Output loss from neighboring building calculator

Understanding your neighboring building shading loss

Why buildings pose a bigger risk than trees or chimneys

A 30 foot building standing 45 feet south of a full array can cost up to 30% of annual output if its shadow reaches across the entire row. A neighboring building is often a far bigger shading risk than a tree or chimney because of its height and full-width shadow. Where a tree or chimney affects a handful of panels, a tall building can shade an entire row at once. A NLR study on shading obstructions modeled how a nearby object casts a moving shadow through the day, providing the basis for translating an obstruction's size and position into an output loss estimate.

Why compass direction matters more here than for other shade sources

In the Northern Hemisphere, the sun spends most of the day in the southern sky, so a building to the south blocks far more sunlight than an identical building to the north, which casts almost no shadow across the array at all. East and west buildings fall in between, mainly affecting morning or afternoon production respectively. NOAA's Solar Calculator can trace the sun's exact path across the sky for your specific location and date, which is useful if you want to confirm how much of the day a building in a particular direction would actually cast a shadow on your roof. Check the chimney shading calculator for a comparable but smaller-scale example of this same shadow geometry.

Why this matters before buying a property

Yes. A tall building close to the south side of a property can eliminate most of a roof's solar potential regardless of the roof's own orientation or condition, so it's worth checking before assuming a south-facing roof will perform well. This is easy to overlook during a home purchase if the shading only becomes obvious once panels are already installed. If solar potential is a factor in what you're willing to pay for a property, the home value increase from solar estimator can help put a number on what a shade-free roof might actually be worth.

The risk from future construction

Yes, and this is a real risk in growing neighborhoods. A new multi-story building constructed on a nearby lot after a solar system is installed can introduce shading that wasn't part of the original site assessment. Checking local zoning and any planned developments near your property is worth doing before finalizing a system design in a rapidly developing area. Before that loss is built, the roof itself needs a check, priced by the roof inspection cost before solar estimator.

What to do with this number next

Run the general shading loss estimator if you have multiple shade sources to combine, or check the morning vs afternoon shading tool to see how an east or west facing building specifically affects your daily production curve.