what is a box gutter

What is a box gutter?

If you can’t see your roof gutter from ground level, then you probably have a box gutter that is ‘boxed’ into your roof.

Most houses don’t have box gutters. They have gutters running around the external perimeter of the roofs and these are called ‘eaves gutters’ (even though some houses now do not have eaves).

A box gutter may look like a box because of its ‘boxy’ shape. But the main reason  for its name is because it is ‘boxed in’ on all sides. The picture above shows the layout of a typical box gutter on a metal roof.

Typically, a box gutter is ‘trapped’ between two roofs that feed rainwater into it. The water is drained via downpipe nozzles, or via a sumps & downpipes built into it.

A good box gutter design will have falls along its length, together with sumps to collect water before it is fed into large downpipes. There will also be an overflow facility on the side or the end. This is very important – so that water will overflow externally to the building, rather than flood into the roof cavity.

The best box gutter design has full width discharge ends. These pour water into rainwater heads on a wall outside the building. There are no internal downpipes and sumps to block up and cause overflows.

What is the best material for a box gutter?

I recommend that (as a minimum) colorbond should always be used. Some severe situations may call for colorbond “ULTRA” or even colorbond stainless…. although care against cathodic corrosion is needed with stainless.

Box gutters get a lot of moist leaves and debris and these can shorten its life – so the rule of thumb is to have the box gutter material as good or better (in the corrosion department) than the roofing material.

Sometimes I see architectural specifications nominating a colorbond roof with a zincalume box gutter. This combination can result in much higher maintenance costs for the roof.


…Because, the box gutter will need replacement a lot sooner than the roof. And a box gutter replacement is quite expensive and time consuming – because it usually involves removal of the roof sheeting.

It is easier to replace a box gutter together with the roof . Doing it with the roof in place is much more time consuming and costly.

Can box gutters be eliminated?

Unfortunately, with flat roofs, larger complex roofs, parapet walls and other architectural building features, rainwater does not always drain out directly to the external perimeter of the roof.

In these instances, box gutters are the only viable option. So, if your roof is not ‘straight forward’ – then you probably have a one of these somewhere on it.

There is no need to stress out about box gutters…if they are designed correctly with overflows and you carry out regular maintenance.

It pays to have these gutters maintained and regularly cleaned out – simply because a box gutter leak has much higher consequences. Water will go into the house!

Whilst with eaves gutters along the edge of your roof, the water just pours outside when it overflows or leaks.

Are box gutters expensive?

There is a lot more work involved.

There is more thought needed to get a design right and the roof framing tends to be more complex.

Because they are much bigger than eaves gutters, the material cost is greater. 

It will certainly cost you more (for the ceiling and internal repair works) if it leaks.

And it takes longer to replace one….

So, the answer is YES. 

…. But you may have no option. And if this is the case, then make sure that it is designed and installed correctly in the first instance. Then be fanatical about keeping them clean!

Do you have a leaking box gutter that needs repairing?

Box gutter repairs are often the first option available for you. There are things to keep in mind if you are looking at box gutter repairs. 

Most factories have box gutters and many houses with edge parapet walls have some type of box gutter that either needs repair of replacement.

When box gutters leak, there are two ways that you will experience the result:

  • A deluge of water inside the property during a heavy rain or…
  • Slight dampness progressing to constant drips over a length of time.

Box gutter repairs for that deluge leak.

If you get flooded inside the property during a heavy downpour – then you have a blockage somewhere along your box gutter.

Box gutters in factories usually have sumps to collect the water and force it down the downpipe.

If the box gutter and sumps are not maintained regularly, you will get this….

box gutter repair sydney - blocked by leaves
Leaves can cause a box gutter to fail. Regular cleaning will stop this.

There are design standards for sizing of box gutters and downpipes. But these designs assume no blockage. It does not matter how large the box gutter is – it will overflow if the downpipe outlet is blocked.

You don’t have trees?

Well, we once found a box gutter sump blocked by the combination of a sweets wrapper and a old coke can. It does not take much to cause a blockage…

box gutter repairs - blocked by can of coke
The coke can has been there for a while…. the hole doesn’t help

At least these box gutter repair situations above can easily be fixed by a bit of clean up work.

