Every good solar project get more info starts with a careful look at the site. Not a quick glance on satellite imagery, but boots on the ground, tape measure in hand, checking structural clues and shading patterns the maps gloss over. The choice between rooftop panels and a carport comes down to a mix of physics, structure, and how the property is used. A seasoned solar site surveyor gathers evidence, puts numbers to assumptions, and explains the trade-offs. If you have ever searched for a solar site surveyor near me or asked a solar site survey company to evaluate your property, you have seen how much hangs on that initial assessment.
This article breaks down how the decision gets made in the field, why one option rises above the other for certain properties, and what details will tip the scales when the differences are not obvious.
What the surveyor is looking for
A solar site survey is equal parts measurement and judgment. The surveyor confirms roof conditions, notes obstructions, and tests assumptions about shading that marketing images try to gloss over. They also look at the electrical service location, main panel capacity, and interconnection path. With carports, they extend their view to soils, vehicle clearances, and footing locations. The work is methodical, and the notes are dull to read, but they often save thousands of dollars and weeks of redesign later.
On a recent suburban home, for example, the aerial imagery showed a clean south roof. On site, the surveyor found a chimney that produced a two-hour shadow in winter mornings, a warped ridge that signaled structural sag, and an attic with undersized rafters from the 1960s. The roof still worked for solar, but the design changed. Fewer modules, higher efficiency, a beefed-up attachment plan, and a stronger case for splitting capacity between roof and a small carport over the driveway.
Energy harvest and geometry
Rooftop modules take whatever orientation the roof gives them. If your best roof planes face south to southwest at a tilt between 15 and 35 degrees, rooftop solar usually wins on cost and simplicity. East and west roofs do well too, especially when the home’s load peaks in the morning and early evening. North-facing roofs in the northern hemisphere usually fall to the bottom of the priority list unless the tilt is shallow and the economics demand every extra kilowatt.
Carports let the designer pick both tilt and azimuth. That freedom can lift annual production by a few percent compared with a suboptimal roof, especially where the roof faces awkward directions. More important, carports can be set to avoid shading from nearby trees or buildings. Imagine a retail plaza with a tall neighboring structure shading the roof after 3 p.m. In a carport layout, columns can shift, spans can increase, and the array can move a few parking bays over to clear the shadow line. That is nearly impossible on an existing roof.
On the flip side, optimal geometry does not automatically make a carport the top performer. If the roof offers 800 to 1,200 square feet of viable area and only light shading, it often produces the same total energy for far less installed cost. You will see this in many residential surveys. The surveyor might run two production estimates: rooftop at 97 percent of ideal irradiance, carport at 100 to 103 percent, then add the price delta. The roof still comes out ahead.
Structural reality, not just square footage
The way a solar site surveyor evaluates structure differs between roof and carport.
For rooftops, the survey focuses on:
- Roof type and condition: asphalt shingles, tile, standing seam metal, low-slope membrane. An asphalt shingle roof under five years old is friendly. Clay tile with brittle pans is not. Flat roofs demand ballast or reinforced attachments and a wind study. Framing details: rafter size and spacing, truss type, ridge condition, and signs of deflection. A common residential rafter might be 2x6 at 24 inches on center in older homes, 2x8 or 2x10 in newer ones. Long spans or visible dips may trigger an engineer’s review and potential reinforcement. Sheathing and fastening: thickness of deck, presence of plank versus plywood, and nail patterns. A seasoned surveyor probes with a screw at a discreet location to confirm bite and judge pullout. Those small checks matter when you stamp the attachment plan. Roof age and warranty: if the roof has five years of life left, many owners choose to re-roof before going solar. That coordination can save a double mobilization later.
For carports, structure means foundations and steel. The surveyor notes:
- Soil conditions: clay, sand, fill, or rock. Where undocumented fill is present, expect a geotech report and larger footings. In frost regions, footing depth needs to be below frost line. Utility and drainage conflicts: buried electrical, gas, water, or storm lines. You need a utility locate service and sometimes as-built drawings. A discovered gas main kills a column position fast. Vehicle clearance and drive aisles: typical light-duty carports clear 9 to 14 feet at the low edge, higher if delivery trucks pass. Columns must not pinch turning radii or encroach fire lanes. Snow, wind, and seismic requirements: regional codes influence steel sizes, connection details, and bracing. Coastal gust zones and mountain snow loads push designs toward heavier structures.
