What Is An Overflow Relief Gully And What Does It Do?

Every property these days is required to have an overflow relief gully. These gullies are a safety device in the case of a blockage in your or providers sewer system.

You may have noticed in the past when you have experienced drainage issues that sewer has been overflowing out of the top of these gullies. This is what they are designed to do.

ORG’s or overflow relief gullies, are installed outside a building and must be installed so that the top of the ORG grate is 150mm lower than your lowest fixture connecting to that particular drainage system. Often your lowest fixture will be a shower or floor waste gully in a bathroom. They also require to be slightly higher than surrounding paved paths or concrete paths to prevent excess water or foreign matter from entering through the grate.

You see if this overflow gully is lower than your internal fixtures, like shower, bath, toilet and basin. Then when you have a major blockage in your system or the sewer main out on the street becomes blocked, sewer will force it’s way out the lowest opening in the drain effectively relieving the pressure build up of the sewer. This allows the inside of the house to be protected from sewer overflows. Because sewer is not just water but also includes paper and waste matter, these grates on the ORG’s need to be loose fitting and able to pop up easily as waste is built up.

Often people will go ahead and put pot plants or other objects over these grates not realizing that they could be limiting the ORG’s functionality and putting the inside of the house at risk of a sewer spill’s.

You’re probably asking yourself what do these ORG’s look like.

Well they can come in various forms as materials and methods of plumbing have changed over the years. They are usually between 100 and 150mm in diameter and can be a plastic dome shape or concrete dome shape with plastic grate inserted in the top. Older forms can be hand concreted dome shapes with cast iron insert grates and these can be larger in diameter. They can be a cast iron grate in the top of old terracotta piping (earthenware), surrounded by a concrete dome also.

Houses built pre 1970’s may not have a ORG, but if the property has been renovated in the last 40 years then one should have been installed. If your property doesn’t have one and you are looking to renovate in the future one will have to be installed to comply with the AS:3500 plumbing code. Not having an overflow relief gully is just a risk that could result in sewer waste overflowing out of your shower or floor waste grate during a blockage and that wouldn’t be something that you probably would want to deal with.

So if you have time just check to see if you can locate your ORG, its usually outside the laundry or kitchen. Check to make sure you haven’t put anything over top of the grate, its slightly above ground, and that the grate can be easily removed.