What about overflow insurance?

You may want to sleep better during those stormy nights (after feeling a bit guilty about forgetting to clean your box gutter). If you have overflows in your box gutter, you can go back to sleep.

If you don’t – then you will need to seriously consider this option. An overflow is the most effective box gutter repair method to counter the sudden deluge leak.

box gutter repair - overflow and leaking joint
A new overflow is the best box gutter repair option
  • Leaking joint
  • Rusty box gutter

Very often, sealants break at the joints or pop rivets break off. Water will weep constantly during any intensity rain.

The repair is quite simple.  Clean the box gutter joint and re-seal.

The rusty box gutter has a temporary solution. A quick patch of the rusted areas will keep water out for a short while  – and allow for preparations for a proper job. Which is…a full box gutter replacement with a colorbond box gutter.

Box gutter repairs - temporary patch over rust
Keeping the water out by a temporary patch over the rust holes

The main thing with box gutters that show premature rust is to find out why.

If there is ponding water – then the new replacement box gutter should not copy this error.

Proper falls to the outlets will increase the life of the replacement box gutter.


Box gutter repairs – the way forward

Putting overflows into box gutters or designing box gutters with a full with discharge through the parapet wall into  rainwater head is the best ‘bank for bucks’ – if you have a overflow problem.

If the box gutter is locally rusty and need replacement, then it pays to find out why it has rusted prematurely and have these factors eliminated with the new box gutter.

Talk to a professional

60 responses to “What is a box gutter?”

  1. James Finn says:

    Looking at the “typical shape” of a box gutter in your iliistration, I note that there is no flashing shown, its simply a “u” shape…is this a normal design ? and if so what stops the water from a down pour overflowing back under the roof ?

  2. jackyuen says:


    It is quite normal for a box gutter to be a simple U shape. There is nothing stopping overflowing back under the roof.
    That is why it is important to have box gutter overflows and sufficient downpipe outlets to stop the water line approaching the top edge of the box gutter.
    Box gutters are not as good as eaves gutters because the overflows go back into the property rather than external.
    That is why particular care with design and maintenance (to prevent blockage of the drainage outlets) is critical when you have a box gutter on your roof.


  3. jane sabine says:

    WE have had a box gutter for new extension roof where it joins gable end of our existing building. However, the new extension bedroom corner wall has become very damp and new paint is now peeling off. There is no leak on roof tiling. I can only think the box gutter is tipping rainwater towards inside block wall although the external wall on both existing and new extn wall are also very wet. Any help would be appreciated to find out the cause, do I need the chippies back to sort it, or is it the roof tilers?

  4. jackyuen says:


    Sorry for the delay. We have just returned from a long Christmas holiday.

    The leak at the box gutter has nothing to do with the chippies. It would have been installed by the roof tilers (who are usually not very good at box gutter work). So, you should get the roof tilers back to check out the problem.



  5. Stuart says:

    Greetings Jack. Planning to construct a roof between twi existing buildings approximately 1.8 metres across from shed to shed. Intend to slope roff from left to right. Will be attaching the roof support frame to the walls of each shed, approximately two thirds up the side of each shed. Intending to install a box gutter. Despite a very significant eave on the existing shed, on the box gutter side. Will need to flash both shed walls to prevent leaking. Both shed walls are external walls, clad with colorbond sheeting. Would screws and silicone be sufficient? Any advice would be appreciated. thanks in advance.

  6. jackyuen says:

    Sounds like a complicated little roof job.
    I assume your question is about how to waterproof the side of the box gutter to the colorbond metal walls of the shed.
    If this is the case, screws and silicone would be what we use. Yes, that will be OK.

  7. tommy says:

    can i replace box gutters with stander gutters i dont care about how the house will look.

  8. jackyuen says:


    Some houses have a hidden (box) gutter on the perimeter of the roof – instead of exposed guttering.The box gutters can be replaced by standard eaves gutters – but there is a lot of work involved with this exercise. So, it can get quite expensive.

