Leaking Internal Gutters: Repair, Reline or Replace Them?
Leaking internal gutters are usually caused by one of four things: a blocked outlet, a failed lining or joint, a gutter too small for the rain it has to carry, or no overflow to let water escape when it backs up. Clearing the outlet fixes the first cause on the day. The other three mean patching, relining with a new membrane or metal liner, replacing the gutter, or, on some roofs, removing it and fitting external spouting instead. Which one is right depends on the age and condition of the lining and on whether the gutter was designed well in the first place.
Why Is an Internal Gutter Leak Worse Than an Ordinary Gutter Leak?
An external gutter, or spouting, hangs off the fascia outside the walls. When it overflows, the water lands on the garden. An internal gutter sits inside the line of the walls: between two roof slopes, behind a parapet, or in a box built into the roof edge. When it overflows or the lining fails, the water goes into the roof space, the top of the wall framing, or the ceiling below.
That is why building guidance treats them as a risk. BRANZ, New Zealand’s building research body, says the best way to deal with internal gutters is to design them out, and that where they stay, good design, sound construction and ongoing maintenance keep the risk of overflow down. They turn up on plenty of Auckland homes, from older villas with a box gutter behind a parapet to newer houses where a flat-roofed section meets a pitched one.
What Are the Signs an Internal Gutter Is Leaking?
You rarely see the leak itself. You see what it does downstream, often a long way from the gutter.
- Brown stains or bubbling paint on a ceiling, usually along a line under the gutter or near an internal downpipe
- Damp skirting boards, swollen linings or a musty smell in a room below or beside the gutter
- Water running down inside a wall or out of a light fitting during heavy rain
- Standing water or dark sludge in the gutter a day or two after rain
- Water spilling over a parapet or out of an overflow outlet, if the gutter has one
A stain that only appears after a big downpour points to capacity or a blockage. A stain that appears after any rain points to a hole in the lining or a failed joint.
What Causes Internal Gutters to Leak?
Most leaks come back to the same short list. Old internal gutter systems tend to have more than one of these at once.
| Cause | What you’ll notice | Typical fix |
|---|---|---|
| Blocked outlet or sump | Leaks in heavy rain, ponding, leaves and silt at the outlet | Clear the outlet and downpipe; fit a leaf guard over the outlet |
| Failed membrane joint or split | Leaks in any rain, often in the same spot | Patch if the rest of the membrane is sound; reline if it is brittle |
| Rusted metal lining | Leaks spreading over time, rust stains at the outlet | Reline or replace; rust rarely stops at the first hole |
| Not enough fall | Water sits in the gutter for days | Rebuild the gutter base to a proper fall |
| Undersized gutter or outlet | Overflows only in downpours | Larger outlet, extra downpipe, or redesign |
| No overflow | Water backs up into the building with nowhere to go | Add an overflow outlet that discharges outside |
| Failed flashing where gutter meets a wall | Damp patches on the wall below | Repair or replace the flashing |
Auckland adds its own pressure. Summer downpours can dump a lot of water in a short time, and leaf litter, pine needles and grit washed off a concrete tile roof all end up in the lowest point of the gutter, which is the outlet. A gutter that copes on an ordinary day can back up in the first ten minutes of a thunderstorm.
Repair, Reline or Replace: How Do You Decide?
Start with the lining, because that is what actually keeps the water out.
Clear and maintain when the lining is sound and the leak lines up with a blockage. If the stain appeared after a dry spell full of leaf fall, clear the outlet and downpipe, check that water runs away freely, and watch the ceiling through the next heavy rain. Our gutter cleaning visits include internal gutters and their outlets, not just the spouting you can see from the ground.
Patch when there is one clear defect, such as a single split or a lifted joint, and the rest of the lining is flexible and well stuck down. A patch on a membrane that is cracking all over will hold until the next split opens a metre along.
Reline when the gutter’s shape and fall are fine but the lining has had its day. A new membrane over a prepared base, or a new folded metal liner, gives the gutter a fresh waterproof skin without rebuilding the roof edge. Low-pitch and flat areas that drain into the gutter often get done at the same time, and our butynol roof coating work covers that kind of membrane job.
Replace when the gutter base is rotten, the fall is wrong, or the gutter is simply too small. That means opening up the area, fixing the timber underneath, and building it back with the right size, fall and outlets, plus an overflow.
