The building will be closed from Monday August 2 until Monday August 16.
West Sussex County Council says that the roof repairs are necessary because the library has experienced a number of leaks over the past few years.
Work will include removing the roof tiles and the existing damaged membrane, fitting a new breathable membrane, rehanging tiles and replacing damaged ones.
Duncan Crow, West Sussex County Council cabinet member for ccommunity support, said: “It’s unfortunate that we are having to close one of our 36 libraries for two weeks, especially as they have just gone back to pre-covid opening hours.
“But this work is entirely necessary to make sure that the building is kept in good condition and so that customers can enjoy the space all year round.
“We ask all our regular Henfield Library visitors to bear with us whilst the work is taking place and I know our staff will be happy to welcome you back when the doors reopen on Monday 16 August.”
Before the library closes, residents will be able to borrow up to 20 items on their library card and no loans from the library will be due back during the two-week closure.
The children’s library Bookbus - which has books suitable for children up to 11 years old - will also be in the car park next to Henfield library on Monday August 2 and Tuesday August 3 between 10am and 2pm.
Any child who wants to take part in the Wild World Heroes Summer Reading Challenge 2021, produced by The Reading Agency, can also visit the Bookbus on these dates to collect their goodybag, filled with everything they need to take part in the challenge, and choose some books to read.
Online services will still be available by visiting www.westsussex.gov.uk/elibrary where library users can download eBooks, eMagazines and eNewspapers, as well as search the catalogue and request books for when the library reopens.
For anyone still wishing to visit a library during the closure, the nearest county council libraries are Steyning or Hurstpierpoint and you can find opening times by visiting www.westsussex.gov.uk/findalibrary.