I once surveyed a school where the open parking lot looked perfect for a carport. The site drawings revealed a stormwater detention system beneath the best rows. Moving columns to avoid it forced long-span structures. Budget jumped by six figures. Meanwhile, the classroom building had a strong metal roof, favorable tilt, and a clear south face. The roof carried the project, and the carport became a second phase tied to a grant.
Shading, trees, and time of day
Shading is rarely just about what blocks the sun. It is about when and for how long. A tree that casts a narrow shadow from 8 to 9 a.m. may have little effect on annual production. The same tree combined with a chimney that shades from 3 to 4 p.m. can knock down output during peak rate windows. A solar site surveyor measures obstructions with a digital inclinometer and 360-degree shading imagery, then feeds that data into modeling software. The analysis assigns hourly losses across the year, not just a single de-rate number.
Carports can help dodge shade from low eastern trees or western structures, since they can be set farther into the lot and elevated above small obstructions. Rooftops have fewer options. That said, many shading issues are solvable with module-level electronics, careful stringing, and array spacing. The surveyor’s job is to quantify, not guess. If the neighbor’s oak tree will grow another 10 feet within five years, the report should say so and show the long-term effect.
Electrical realities and interconnection
Electricity follows the path of least resistance, and so should your conduit. On rooftops, the run from the array to the main service panel is often short. Dropping down from the attic, or along the exterior wall, keeps cost and losses low. On large flat roofs, gear can sit near existing mechanical areas, again simplifying the run.
Carports introduce distance. If the parking lot is 150 feet from the main electrical room, that run needs conduit, trenching or boring, and sometimes a dedicated equipment pad. Long runs raise voltage drop, which means upsizing wire. Trenching across asphalt adds cost and traffic disruption. A competent solar site survey company flags all of this in the initial visit. They walk the route, count transitions, note obstacles like retaining walls and sidewalks, and provide realistic trench lengths.
Interconnection capacity matters as well. Many homes have 100 to 200 amp service. Backfeeding limits may require a main breaker downsizing or a service panel upgrade. With carports on commercial sites, service upgrades sometimes become the long pole in the tent. If the utility requires a new transformer, lead times can stretch months. A rooftop array tied near existing gear may avoid that headache.
Codes, permitting, and approvals
Rooftop permitting usually focuses on structural attachments, fire setbacks, electrical diagrams, and wind uplift. Fire code requires clear walkways and edge offsets. Tile roofs often trigger more detailed attachment details. Historic districts may require visual mitigation or exclude front-facing arrays. Those constraints are manageable, and the process is standardized in many jurisdictions.
Carports invite more cooks into the kitchen. Now you are in the realm of planning approvals, zoning, parking counts, stormwater review, and sometimes architectural review. Turn a row of parking into a structure and you may impact accessible space counts, emergency vehicle paths, and landscaping requirements. The building department will ask for structural calculations and footing designs. The planning department may want sight line studies or setbacks from property boundaries. None of that is a reason to avoid carports, but it adds time and fees. A surveyor with commercial experience will raise these early so that owners and developers do not underbid the schedule.
Cost, incentives, and lifetime value
Installed costs vary widely by region, but rooftop arrays typically land lower than carports by a meaningful margin. As a rule of thumb, a residential rooftop may sit in the ballpark of a few dollars per watt all-in, while a small custom carport can run higher because steel, foundations, and labor stack up. On commercial projects, carports narrow the gap, but the uplift remains, often tens of percent more for the same wattage.
The calculus changes when incentives value shade structures, EV charging integration, or parking lot improvements. Some jurisdictions offer bonus credits for canopies that include battery storage or serve disadvantaged communities. A company that wants to showcase sustainability to customers may view the carport as a marketing asset. Visibility has value. So does reserved covered parking that keeps snow and sun off vehicles. That added utility, time to approval for solar permit when amortized over years of use, can justify the premium.
The solar site surveyor’s job is to surface these numbers and soft benefits honestly. If your target is lowest cost per kilowatt-hour, rooftop likely wins. If your target includes covered parking and public visibility, carports can compete.
