Site Assessment

Two angles define how well a roof surface captures sunlight: azimuth (the compass direction your roof faces) and tilt (the pitch or slope of the roof relative to horizontal).

In the United States, south-facing roofs produce the most energy annually because the sun tracks across the southern sky. Due-south is an azimuth of 180°. But you don’t need a perfect south-facing roof to have a productive system. Here’s a general sense of how orientation affects annual production:

These are rough approximations for a typical residential tilt in the mid-latitudes of the US. Actual results depend on your exact location, tilt angle, and local weather patterns. The key takeaway: south is ideal, southwest and southeast are excellent, east and west are workable, and north-facing is usually not worth it unless you have no other option and your tilt is very low.

Tilt angle matters too, but less than most people think. The optimal tilt for annual production roughly equals your latitude (e.g., ~35° for Phoenix, ~42° for Chicago). Most residential roofs fall between 15° and 40°, which is a perfectly productive range. Flat and very low-slope roofs work well too — panels are typically mounted on tilt frames to add pitch. Very steep roofs (>45°) lose some production in summer when the sun is high.

Shading is the single biggest killer of solar production. Even a small amount of shade on the wrong part of an array can have an outsized effect — especially on string inverter systems, where shade on one panel can drag down the output of every panel on that string.

Common shading sources to look for:

• Trees. The most common shading obstacle. Look at both existing shade and future growth — a tree that doesn’t shade your roof today may shade it significantly in five years. Deciduous trees drop their leaves in winter but still cast some shade from bare branches, and winter is when the sun is lowest in the sky and shade reaches furthest.
• Neighboring structures. Adjacent buildings, chimneys, or rooflines that are taller than your array location can cast shade, particularly during morning and afternoon hours or in winter when the sun angle is low.
• Roof features. Dormers, chimneys, plumbing vents, skylights, and satellite dishes all cast shade and create obstructions you have to design around. Some of these can be relocated; others can’t.
• Self-shading. On low-slope or flat roofs, tilted panel rows can shade the row behind them. Proper row spacing during design prevents this, but it reduces the total number of panels you can fit.

During the design process, we use satellite imagery and shade modeling tools to analyze your site’s solar access throughout the year. You can help by taking photos of your roof from the ground, noting any trees or nearby structures that are taller than your roofline, and identifying which direction each roof face points.

Solar panels and racking add weight to your roof — typically 3–5 pounds per square foot for a standard flush-mount system. Most residential roofs built to modern building codes can handle this without any structural modifications. But “most” isn’t “all,” and there are situations where it’s worth verifying.

If there’s any doubt about structural capacity, a structural engineer can evaluate your roof framing. This is a relatively inexpensive assessment and some jurisdictions require it as part of the permit process, especially for older homes or ground-snow-load zones above 30–40 psf.

You can’t cover your entire roof with panels. Building codes and fire codes require clear space around the edges and along the ridge of your roof. These setback and access pathway requirements reduce your usable area, sometimes significantly.

The specific requirements depend on your local AHJ (authority having jurisdiction) and which edition of the fire code they enforce. Here are the common constraints:

• Ridge setback. Typically 18″ to 36″ from the roof ridge, depending on jurisdiction. This gives firefighters access to ventilate the roof in an emergency.
• Eave, rake, and hip setbacks. Required clear space from the edges of the roof, usually 12″ to 18″. Some jurisdictions require more on the side facing the street.
• Fire access pathways. Many jurisdictions require a 36″ clear pathway from the eave to the ridge on at least one side of the array, and sometimes a horizontal pathway along the ridge. These pathways allow firefighters to walk on the roof and access the ridge for ventilation.
• Obstructions. Plumbing vents, chimneys, skylights, and HVAC equipment all require clearance around them. The panel layout has to work around these features.

We account for all applicable setbacks and pathways during the design process. This is one of the most common areas where DIY designs go wrong — someone counts all the panels that physically fit on a roof without accounting for fire code, then discovers during permitting that they need to remove several panels. Better to know the real number from the start.

If your roof isn’t ideal — wrong orientation, too much shade, too old, not enough space, or structural concerns — a ground-mount system may be a better option. Ground mounts install on a dedicated racking structure anchored to the ground, usually with driven posts, ground screws, or concrete piers.

Ground mounts are particularly popular in rural areas with ample yard space, on properties where the roof faces north, or when the homeowner plans to reroof in a few years and doesn’t want to deal with panel removal. We design both roof-mount and ground-mount systems — the engineering process is similar, with different structural and code considerations.

You don’t need specialized tools to start evaluating your site. Here’s what you can gather on your own to make your consultation more productive:

• Compass direction of each roof face. Use a compass app on your phone while facing the same direction as the roof slope. Note the approximate azimuth for each roof face you’re considering.
• Photos of your roof from the ground. Capture each side of the house, including any obstructions (vents, chimneys, skylights, satellite dishes). If you can safely take photos from an upstairs window or a neighbor’s vantage point to show the roof surface, even better.
• Shading observations. Walk your yard at different times of day and note what shades the roof — trees, neighboring buildings, or roof features. Pay particular attention to shade during the midday hours (10 AM–3 PM), which are the highest-production hours for solar.
• Roof material and approximate age. Asphalt shingle, metal standing seam, corrugated metal, tile, flat membrane — knowing your roof type helps us select the right mounting system. If you know when the roof was last replaced, note that too.
• Electrical panel location and photos. Take a photo of the front of your main electrical panel with the door open (breakers visible) and a photo of the panel label/schedule. Note where the panel is relative to where the solar equipment would likely go — the conduit run distance between the array and the panel affects wire sizing and cost.

We use satellite imagery and aerial data for much of the design work, but your on-the-ground perspective catches things that satellite images miss — recent tree growth, new construction next door, or a roof condition that isn’t visible from above.