Gutter Overflow Spout: What Are They And How To Install An Overflow Spout

In my opinion, if you don’t have slotted gutters, then gutter overflow spouts are a must-have for property owners.  Using gutter overflow spouts provides peace of mind that if there are issues with your gutter systems water can escape without damaging your property.

Gutter overflow spout
Example of a gutter overflow spout on standard house gutter

About gutter overflow spouts

Most gutters are designed in a way that the front of the gutters are higher than the back of the gutter.  If you have no slots in the front of your gutters and there is a storm or a blockage in your downpipes and the water can’t escape, the water will then flow over the back of your gutters.

Depending on the design of your roof this means that the water can then backflow directly into your eaves, or even worse if it’s a boundary gutter or you have no eaves then the water can flow directly into your external wall cavities.

Installing an overflow spout mitigates this issue and allows any excess water to escape and flow out the front of the gutter ensuring no damage to your property.

How do gutter overflow spouts work?

As water builds up in your gutter it will keep rising until it reaches the bottom of the gutter spout.  At this point, the water will escape out through the spout rather than continuing to rise until it’s got nowhere to escape and backflows into your property.

Where should I install gutter overflow spouts?

Prior to installing your gutter overflow spout, the first thing you need to decide on is the location.

If you’re installing an overflow spout to address a known area where your gutter overflows (perhaps due to a lack of downpipes or inadequate capacity) then your location is already decided.  However, if you’re installing your overflow spout as a safety measure some areas to consider would be:

  • long runs of gutter where downpipes are more than 6m apart;
  • toward the end of a gutter where there is no downpipe, though water often pools in the gutter; or
  • near a roof valley where the water runs off the roof into the gutter;

In addition to the above, also be mindful of the area directly below the overflow spout you plan to install.  What I mean by this is that when it’s raining, water can flow out of the spout at a decent rate, wetting and disrupting the ground below hence if this is of concern perhaps choose a different location.

How to install a gutter overflow spout?

Once you’ve decided on the location, follow the below steps as a guide on how to install an overflow spout:

  1. Measure halfway up the back of your gutter and make a note of this measurement;
  2. Measure the radius of your overflow spout;
  3. Combined the two measurements from #1 & #2 and measuring up from the bottom, mark this measurement on the face of your gutter (this mark will become the centre of your spout);
  4. Grab a metal hole saw equal to the diameter of your overflow spout and drill a whole in the face of your gutter;
  5. Using a metal file, clean off any swarf around the edge of the hole you’ve just drilled and also clean up any swarf that may have entered the gutter (a magnet is great for this!);
  6. From the inside of the gutter put a small line of silicone around the edge of the hole;
  7. Insert the overflow spout and wipe off any excess silicone.  Once inserted, now seal around the top edge of the overflow spout from the inside of the gutter.

(Note, the above instructions are for installing an overflow spout on a standard residential fascia gutter.  These instructions do not apply to other styles of gutters, such as box gutters)

Where can you buy gutter overflow spouts?

Within Australia you can find overflow spouts at most of your large hardware stores including Bunnings and Stratco, however, the ones sold here are usually zincalume.  If you require spouts to match the colour of your gutters then I’d recommend to go to the likes of Fielders who stock overflow spouts in most colorbond colours, or if not you can place a custom order to get some made up.

Overflow spout alternatives

If you’re looking for an alternative to steel spouts then another approach is to cut and install small lengths of PVC pipe.  Although not as aesthetically pleasing PVC pipe can be just as effective as purposely built overflow spouts.

Final thoughts

I hope you’ve found the above article to be helpful.  You’ll be pleased to note that the building code of Australia states that it’s necessary to install overflow provision where the front edge of the gutter is higher than the back edge, therefore if you’re building a new house and see no provisions for gutter overflows be sure to speak with your builder.

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