Maintenance and long-term ownership
Owners sometimes assume rooftop arrays are set-and-forget. For the most part, they are. Annual visual checks, occasional cleaning in dusty regions, and remote monitoring handle most needs. Roof penetrations and flashing, when done correctly, do not leak. When they do leak, it shows up years later and is usually traceable to rare workmanship issues or roof aging. A surveyor inspects the roof carefully to reduce that risk before anything gets installed.
Carports concentrate equipment outdoors and at height. That means lift access for maintenance and inspections. Snow shedding can be a factor in cold climates. Birds may nest on purlins, which calls for physical deterrents. That said, some owners prefer having equipment off the roof entirely, especially if they plan to reroof within 10 to 15 years. Carports keep solar generation independent from roof life cycles. In large commercial portfolios, that simplicity pays for itself when roofs are replaced on a regular schedule.
Occupant experience and site use
Rooftops are nearly invisible day to day. Neighbors may notice panels from the street, but the building occupants barely know they exist beyond the utility bill. For homes, that low profile is often a plus. For apartments or hotels, rooftop arrays avoid the legal and logistical headaches of re-striping parking or reallocating spaces.
Carports change how the site feels. They add shade, reduce heat islands, and look like an investment in comfort. Tenants remember covered parking on a 100-degree day. In snowy climates, carports reduce plowing and scraping. There is one catch: columns take up space, and clearances must be respected. Misplaced columns can create blind spots or complicate delivery routes. Surveyors watch for these issues, mock up parking bay impacts, and adjust spans to keep traffic flowing.
When rooftops clearly win
In my experience, rooftop arrays are the obvious choice when the building has:
- A sound, relatively new roof with favorable orientation and minimal obstructions. Short electrical runs to a service with adequate capacity. Parking lots full, tight, or layered with utilities, making carport footings painful.
Think of a typical two-story office with a standing seam metal roof facing south, clear parapets, and a main electrical room on the top floor below the array. The cost per watt is low, the production is solid, and the permitting is straightforward. Unless the owner wants carports for user comfort or marketing, the roof is the rational pick.
When carports earn their premium
Carports shine where:
- Roof geometry is poor or shaded, yet the site has open lots with good sun. The owner values covered parking, brand visibility, or EV charging integration. Structural concerns on the roof would require expensive reinforcement or reroofing.
Picture a grocery store with a cluttered roof full of HVAC units and vents. A carport spreads clean rows of modules above parking, keeps shoppers out of the rain, and becomes a branding feature. The array is easy to expand in phases as demand grows. If the grocery chain wants to add DC fast chargers, the carport’s steel can carry conduits neatly to pedestals.
Hybrid solutions: the quiet middle
Many properties benefit from a mix. Put the highest efficiency modules on the best roof planes and add a modest carport where parking is underused or easy to trench. This split approach often balances cost and performance while solving aesthetics or shading problems. On a university campus I surveyed, the rooftops carried the base load because they were fast to permit and wire. Carports followed a year later, timed with a parking lot resurface and an EV charging rollout. Spreading the work reduced disruption and matched available capital.
How a survey turns into a decision
Owners sometimes ask for a yes-or-no on the first call. An experienced solar site surveyor does not guess. They run a short, disciplined process:
- Document the site with photos, measurements, roof and parking layouts, and shading scans. Capture structural details and electrical routes in enough detail for an engineer to trust. Produce two conceptual designs, one for roof and one for carport, each with modeled production, losses, and interconnection paths. Keep them apples-to-apples where possible. Price both options with realistic soft costs: permitting, engineering, trenching, structural steel, and potential utility upgrades. No optimistic placeholders. Evaluate non-energy benefits and constraints, such as covered parking value, site branding, snow management, historic district requirements, and roof replacement timing.
Most owners reach clarity when they can see the total lifecycle picture, not just a sticker price or an annual kilowatt-hour number.
Finding the right survey partner
If you are searching for a solar site surveyor or typing solar site surveyor near me, look for a few signs of maturity. They should ask for roof ages and structural drawings before the visit. They should bring measuring tools, not just a camera phone. They should talk about setback rules and fire access without being prompted. For commercial sites, they should call out parking geometry, ADA impacts, and the likely permitting departments that will weigh in. A capable solar site survey company will not promise a carport without a geotechnical plan or claim every roof fits solar at a bargain.
