Part of Norwich's Castle Museum will be closed for six months, to replace a 22-year-old air conditioning system which is a threat to artefacts.
The current air chiller system was installed at the castle in 1999, above its Tee Gallery and is now in need of replacement.
It is feared that if it is not replaced, it runs the risk of causing "moisture and thermal distress" to items displayed in the gallery - and may also put off potential lenders for major future exhibitions.
Therefore, the Norfolk Museum Service has applied to Norwich City Council for permission to make alterations to the air conditioning system of the attraction.
A spokesman for the museum service said: "The works will not only replace the chiller unit, but also add additional air handling plant that will enable us to better control the environment within the Norwich Union and Bernard Matthews Galleries.
"We will also be making physical changes to the building in order to better insulate the gallery spaces."
Papers submitted with the application say the current system often makes it difficult for curators to meet the requirements of people lending precious artwork to the gallery - while the changes would also help prevent damage to artefacts on display.
The NMS spokesman added: "There has not been any damage to collections. However, completing the works will ensure that we are able to effectively control the environment.
"This is important as we need to be able to demonstrate stable control of the environment in order to satisfy potential lenders to our major exhibitions programme."
The cost of updating the system is yet to be finalised and, should it be approved, the project will begin in September 2021 and take around six months to complete.
And during this period, the gallery will be closed off to the public.
It comes with the attraction already undergoing its biggest transformation in a generation, a £13.5m project to restore the 12th century layout of the Castle Keep which began in August 2020.
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