Solar Structural Letter and Roof Load Analysis
A solar structural letter that checks your roof framing, attachments, wind uplift and snow load, sealed by a PE licensed in your state.
- Stamped by a PE licensed in your state
- Built to IBC, IRC and local amendments
- Plan-check comments answered
Confirm the roof is ready before the panels go up
Most building departments want proof that a roof can safely carry a solar array before they issue a PV permit. A solar structural letter provides that proof. It identifies the existing roof framing, adds the weight of the panels and racking to the loads the roof already carries, checks the attachments against wind uplift, and confirms the roof is adequate or specifies the reinforcement it needs.
PE Engineer prepares solar structural letters for residential and commercial rooftop systems, along with structural design for ground-mounted arrays and solar carports. We work directly with solar installers, PV designers and homeowners, and every letter is sealed by a PE licensed in the state where the system is installed.
Letters are usually prepared from attic photos, roof measurements and the PV layout, so no site visit is needed for most homes. We keep the format consistent and easy for plan reviewers to follow, and we answer plan-check comments within the original scope at no extra charge.
What you receive
- Existing roof framing summary
- Dead, snow and wind load analysis
- Rafter or truss capacity check
- Attachment spacing and uplift check
- Reinforcement details if required
- PE sealed solar structural letter
Solar structural services
We cover the structural side of solar permits for rooftop, ground-mounted and canopy systems.
Residential rooftop letters
Evaluation of rafters or trusses on pitched roofs for the added array weight, with attachment spacing confirmed for the wind zone and roof pitch at your address.
Commercial rooftop review
Structural review of low-slope roofs with wood framing, steel joists or concrete decks for attached or ballasted arrays, including drainage and ponding considerations.
Ballasted system analysis
Checks of roof capacity for ballast weight, plus sliding and uplift resistance for non-penetrating systems in wind and, where it applies, seismic conditions.
Roof reinforcement design
Sistering, purlin and strut bracing, added blocking or other reinforcement when existing framing falls short, detailed so the installer can complete it quickly.
Ground-mount foundations
Foundation design for ground-mounted arrays on driven piles, helical piles or concrete piers, sized for the racking reactions and your soil.
Solar carports and canopies
Steel canopy structures that support PV modules over parking, with columns and footings designed for module weight, wind and snow.
Your Stamped, Permit-Ready Plans Start With One Upload
Send your drawings or describe the project. A licensed engineer reviews it and sends a clear, fixed-fee proposal, often within hours.
- Free and no obligation
- Reviewed by a licensed PE
- Secure file upload
What a solar structural letter covers
A solar structural letter is a sealed engineering document that answers one question for the building department: can this roof safely support this solar array? To answer it, the letter typically includes:
- A description of the existing roof framing, such as rafter or truss size, spacing and span, roof pitch, sheathing and roofing material.
- The design loads at the site: existing dead load, the added weight of modules and racking, roof live load, ground snow load and wind speed and exposure from ASCE 7 and the code your jurisdiction has adopted.
- A capacity check of the governing framing members with the array in place.
- An attachment check showing that the mounts, fasteners and spacing resist wind uplift in each roof zone.
- A conclusion stating that the structure is adequate or listing the reinforcement required.
Plan reviewers look for those items in a predictable order, so our letters follow the same structure every time. That consistency matters for installers who submit many permits and want each one to move through review without questions.
Some jurisdictions use streamlined or automated solar permitting with prescriptive structural criteria for simple residential systems. When a roof meets those criteria, a separate letter may not be required. When it does not, because of span, framing size, snow load, roof age or an unusual layout, a stamped solar structural letter is the usual path. The electrical side of the permit, including the single-line diagram and system layout, is covered by our solar PV plans service.
How we evaluate a roof for solar
The evaluation starts with the existing framing. For most homes we work from attic photos with a tape measure showing rafter or truss size and spacing, a measurement of the span, the roof pitch, and the type and number of roofing layers. Truss roofs are identified from their webs and plates, and if the original truss drawings are available, they help.
We then compare the loads with and without the array. A residential PV array usually adds only a few pounds per square foot of dead load, but it is not evenly spread: each mount concentrates load where it attaches. On older homes with undersized rafters, long spans or multiple roofing layers, even that modest increase can push members past their capacity.
Snow and wind need particular care:
- Snow. Panels are slippery, so snow can slide off and pile up at the eave or against lower roofs. In snow country we check the framing for the snow loads the array may create, not just the uniform roof snow load.
- Wind. ASCE 7 includes specific wind provisions for rooftop solar panels, and uplift is highest near roof edges, ridges and corners. We confirm that the mount spacing and the fastener withdrawal capacity into the rafters, checked to the NDS, resist the uplift in each zone.
We also confirm the racking manufacturer’s span limits between attachments and coordinate them with the framing layout, so mounts land on rafters or trusses rather than only on sheathing. The result is a clear yes or a clear list of what needs to change.
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- Free and no obligation
- Reviewed by a licensed PE
- Secure file upload
Commercial, low-slope and ballasted solar systems
Commercial rooftops bring different structures and different questions. Low-slope roofs may be framed with wood joists, open-web steel joists, steel beams with metal deck, or concrete. Each has its own capacity limits and reserve.
Open-web steel joists are common on warehouses and retail buildings, and they are often designed with little spare capacity. Adding an array, and especially ballast, can overload individual joists or concentrate load at points the joists were not designed for. We evaluate the joists using the original design criteria where available and the joist manufacturer’s published load data, and we identify where reinforcement or a different layout is needed.
Ballasted systems avoid roof penetrations by using concrete blocks to hold the array down. That trades uplift anchorage for added weight, so the roof must carry the ballast as well as the modules. The array must also resist sliding and uplift without attachment, and in higher seismic regions the code includes specific provisions for unattached rooftop arrays. We check each of those conditions and coordinate with the racking manufacturer’s engineering for ballast layout.
