Proof House Approximately 10 Metres South South West Of Gate House, Marsh Works

The Proof House, located approximately 10 meters south-southwest of Gate House at Marsh Works in Faversham, is a disused building from between 1800 and 1810, originally part of the Royal Gunpowder Factory established in 1786. Constructed of brick, it features a pyramidal slate roof.

The building has a square single-cell plan, with a segmental-arched doorway and flanking sash windows. A lantern is situated on the roof to allow light in and fumes out.

The Marsh Works played a significant role in improving British gunpowder production during the Napoleonic Wars under William Congreve, who established a saltpetre refinery in 1789 to enhance the quality of gunpowder ingredients. The proof house, a laboratory for testing gunpowder, was added during the early 19th-century refurbishment of the refinery, making it likely the oldest example of its kind. The refinery was privatized after World War I and closed in the 1920s. The Proof House is associated with the late 18th to early 19th-century saltpetre refinery at Marsh Works, which is noted as the best preserved of its type in the country and comparable to similar facilities in France and Sweden.