The house on the Rawhiti Domain side of New Brighton had a leak nobody could find for eleven years. Water appeared on the hallway ceiling perhaps three times a winter, never in the same spot twice, never in a nor’wester, only in a slow easterly drizzle. I went into the roof space and found what I have found in perhaps sixty Christchurch houses since 2011: a rectangle of 2012 Colorsteel let into 1968 galvanised sheeting where a brick chimney used to be, held by sealant that had given up around 2016, above a boxed-in hole in the ceiling framing where the chimney breast had been.
What the chimney removals left behind
After the February 2011 earthquake, tens of thousands of chimneys across the city were removed to roof level in a hurry, and the roofs were patched under repair programmes dealing with volumes nobody had planned for. The patches took a few forms. The best ones removed the affected sheets to the ridge and ran new full-length sheets over new underlay, leaving no horizontal joint. The common ones cut the opening square, let in a new panel of steel, and lapped it over the sheet below and under the sheet above with a soaker flashing. The worst ones dropped a flat plate over the hole, screwed it through the ribs, and ran sealant around the edges. On tile roofs, the opening was often filled with mismatched tiles from a demolition yard with no sarking beneath.
The Earthquake Commission repair records, where owners kept them, are worth reading before anyone goes on the roof, because they usually describe what was done and sometimes what was deliberately left. Many New Brighton and Woolston records I have seen say “make weathertight” and nothing more.
Why they leak now and did not then
A flat plate with sealant is watertight on the day it is done. Canterbury UV hardens and cracks sealant in eight to ten years, which is why many patches sealed in 2012 and 2013 began leaking between 2020 and 2024. The lapped-panel patches fail differently. A panel lapped under the sheet above relies on a lap long enough that wind cannot drive rain up under it; 150 mm is the minimum and I regularly measure 80. In an easterly, water creeps up an 80 mm lap by capillary action and sits on the underlay or the ceiling below. It does not happen in a nor’wester because the wind comes from the other side of the ridge. That is why the New Brighton leak only showed in drizzle.
In the eastern suburbs, cut edge corrosion works inward from the four bare edges on each patch until it becomes a lace of rust along the laps.
Finding the patch from inside
- Go into the roof space in daylight and look for different-coloured steel, a rectangle of different underlay, or no underlay at all.
- Find the chimney base. The hearth footing is usually still in the floor and the framing will show a boxed-in opening.
- Run a hose on the patch from above for twenty minutes, someone watching from below with a torch. Start at the bottom lap and work up.
- Check the ceiling insulation under the patch. Wet or compressed insulation shows where water has gone for years even if the ceiling stayed dry.
Repairing it properly
The only repair I put my name to is removing the patch and the sheets it interrupts, and running new full-length sheets from ridge to eave over new underlay. On a 1960s long-run roof that is typically three to five sheets, NZ$1,800 to NZ$3,500 including flashings and disposal at 2026 prices. On concrete tile, the repair is new sarking, battens and matched tiles across the opening, NZ$1,200 to NZ$2,800, and the tiles either side need checking for cracks from demolition foot traffic in 2011.
What does not work is another bead of sealant. Nor does a flexible membrane sheet stuck over the patch; the adhesive lets go at the ribs.
One thing to check while the roof is open: the old chimney often sat above an internal gutter or valley, and the patch may have altered how water reaches it. A blocked internal gutter produces a ceiling stain identical to a patch leak; the case on this site about an internal spouting overflow describes the diagnosis.
The New Brighton house had its four sheets replaced in September 2023 for NZ$2,650. The hallway ceiling has been dry through two winters. The leak was in an 80 mm lap on a 2012 patch above a chimney that had not existed for twelve years.
Frequently asked questions
Why is my post-quake chimney patch leaking now? Sealant applied in 2012 or 2013 has reached the end of its eight to ten year life, and short laps on let-in panels admit wind-driven and capillary water in easterly drizzle. Both faults were invisible when new.
How much does it cost to fix a chimney removal patch in Christchurch? Removing the patch and running new full-length sheets over new underlay is NZ$1,800 to NZ$3,500 on long-run steel, or NZ$1,200 to NZ$2,800 on concrete tile.
Can the patch be sealed again instead of replaced? Sealant buys one to two years at most on a patch that has already failed. Replacing the interrupted sheets from ridge to eave is the repair that lasts.