How to tell it's the valley
Where the stain is. Picture the roof from above. If the mark is near where an L-shaped house turns a corner, or where an extension's roof joins the main roof, there's almost certainly a valley over it.
When it leaks. Only in downpours points to the valley overflowing. Every rain, even a light one, points to a rust hole or a gap along the edges.
What you can see from the ground. Leaves or moss sitting in the channel, tiles along it sitting crooked, rust streaks on the metal, or water spilling sideways out of it in heavy rain.
What's in the roof space. From the manhole, shine a torch along the timbers that run up under the valley. Dark water marks running down them are a strong hint.
Why valleys work so hard
Every drop that lands on two slopes ends up in one narrow channel. On a big roof that's a lot of water arriving at once, and anything that slows it down, like a clump of leaves or a dip in the metal, makes it spill over the sides and under the roofing.
The NCC only allows valley gutters on roofs pitched more than 12.5 degrees, and asks for at least 15 mm of freeboard, which is spare depth above the water. It also wants downpipes as close as possible to valley gutters. Where a valley empties into a gutter a long way from any downpipe, that corner of the gutter often overflows too.
Signs your valley needs attention
- Leaves, seed pods or moss still sitting in the channel days after rain
- Rust streaks, or a dull, flaky surface on the valley metal
- Tiles along the valley sitting crooked, cracked or slipped
- Crumbled mortar along the valley edges, or pieces of it in the gutter below
- The gutter at the bottom of the valley overflowing in rain
- Water stains on the ceiling near an inside corner of the house
Valleys are roof work
Clearing a valley means standing on the roof, usually on the steep, slippery strip where two slopes meet, with wet leaves and moss underfoot. Look from the ground or an upstairs window instead, and leave the clearing to a roofer. If the roof might be asbestos cement sheeting, which was common on homes built before 1990, nobody should be walking on it at all until it's been checked.
How to keep valleys clear and dry
Book a yearly clean
Monier recommends cleaning gutters, downpipes and valleys at least once a year, and twice in tree-lined areas. When you book a gutter clean, ask whether the valleys are included.
Deal with the trees
Branches over the roof are the usual source of valley blockages. Trimming them back, by an arborist if they're big, cuts down how often the valley fills.
Ask about valley guards
Mesh over the valley keeps out leaves. In bushfire areas, NSW RFS guidance says gutter and valley leaf guards should be non-combustible and installed in line with AS 3959.
Clear them before fire season
The NSW RFS recommends clearing leaves from roofs, valleys and gutters before the bushfire season, because dry leaves catch embers.
Get them checked with the rest of the roof
Monier suggests a professional roof inspection every five to seven years. Ask the roofer to look closely at the valley metal and the edges while they're up there.
Your part, and the roofer's
You can
- Watching the valley from the ground in heavy rain
- Checking the timbers under the valley with a torch from the manhole
- Trimming branches you can reach from the ground
- Booking a yearly gutter and valley clean
Leave to a roofer
- Clearing leaves and moss from the valley
- Resetting tiles and sealing the valley edges
- Replacing a rusted valley
- Fitting valley guards
Where we'd begin
If the stain is near an inside corner and the valley is full of leaves, we'd start with a clean and see whether the next downpour stays outside. If it's clear and still leaking, or the metal is rusty, we'd ask the roofer for close-up photos and a straight answer on whether it can be resealed or needs replacing. A new valley costs more on the day and stops you paying for the same leak every winter. Our page on flashing and valley repairs covers the work itself.
Want a roofer to take a look?
Tell us the job and your postcode. We match it with a Find My Roofer certified roofer who specialises in that kind of work, and they call you to quote. Your number goes to them alone.