A gutter does not fail gradually. It works, and then during one heavy afternoon it does not, and the water goes somewhere it was never meant to go. On this stretch of coast the odds of that afternoon arriving are higher than most people assume, and the reason is in the rainfall record.
The short version
- The Bureau of Meteorology records about 1,580 mm a year at Murwillumbah and about 1,535 mm at Coolangatta. Roughly four tenths of it falls in January, February and March.
- The building code sizes an eaves gutter for a one in twenty year downpour, and it says so on the condition that the gutter is not blocked.
- Blocked gutters push water under the eaves and into the roof cavity, which is the failure the NSW SES warns about every storm season.
- Salt is the coastal half of the problem. The steel manufacturer asks for unwashed areas to be hosed every six months, and more often near the sea.
- August and September are the driest months here, which makes late winter the sensible window to get it done before the storms return.
What the rainfall record actually says
Kingscliff sits between two long running Bureau of Meteorology stations, and both tell the same story. At Murwillumbah (Bray Park), station 058158, the mean annual rainfall is 1,579.9 mm across 52 years of record. Twenty two kilometres away at Coolangatta, station 040717, it is 1,535.1 mm. Those are big numbers. Sydney's long term average sits well below them.
The total is not the interesting part though. The distribution is.
Four tenths of the year in three months
At Murwillumbah the three wettest months are February at 226.6 mm, January at 211.1 mm and March at 210.5 mm. Add them up and you get 648 mm, which is about 41 per cent of the entire annual average landing in a quarter of the year. Coolangatta runs the same pattern, with March at 210.9 mm leading February and January, and the same three months carrying about 37 per cent of the year.
Then it stops. September averages 39.0 mm at Murwillumbah and 43.3 mm at Coolangatta, roughly a sixth of what February brings. August is barely wetter.
So a gutter on this coast does not face a steady drizzle it can keep up with. It faces a long dry run in late winter while the trees drop and the wind moves the litter around, and then it faces summer, when the water arrives in volume and all at once.
What the building code assumes about your gutters
This is the part most homeowners have never been told, and it changes how you think about the job.
Under the National Construction Code, Housing Provisions Part 7.4, an eaves gutter is sized for rainfall with a 5 per cent annual exceedance probability. In plain terms, the gutter on your house was sized for a downpour with about a one in twenty chance of happening in any given year. Overflow measures are sized for a 1 per cent event, which is the one in a hundred year rain.
The code's own explanatory note attaches a condition to that. Stormwater systems, it says, are designed to remove water arising from rainfall events with an annual exceedance probability of 5 per cent "provided they are not blocked".
Read that again, because it is the whole argument for maintenance in one clause. Every calculation the plumber did when your house was built assumed a clear gutter. Fill a third of that gutter with compacted leaf litter and you have not reduced its capacity by a third. You have moved the whole system down to a storm size it was never designed to handle, and you have done it without changing anything you can see from the ground.
What actually ends up in a gutter here
The litter is not just leaves
Inland, gutters mostly collect leaf. On the Tweed coast they collect leaf, seed pods, bark strips, flower spikes, and the fine grit that blows off the dunes and settles into the low point of the run. The grit is the part people miss. It packs into the leaf litter and turns a light, loose blockage into something that holds water like a sponge and stays wet for weeks.
Overhanging branches make it worse and the NSW SES puts tree work on the same list as gutter work, advising residents to clean up garden debris and trim overhanging branches that could fall on the property.
Salt, which does not wash off by itself
The second half of the coastal problem is invisible. Marine salt settles on everything near the water, and rain only rinses the surfaces it actually reaches. The manufacturer of the steel most local gutters are made from is specific about this. Its maintenance guidance asks that unwashed areas be hosed down at least every six months, and "more frequently in coastal areas where marine salt spray is prevalent".
The examples it gives of unwashed areas include the underside of eave gutters. That is the surface directly under a blocked run, kept damp by trapped water, carrying salt that never gets rinsed. It is where a gutter starts to go, and it is why a gutter clean on this coast is doing more than moving leaves.
