Hi Aker,

Sounds like you are doing some great due diligence before making an offer on this property.

There are lots of underground services that run throughout all cities and it is not uncommon to have services such as a public drain running through a property.

A 1200 diameter public sewer is a very large drain and a critical piece of infrastructure that likely serves a significant number of properties.

How long the concrete drain will last is difficult to know, but it is common for asset managers to ensure critical infrastructure such as this is regularly inspected to assess its condition. In the case of a drain like this, it is most likely periodically CCTV camered.

You could enquire with Water Care in Auckland to see if they have a recent report on the condition of this pubic sewer main, if they have any scheduled maintenance planned and if they have plans to renew or replace this drain at some stage. Watercare should also be able to give you the invert depth of the drain, or, you could open the nearest sewer manhole to get an indication of the depth.

Regarding smelling/leaking, if the drain is in sound condition, there should be no issues. As I mentioned above, assessment of the condition of the drain would likely be done by CCTV camera. If Water Care does not have a recent report on its condition, or you were concerned, you could engage a suitably qualified drainlayer yourself to camera the drain to give you an independent opinion of the current condition of the asset.

When access is needed to the property to renew or repair the drain, the cost of the work and any associated damage would likely be borne by the asset owner (Watercare). Be aware that there are a number of ways that drains under a building can be repaired or renewed, including trenchless methods.

Another thing to consider is for the future, if you extend the existing dwelling over the public drain, or you demolish the existing house and rebuild on top of the public drain, you would likely be required to renew the drain below the footprint of the new building at your own expense.

All the best with the house hunt!

We have recently come across a job where the public manhole was located in the back of property. The owner wanted to extend the house and during consent application council specified an upgrade of this manhole as a condition for approval. Cost to do this was $16.000 + GST.

If you purchase a place that incorporates public services you would normally (although this may change depending on whether whats there was done by previous owners without councils knowledge etc..) not be required to pay for upgrades or repairs, but you will have the inconvenience of it happening when it applies.

If you intend to develop or do works that require consent, council may (in most cases they do) ask you to upgrade, relocate, repair or otherwise prior to approval. In any case you will always have to provide a CCTV of the drains as part of the application. So either way more costs and inconveniences will apply. 

Personally, I would stay away from such properties. Drainage costs could evolve into thousands and thousands of dollars very quickly.

If you end up buying the place make sure everything is on the existing plans and that everything complies. Get a surveyor in and document the existing state of the drain. Whatever you can get in writing from council removing your responsibility, make sure you get for later date.