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.

A rusty roof valley which needs to be replaced
A rusty valley on a tile roof which needs to be replaced
typically where a roof valley is located
typically where a valley is 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. “

17 Responses to “What is a valley on a roof?”

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  1. Raj says:

    Thanks for the video.Do you have any branches or do you know any roof repairs in Brisbane? I need to fix my valley leakage.

  2. Christiane says:

    What is Prestite as materials?

  3. Helen says:

    The old valleys on my tiled roof were pointed. Is it advisable to re-point them where they are damaged?

    • Jack Yuen says:

      Hi Helen,

      We do not bed the tiles along the edges of the valleys.
      Firstly, it is not required for waterproofing.
      Secondly, the bedding corrodes the edges of the valleys.
      Thirdly, the bedding can suck water in under the tiles along the valley and cause leaks.

      Since there is no bedding – thus no pointing.

      If the valleys are too flat and the previous roofer has bedded the valleys to try to stop leakage – then bedding was the wrong solution anyway.

      Hope this helps.

      Jack

      • helen says:

        thanks Jack.

      • Vicky says:

        Hi Jack
        When you mentioned not to bed the tiles along the edge of the valley, do you mean putting cement at the edge of the tiles at the valley? I’m trying to understand the meaning of this professional term. Thanks!

        • Jack Yuen says:

          Hi Vicky,
          The sides of the valley (along its length) do not need cement bedding.
          The upstream end (top) of the valley usually terminates under ridge caps which have their own bedding.
          Thanks,

          Jack

  4. Debra Ottway says:

    I have a cement valley with terracotta tiled roof. the Valley constantly leaks with driving winds. Will gutter guard help keep it clear of debris? What other measures can I take to fix it from leaking again

    • Jack Yuen says:

      Hi Debra,

      I have not come across ‘cement valleys’…
      Leafguard over the valleys can limit the amount of leaves in the valleys. Sometimes, if the leafguard is not detailed correctly where it terminates at the gutter, it can actually block the ‘washing away’ of debris travelling down the valley. Over time, this forms a dam and causes an overflow leak.

      The trick is to find out what actually causes the leaks and fix that directly.

      Hope this helps,

      Jack

  5. Stormygirl says:

    How much as a ball park figure would it be to replace 5 valleys? 1k, 2k??

  6. Glenn Sampson says:

    Is there a difference in performance from using a colorbond valley vs a valley seal foam strip impregnated with bitumen?

    I’m looking to get my tiled roof restored my roof plumber says colorbond whilst the restorer says valley seal

    thanks

    • Jack Yuen says:

      Hi Glenn,

      I think there is a mis-understanding.
      Your plumber says a colorbond valley because he is assuming that you are replacing the valley. Therefore a colorbond valley is the way to go.
      Your roof restorer is not thinking of replacing the valley. That is why he is suggesting putting foam along the edges of the existing valley.

      Personally, I hate the foam idea. It perishes over time and drops out and block the valley – causing damming and overflows.

      Hope this helps.

      Jack

  7. Pat says:

    When replacing valley, do you recommend to use valley press ?

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