How Stormwater Can Impact Your Duplex Build
Building a duplex isn’t simply building two houses on one block.
There are additional planning, engineering and infrastructure requirements that need to be considered from the beginning.
One of the big ones is stormwater management.
Depending on the site and council requirements, you may need an On-Site Detention (OSD) system.
And this is something many people don’t account for when putting together their duplex budget.
So, What Does an OSD Actually Do?
An OSD system temporarily stores stormwater on the property rather than allowing large volumes of water to discharge into the street drainage system all at once.
The water is then released at a controlled rate through the property’s stormwater system.
This becomes particularly important on sites with challenging drainage conditions, including properties that fall toward the rear or are affected by flooding.
Why Does This Matter for Duplexes?
A duplex can have significantly more roof and hard surface area than a typical single dwelling.
That means more water needs to be managed.
And depending on the site, you may need multiple OSD tanks or other stormwater infrastructure to meet the relevant engineering and council requirements.
These systems also take up physical space and can add to construction costs — which is exactly why they should be considered during feasibility and design, not after you’ve already committed to the project.
The Lesson?
When you’re assessing a duplex site, don’t just ask:
"Can I fit two homes?"
You also need to ask:
"How will this site manage water?"
Slope, flooding, stormwater infrastructure, site levels and council requirements can all affect the design, cost and feasibility of your project.
At Neogen Homes, we look at these factors early so you have a clearer understanding of what your duplex project actually involves before construction begins.
A duplex feasibility assessment needs to look beyond the homes themselves. Drainage and stormwater requirements can have a major impact on both design and budget.
Thinking about building a duplex?
Visit our website to learn more about our duplex process and how we can help assess your site.