  9. brendan says:


    Looking at purchasing a property with box gutters and wood fascia. The wood fascia has some rot and some of the downpipes may be blocked with leaf litter. Would you know if the fascia replacement is expensive to fix. The roof itself is in good condition

  10. jackyuen says:

    Hi Brendan,

    We usually cover the ‘tired’ wooden fascia with a colorbond flashing to provide a maintenance free fascia. The actual box gutters may need replacement also.
    Hard to estimate a price. $5000 for the fascia work will be a good stab for your purposes.

    All the best.

    Jack Yuen

  11. milan says:

    i need a detail drawing of a box gutter to a brick partition wall (car port wall on the boundary) thanks

  12. Jack Yuen says:

    If you send me the details of your box gutter through my contact form, I will take a look for you.


  13. petrina says:

    recently we had a roofer come out and install a box gutter in between two buildings however it still leaks we have put two downpipes from each end of gutter but still no luck . can u help please?

  14. Jack Yuen says:

    Sorry, we are closing up for the Christmas holidays and do not return until 19th January.
    If you have not resolved the situation by then, contact me via the contact box.

  15. Arthur Murphy says:

    Can you or is it legal to put a side outlet out of a roof sump and not use pops as outlets

  16. Jack Yuen says:

    Hi Arthur,

    The reason for a ‘pop’ outlet into a downpipe is to drain normal rain flows into the stormwater system. A side outlet is normally used as an overflow to drain excess water due to very heavy storms. This overflow will drop the water onto the ground and it will become another source of ‘surface run-off’

    If you block off the ‘pop’ and cut in a side outlet that drains all the rainwater onto the ground, it goes against most local council regulations that require rainwater collection from the roof to drain into the storm water system. You will also have a large volume of water consistently running off your roof and splashing onto the ground next to your wall. You will end up with a wet wall and a crater in the ground….

    Hope this helps.


  17. Chris says:

    Hi There ,

    I am just having a box gutter installed on our house that is being renovated at the moment .

    The roofer says that by Australian Standards the colourbond box gutter insert must sit on either a plywood or AC sheet base to be compliant .

    Is this correct ?


  18. Jack Yuen says:

    Hi Chris,
    I am not sure which Australian Standard is being referred to…
    But a standard is written based on safe and sensible ways of doing things. Box gutters of any decent width will be walked on by someone during its life.
    An unsupported box gutter will either collapse or buckle under load. That is why box gutters are always supported by gutter boards (ply, metal sheeting or otherwise)
    Hope this helps.


  19. Alka N says:

    Our townhouse is 5 years old with a box gutter. After the recent heavy rains,the water came from the roof into the bedroom like a curtain waterfall down two walls, and also leaking down into the ground floor. After cutting open the ceiling, the water was found to be coming down between the wall and the brick outer wall. The plumber has put bitumen on the gutter joint, which has not helped, as the water leak has not stopped completely. Could you advise what needs to be done. Thanks..

  20. Jack Yuen says:

    Hi Alka,
    There are two types of leaks from box gutters.
    The slow leak: This is typical of a leaking joint (if the box gutter is fairly new) or a rust hole (if the box gutter is very old). So, the joint has to be re-sealed in the first case or the box gutter replaced n the second case.

    A sudden flood of water during very heavy rain: This is typical of an overflow situation. The outlet of the box gutter may be blocked by debris, or the box gutter outlet simply cannot discharge the water fast enough. If the box gutter has no overflow provisions, this causes a ‘waterfall’ over the sides of the box gutter – typically running down the walls.

    It sounds like you have an overflow situation. Check the outlet first to see if it is blocked.
    If the outlet is too small and there is no ‘box gutter overflow provision’ – then these have to be rectified.

    Hope this helps.


  21. Leo says:

    I have a 79 year house with galvanized box gutters, I noticed water is pounding in the middle. Is this normal for box gutters or should they be adjusted to run off better.

