7 most common reasons why roofs leak

7 common reasons why roofs leak

Leaking roofs are as common as the number of rainy days in Sydney.

We have spend many years repairing leaking roofs in Sydney and we have a decent database containing the causes of roof leaks. Most roof leaks fall into the categories below. If your roof is leaking, then you will quite likely be able to find out the causes on this post.

There are always exceptions to the rule and some roof leaks are quite hard to track down and this is where we can be the most use to you. The uncategorised roof leaks will stretch our knowledge base and I come across these from time to time. Sometimes, I feel like throwing up my hands and giving up.

…..But the challenge of finding the cause(s) of a leak and fixing it is always met with dogged determination.

The 7 most common causes of roof leaks are (now there are 8 because the blocked gutter category rears its ugly head so often recently):

This is a typical faulty skylight

This is a typical faulty skylight

1) Skylights:

As soon as holes are cut on a roof to put skylights in, the natural waterproof nature of roofs are violated. Some skylight installations leak the day they are cut into a roof. This is usually the result of a poor selection of skylights or a faulty installation. Then during its life, leaf blockage is the usual reason for skylight leaks. Finally, the life of a skylight is usually less than the roof – so old rusty skylights leak and will need replacement.

I have a FAQ page dedicated to leaking skylights … <so pop over there if you think your skylight is the problem.

There is also a page about choosing skylights …<



2)  Broken roof tiles: cracked-terracotta-roof-tile-thumbRoof tiles do not often break by themselves. If you have overhanging trees, falling branches will break tiles. As soon as you let people walk on your tile roof, there is a danger of broken tiles. Children like throwing things and these things can break fragile roof tiles. The worst I have seen is freshly broken roof tiles caused by another roofer (doing a roof inspection and quote) and just left there. We always carry spare roof tiles around with us and replace any that we break during roof inspections… but it clearly seems that other roofers do not bother.

Broken roof tiles can be repaired (if a replacement is not handy)

A break on a roof tile can be quite difficult to trace if it is on the water (drainage) course. I have a post about these tricky leaks caused by broken water courses.


rusty valley3) Rusty or blocked valleys: While tile roofs do not rust, there are valleys on most roofs and in the old days, they just used galvanised metal valleys. These have a 20 to 30 years life … so rusted valleys are quite common on Sydney roofs.

Leaves and valleys do not go together. If you have leaves crammed into your valley, a sudden downpour will create a dam. A rush of water will spill over the edges of the valley and you will see water gushing out of your ceiling…

I have a page dedicated to roof valleys.. < so pop over there if you have a valley problem.



PageLines-watertrappedbehindcrackedbeddingatridgecapping.jpg4) Faulty tile ridge capping: The bedding and pointing under tile ridge capping crack over time. Water seeps into the cracks and does three things.

…It can pool behind the bedding (if it is sealed to the roof tile) on the roof tile and eventually overflow into the roof cavity (this is why weep holes are essential).

…It can run along the back of the bedding, find a drainage path along the tile and seep out again – with out causing any harm (the usually case).

…Or it can run along the back of the bedding and NOT find a release drainage path, but the edge of the roof tile. The result is a leak. These leaks are hard to spot without removing the ridge capping first.

If you want to find out more about weep holes and ridge capping repair work < go to my dedicated pages on this subject.


chimney fault5) Chimneys: A chimney is another hole on the roof that needs to be waterproofed correctly. The flashings around chimneys deteriorate and often cause leaks. Chimney pots break.

Most tile roofs have lead soaker flashings on the upstream side and the lead will crack after a while. A simple fix is to reseal with silicone sealant. The expensive alternative is to replace the flashing with a new one.

Some chimneys have hidden soaker flashings along the side and these can also rust out.



1 oxford rear gable gap in flashing6) Faulty flashings: The edges of roofs have to be waterproofed by flashings. It takes a lot of roofing experience to be able to detail complicated roof flashings so that they look good and do not leak. If a new roof leaks, then the roofer usually has made a mistake on the roof flashing. We can usually gauge the quality of the roof installation by how the flashings are finished off.



rusty roof7) Rusty roofs: This reason may seem quite obvious. It is easy to see if a roof is rusty. But it takes a while between when a roof begins to rust and when holes form and water starts dripping. Also, often, the rusty areas are very localised and hidden. In these instances, only close inspection will reveal the rust spots at laps and under flashings.



blocked gutters8) Blocked gutters: I am adding this to my original 7.