What overflowing gutters do to a house
Under the eaves and into the roof
When a gutter cannot take the flow, the water does not politely run over the front lip. Surface tension pulls a good part of it backwards, under the eaves and into the roof cavity. The NSW SES makes exactly this point in its storm preparation advice: "Clear your gutters, downpipes and drains regularly to prevent leaves and debris build-up. Blockages can trap water and cause it to overflow under the eaves into your roof cavity." You can read the full advice on the SES prepare your home page.
That water lands on ceiling plaster, insulation and framing. By the time a stain shows on a ceiling it has usually been happening for several storms.
Into the ground next to your footings
The other direction is down. CSIRO's homeowner guide to foundation maintenance and footing performance lists roof plumbing among the causes of rainwater being concentrated in a small area of soil. It names the failure modes directly: "Incorrect falls in roof guttering may result in overflows, as may gutters blocked with leaves etc," and "Corroded guttering or downpipes can spill water to ground."
Where that concentrated water reaches soil next to the footings, CSIRO describes the result as erosion, saturation and migration of water under the building. On reactive clay, which plenty of the Tweed valley is, uneven wetting and drying around the perimeter of a slab is the mechanism behind a lot of cracking that gets blamed on the builder.
Standing water and mosquitoes
A blocked gutter holds water long after the rain stops, and NSW Health puts roof gutters on its list of breeding sites to control, advising people to clear drains and roof gutters so water runs freely. The same guidance notes that some mosquitoes can breed in very small amounts of water, "such as in the water that collects in a discarded drink can". A gutter holding a centimetre of water along ten metres of run is a great deal more than a drink can.
When to clean, on this coast specifically
Generic advice says twice a year. The rainfall record here suggests something more specific about the timing.
The NSW SES puts storm season between September and April, noting that in one recent season its volunteers responded to more than 29,000 storm incidents, with fallen trees and leaking roofs making up a large share of the work. Bureau records put the driest months at Murwillumbah in August and September, at 53.7 mm and 39.0 mm.
Those two facts line up neatly. Late winter is dry, the trees have dropped, and storm season has not started. That is the window. Clearing gutters in August or September means the system goes into the wet months empty, which is the only condition the code ever assumed it would be in.
A second clean after the summer peak, once February and March have finished loading the gutters with whatever the storms brought down, covers the rest of the year. Properties under heavy tree cover need more than two. If you are in Kingscliff, Casuarina or Cabarita Beach with tuckeroos or paperbarks over the roof line, you already know which category you are in.
Cleaning is only half of it
A gutter clean that only removes debris misses the point of being up there. While the run is empty is the one time anybody can see the condition of the metal, the brackets, the joins and the fall.
Things worth catching at that moment: rust starting on the inside of the base, where it is invisible from the ground until it is a hole. Joins that have opened up. Sections that have dropped so water pools instead of running. Fixings that have backed out. Any of those turn into a gutter repair if caught early, or a gutter replacement if left.
The downpipe matters as much as the gutter and gets a fraction of the attention. A perfectly clear gutter feeding a blocked downpipe overflows exactly like a blocked one.
Doing it yourself, and when not to
Plenty of single storey homes with a safe, level place to stand a ladder are a reasonable weekend job. What makes it not a weekend job is height, pitch, wet metal, brittle tiles, and working above a hard surface with your arms over your head. Falls from ladders at domestic height are not minor.
First Choice Gutter Services is licensed and insured and holds working at heights certification, and does this on single and double storey homes, strata and commercial buildings from the Northern Rivers to the Gold Coast.
Where to start
If your gutters have not been looked at since last summer, they are carrying a winter's worth of litter into the wettest quarter of the year. Gutter cleaning starts from $200, and it includes clearing and flushing the downpipes rather than treating them as a separate visit. Quotes are free before anything starts.
The work happens on a roof most people never see, so First Choice Gutter Services sends before and after photos of the work and explains what caused the problem in the first place. If something is missed, First Choice will come back. Get in touch and say which suburb you are in.