What is a valley on a roof?

Roof valleys are the Vee shaped metal channels that run up and down the ‘folds’ of a roof.

These pictures show where roof valleys are located on a roof.

Roof valley replacements are fairly common – especially on tiled roofs.

This is because the old valleys used to be galvanised and they start corroding with time (especially if they trap leaves).

You will know when you are getting a leak from a rusted valley when you start experiencing a stained ceiling under the area on the roof that has a valley.

When a rust hole develops on a valley, there will be a leak that gradually gets worst – rather than a sudden big leak.

There are times when roof valleys in good condition gets blocked with leaves and debris. There will be a damming effect during very heavy rain (especially after a long dry spell) and a large amount of water can then pour into the roof cavity.

So, roof valleys are important elements on a roof to be maintained properly…

Sometimes, it is even advisable to put leafguard over valleys to limit the amount of leaf debris jamming up and causing leaks.

The following video shows what happens when a valley on a tile roof has to be replaced on a tile roof.

A while ago, I posted about valleys at my Sydney Roof repair Blog. To save you going there, an excerpt is pasted below:

“Most roofs will have one or several valleys on it.

…And it is the roof element that will deteriorate over time and will need replacement to stop or prevent roof leaks.

Valleys can last for a long time. Even over 20 years. But there are some valleys that have short life spans and this is usually caused by leaves caught in the valley – creating a corrosive environment. When your roof is under trees – especially gum trees, the valleys on your roof will have a short lifespan. This means a frequent roof repair.

What finish should the valley be? …In the case of the Sydney roof in the video above, the valleys were galvanised metal and the roof was under a big gum tree. The sap from the gum tree that drop down with the leaves are very corrosive and this eats away the galvanising coating very quickly. Rust bubbles start forming and soon, holes start to develp and a roof leak starts.

My advice to property owners is to NEVER consider installing any valley that has not got a minimum finish of colorbond. It does not make sense to have to spend money to change valleys too often. It is often more economical to install a colorbond valley at the very start and have the life of your valley increased by another 10 years… So do not even consider a galvanised or a zincalume finish metal valley. Go straight for colorbond.

When to change a valley? Another point to to remember is this. To change a valley on a tiled roof, the ridge capping at the top of the valley has to be removed. Then it has to be reinstated after the valley change. So when it is time to have your ridge capping repointed on your tiled roof, take a good look at the valleys. If they are showing any sign of rust, it makes more sense to change the valley before the ridge capping work. Otherwise, if the valley is changed after the ridge caps are repointed, all the ridge capping work has to be Re-done! again. Not very clever. “