Commercial Box Gutter Repair
Box gutters carry large volumes of roof water on commercial and heritage buildings. We repair splits, corrosion and failed joints to stop leaks into ceilings and wall cavities, with care.
Wellington Box Gutters
Internal Gutters That Fail Inside the Building Box Gutters
Box Gutters in Wellington
Box gutters are gutters built into the roof rather than hung on the outside of it. You'll find box gutters in Wellington between roof planes, behind parapets and along the edges of commercial and industrial buildings, where they collect water from large areas of roof. Because they sit inside the building envelope, a box gutter that leaks or overflows sends water into ceilings, walls, stock and electrical services rather than onto the ground.
Wellington has plenty of them: on warehouses in Seaview and Gracefield, older retail buildings with parapet fronts, apartment blocks, and villas and terraced houses with hidden gutters. Many were built decades ago in galvanised steel, without the overflows current practice expects. We inspect, repair, reline and rebuild box gutters for owners and property managers, with the work planned around tenants and the weather.
Box Gutters
Box Gutter Services in Wellington
Box Gutter Relining and Replacement
When repairs are no longer practical, we reline or replace box gutters with durable membranes or metals, designed to handle intense Wellington rainfall without overflowing, for Wellington homeowners and businesses.
Overflow and Outlet Upgrades
Adequate outlets and overflow provisions are essential. We improve drainage capacity and add overflow protection, reducing the risk of flooding and costly water damage inside the building, from day one.
Box Gutters
Why Box Gutters Fail
Box gutter failures tend to follow the same few patterns. Most of them come down to water that has nowhere to go once something goes wrong.
Blocked outlets and sumps
One outlet often serves a long length of gutter, so a single plastic bag, nest or mat of leaves can back water up quickly. Without an overflow, it rises over the gutter sides and into the building.
Ponding and corrosion
Gutters with little or no fall hold water in low spots. Galvanised steel corrodes fastest where it stays wet, and pinholes form along the sole, often well out of sight.
Thermal movement at joints
Long metal gutters expand and contract every day. Soldered or riveted joints without expansion provision crack and leak only in certain conditions, which makes them hard to trace.
Undersized for the roof
Extensions and added roof areas mean some box gutters now carry more water than they were designed for. They overflow in heavy rain even when they are perfectly clean.
Damaged by foot traffic
Box gutters are often the walkway to plant on the roof. Boots, ladders and tools dent linings and crack joints, especially where the gutter has no protective walkway over it.
Ageing membrane linings
Box gutters relined in the past with bitumen or older membranes shrink, crack and lift at laps and corners. Water then tracks under the lining and shows up well away from the fault.
Box Gutters
Overflow Provisions and Sumps
The most important question about any box gutter is where the water goes when the outlet blocks. A well-designed system has an overflow that discharges somewhere visible, outside the building, before water can rise over the gutter sides. That might be a rainwater head with an overflow spout, an overflow outlet through a parapet, or a secondary outlet set slightly above the main one.
Sumps are boxes formed at outlets to collect water and give the downpipe a better entry, so the gutter drains faster. They need to be reachable for cleaning and fitted with grates to keep debris out of the downpipe. When we assess a box gutter we look at outlet size, sump design and overflows together, because lining a gutter that has no overflow still leaves the building at risk. Changes to outlets or overflows may need consent; we'll confirm with council.
Box Gutters
Repair, Relining or Rebuild
Once we know why the gutter is failing, the options usually fall into one of these approaches. We set out the reasoning in a written quote so you can compare them.
Temporary make-safe
When a box gutter is leaking into a tenancy, the first visit may be a make-safe: outlets cleared, the worst joints patched and temporary protection fitted. It holds until the permanent repair is planned and scheduled.
Targeted repair
Localised leaks at a joint, an outlet or a small corroded area can be repaired with patches, new outlet spigots and resealing. This suits gutters that are generally sound with one clear fault.
Membrane relining
The gutter is cleaned and prepared, a substrate added where needed, and a membrane such as butyl rubber, EPDM or TPO bonded in and dressed under the roofing. See gutter relining and sealing for more.
Full rebuild
Where the gutter has no fall, is undersized or sits on rotten timber, it is rebuilt: new framing to set falls, a new gutter in metal or membrane, and properly sized outlets, sumps and overflows.
Adding overflows
On a gutter with no overflow, retrofitting one is often worth doing first: a parapet overflow, a rainwater head with a spout, or a secondary outlet. It can go in alongside a repair or on its own.
Scheduled maintenance
A box gutter needs regular clearing, especially near trees or where birds roost on parapets. A roof maintenance plan puts that on a schedule instead of waiting for a ceiling stain.
Box Gutters
Working Safely on Commercial Roofs
Box gutter work usually means working along a roof edge or parapet, near skylights and roof plant, often above occupied space. We plan access and edge protection in line with WorkSafe guidance on working at height, using anchors and fall arrest to AS/NZS 1891 or temporary edge protection to AS/NZS 4994 as the site requires. Work is scheduled around tenants, with temporary protection over open gutters if the weather turns. Larger projects sit within our commercial roofing work.
Box Gutters
Why Choose Our Box Gutter Specialists in Wellington
Box gutters carry huge volumes of water on commercial and heritage buildings, and when they fail the damage inside walls and ceilings can be severe. Our specialists inspect box gutters thoroughly, repairing splits, corrosion and failed joints or relining and replacing them where repairs no longer make sense. We design outlets and overflows to handle intense Wellington rainfall, reducing flooding risk when storms arrive. Work is planned around your building's operation, with minimal disruption to tenants and staff. You receive detailed reports, clear recommendations and workmanship built to last, giving property managers and owners genuine confidence that their roof drainage will perform when it matters most.
- Thorough inspection of box gutters and outlets
- Repair, reline or replacement options explained
- Overflow capacity designed for heavy rain
- Minimal disruption to your building's operation
- Detailed reports for owners and managers
Box Gutters
Related Services
Box gutters connect to the rest of a building's roof drainage and waterproofing. These pages cover the related work in more detail.
Helpful answers
Box Gutters FAQs
Call our team if you need advice for your property or roofing project.
04 888 0115What is the difference between a box gutter and an internal gutter?
The terms overlap. A box gutter is a rectangular-section gutter, usually built into the roof structure. An internal gutter is any gutter located within the line of the building, so that overflow would enter the building. Most box gutters on commercial buildings are also internal gutters, which is why overflow provision matters so much.
How often should box gutters be cleaned?
At least once a year, and more often on buildings near trees, beside open ground where wind carries debris, or where birds roost on parapets. Outlets and sumps are the critical points. A quick check after major storms is worthwhile, because one blocked outlet can put water into the building within a single heavy shower.
Can a leaking box gutter be relined instead of replaced?
Often, if the gutter has adequate fall and size and the substrate beneath it is sound. Relining with a membrane is less disruptive than lifting roofing and rebuilding the gutter. If the gutter ponds because it has no fall, or overflows because it is too small, relining only treats the symptom, and a rebuild with correct falls and outlets is the better long-term spend.
Why does my box gutter only leak in some storms?
Leaks that come and go usually point to water backing up over a joint or lining edge when outlets are slow, wind driving water up under the roofing at the gutter edge, or thermal cracks that open only when the metal is cold. Tracing it often needs controlled water testing, which our roof leak detection service covers.
Do box gutters need overflows?
Current practice expects internal gutters to have overflow provision that discharges visibly outside, so a blockage cannot send water into the building. Many older box gutters predate this and have none. If we modify a box gutter, we'll confirm consent requirements with council and include properly sized overflows in the design.
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