Internal Gutter Conversion

What Is an Internal Gutter?

An internal gutter (also called a concealed gutter or box gutter) is a drainage channel built into the roof structure rather than fixed to the outside of the fascia. Instead of visible external spouting, rainwater drains into a channel concealed behind a parapet wall, inside a roof cavity, or beneath the roof cladding.

Internal gutters were commonly used on Auckland homes and commercial buildings constructed from the 1960s through to the early 1990s. They are most often found on flat or low-pitched roofs, homes with parapet walls, and buildings with concealed roof edges.

Why Internal Gutters Fail

Internal gutters are difficult to inspect, almost impossible to clean properly, and when they fail, water enters the building structure silently — often tracking metres from the failure point before becoming visible as a ceiling stain or internal leak.

Common failure modes include:

• Corrosion of the gutter lining over time
• Leaf and debris accumulation causing overflow into the building cavity
• Joint and seal failure from movement and thermal cycling
• Inadequate falls causing water to pond rather than drain
• Blocked outlets causing water to back up under the roof cladding

Because the failure is concealed, internal gutters often cause significant structural damage before the problem is identified. By the time a leak appears on a ceiling, water may have been tracking through framing, insulation, and lining for months.

Signs You May Have an Internal Gutter

• Flat or low-pitched roof with no visible external spouting at the eaves
• Parapet walls at the roof edge with no obvious drainage point
• Water staining on interior ceilings or walls during or after rain
• Older home or building (typically pre-1990) with a concealed roof edge detail
• Recurring leaks that have been patched but not resolved
• Mould or dampness in roof cavity or top-floor rooms

The Conversion — What We Do

We convert internal gutter systems to external spouting: a proven, permanent solution that eliminates the underlying failure mode rather than managing it.

The conversion involves:

• Full site assessment and written quote before any work begins
• Removal of the existing internal gutter system and associated lining
• Inspection of roof structure and substrate for water damage (any remediation separately costed and approved)
• Re-detailing of the roof edge to suit external spouting
• Installation of external gutters and downpipes, correctly graded and secured
• Building consent assessment — requirements vary by scope and are confirmed at consultation
• Post-conversion inspection and photo documentation

The result is a drainage system that can be seen, cleaned, inspected, and maintained — and that does not route water through your building structure when it fails.

Commercial Properties

Internal gutters are also common on commercial buildings of the same era — warehouses, retail premises, and older office buildings. For commercial clients, we provide full H&S documentation (SSSP, SWMS) and can coordinate around occupied premises and operational requirements. Contact us via the RFQ form for commercial enquiries.

The Process