If you’re a solar installer in the Southeast, you’ve almost certainly had a permit application kicked back with the same note: “Structural analysis by a Professional Engineer required.” That’s the jurisdiction asking for a PE letter — and if you don’t have one ready to go, the project stalls.
This guide explains exactly what a PE letter for solar is, when it’s required, what a structural engineer evaluates, how long the process takes, what it costs, and how requirements differ across the Southeast states where Strut E&I works. We issue PE letters for residential and commercial solar projects every week, and most of the confusion we see from installers comes from not understanding what the deliverable actually is.
A “PE letter” (short for Professional Engineer letter) is a signed and sealed document from a licensed structural engineer certifying that a specific building can safely support a specific solar installation. It’s the engineering equivalent of a medical clearance — the PE reviews the proposed installation, performs the required calculations, and issues a formal letter on engineering letterhead with their seal and signature.
A PE letter typically confirms:
A PE letter is NOT a full structural analysis of the building — it’s limited to the solar installation scope. And it’s only valid in the state where the signing engineer is licensed.
Most jurisdictions in the Southeast require a PE letter (or equivalent engineered design) for:
Some jurisdictions allow small residential installations to be permitted without a PE letter if the system meets specific criteria (panel weight below a threshold, standard roof framing, etc.). When in doubt, check with the local building department before pulling the permit.
Residential solar typically requires a simpler PE letter. The engineer verifies:
– Existing rafters or trusses are adequate for added dead load
– Attachment points don’t create stress concentrations
– Wind uplift at the attachment points is within capacity
A residential PE letter for a standard single-family home with visible, accessible framing can often be turned around in 3–5 business days.
Commercial solar is more involved. Commercial roofs vary widely — built-up membrane, EPDM, TPO, metal deck, concrete, wood. Each requires different structural analysis. Commercial projects also often use larger arrays, ballasted systems, and more complex mounting configurations. Commercial PE letters typically require:
– Roof framing drawings or on-site verification
– Load tables for the specific racking and module combination
– Wind load calculations per ASCE 7
– Analysis of purlins, joists, and primary framing
– Sometimes reinforcement design if existing capacity is inadequate
Commercial projects often go beyond a simple “letter” and become a full structural analysis with stamped drawings. Strut E&I handles commercial solar structural engineering across 28+ states.
A comprehensive solar structural analysis looks at four load cases:
1. Dead load. The weight of the panels, racking, wiring, and (if used) ballast. Modern modules run 40–50 lb each. A typical residential array of 20 panels adds roughly 800–1,000 lb distributed across the roof — plus the weight of the racking system.
2. Wind uplift. Wind flowing over a roof creates negative pressure (suction) that tries to lift panels off. The engineer uses the applicable building code (usually ASCE 7-22 in 2026) to calculate the uplift force at each attachment point. This is the most critical analysis for solar in the Southeast — wind loads in Miami can exceed 185 mph, and the uplift forces are significant.
3. Snow load. Less critical in most Southeast states, but Nashville and parts of North Carolina get snow. The engineer confirms that the added roof surface area from the panels doesn’t create unbalanced snow drifts.
4. Seismic load. Rarely controlling in the Southeast, but the engineer includes it for completeness.
The engineer also looks at existing roof capacity. If your building is old, has a damaged deck, has evidence of water intrusion, or has unknown framing, the PE will want to verify the existing structure before certifying it for added load.
A clean residential project with adequate existing framing moves through this process in 3–7 business days. Complex commercial projects can take 2–6 weeks.
| Project type | Typical turnaround (2026) |
|---|---|
| Simple residential, existing framing adequate | 3–5 business days |
| Residential, site visit required | 5–10 business days |
| Simple commercial, clear roof deck info | 7–10 business days |
| Complex commercial, ballasted or older building | 2–4 weeks |
| Reinforcement design required | Add 1–3 weeks |
Solar installers running on tight permitting schedules should build 1–2 weeks of PE letter time into their project calendars. Rush turnaround is often available but typically carries a premium.
Georgia. Enforced at state and local level. Most jurisdictions require a PE letter for commercial solar and for residential installations that exceed prescriptive roof loading. Licensed Georgia PEs only.
Florida. Florida Building Code (FBC) is among the strictest in the country. HVHZ (Miami-Dade, Broward) has the tightest requirements — many jurisdictions require full engineering rather than a simple letter. Wind speeds in the FBC can exceed 185 mph at the coast, which drives up uplift calculations significantly.
South Carolina. Most jurisdictions require a PE letter for commercial solar and for residential in coastal counties. Wind loads are significant in Charleston and along the coast.
North Carolina. Similar to SC — most commercial solar requires PE engagement, and coastal or Outer Banks projects almost always require engineering.
Tennessee. Less strict than the coastal states but most jurisdictions require PE letters for commercial solar. Snow load is a factor in the northeast part of the state.
For installers working in Florida, Strut E&I provides PE letters across Orlando, Tampa, Miami, and Key West.
Permit departments reject PE letters more often than installers expect. The most common reasons:
A competent structural engineering firm with solar experience will preempt all of these issues in the original letter.
How much does a PE letter for solar cost?
PE letter fees vary with the scope of the engineering review. Residential PE letters for simple installations are the most affordable, because the engineering work is limited and predictable. Commercial PE letters — and anything involving ballasted systems, older roofs, reinforcement design, or complex load paths — require more engineering time and are priced accordingly. Ask for a scoped quote rather than a flat rate.
Can any engineer provide a PE letter for solar?
Only a Professional Engineer licensed in the project’s state can issue a valid PE letter. Licensure is state-specific — a PE license in Georgia is not valid in Florida or any other state. For multi-state installers, work with a firm that carries licensure in all your markets.
Do I need a PE letter for ground-mounted solar?
Yes — almost always. Ground-mounted systems require foundation design for the posts and wind load analysis for the racking. Ground-mounted solar typically requires more engineering than roof-mounted, not less.
What happens if I install solar without a PE letter?
You may fail the permit inspection and be forced to hire a PE after the fact to analyze the as-built installation — which is significantly more expensive than doing it right initially. You may also void the homeowner’s insurance on the roof, create liability for the installer, and lose the ability to interconnect with the utility.
How long is a PE letter valid?
A PE letter is valid for the specific project it was issued for. It doesn’t expire per se, but if the project scope changes (different panels, more panels, different racking, a modified layout), a new letter is required. Most AHJs accept PE letters up to a year old if the project scope hasn’t changed.
Do all states require a PE letter for solar?
No — some states and some jurisdictions allow small residential installations to be permitted under prescriptive standards without engineering. But most Southeast jurisdictions require a PE letter for anything larger than the smallest residential systems, and all commercial solar requires PE involvement.
Need a PE letter for your next solar project? Strut E&I provides fast structural certification for residential and commercial solar installations across 28+ states, including all 5 Southeast states. Request a PE letter quote — typical turnaround is 3–10 business days.