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….

Leaves will choke the drainage from box gutters and cause leaks

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…

There is a leaking hole at the edge of the sump. The Coke can made things worse,,,

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.

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.

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 sloping the wrong way

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.

If you are in Sydney, do your research about how to find good roof repairers in Sydney and find a trained roofing professional