This project was the winner of the Hornsby Shire Council Heritage Award in 2005 in Category A - Restoration : Encouragement Award for restoration for Stage 1 of the work on the original house. The property is listed on the Register of the National Estate, the State Heritage Register and the house and grounds is identified as a Heritage Item under the Hornsby LEP 1994.
The site of Mt Wilga has undergone a series of distinct development phases from 1907 onwards. The first phase was the use of the site as a residence commenced by Marcus Clark, the successful Sydney retailer. Marcus Clark retired from business in 1911 because of poor health and concentrated his efforts on constructing his summer home at Mt Wilson (Sefton Hall) and planning his winter home at Hornsby (Mt Wilga) to similar plans. The site was subsequently used by the Commonwealth Government as a rehabilitation hospital. All the former hospital rehabilitation buildings, Marcus Clark's former garage and his former laundry building have been demolished.
Much of the original fabric and details of the building remain from Marcus Clark's time but during the occupation of the building by the Commonwealth Government a number of items were removed from the building such as some of the fireplaces. No original light fittings remained. The Commonwealth also enclosed the tower as an expedient way of reducing water penetration. A theft in the early days of our commission meant that most of the remaining fireplaces and the last remaining original light fitting were stolen. One of the objectives of this stage of conservation and repair work was to recreate all those items stolen and to remove as much as possible of the intrusive alterations to the building undertaken by the Commonwealth. Another major objective was to ensure that the building envelope was watertight and to reinstate the stormwater drainage system around the house. Conservation work undertaken in 2004 included electrical and security services upgrade, retiling the roof and replacing gutters, repainting the exterior of the house and the major rooms of the interior, rebuilding the north-west corner of the verandah, rebuilding the stone entry gate on the east boundary, restoring the tower, renovating flying gables, installing new fireplaces to replace stolen fireplaces (built to match the original from photographs and careful on-site measuring), installing new door furniture manufactured to match original using the few surviving original pieces, laying new step riser tiles manufactured (in New Zealand) to match the original tiles, installing new stained glass and installing new light fittings. This partly-restored building was used as the set in the March 2008 television drama, Emerald Falls.