The short answer
Solar-suitable roofs face south (or southeast/southwest), tilt 20-40 degrees, have minimal tree shading, are under 15 years old, and have 250+ sq ft of unobstructed area. South-facing produces 15-25% more than north-facing. Heavy shading can cut output 50%. Ground-mount or carport solar handles unsuitable roofs.
Not every roof is right for solar. Orientation, tilt, shading, age, and structural condition all affect production and project economics. South-facing roofs in the US produce 15-25% more than north-facing. Heavy shading from trees can cut output by 50%. Old roofs (20+ years) should be replaced before solar install since panels last 25+ years. This guide shows how to estimate suitability before you invite installers — and what to ask them when you do.
Orientation + tilt
Best: south, southwest, southeast at 20-40 degree tilt. Good: east or west at 20-40 degree tilt (10-15% less production than south). Marginal: north-facing at any tilt (25-40% less production).
Tilt: most asphalt-shingle roofs are 18-30 degrees, which is near ideal for the contiguous US. Flat commercial roofs use ballasted racks tilted to 10-15 degrees to balance production vs row spacing.
NREL PVWatts (pvwatts.nrel.gov) is the free industry-standard production estimator. Plug in address, roof azimuth, tilt, and panel watts. PVWatts uses 30 years of NREL solar resource data.
Shading + roof condition
Heavy tree shading (>50% midday shadow on the array) cuts production 30-60%. Partial shading on a string-inverter system can drop the entire string. Microinverters (Enphase) and DC optimizers (SolarEdge) help — each panel produces independently.
Roof age: replace shingles before install if the roof is 15+ years old. Removing and reinstalling solar costs $2,000-$5,000 — better to do it before panels go up.
Structural: most asphalt-shingle, metal, and standing-seam roofs handle solar fine. Tile roofs cost more to install ($0.30-$0.50/W premium). Wood shake, slate, and old built-up roofs may need engineering review.
Alternatives when the roof does not work
Ground-mount solar: works on any flat or gently sloped land with sun access. Costs $0.30 to $0.60 per watt more than rooftop because of additional racking, ground trenching, and longer DC runs. Best for homes with large yards, north-facing roofs, heavily shaded roofs, or HOA roof restrictions. Most rural and large-lot suburban properties can support a 6 to 12 kW ground-mount without difficulty.
Solar carport or pergola: covers parking, generates power, and doubles as an EV charging shelter. Typically costs $4 to $5 per watt (a 50 to 100 percent premium over rooftop) but adds tangible structural value to the property. The carport itself can be financed alongside the panels for tax purposes in most states.
Community solar: subscribe to a shared off-site solar array, typically located within your utility service territory. The community-solar-vs-rooftop-solar guide breaks down savings (5 to 15 percent of utility rate, no upfront cost, no roof or land needed). Available in 24 US states. Best for renters, condo owners, and homeowners with unsuitable roofs and no land for ground-mount.
Roof replacement plus solar: if your roof is 15 years or older, the cost-effective move is to replace the roof first, then install solar. Many installers offer combined roof-plus-solar packages with bundled financing. The federal credit applies only to the solar portion of the combined project, but new asphalt-shingle roofs are typically eligible for state and utility energy-efficiency rebates separately.
Recap
Bottom line
Roof suitability is the single biggest constraint between a homeowner who wants solar and one who actually breaks even on the investment. South-facing or south-southwest-facing roofs at 20 to 40 degrees of tilt with minimal shading represent the ideal — most US rooftops fall somewhere in the 70 to 95 percent of ideal range. Modern microinverter and DC optimizer systems handle partial shading and split-orientation roofs much better than the string-inverter installs from a decade ago, which has expanded the universe of solar-suitable homes substantially.
Before committing to a quote, run your own suitability check: pull up your address on Google Earth or Apple Maps and identify the largest unshaded roof section, note its compass orientation, estimate shading from trees that may grow over the 25-year system life, and check your roof age against the planned solar warranty period. The solar-panel-cost-by-system-size guide shows what to expect from each size class, and the community-solar-vs-rooftop-solar guide is the right alternative for homes where the roof simply does not work.
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