## Facts

- Glenn Prah owned a single-family home equipped with a rooftop solar energy system supplying heat and hot water.
- Prah installed the system at substantial cost, with solar collectors positioned to receive sunlight from the south.
- Richard D. Maretti purchased the adjoining lot immediately to Prah’s south and planned to build a residence.
- Maretti’s proposed house conformed to zoning requirements and subdivision deed restrictions and received governmental siting approval.
- Prah alleged the proposed structure, as located, would materially reduce sunlight reaching his collectors, impairing system performance and causing damages.
- Prah requested that Maretti relocate the house farther south; Maretti did not alter the plan to Prah’s satisfaction.
- Prah sued for an injunction to prevent construction and for damages, asserting a right to continued access to sunlight for solar energy use.

## Issues

1. Whether a landowner states a claim for private nuisance when a neighbor’s lawful residential construction allegedly blocks sunlight needed for an existing solar energy system.
2. Whether the traditional rule rejecting a legal right to light bars nuisance liability for obstruction of sunlight used as an energy source.
3. Whether compliance with zoning and deed restrictions forecloses a private nuisance claim as a matter of law.

## Decision

- The Wisconsin Supreme Court reversed the grant of summary judgment for Maretti and remanded for further proceedings.
- The court held that Prah’s complaint stated a legally cognizable private nuisance claim based on alleged unreasonable interference with access to sunlight used for solar energy.
- The court declined to adopt an absolute rule either guaranteeing solar access or immunizing lawful construction from nuisance claims.
- The court ruled that whether Maretti’s conduct was unreasonable required factual development and could not be resolved on summary judgment.
- The court treated Maretti’s regulatory and deed-restriction compliance as relevant to reasonableness but not dispositive.

## Legal Principles

- Private nuisance involves a substantial, nontrivial interference with another’s use and enjoyment of land, and liability turns on whether the interference is unreasonable.
- Unreasonableness is assessed by balancing the gravity of harm against the utility of the actor’s conduct, evaluated in context.
- The absence of an express easement for light does not categorically bar a nuisance claim when the alleged harm involves sunlight used as an energy source rather than mere illumination or aesthetics.
- Compliance with zoning ordinances and private restrictions does not automatically preclude nuisance liability; lawful conduct may still be enjoined or give rise to damages if it causes substantial and unreasonable interference.
- Nuisance doctrine may adjust to changes in land use and social conditions, permitting case-by-case evaluation of conflicts between solar energy use and neighboring development.

## Conclusion

The court held that unreasonable obstruction of sunlight needed for an existing solar energy system may constitute a private nuisance, reversed summary judgment for the neighboring builder, and remanded for a factual determination of reasonableness under nuisance balancing principles.


Prah v. Maretti, 108 Wis. 2d 223, 321 N.W.2d 182 (Wis. 1982)