She married Malcolm Nugent Ross in 1844 and he leased the coal rights under the estate to Astley and Tyldesley Collieries in 1857. Katherine Durie became lady of the manor on the death of her mother in 1860. By now the estate was in decline. Katharine married Henry Davenport who died in 1845, and secondly Sir Edward Wetherall. In 1856 he was living at Dam House. Upon his death in 1869 he was succeeded by George Nugent Ross Wetherall and then by his brother Henry Augustus Wetherall who was in financial difficulty. Dam House was sold in November 1889 and remained empty until 1893 when it was sold to the Leigh Council for use as a sanatorium for treating infectious diseases. Four isolation wards were built to house patients with scarlet and typhoid fevers and the house was used as offices and a nurses' home. An earlier building on the site was a stone and timber hall close to a large barn and cornmill powered by a water wheel. The house gets its name from the dam on the brook that was built to power the wheel. The manor house Adam Mort built, dating from around 1600, is described in his will, He died in 1631. The house had a kitchen, parlour with a parlour chamber over it, bed chamber, little chamber, buttery, dairy, loft and clock loft with a bell. The house may have had a chapel. Outside there were stables, pig sties and a ruined stone and timber barn. The three-storey building was built of handmade bricks with a timber frame. A timber lintel over an inglenook fireplace has been dated to before 1600. Much of this building survives though Mort's grandson altered the front of the building in 1650 as evidenced by a plaque over the door. Considerable additions were made in the 18th and 19th centuries when the two-storey east wing was built for the Froggatts. It contains a large first-floor billiard room with four decorative gothic roof trusses. A single-storey north wing with a two-storey coach house was added before 1845 and a single storey west wing added sometime after 1845 when the house was restored by Sarah and Malcolm Ross. The house, built around a quadrangle, open at the south west corner is built of rendered brick with stone details and a slate roof. The three-storey frontage has five unequal bays with stone mullioned windows and crosswing gables.