum row length relative to chord. Single-axis trackers fall outside that method. They are designed from wind tunnel testing that accounts for dynamic effects such as torsional instability and stow position.

Snow Loads: Sliding, Drift and the 7-22 Maps

Solar panels are slippery, unobstructed surfaces, so snow slides off them. ASCE 7 treats that through the roof slope factor and sliding snow provisions, and the snow that leaves the array has to land somewhere: on a lower roof, against a parapet, or in the space between rows. Tilted rows on flat roofs can also create drift conditions the original roof was never designed for.

ASCE 7-22 replaced the 50-year ground snow maps with reliability-targeted, strength-level ground snow loads, with separate maps by Risk Category. The load factor on snow in strength design dropped from 1.6 to 1.0 to match. The 2024 IBC also defines an allowable stress design ground snow load. Mixing strength-level and allowable-stress values is a common source of overstated or understated roof loads, so the basis of every snow number should be stated in the calculations.

Load Combinations: ASD and LRFD

Wood framing, light-gauge steel and many racking components are checked with allowable stress design (ASD). Steel and concrete members are often checked with load and resistance factor design (LRFD). The two use different load combinations and different load levels. A clean calculation package keeps each check in its own method and never mixes a strength-level load into an allowable stress check.

Seismic: ASCE 7 Section 13.6.12

Rooftop arrays are nonstructural components under ASCE 7 Chapter 13. Section 13.6.12 allows ballasted, unattached arrays on low-slope roofs when a set of conditions is met, including a calculated seismic displacement, minimum clearance to roof edges (or a parapet designed for impact) and wiring that can accommodate movement. ASCE 7-22 added that panels may not be counted as part of the load path that holds an array together unless they have been evaluated or tested for that load.

Racking, Attachments and Connections

The load path does not end at the rail. Attachments must transfer uplift, downward and lateral loads into framing through fasteners with documented capacity. Wood connections use NDS withdrawal and lateral values. Steel connections are checked for bolt shear, bearing and local member effects. Racking manufacturers publish component capacities and span tables, and the engineer of record confirms those components work with the actual structure underneath.

Carports and Elevated Structures

Solar carports and canopies are full structures, not roof additions. They need foundation design, lateral system design, and attention to vehicle impact and clearance. The IBC allows roof live load on certain open-grid elevated PV structures to be reduced to 12 psf when people cannot occupy or store materials on them. Snow and wind on canopies follow the open-structure provisions of ASCE 7.

Adding Solar to Existing Buildings

The IEBC prescriptive method uses two thresholds that decide most rooftop solar projects:

• Gravity (Section 503.3): if the alteration increases the design dead, live or snow load on an existing element by more than 5%, that element must be altered or replaced to meet the IBC for new structures. Some engineers apply the 5% per load type, others to the total load effect. We apply the more conservative reading unless the AHJ directs otherwise.
• Lateral (Section 503.4): an existing element can remain unaltered if its demand-capacity ratio with the alteration is not more than 10% greater than without it.

The 2024 IEBC added a specific relief for solar: seismic demand-capacity increases need not be evaluated for rooftop PV systems that add no more than 5 psf of dead load, including ballast, and no more than 10% of the existing roof dead load. States and cities amend these sections, so we confirm the local version on every project.

Exceeding 5% does not automatically mean reinforcement. It means the element must be shown to meet current code. A detailed check with actual member sizes, spans and material grades often finds capacity that a screening check misses. That is how marginal roofs get approved.

A simple example shows why the threshold matters. A light residential roof with 10 psf of dead load and a 20 psf roof live load has a total gravity load of 30 psf. A 3 psf PV system increases that total by 10%. That is above 5% no matter how the threshold is read, so the framing must be shown to meet current code with the array in place. In practice, many roofs do, once actual member sizes and spans are used.