  22. Jack Yuen says:

    Hi Leo,

    In theory, all gutters should have a fall towards the outlet. In practice, a lot have no fall or too little fall. So, it is normal for some sort of ponding to happen…although not desirable.
    There are plenty of reasons why box gutters have little fall and the resultant ponding. These may prevent any easy adjustment to eliminate the ponding.
    A compromise is to leave the box gutter they way it is and just give it more regular cleaning to eliminate silt build up and premature rusting. Then when the box gutter gets towards the end of its life, look at ways to replace it with a colorbond box gutter with a fall…

    Hope this helps,


  23. Chris says:

    My sons home is only 4 years old and has a flat roof with box gutters when we had a bad storm mid April 2015 we had lots of hail very small built up and block the drains causing water to pour into house bedrooms plus. How can we correct this happening once again.

  24. Jack Yuen says:

    Hi Chris,

    It sounds like the box gutter has no overflow protection. An overflow (large enough to pass lots of hail stones through) will provide the safety relief against this happening again.
    Depending on how the box gutter has been built, this may be a simple or very complicated solution….

    Hope this helps,


  25. Ethan says:

    Hi Jake,
    Hope you are well.
    I recently replaced my old box gutter. However, the new one doesn’t have enough fall to let water flow to downpipe. The tradesman said that they cannot make enough fall as box gutter need to align with eave. My eave doesn’t have enough fall. Is this true?
    The new box gutter blocks old overflow point. The tradesman said that it is a more advanced system ( the front of new box gutter is lower than the back). No overflow point will be required as the water can over flow from the front of box gutter. Is this true?
    Thanks for your time.

  26. Jack Yuen says:

    Hi Ethan,

    It sounds like what you have described is a ‘FASCIA gutter’ – rather than a ‘box’ gutter.
    Or you have a box gutter around the perimeter of the roof just above the edge of the eaves. If you have this type of box gutter, then it can be installed with a fall to the down pipes because it is independent of the eaves.
    The front of this type of box gutter can be fabricated to be lower than the back and overflowing will occur over the front edge and no other overflow provisions are required.

    Hope this helps.


  27. Maz says:

    We have a box gutter on our new renovation. It is 9 metres long. The pitch is sloped slightly the wrong way at the beginning causing a few mm of water to stand there for many days after a rain. Is this bad for the gutter? Is this compliant?

  28. Jack Yuen says:

    Hi Maz,
    Ideally, a box gutter should drain to the outlet and not pond water. Ponding water can shorten the life of the box gutter – by causing premature rust.

    Hope this helps.


  29. paul walton says:

    I have installed box gutter in a church .it was originally installed the same as previous box gutters .They were not happy that it held water so they wanted a fall on it .So I had to take out again and cut one side down and indoing so cut the turn down of to get a fall .My question is ,because I had to cut it down to fit it so it has fall it dosent have the turndown ontop edge , does it void there warranty?

  30. Jack Yuen says:

    Hi Paul,

    It depends on who has provided the warranty and what the nature of the warranty is. Is it a performance warranty (that the box gutter will not leak) or is it a method of construction warranty?
    In my experience, if the top of the side of the box gutter is hard up against the underside of the roof sheets. then it performs just as well as a box gutter that has a lip that folds back under the roof sheets.

    Hope this helps.


  31. Hilton says:

    Hi Jack
    My son is building a house which has a surrounding parapet on the front and sides. They are using standard 1/2 round gutters of 150mm. Iits a flat colourbond roof and i am concerned these will not cope in a big downpour. Any ideas on this. The buikder says if it overflows it wont come in the house. What questions and warranties should we try and get from him. Many thank

  32. Jack Yuen says:

    Hi Hilton,
    I would not get too worried about it.
    Just make sure that the gutters are slotted and that there are enough downpipes.
    Hope this helps,


  33. Hilton says:

    Hi Jack
    Thanks for the advice. All the best

  34. R. Bassett says:

    Thanks for the advice here, it is very useful. We are going to have an unavoidable box gutter about 8m long, with one down pipe of 100mm, draining a pop up roof that is about 8 x 5m. There are a lot of gum trees above and maintenance will be high. I’ve had conflicting advice about gutter guards. Do you recommend some sort of gutter guard or will this make cleaning more difficult?

