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Box gutter repairs that stop water getting inside
Box gutter repairs matter more than most roof work because these gutters sit inside the building line. When one blocks or fails, water goes straight in. We clear, repair or reline them and fix how they drain.
- Free quote
- Central Auckland based
- Written scope before work starts
- Photos of what we find
Why box gutters cause so many leaks
A box gutter is built into the roof, often behind a parapet or between two roof sections, instead of hanging off the outside edge. That keeps the outside of the building clean looking, but it means the gutter has a lot to do. It collects water from large roof areas, it has to carry that water to an outlet, and if anything goes wrong, the overflow is towards the inside.
Leaves, dust, tennis balls, packaging and bird nests all end up in box gutters. When an outlet blocks in heavy Auckland rain, the gutter can fill in minutes. A gutter that has sagged, rusted at its joints or been laid without enough fall holds water even when the outlet is clear.
Box gutter problems we repair
- Blocked outletsThe most common cause of box gutter leaks. One blocked outlet can send a whole roof’s water into the building.
- Missing or poor overflowsWithout a proper overflow, rising water has nowhere safe to go. Overflows should discharge where you will notice them.
- Undersized sumpsA sump that is too small for the roof area can be overwhelmed in heavy rain even when it is clear.
- Failed joints and corrosionSoldered, riveted or sealed joints open up, and steel gutters rust where water and debris sit.
- Flat spots and pondingIf the gutter sags or was laid without enough fall, water sits in it and speeds up corrosion.
- Worn membrane linersMembrane linings can split, lift at their edges or be damaged by foot traffic and debris.
Repair, reline or rebuild
The right box gutter repair depends on what is underneath. If the gutter is in good shape apart from a blocked outlet or a few failed joints, clearing it and repairing the joints may be all it needs. If the gutter is rusted or the liner is worn but the support below is sound, a new liner can go in over the top, either a suitable membrane or a new folded metal liner.
If the boards or framing under the gutter are rotten, or the gutter falls the wrong way, relining just hides the problem. In those cases the gutter needs to be rebuilt with proper fall to its outlets. We will show you photos of what we find so you can see why we are recommending one option over another.
Our box gutter repairs process
Clear and inspect
We clear the gutter and outlets, then check the lining, joints, fall and the condition of the support underneath.
Flood test
The gutter is blocked off and filled with water to show where it leaks. This confirms the cause before we repair it.
Repair or reline
Joints are repaired, outlets and sumps fixed or upgraded, or a new liner is fitted where the existing one is past saving.
Check the overflows
We make sure there is a working overflow that will show you when an outlet is blocked, before water gets inside.
Keeping box gutters working
Most box gutter leaks are preventable. Clearing gutters and outlets at least once a year, and after big storms, makes a real difference. Leaf guards on outlets help, but they also need clearing. If you see water spilling from an overflow, treat it as a warning that an outlet is blocked.
If your box gutter is part of a larger roof with rust or flashing problems, our rusted roof repairs page explains how we deal with corroded sheets. If you are not sure the gutter is the cause, we can confirm it with commercial roof leak detection first.
Box gutter repairs questions
What is a box gutter?
It is a gutter built into the roof rather than hung off the edge, often along a parapet wall or between two roof sections. Because it sits inside the building line, any water that overtops it can end up inside.
Why does my box gutter overflow into the building?
Usually a blocked outlet, a sump that is too small, or no overflow at all. When the outlet blocks, water rises until it finds a way out, and if there is no proper overflow, that way is often inside.
What is a rainwater head or overflow?
An overflow is a planned way for water to escape the gutter if the outlet blocks, ideally somewhere you will see it so you know there is a problem. A rainwater head is a box on the outside wall that the gutter drains into, often with its own overflow.
Can an old box gutter be relined instead of replaced?
Often, yes. If the support underneath is sound, a new liner can go inside the existing gutter. If the support is rotten or the gutter falls the wrong way, replacement or rebuilding is the better option.
How often should box gutters be cleaned?
At least once a year, and more often if there are trees nearby or the roof collects a lot of debris. Outlets and leaf guards are the most important parts to keep clear.
Do box gutter repairs need a building consent?
Like-for-like repairs and relining are usually maintenance. Changing how the roof drains, such as adding outlets or rebuilding the gutter to a new design, may need consent. We will flag this in the scope if we think it applies.
Other repairs we carry out
Commercial roof leak detection
Tracing where water actually gets in, with staged water testing and moisture checks.
Read more
Rusted roof repairs
Cut edges, laps and fixings assessed, then treated or replaced sheet by sheet.
Read more
Warehouse roof repairs
Long span roofs repaired around your stock, staff and trading hours.
Read more
Skylight and flashing repairs
Clear sheets, plant penetrations and flashings sealed and made watertight.
Read moreGet your box gutters checked
Tell us where water is coming in and how the roof drains. We will inspect the gutters and give you a free quote.
Get a free commercial roof repair quote
Tell us where the property is and what you need. Prefer to talk? Call 027 929 6889.