Earthquake strengthening and repair work will start next week at the Mona Vale Bath House in Fendalton.
Contractor Armitage Williams is expected to complete the project in the summer.
The small building, made of finely crafted timber framing and glazing bars rather than steel framing, was closed after 2011 quake.
Its restoration is the final quake-related project still to be completed at Mona Vale.
Due to budget constraints the work was to be pushed back to 2029. But a Friends of the Christchurch Botanic Gardens' fundraising campaign last year helped with the cost of the repairs, ensuring the structure will not deteriorate further.
Mona Vale sub-committee convener Jeanette Christensen said: "We are thrilled that our fundraising efforts have allowed this restoration to be brought forward.
"Many Cantabrians supported our campaign which began with an Edwardian Garden Party very fitting for this beautiful garden and homestead."
The Waimāero Fendalton-Waimairi-Harewood Community Board also helped pay for the restoration.
"It’s been a true community effort to get to this point and is a testament to what can be achieved when we all work together towards a common goal,” said board chair Jason Middlemass.
"To have this lovely building play its part in the fabric of Christchurch life again and to have all the structures at Mona Vale restored to their original glory, is wonderful.”
Acting director of the Botanic Gardens and garden parks, Nicky Brown, said it is an important milestone in the Mona Vale restoration.
“Once complete, all of Mona Vale will be open for the whole community to enjoy for years to come.
"We cannot say thank you enough to the Friends of the Gardens and the Community Board for their support.”
The Bath House will be home to a semi-tropical collection of plants and used as a public venue for small events.
Originally designed to replicate an Edwardian conservatory, it previously had an indoor swimming pool and a rare collection of sub-tropical plants imported by wealthy heiress, Annie Townend.
A keen gardener, Townend bought the property - known at the time as Karewa - for £6000 (pounds) in 1905.
She changed the name to Mona Vale, added another 3.6ha and built the two bridges and gatehouse.
The Bath House was built between 1905 and 1914 to resemble the conservatory at Glenmark Station, which was Townend's father’s property in Waipara.
Mona Vale was purchased in 1939 by Tracy T Gough. Gough’s great-grandson is Fendalton Ward city councillor James Gough.
"This is the final piece of the puzzle in Mona Vale’s restoration, and I am looking forward to it being finished for everyone to enjoy,” James Gough said.
"I know my great-grandfather would also be pleased to see this work completed and the legacy of this important Christchurch heritage site protected for the next generation.
"To have the Bath House restored means that the Mona Vale staff can reinstate the building to house a collection of semi-tropical plants.
"Mona Vale staff are working with the conservatory staff at the Botanic Gardens to put together a collection which will complement those grown in Cunningham House and the other conservatories.