  35. Jack Yuen says:

    Hi Robynne,
    Leafguards have limited use over most box gutters. The leafguard does not deflect leafs off the roof and the leaves just sit on the roof and the leafguard. Some leaves still get under the leafguard and into the box gutter. Then in order to clean the box gutter, you will have to remove the leafguard.
    I recommend investigating the possibility of ‘poking’ the outlet end of the box gutter through the side wall of the house and having the full box gutter discharging into a rainwater head mounted on the external wall. (this eliminates the regular blockage of the ‘tiny’ 100mm outlet).
    With regular cleaning of the box gutter, this box gutter setup will virtually eliminate overflowing of the box gutter.

    Hope this helps.


  36. Jeremy Horrocks says:

    Hi Jack,
    My roof is a flat roof with box gutters and very little fall, definitely less than 5 degrees. In heavy rain there is no problem but in light rain the water seems to go back up under the sheeting and drips into the eaves. My question is: is there a product that I can slide up under the sheeting to stop this back-flow problem?

  37. Jack Yuen says:

    Hi Jeremy

    You should not need any additional flashing.
    The roof sheets should just be turned down properly.
    See my post below.


  38. Jeremy says:

    Thanks Jack,
    One local roofer just quoted $800 to fix the problem!
    I will try to locate the turn down tool and do it myself. Worth a try!!

  39. Lovely s says:

    Hello, I have a older home 1910 in Pittsburgh,pa! I notice several leaking areas in my house and was told it’s my box gutters. I have build in box gutters. Some say repair while other roofers say replace them because repairs are short term. I was told my box gutters in the back is bad. Money is tight and I want to stop water from leaking into my house or side of building! My house is about 2300 sq. I was also told I can get rid of the box glutter system all together and than do the regular hang glutter. What do you think? I do not care about the look of the house!

  40. Jack Yuen says:

    If money is tight – then consider a repair.
    If you can afford it – then replace the box gutters.
    If you want the expensive long term option – then getting rid of the box guttters is the way to go.


  41. deborah Joanne says:

    Hi there,

    we are really at the end of our tether. We had a conservatory installed 2 years ago and usually in the winter months it leaks a great deal more in one place. This is in a corner which takes a lot of rainfall from the main roof and it fills up very quickly. Also I don’t feel as though the drainage to the down pipe is quick enough. However, when we have spoken to the company who erected it, they say a box gutter should not have a fall on it. On dry days significant water pools in this area without draining away. I am wondering whether the gutter needs more fall on it and whether a wider box gutter is needed to take away the volume of water we get from the main roof. How would you recommend we try to get to the bottom of the issue. Also we have the issue of condensation as no trickle vents were ever fitted and a build up of moisture is occurring under the aluminium gutter causing the insulation underneath the box gutter(inside) to become damp.
    Any suggestions would be most welcome

  42. Jack Yuen says:

    Hi Deborah,

    I would suggest piping the flow from the main roof some where else – not into the box gutter.
    The box gutter should have a fall in it so that it does not pond water. Looks like you may need a new box gutter (may be bigger?) to be installed that has a building blanket underneath to prevent condensation.

    Hope this helps.


  43. Rubyet Rahman says:

    Hi jack
    We are currently building with a project builder. we loved the look of parapet. and apparently builder using box gutters. And reading all the reviews I am worried if it was good idea ot problems to come . please I would like to provide with some details of the design and get your advise on if they are doing the right thing.
    warm regards

  44. Jack Yuen says:

    Hi Ruby,

    Box gutters work ok if there is enough attention to its design and construction. They however need more maintenance.
    If you need to send me drawings, use my contact form.


  45. Nicola Worthington says:

    Hi Jack
    Thanks for your help. I have just had my whole flat roof and gutters replaced. I have box gutters and noticed that the overflow spouts in the old system were not in the new system. I’m worried that there are no overflow provisions at all and when I asked the contractor he said he didn’t keep overflow spouts as he didn’t think I would like the look of them. This did not give me a great sense of confidence. What I should be asking for or expecting in relation to overflow provisions for a large flat roof with 5 x 90mm downpipes? Cheers Nikki

  46. Jack Yuen says:

    Hi Nicola,

    My suggestion is for overflows at the same locations as the old ones and rectangular in shape. Nominal 100mm x 100mm.