Ask for references with similar property types. A surveyor who has done dozens of suburban homes may be excellent, but a pharmacy chain rollout with combined rooftop and carports takes a different playbook. The right fit accelerates permitting, reduces change orders, and keeps neighbors and tenants happy.
Real-world edge cases
Oddities crop up. A low-slope urban roof with high parapets may create wind vortices that raise ballast requirements to unreasonable levels. A carport located under high-voltage transmission lines might run into clearance issues and stray field concerns. In wildland-urban interface zones, fire code can eliminate carports near certain vegetation or set strict defensible space requirements. After a hurricane, some jurisdictions harden code provisions for canopies well beyond national minimums.
In those cases, the surveyor’s role is to say, here is the constraint, here are our options, and here is the cost of each path. Sometimes the answer is to downsize the project, optimize the best roof plane, and keep future expansion in mind.
A brief homeowner example
Take a 2,200-square-foot ranch house with a composite shingle roof, built in 1998, reroofed in 2017. The south roof is 35 feet by 18 feet clear, with one vent stack and a satellite dish. Main service is 200 amps, panel in the garage on the south wall. The driveway is on the west side, long enough for a two-car carport without blocking sidewalks.
The survey shows annual usage around 9,500 kWh, with evening peaks. The roof option fits a 7.2 kW array with high-efficiency modules, produces roughly 10,000 to 11,000 kWh a year depending on climate, and feeds neatly into the garage panel. The carport option could fit 6 to 8 kW, depending on span and aesthetics, but requires two footings near a retaining wall and a 60-foot trench back to the garage. The cost delta per watt is significant. Unless the homeowner really wants covered parking, the roof wins. If they plan to convert to an EV soon and value shaded charging, a small carport with integrated charger may still be worth it, but the roof remains the backbone.
A brief commercial example
Consider a 50,000-square-foot retail box with a flat TPO roof, dozens of RTUs, and parapets. Parking covers most of the parcel, aligned north-south, with 14-foot light poles every third bay. The main electrical room sits at the back, 200 feet from the front lot.
Rooftop layout dodges around RTUs, leaving about 35,000 square feet of usable space. Ballasted racking at a shallow tilt avoids penetrations, but wind exposure at the roof edge forces heavier ballast. Production is good, and the electrical run is short. The carport concept spans two central parking rows, clearing light poles and maintaining accessible spaces near the entrance. Trenching to the electrical room crosses a drive lane and a landscape strip with irrigation. Costs are higher for the canopy steel and foundations, plus traffic control during construction.
The retailer wants visible sustainability features and shaded parking for customers. They accept the higher price because the brand lift matters. The surveyor’s report quantifies both options. The owner chooses a hybrid, installs rooftop first for quick savings, then adds the carport in a slower retail season.
Common pitfalls a careful survey avoids
- Underestimating soil or utility conflicts under parking lots that drive up carport footing costs. Overlooking roof age and ending up with a reroof two years after installation, which forces a remove-and-reinstall and strains warranties. Assuming interconnection capacity without utility confirmation, then facing main service upgrades late in the game. Ignoring small but persistent shade sources, like a neighbor’s vent stack or a ridge-mounted antenna, that nibble away production month after month. Designing carports that pinch fire lanes or violate sight line rules at drive entries, which triggers costly rework in planning.
Experienced surveyors flag these in a single site visit because they know what to look for and how to document it. The best complement you can pay a surveyor is that the project went exactly as predicted, with no surprises in the field.
The bottom line
Choosing between rooftop and carport solar is rarely about preference. It is about matching the site’s constraints and the owner’s goals to the option that delivers the best lifetime value. A thorough solar site survey makes the answer obvious on paper. When the numbers are close, the tie usually breaks on non-energy benefits. Covered parking, visibility, ease of future expansion, or the desire to keep solar independent from roof maintenance can tilt a project toward carports. A strong, clean roof with short electrical runs keeps rooftop solar on top for many homes and a good share of businesses.
If you are just starting the process, bring in a qualified solar site surveyor early. Ask them to model both options and to show their measurements, not just their conclusions. A careful survey costs far less than a change order, and it sets the project up for years of quiet, productive service.