Blocked box gutters  can cause havoc if there are no overflows to act as a relief valve system. If you experience flooding inside your house and you have a box gutter – then it is quite likely a blocked outlet in your box gutter. The temporary solution is simple – just clear off the blockage. Long term, a system to prevent the blockage and overflow protection is needed.

Normal Eaves gutters are often left full of leaves and  this will start a nice garden in the gutter as well as overflowing gutters. They do not normally cause problems with leaks into the house. The exception is when the eaves extend over windows. Overflowing water will run along the eaves and fall onto the head of the window – causing a cascade of water along the inside of the window.


27 Responses to “7 most common reasons why roofs leak”

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  1. Janet Morrissey says:

    Love your website but I live in Wollongong with a 55 yo tile roof that is in need of ridgecap repointing. Do you know a reputable roofer in Wollongong area?
    Have been aproached by a few guys cruising the area but they seem too pushy and wanting instant agreement.

    • Jack Yuen says:

      Hi Janet,

      Sorry, I do not know of any good roofers in the Wollongong area who I can recommend.

      My advice is to keep away from guys who come ‘door knocking’ and offer special deals for ‘sign up now’ conditions.
      Just tell them to leave you their website and contact details so that you can check them out first …and see how they respond.
      A roofer who is any good will gladly give you that information – where else the dodgy ones will usually come up with all the reasons for not checking them out first.

      All the best.

      Jack Yuen

      • I have to agree with Jack. As much as possible stay from these people who are offering instant services or asking you to sign up. It’s better to ask for their website first so you can check about what services they offer. It’s also important to read online review, if there are any, about a particular roofer or service company. Great post by the way and advance Happy New Year!

  2. Awesome article. After researching the cause of leaking roofs, I totally agree with what this article has to say. I do believe that cleaning the gutters is underrated. People should perform monthly checkups on their gutters; this will ensure that there are no buildups and unwanted flooding. Yes, this can cause roof leaks.

  3. I like that you added number eight to your original seven. My house has a large tree over it, so the leaves frequently fall on my roof. I have to clean out the gutters often like you said to prevent long term damage.

  4. Connie says:

    Hi Jack

    I live in Melbourne. Do you know any good roofer in Melbourne that you would recommend? Also, is it a good idea to re bed and re point in summer? Does hot weather make a different? Thanks

    • Jack Yuen says:

      Hi Connie,

      Sorry, I do not have any good contacts in Melbourne.
      Bedding and pointing can be done in summer. The bedding goes stiff a bit quicker and the pointing solidifies a bit quicker.
      It is the roofers who will feel the heat more than the cement or the pointing!


  5. Chantal says:

    Anyone know any good people to look at my roof in townsville

  6. Hugo Preyer says:

    We have a color bond roof, when it rains with a strong wind the water blows back up under the flashing and also back up the valleys and then the water hits the insulation which soaks up the water, my query is there something we can put under the overhang of color bond to stop the water being blown back.
    Regards Hugo

    • Jack Yuen says:

      Hi Hugo,
      There is a range of foam products to suit various roof profiles that you can tuck under the flashings.
      You can also use foam along the valleys.
      See your local Bunnings if you want to do it yourself.


  7. Ying says:

    Hi Jack,

    I have recently replaced the valley irons with colourbond, installed dry with valley seal to bottom of 2 valleys.

    When I inspect the work done, would I be able to see the ‘valley seal’? If so, how can I tell if the valley seal is inplace?


    • Jack Yuen says:

      Hi Ying,

      We don’t normally install ‘valley seals’.
      Just lift the roof tiles up on either side of the valley and you will be able to see if there is anything there.


  8. Connie says:

    Hi Jack,

    The roofer re beaded and re pointed the roof for my house. I have noticed that on the horizontal part of the roof, the first row of the tiles where the ridge caps sat, there are four to five tiles on that row not touching the top of the next row of tiles underneath them. There is room enough to tuck a finger in. The top tiles are about 10 mm above the surface of the tiles underneath.

    Does it need to be fixed? If so, how and what the roofer should do now? More importantly, would it cause leaking?


    • Jack Yuen says:

      Hi Connie,
      When the batten support behind the top row of tiles is too low, the tiles sit on a lower pitch. They lay flatter and this is the cause of the gap to the tiles on the row below.
      Whether it is a problem depends on the pitch of the tiles under the capping. If it is steeper than around 20 degrees… it will be ok.
      It is not the 10mm gap you mention that will be the problem. Just the pitch of the top tile.
      Also, if the top tile is not a full tile and it has been cut to suit the ridge capping… then it is critical to have weep holes.

