Box gutters: inside the roof, not on the eaves
Box gutters sit within the roof - behind a parapet, or where two roof sections meet - rather than on the edge like an eaves gutter. When they fail, water comes through the ceiling in heavy rain. You often see nothing spilling outside.
An internal gutter, not the one you see from the street
A box gutter is a channel that sits inside the roof. It is not the eaves gutter along the fascia. On Victorian and Edwardian terraces it often runs behind a parapet, or where two roof sections meet. Water is meant to travel along that channel to an outlet, then out of the building.
That is why box gutters are the defining roofing failure in inner Melbourne. They rust, they block, they were laid with poor fall, they were sized for a smaller catchment than the roof now has, or they were built without a proper overflow. None of that shows as water sheeting off the front of the house.
What you notice is indoors. In heavy rain the gutter fills, ponds, and either overflows into the roof space or finds a rusted seam. The stain on the ceiling is the first sign. The gutter itself is still hidden until someone is on the roof.
Signs a box gutter may have failed
These are typical reasons people get in touch. They may indicate the internal gutter needs looking at - they are not a diagnosis from the ground.
- Water through the ceiling in rain Staining or dripping that appears in heavy rain, often with nothing overflowing at the eaves where you can see it.
- Water pooling on the roof A box gutter that no longer falls to the outlet will hold water. You will not see that from the street.
- Rust in the internal channel The sole of a steel box gutter rusts from the inside. Once it is holed, rain has a path into the building.
- Blockage, or no overflow Leaves and debris sit in a box gutter the same way they sit in an eaves gutter - except a blockage here discharges into the house unless there is a working overflow.
- A terrace, a parapet, or two roofs meeting Victorian and Edwardian stock, and later additions butted into an older roof, are where these gutters sit. The covering can look fine while the channel has gone.
What box gutter work can involve
Inspect the channel, then repair or replace it so water leaves the building. Overflow is part of that job, not an extra.
Work starts on the roof. We look at the box gutter, the fall toward the outlet, the condition of the sole and the seams, and whether there is a sump, a rainhead and an overflow that can actually discharge outside. Repair is appropriate where the channel is still sound. Replacement is appropriate where it is rusted through, undersized, or laid without fall.
Design is not guesswork. Box gutters are sized and given fall under AS/NZS 3500.3. Victoria calls up HB114 in legislation for the design of eaves and box gutters. That is the framework we work to: catchment, rainfall, fall to the outlet, and overflow so a blockage does not fill the roof. We describe the principle in the quote rather than treating the original gutter as automatically correct.
Overflow has to sit below the level of the box gutter sole. If it does not, a blocked outlet fills the channel until water goes over the sole and into the building. A rainhead, a sump and an overflow that can spill outside are how that water is meant to leave. Replacing an undersized original with the same size, the same fall and the same missing overflow is not automatically compliant - even if that is what the house was built with.
- The box gutter inspected, including fall, outlets and overflow
- Cause of any leak traced where it can be seen from the roof
- Repair where the channel is still sound
- Replacement where rust, fall or capacity means the original will not do
- Sumps, rainheads and overflow included where they belong with the job
When the sole rusts through, the water is already inside
A blocked or rusted channel does not spill at the eaves. It finds a hole in the sole, or it overflows into the roof.
Find whether the channel still works, then put it right
The first look is whether water can leave the building. Nothing is stripped by default.
Why choose Kestrel for box gutters
This is roofing drainage, not an eaves replacement with a different name. The channel has to work in rain, including when it is blocked.
Box gutters, sumps and rainheads handled with the covering, not treated as a separate plumbing job.
If the original was undersized or had no working overflow, repeating it is not automatically the right repair. We will say so before work starts.
Hands-on work on Melbourne roofs, including the internal channels that fail inside the building rather than at the eaves.
Cover in place on every job. You deal with the person doing the work.
The channel on the roof
Box gutters sit within the covering - behind a parapet, or between two roof planes - not on the eaves.
Related roofing services
If this is close but not quite the work you need, these are the usual next pages to look at.
Questions about box gutters
If the answer you need is not here, call and ask. We would rather explain it than have you guess.
Need a box gutter looked at?
Tell us what you have noticed - a ceiling stain in rain, a terrace or parapet roof, water that does not show at the eaves. We will look at the channel and quote the work it actually needs.