rusty valley on a tile roof

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

The pictures on this page show where roof valleys are located on a roof.

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

valley replacement on a tile roof img-fluid

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 this about valleys:

“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. “

Why does the sarking on the sides of the valleys get wet and will it cause leaks?

A lot of roofers do not know that the sarking alongside the sides of the valley should NOT be cut and left overlapping onto the sides of the valleys.
The sarking has to be folded back onto the valley batten instead.

If there is sarking on the sides of the valley, it will draw water into the roof cavity and cause roof leaks.

When the tiles are lifted up. you should not see any sarking on the sides of the valleys at all.

detail od sarking at roof valleys
There should be NO sarking seen along the sides of the roof valleys. It should be kept away from the edge of the valleys,

27 responses to “What is a valley on a roof?”

  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. Jack Yuen says:

    Hi Raj,

    I only operate around the inner western suburbs of Sydney.
    Sorry, I do not know any good roofers in Brisbane.


  3. Christiane says:

    What is Prestite as materials?

  4. Jack Yuen says:

    Hi Christiane,
    it is supposed to be a waterproofing tape.
    We do not use it at all.
    I just have not found a reason to like it yet…


  5. Helen says:

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

  6. 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.


  7. helen says:

    thanks Jack.

  8. 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

  9. 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,


  10. 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!

  11. 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.


  12. Stormygirl says:

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

  13. 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


  14. 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.


  15. Pat says:

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

  16. Jack Yuen says:

    Hi Pat,

    I am not sure what ‘valley press’ is??
    We normally just install colorbond valleys without any additional ‘add-ons’.


  17. Rishad says:

    I have recently installed a new tiled roof with a valley. Its only 4 days gone and we have some moderate rain. I notice the roof membrane is wet on either side of the vally.
    What can cause this

  18. Jack Yuen says:

    Hi Rishad,
    I assume you mean that the sarking is wet on the side of the valley.
    A lot of roofers do not know that the sarking alongside the sides of the valley should NOT be cut and left overlapping onto the sides of the valleys.
    The sarking has to be folded back onto the valley batten instead.
    When the tiles are lifted up. you should not see any sarking on the sides of the valleys at all.
    See picture above on this page for the correct positioning of the sarking.

  19. well done you have explained this really well 🙂

  20. Tony Jones says:

    In heavy rain I seem to get over flow from my gutter at the point the valley terminates to the gutter. I have a corrugated iron roof but gutter and valley are free of debris. Am I corre
    ct in thinking the valley is not terminated correctly into the gutter & if so how do I correct. Tony , Semaphore.

  21. Jack Yuen says:

    Hi Tony,

    If the overflow ia at the back of the gutter, then the valley may not be long enough. Or if it is a high front gutter, the internal corner of the gutter is a low point and not draining to the downpipe quickly enough.
    If the overflow is over the front of the gutter, then the valley is too long into the gutter.

    Then solution depends on the cause.


  22. Frank says:

    Roughly much does it cost to replace a single valley roughly 4m long on a tiled roof?

  23. Jack Yuen says:

    Hi Frank,

    Roughly $800


  24. Rawender Guron says:

    The original builder did not install the valleys properly some 30 years ago. The problem is that the top of the timber fascia was not trimmed to match the valley’s profile and the valley itself was bent upwards as it flowed into the gutter. The result has been leaking on the sides of the valley and ponding and rusting on the valley at the bottom. How much the top of the fascia needs to be trimmed? The typical valley profile is 58 mm from to top of the side to the lowest part that should sit on the fascia internal corner. Trimming 58mm seems excessive and that means top of the gutter (and internal corner bracket) would also need some trimming. That does not sound alright.

  25. Rawender Guron says:

    Hi Jack,

    Thanks for sharing your knowledge and experience.

    My house is 30 years old and has 2 valleys. Both of them are rusty at the bottom where they flow into gutters. The reason is that the original installation was faulty. The bottom of the valley was bent upwards to flow over the fascia instead of trimming the top of the timber fascia to fit with the valley’s profile. It caused ponding on the valleys at the bottom and leak from the sides right at the bottom. I am looking to replace the valleys and my question is how much off the top of the fascia should be trimmed. It appears that fitting the valleys’ profile might require upto 50 mm trimming at the internal corner. It might also require trimming the top of the gutter including the top of the internal corner bracket. How should this problem ne approached?

    Thanks in advance.

  26. Jack Yuen says:

    Hi Rawender,
    DO NOT trim the fascia or the back of the gutter.
    This will cause problems with gutter capacity.
    It sounds like the builder installed the valley board (the timber that the valley rests on) incorrectly.
    Just let the roofer know your problem (he should already know this without you telling him) and he will install packing on the existing valley board to lift the new valley up. Some modifications to the adjacent roof battens may be required also.
    It is not a DIY project.


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