      If it is not complying… then the solution is to remove the ridge capping and relay the tiles on additional timber battens to achieve the correct pitch. …followed by re-bedding (with weep holes if required) and re-pointing.

      Hope this helps.


  9. Connie says:

    Hi Jack,

    Also, does cement cause rusting on colourbond?

    Thanks again.

  10. Connie says:

    Hi Jack,

    Thanks for the replies.

    Following your comments, there are old mortar between the edge of the tiles and the side of the gable. The side of the gable where the mortar sits on is metal and it appears they are Colorbond (but it could be any other painted metal.) The old mortar has loosen up and some of them broking up into small pieces.
    What material should be used to repair the old mortar? should the old mortar/the edge tiles be re-bed and repointed? What material should be used that will not cause rusting over time?

    Thanks again.

    • Jack Yuen says:

      Hi Connie,

      Often, the gables of a tile roof have the roof tiles bedded on a metal flashing with a fibro strip. The mortar sits on the fibro strip and not on the metal flashing.
      Repair of loose mortar will involve removing the loose stuff and replacing with fresh cement mortar – which sits on the fibro strip and not on the metal flashing.


  11. bob says:

    Hi Jack,
    Thanks – great points! I’m having a colorbond roof completely replaced at the moment by a company with a long history and good reputation. They seems to have done a good job overall but there is one sheet where they have put three roofing bolts through the “dip” in the colorbond (i.e. down in one of the valleys of the sheet rather than on the top of the curves).

    It will be under flashing (not yet installed), but the sheet extends up beyond where it’s flashed, so there will definitely be water running down there.
    See pic here: https://ibb.co/HCMCypF
    I always thought this was number one roofing no-no… is there ever a time when you would say it’s ok to do it this way?
    Thanks again

    • Jack Yuen says:

      Hi Bob,
      Looks like the roofer put the screws to hold the edge of the sheet down prior to putting the barge flashing on.
      The barge flashing should cover the edge of the roof where the screws are.. and the screws should never get wet.
      It is a tricky detail and I usually continue the barge flashing up to the ridge flashing with a tray flashing.
      If there is no tray, the upstream end of the barge is usually silicone sealed to stop water going under the flashing.
      … not my preferred way, but can perform OK.

      Hope this helps.


  12. bob says:

    Thank you – very helpful.

  13. John Morgan says:

    Hi Jack I’m having troubles with several leaks around my tiled roof. The tiles appear intact and it only happens in heavy rain. The water seems to be somehow getting up under the edge of the tiles. Does that sound right and what can I do?

    • Jack Yuen says:

      Hi John,

      If you have concrete roof tiles at less than a 20 degree pitch… wind will force water up the tile and cause dripping off the upstream edge of the tile and onto the sarking or roof cavity.


  14. Helena says:

    Had watermark on the lounge ceiling and cornice in the hallway. First-ever as repointing and bedding were done two years ago. The insurance company put a drone over the roof and said it was neglected and gutters were blocked. I arranged an independent inspection and was told by a roofer that the roof was in good condition. We had torrential rain and 90klm winds on the coast a month ago. Would this cause water stains and what do you think of drones being used for this purpose? Gutters were not blocked nor rusted. Wrong photos looked at?

    • Jack Yuen says:

      Hi Helena,

      Drones are great for taking photos. But they are not capable of close-up inspections and removing tiles to check for evidence of water penetration.
      If you have a relatively low pitched roof, the tiles will leak on the upstream edge in high winds.
      Hope this helps.

  15. Hayden says:

    Over my back deck I have a flat tin roof that joins up to the main house tiles. Unfortunately, during heavy rain with a strong northerly wind, my house leaks water into the lounge room. I suspect the wind is forcing water back up and under the tiles as 1. The tin roof pitch is very slight and 2. The tin roof in this section has a depression that would hold a small amount of water. The leak only happens with heavy rain and strong northerly wind, and only in a small section where the tiled roof meets the tin roof.

    What can I use to stop this leak without having to replace the depressed tin and/or re-pitch the tin roof?


    • Jack Yuen says:

      Hi Hayden,
      If the problem is wind driven water, one solution is to install a foam infill just under the edge of the existing tile flashing. Then install another piece of ‘extension flashing’ on top of the existing tile flashing. The purpose of this is to extend the width of the flashing so that the wind driven rain has further to travel before it reaches the upstream end of the roof sheets.
      And on the way up the roof sheet, the water meets the foam infills – which forms another barrier to slow down the travel of the wind driven rain.

      This could be worth a try.


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