  47. Erik Sanders Wayne says:

    Hi Jack!
    My house has a metal roof with pretty old box gutters.
    Is it possible to have the box gutters removed and replaced with seamless modern gutters that are a lot cheaper?

    I saw online its not expensive to install seamless gutters but not sure if a lot of labor hours could be involved in the removal of the old box gutters and if the removal can be pricey?

  48. Jack Yuen says:

    Hi Erik,

    If you have hidden gutters (box gutters) around the external perimeter of your roof… It is quite difficult to then put in normal eaves gutters.
    A lot of things (mainly semi-structural) need to be done.


  49. Greg says:

    Hi jack

    We have a box gutter above our bedroom. Every night it drips. I assume it’s from condensation. The sound echos and keeps us up. Are there any methods of stopping the dripping. Or the sound? Thanks. Greg

  50. Jack Yuen says:

    Hi Greg,
    I assume that the noise is coming from the downpipe and not the box gutter.
    One option is to replace the metal downpipe with a PVC downpipe. PVC does not echo.


  51. Anthony says:

    Hi Jack,
    We’re under construction now, lock up. When we’re in the house, we notice how loud the box gutters are with the wind. The colorbond roof sheets banging the top of one side of the u shaped box gutter. Maybe when we’re insulated and plastered it won’t be as obvious, but is that normal?

  52. Jack Yuen says:

    Hi Anthony,

    If the roof sheets are secured properly, it should not bang onto the top of the box gutter side – even with wind.

    Hope this helps.


  53. Pene says:

    Hi jack
    I have been quoted $6500 to replace a box cutter – I think about an 8m section – They said it would be a days work for one guy
    Does this seem reasonable to you. Thanks also for your message board – for someone who is clueless like me it really helps to get advice – not sure if I’m being fleeced

  54. Jack Yuen says:

    Hi Pene,
    I am not sure where you are in the world.
    In Sydney, we would typically replace a 8m box gutter for around $4000.
    A lot depends on the complexity of the box gutter replacement job and we send out at least two roofers for a day to do a box gutter replacement.
    Hope this helps in giving you a ‘ball park’ idea of what we would do in this situation.


  55. Adele says:

    High I have box guttering in my conservatory. The firewall side now had a drip running. Not always there, noticed it in cold days and not so much when raining. I have had a roofer up and put hose up for over an hour and no leaks evident. Wall had to be plastered due to being wet and now I have noticed another drip on the plaster. Is this due to condensation?

  56. Jack Yuen says:

    Hi Adele,
    If there are no drips when it is raining, then it is quite likely that the box gutter is not leaking.
    Most box gutters do not have any anticondensation blanket around it and depending on various factors, condensation can happen under the box gutter on cold damp mornings.
    Looks like it is a condensation issue.


  57. Herb says:

    Hi Jack,
    I stumbled on your website through a google search trying to decide whether on box gutter design versus normal quad gutters. Currently in concept design with my architect who has designed with box gutters however i reading more and more into it they appear to have a bad wrap. Last thing i want is to invest in something new only to have problems (leaking walls etc.) later.

    Based on your knowledge & experience, would you recommend against a box gutter versus normal quad gutters given the option?

    Appreciate your reply.

  58. Jack Yuen says:

    Hi Herb,
    Eaves gutters means that your house roof has eaves.
    Modern architectural designs like the look of parapet walls hiding parts of the roof – which will lead to the necessity for box gutters.
    It is a push for form over function.
    But there is no need to be scared of box gutters.
    They just need to be designed to be maintenance free and to allow for large outlets into rainwater heads if possible. Overflow provisions should be designed in also.
    This type of box gutter will perform OK.


  59. Simon says:

    Hi Herb,
    I have a flat colour bond roof with a box gutter flowing into a rain head at one end. Above this roof and is a wooden deck. The box gutter is leaking into the ceiling of the room below. That said, as access from above is obstructed, is it possible to repair a box gutter from the underneath (I.e. through the ceiling of the room below)?

  60. Jack Yuen says:

    Hi Simon,

    It is possible to install a patch from the underside. But it will only be a temporary patch because the rust will keep growing.
    The long term solution is a box gutter replacement – which will require removal of the deck.


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