Remove and convert when the roof shape allows the water to be taken to the outside of the building instead. Internal gutter removal is a bigger job, because the roof edge, fascia and sometimes the roofline itself change, but it takes the risk away permanently. The water then goes into new external spouting, which our spouting installation team measures and fits.
Do You Need a Building Consent?
Sometimes. New Zealand’s Building Act lets owners repair and maintain a building without a building consent, provided comparable materials are used, and allows replacement with a comparable component in the same position. MBIE’s guidance on exempt building work also notes two limits that matter here. The exemption does not cover repair or replacement, other than maintenance, of something that has failed the Building Code’s durability requirements, for example by letting water in. And all work, consented or not, must still comply with the Building Code.
A leaking internal gutter can fall on either side of that line, so ask before work starts. Converting an internal gutter to external spouting changes how the roof drains and is not a like-for-like replacement. Get the roofer’s view in writing, and check with Auckland Council or a building professional about consent before you commit to a redesign.
How Do You Stop It Happening Again?
Most internal gutter failures are maintenance failures that went on too long. A few habits make a real difference.
- Clean internal gutters at least twice a year, and after any big storm. Every three months is sensible under trees.
- Keep outlets clear with a guard over the outlet, not a cover over the whole gutter that hides the lining.
- Look at the gutter, not just the ceiling. Ponding, cracked membrane or rust at the outlet are early warnings.
- Check that there is an overflow and that it is not blocked.
- Deal with ceiling stains straight away. Water that has been getting into framing for months costs far more than the gutter.
If water is already coming through the ceiling, our roof leak repair team can trace where it is getting in, which is not always the gutter. Failed flashing where the gutter meets a wall produces exactly the same stain.
Leaking Internal Gutters: Common Questions
Why does my internal gutter only leak in heavy rain?
Usually because the outlet or downpipe can’t take the volume. A partly blocked outlet, an undersized gutter or a missing overflow lets water rise above the lining during a downpour, and it spills into the roof space or wall instead of over the edge. A clear outlet in light rain hides the problem.
Can a leaking internal gutter be patched?
A small, isolated split in a lining that is otherwise sound can often be patched. If the lining is brittle, rusted through in several places, or the gutter has repeat leaks at joints and outlets, a patch only buys time and relining or replacement is the better spend.
How often should internal gutters be cleaned?
At least twice a year, and after any big storm. Under trees, every three months is sensible. Because an internal gutter overflows into the house rather than the garden, it needs more attention than ordinary spouting, not less.
Do I need a building consent to replace an internal gutter?
Like-for-like replacement with comparable materials in the same position is generally exempt under the Building Act, but the exemption excludes parts that have failed the Building Code’s durability requirements, such as by letting water in. Converting an internal gutter to external spouting changes the roof design. Check with Auckland Council or a building professional before you commit.
What to Do Next
If you have a ceiling stain under an internal gutter, clear what you safely can from the outlet, put a bucket under any drip, and photograph the stain so you can see whether it grows. Then get someone up to look at the lining, the outlets and the overflow before the next big rain. Call Auckland Gutter & Roof on 09 974 1488 and we will tell you whether it needs a clean, a patch, a new lining or a rethink, and what each option involves before any work starts. For other gutter problems, see our gutter repair service.
Frequently asked questions
Why does my internal gutter only leak in heavy rain?
Usually because the outlet or downpipe can't take the volume. A partly blocked outlet, an undersized gutter or a missing overflow lets water rise above the lining during a downpour, and it spills into the roof space or wall instead of over the edge. A clear outlet in light rain hides the problem.
Can a leaking internal gutter be patched?
A small, isolated split in a lining that is otherwise sound can often be patched. If the lining is brittle, rusted through in several places, or the gutter has repeat leaks at joints and outlets, a patch only buys time and relining or replacement is the better spend.
How often should internal gutters be cleaned?
At least twice a year, and after any big storm. Under trees, every three months is sensible. Because an internal gutter overflows into the house rather than the garden, it needs more attention than ordinary spouting, not less.
Do I need a building consent to replace an internal gutter?
Like-for-like replacement with comparable materials in the same position is generally exempt under the Building Act, but the exemption excludes parts that have failed the Building Code's durability requirements, such as by letting water in. Converting an internal gutter to external spouting changes the roof design. Check with Auckland Council or a building professional before you commit.