Other commercial considerations include roof drainage and ponding, since an array can change how water flows and where it collects, as well as rooftop equipment, parapets and future maintenance access. Metal roofs often use clamp-on attachments to standing seams, and we check those attachments and the roof panels’ ability to transfer the load to the purlins below. For buildings where the structure is uncertain, a broader structural assessment may come first.
Roof reinforcement, truss roofs and ground mounts
When a roof does not pass, it usually does not mean the project is over. Most reinforcement for rooftop solar is simple and quick for an installer or framer to complete:
- Sistering new rafters alongside existing ones for the length of the array.
- Purlins and struts that shorten the effective span of the rafters by bracing them down to a bearing wall below.
- Blocking between rafters to give mounts a solid attachment where spacing does not line up.
- Truss repairs where webs or chords are damaged or were previously cut.
We detail the reinforcement on a sheet attached to the letter, with member sizes, fastening and extent, so the inspector can verify it. Trusses deserve special care because each member is working, and modifications must be engineered. Our truss review and stamping service covers repairs and added-load checks in more detail.
Sometimes the better answer is to move the array. A ground-mounted system avoids roof limitations entirely. We design ground-mount foundations on driven posts, helical piles or concrete piers, using the racking manufacturer’s reactions and the soil and frost conditions at your site. For arrays over parking areas, our carport and canopy engineering covers the steel structure and foundations that carry the modules.
Most residential solar structural letters are delivered within a few business days of receiving complete photos and the PV layout, and rush service is available when an installation date is set.
You likely need this if
- Your jurisdiction requires a solar structural letter
- The roof has long spans or older framing
- You are in a heavy snow or high wind area
- The roof has multiple layers of roofing
- You are adding a commercial or ballasted array
- The plan reviewer asked for structural review
How it works, start to finish
From your first message to stamped drawings, you work directly with the engineering team.
- 1Share your projectSend the address, scope and any drawings, photos or plan-check comments. Two minutes is enough.
- 2Receive a fixed-fee proposalAn engineer reviews the scope and replies with a firm price and delivery date for your solar structural letters drawings.
- 3Engineering and draftingWe run the calculations and prepare drawings to the codes your jurisdiction enforces, checked before sealing.
- 4Stamped set deliveredYou receive a sealed PDF set ready to submit, and we answer any plan-check comments within scope.
Codes and standards for solar structural review
Solar structural letters follow the codes your jurisdiction has adopted and the standards that apply to rooftop and ground-mounted arrays:
- International Residential Code (IRC) and International Building Code (IBC) solar energy system provisions
- International Existing Building Code (IEBC) for added loads on existing roofs
- ASCE 7, including wind and snow provisions for rooftop solar panels
- AWC National Design Specification (NDS) for framing and fastener withdrawal
- UL 2703 for PV mounting systems, as listed by the racking manufacturer
- Steel Joist Institute (SJI) specifications for open-web steel joist roofs
How licensing works. Engineering drawings must be sealed by a Professional Engineer licensed in the state where your project is located. PE Engineer works with a network of state-licensed PEs, so every set is reviewed and stamped by an engineer with an active license in the state where your project is located. Their name and license number appear on the seal, exactly as your building department requires.
Related services
Solar PV PlansSolar PV permit plans with string sizing, single-line diagrams, rapid shutdown, interconnection details and code labels, prepared to NEC Articles 690 and 705.Explore More
Structural Inspections & LettersSealed structural inspection reports and engineer letters for foundations, cracks, framing, damage, unpermitted work and existing buildings, written for the people who requested them.Explore More
Truss Review & StampingIndependent review and PE stamp of wood and metal truss drawings, girder and bearing checks, and engineered repairs for cut or damaged trusses.Explore MoreFrequently asked questions
Do I need a solar structural letter for my permit?
Many jurisdictions require one, especially when the roof falls outside prescriptive criteria for span, framing size, snow load or roofing layers. Some accept streamlined checklists for simple residential systems. If your building department has asked for structural review, or you are not sure, send us the PV layout and we will tell you what is needed.
Can you prepare the letter from photos?
Yes, for most homes. We need attic photos showing rafter or truss size and spacing with a tape measure, the span, the roof pitch, the roofing type and number of layers, and the PV layout with racking and attachment details. If the framing cannot be seen, we will tell you what else is needed.
What happens if my roof fails the structural check?
We specify reinforcement, usually sistered rafters, purlins and struts, or added blocking, and include the details with the letter. These repairs are typically simple for an installer or framer. In some cases moving the array to a different roof plane or the ground is the better choice, and we can design that too.
Do you work with solar installers on multiple projects?
Yes. Installers send projects as they come in, and we return letters in a consistent format that plan reviewers recognize. We can also check your standard attachment details against local wind and snow loads so your designs start from a sound baseline in each jurisdiction.
Can you check the racking attachment spacing?
Yes. We check the spacing between mounts against the racking manufacturer’s span limits and against wind uplift in each roof zone, and we confirm the fastener embedment into the rafters or trusses provides enough withdrawal capacity for the uplift at each mount.
How fast can I get a solar structural letter?
Most residential letters are delivered within a few business days of receiving complete photos and the PV layout, with rush service available when an installation date is set. Commercial reviews depend on the roof structure and the information available. We quote a fixed fee, usually the same day.
Get your free solar structural letters proposal
Tell us where the project is and what you need. Attach any drawings, photos or plan-check comments. A licensed engineer reviews every request.
- Upload your filesPlans, sketches, photos or comments
- Get a fixed-fee proposalUsually the same day
- Receive stamped drawingsSealed by a PE licensed in your state