Don't buy a dream plan until you understand what truthly sits beneath it

A while ago, a friend’s mate asked me for some advice about a home they had recently purchased: a 4-bedroom terrace house with a sewer line ran along one side of the property, then turned across the rear to service both their house and the neighbouring property.

When they bought the house, the vendor had provided plans for an approved rear extension from the water authority, with much of that proposed extension sat directly over the sewer infrastructure. Naturally, they assumed: “We can build something like this later since it's been approved already.”

What looked straightforward on paper became a much more complicated question of authority requirements, access to the sewer, structural design, clearances, approvals and potentially significant additional costs.

In the end, they chose to make only relatively minor improvements to the rear of the house. The larger extension — and the version of the dream home they had imagined when purchasing the property — was never realised.

So, there are 3 practical lessons I would take from this: 1. Be very cautious when a sewer runs across the backyard. If your future extension relies on that area, the sewer can materially affect what is practical, how it is designed, and what approvals or engineering may be required. It may also affect the resales in the future.

2. If the sewer crosses the backyard and also serves the neighbouring property, that is usually a hard no-go for me unless there is a compelling reason to proceed, eg. a large lot you can expand to other directions or it can be subdivided if needs to. Otherwise, you may still have options, but the dependency is greater and the consequences of getting it wrong are more significant. This may have more impact on resale values.

3. If your project depends on relocating, building over or working around authority infrastructure, be prepared for a potentially long, complex and expensive process. Approval is not always automatic, and the final solution may be very different from the one you firstly imagined.

My final practical rule of thumb on the above? - Item 1: be cautious. - Item 2: usually a no-go unless there is a very good reason. - Item 3: expect a major commitment in time and cost — or be prepared to compromise on the original ambition.

For me, the broader lesson is simple: Don't buy the dream shown on a plan until you understand what sits underneath it — literally and metaphorically. A good thorough investigation before committing into it can be far less costly, with less headaches than discovering the constraints after the property has been purchased.