Soil-Structure Interaction for Ground Mounts

A ground-mount foundation is only as good as the soil model behind it. Lateral wind and uplift govern most solar piles, and both depend on soil stiffness near the surface. Typical design steps:

• Translate the geotechnical report into lateral soil parameters for analysis (p-y curves in software such as LPILE, or Broms-type methods for short, rigid piles).
• Check combined bending, axial and torsion demands from fixed-tilt racking or tracker reactions.
• Account for frost heave and adfreeze in cold climates, and for corrosion based on soil resistivity, pH and chemistry.
• Confirm design capacities with a pre-production pile load test program using ASTM D1143 (compression), D3689 (tension) and D3966 (lateral).

Read more in utility-scale solar foundation design.

Why Solar Projects Fail Plan Check

Across 100s of AHJs, the same structural corrections come back again and again:

• no stated code edition, or a mix of editions within one package,
• wind zones and array edge factors that do not match the layout,
• no check of the roof without panels under full roof live load,
• missing concentrated load checks at attachments and ballast trays,
• ballast designs that ignore seismic displacement or lack a justified friction coefficient,
• existing building thresholds not addressed at all.

Each one is avoidable. A package that answers the plan checker's questions before they are asked is the fastest route to approval.

What a Solar Structural Package Includes

• Residential: PE-stamped structural letter, roof framing calculations, and reinforcement details only where required. Dynamo returns residential letters within 24 hours of a complete submittal.
• Commercial & industrial: reserve capacity analysis, racking and ballast review, reinforcement design, equipment pad and anchorage details, material staging plans and plan check responses.
• Utility-scale: pile and foundation design calibrated to the geotechnical report, BESS and electrical equipment foundations, IFC drawings, and support through submittals and RFIs.

How to Choose a Solar Structural Engineer

• Licensure where you build. The stamp must match the project's state, and some jurisdictions require an SE for certain structures.
• Edition discipline. The package should state which ASCE 7, IBC and IEBC editions it uses, and why.
• AHJ experience. Plan checkers differ on wind methods, ballast documentation and existing-building interpretations. An engineer who has seen your jurisdiction saves a resubmittal.
• Willingness to look harder. The cheapest letter is the one that approves a marginal roof with real calculations, not the one that fails it on a screening check.
• Coordination. Civil grading, geotechnical findings and electrical layouts all affect structural design. Good engineering accounts for them up front.

Why Developers, EPCs and Installers Work with Dynamo Structures

• Licensed where you build: PE in CA, NY, NJ, PA, FL, IL, HI and TX. SE in Illinois and Hawaii.
• 10 years of solar structural work across residential, commercial and utility-scale projects.
• 100s of AHJs: we know what plan checkers ask for and design to it.
• Thorough review: we look for capacity before we specify reinforcement, so marginal roofs get a fair answer.
• Efficient design: structural design that accounts for civil, geotechnical and electrical constraints from the start.
• Residential speed: stamped residential letters within 24 hours of a complete submittal.

Frequently Asked Questions

Do I need a structural engineer for solar panels?

Most AHJs require a structural review for rooftop solar, either a stamped letter and calculations or proof that the project meets a prescriptive path such as SolarAPP+. Commercial rooftop and ground-mount projects almost always require stamped structural calculations.

What is included in a solar structural engineering report?

The code basis and editions, design loads (dead, live, wind, snow and seismic), checks of the framing or foundations that support the array, attachment or ballast design, and reinforcement details where required, stamped by a licensed engineer.

Which ASCE 7 edition applies to my project?

The edition referenced by the building code your AHJ has adopted. The 2018 and 2021 IBC reference ASCE 7-16. The 2024 IBC references ASCE 7-22. Local amendments can change this, so confirm with the jurisdiction.

What is the difference between a PE and an SE for solar?

A PE (Professional Engineer) license covers most solar structural work. An SE (Structural Engineer) license is an additional credential that some states, including Illinois and Hawaii, require for certain structures. Dynamo holds PE licenses in 8 states and SE licenses in Illinois and Hawaii.

This article is general technical guidance, not engineering for a specific project. Code editions and local amendments vary by jurisdiction.