Why Valleys and Flashings Leak First on Wellington Homes

When a Wellington roof starts to leak, the cause is often not the main roof surface at all. It is the joins: valleys where two roof planes meet, flashings around chimneys and walls, and the seals around vents and skylights. These details carry the most water and take the most movement, so they tend to give up first.

Valleys carry a lot of water

A valley gathers runoff from two slopes and funnels it to the gutter. In a heavy downpour that is a lot of water moving fast through a narrow channel. Leaves, moss and grit settle in the valley and slow that flow, and once water backs up it can find its way over the edge of the valley tray and under the roofing. Older valley irons can also rust through from the inside where debris holds moisture against them.

Flashings move with the house

Flashings bridge the gap between the roof and something else, such as a wall, chimney or parapet. Timber houses move with temperature, wind and the odd earthquake, and over time that movement can crack sealant, pull rivets and open small gaps. In Wellington, wind-driven rain is quick to find any gap that faces the weather.

Penetrations rely on seals

Every pipe, flue, aerial bracket or skylight is a hole in the roof. The rubber boots and sealants around them break down in sunlight, and a boot that has split can let in a steady drip that shows up metres away from where it started.

Why the stain is rarely under the fault

Water runs along purlins, rafters and sarking before it drips. A stain in the hallway can start at a flashing near the chimney. That is why patching the spot above the stain often fails, and why tracking down a roof leak at its source matters more than a quick dab of sealant. A careful roofer traces the path, checks the likely joins and confirms the cause before fixing it.

What you can do

Keep valleys and gutters clear, look for cracked sealant around penetrations when you can safely see them, and note when a leak appears. If it only shows during a southerly, that points to wind-driven rain at a flashing facing south. Our ten-point southerly checklist is a useful starting point, and gutters that overflow into valleys are covered in our guide to gutters on hill sites.