Historic England visited the hall in 2022 to assess areas of the building which had become a cause for concern.
The Grade I listed Elizabethan mansion, built between 1580 and 1588, was then added to the organisation’s Heritage at Risk Register in November last year.
The hall was bought by Nottingham City Council in 1925 and opened as a museum in 1926.
To help pay for urgent repairs, the Labour-run authority was awarded a grant of £469,992 by Arts Council England to go towards fixing the roof, drainage, stonework, render, windows, walls and other decorative features.
Architects, masterplanners and heritage consultancy firm Purcell was then commissioned by the council under Arts Council England’s Museum Estate and Development (MEND) fund to plan the works.
Before any work could take place, Listed Building Consent (LBC) had to be sought, due to some of the invasive procedures required to install measures to prevent further water damage.
Planning consent was granted on January 18.
“Following pre-application site meetings with the conservation officer and Historic England, it was agreed that a LBC application was deemed appropriate for the interventions to the towers, in particular the holes through the ceilings and walls for the new downpipes,” council planning documents say.
Documents show water ingress is an issue in the North Terrace, alongside “serious” water ingress in the Tudor kitchen area which has left it in a “very poor condition” according to Historic England.
In the Tudor kitchen previous repair schemes have been “harmful”, it adds.
In the Thornhill South stairwell, water ingress has been “damaging the important painted ceilings”, largely due to the limited capacity of the guttering in the roof overhead.
Water is also affecting the roofing and internal spaces of all four towers, while the timber frames of some windows are “failing”.
Work to fix these issues will include the enhanced collection and discharge of surface water from each of the tower roofs, including the installation of new guttering.
Work will also improve the collection and discharge of surface water from the lead-lined gutters, following significant levels of water ingress and damage to the south stair Thornhill decorative ceiling and cornice.
It will be done in two phases.
The first phase will enable the works and allow the building to dry out, and this work will take place from February to May this year.
Meanwhile the second phase will include conservation repairs, and these are due to take place in March 2025 subject to the building being dry enough.
“At roof level, the existing gutters will be lifted and modified to enlarge the catch pits and to better manage heavy rainfall and blockages,” planning documents add.
“The proposal is to relocate the outlet, for an internal lagged plastic downpipe to express a modern intervention and to minimise visual impact on the existing external historic appearance, with a short nominal one-metre length of cast iron downpipe installed externally at low level, so not seen from ground.
“The existing lead rainwater goods will be redundant, however will be repaired for historic reference and to maintain historic arrangements.
“Rodding points will be provided for ease of maintenance, along with a lead overflow installed to the rear elevation of each tower.”