Donald and Mary Miller had long owned an odd-shaped lot, in an area zoned for residential use, on which they grew hay and kept some animals. The lot was across the street from a historic house owned by Philip and Babette Detwiler (plaintiffs). The Millers wanted to build a house on their own lot, but the township's rear setback line requirement uniquely reduced the odd-shaped lot's buildable footprint. The Millers applied to the Zoning Hearing Board of Lower Salford Township, Pennsylvania (defendant), for a variance reducing the rear setback line from 75 to 40 feet. The Detwilers opposed the application, in part on the grounds that a variance would reduce the value of their historic house as a community asset. The board found that (1) without a variance, it would be impossible for the Millers to build their house and (2) that the variance would have no discernible negative impact on neighboring properties. When the board granted the variance, the Detwilers sued. The Court of Common Pleas of Montgomery County affirmed the board's decision, and the Detwilers appealed to the Commonwealth Court of Pennsylvania.