If you’re thinking about an ADU plumbing project London Ontario or St. Thomas, here’s the short version: what you do today during a renovation can save you thousands down the road, or cost you thousands if you skip it. I’ve seen both sides of this on real jobs this year, and the difference wasn’t luck. It was planning.
I’m Aron Oretan, owner of Triton Home Service. My crew just wrapped a backyard ADU on Simcoe Street, and we’ve also prepped a couple of basement renovations in London and St. Thomas for future units that haven’t been built yet. Same goal, two completely different price tags. Let me walk you through both.
How ADU Water and Sewer Connections Actually Work in London
Before I get into the jobs, here’s the rule that surprises most homeowners. An ADU can’t have its own separate connection to the city’s water main or sewer main. Ontario’s ADU rules require the new unit’s drainage to tie into the existing home’s drain line. And for water, you’re not getting a second municipal meter. You install a private meter downstream of the one meter the city already reads. Everything for the ADU branches off your existing service after that point.
That single rule is why planning ahead matters so much. Every pipe for a future ADU has to eventually connect back to your existing house, one way or another.
The Simcoe Street Job: A Full Backyard ADU, Built Right, But the Hard Way
The Simcoe project was a full backyard structure, a two-bedroom unit built from scratch. We ran new water and drain lines out to it, and thankfully we managed to get a full gravity drain from every fixture in the ADU. No ejector pump needed for the unit itself.
Here’s where it got complicated. The main house had a finished basement apartment. That setup prevented a short, easy path to the front sewer connection. We had to hand-dig a long trench between the two houses to reach it. Water and drain were laid in the same trench. A tracer wire was placed on the water line. This allows future location without guesswork.
That hand-dig added real cost. The project ended up about $4,500 plus tax over my original quote. This was due to the extra length, the extra labour, and the extra fittings the trench required. And honestly, I think that was a fair price for what the work involved. It wasn’t padded. It’s just what it costs when there’s no existing connection point to work from.
The Foundation Decision Nobody Warns You About
The other lesson from Simcoe is about the ADU’s foundation, not the trench. The owner’s designer specified a crawl space foundation with a ducted heat pump system. All the sheet metal duct work runs through that crawl space. The crawl space has a floor drain. Code required us to install a sewage ejector pit to service it. We never used that pit for any actual plumbing fixture in the unit.
Had the owner chosen a ductless Mitsubishi Hyper-Heat system, he would have saved thousands of dollars in sheet metal alone. He could also have skipped the crawl space entirely. That would have meant a slab-on-grade foundation. There would be no ejector pit required. The electric water heater would be tucked into a closet instead of a mechanical space beneath the building.
Skipping the Gas Line: Why Ductless Beats Ducted for an ADU
Another key point if you’re planning an ADU is this. You don’t automatically need a gas line. Duct work isn’t needed either. We used a Mitsubishi Hyper-Heat system on Simcoe. The manufacturer rates it to operate and keep the space warm even when temperatures are coldest in this area. But it was installed as a ducted system, running all that sheet metal through the crawl space. A ductless version of the same heat pump would have delivered the same performance without the duct work, the crawl space, or the ejector pit it triggered. That’s a lesson worth passing on: ductless isn’t just simpler, it can eliminate an entire layer of foundation cost.
Forest Avenue and Plymouth Avenue: How to Do It Right the First Time
Now here’s the job that shows the better way. On a basement renovation on Forest Avenue in St. Thomas, the homeowners were already thinking about a future addition. They were considering an ADU, even though it wasn’t being built yet on Plymouth Avenue in Oak Ridge.
During the basement renovation, we opened the foundation. We installed a sewer line to the back of the house with a ground-level clean-out. We stubbed a water line out to the same spot. Everything was capped and ready. We tagged the water valve with a zip tie labeled ‘future water line to ADU’. This would prevent anyone from mistaking it for something else years later.
That extra work added roughly $1,200 to $1,500 to the cost of the basement renovation. By contrast, the Simcoe hand-dig costs $4,500 plus tax. For the exact same result, it provides a working connection point at the back of the house. The only difference was timing.
What This Means If You’re Planning a Renovation
If you’re renovating your basement, or doing any project that opens up your foundation, and there’s any chance you’ll want an ADU or addition someday, ask your plumber about stubbing out a drain and water connection while the walls are already open. It’s a small cost added to work you’re already paying for. Waiting means paying for a standalone excavation later, on its own, at full price.
If you’re ready to talk through an ADU plumbing project, or you want a basement renovation planned with a future addition in mind, you can look at our full range of plumbing services or book a visit directly.
For the zoning and permitting rules around ADUs specifically, the City of London’s Additional Residential Units page is the right place to start.
Frequently Asked Questions
Can an ADU have its own separate water meter in London, Ontario? No. An ADU connects to a private meter downstream of your existing municipal meter. The city only reads the one primary meter on the property.
Does an ADU’s sewer line need its own connection to the municipal sewer main? No. ADU drainage must tie into the existing home’s drain line, not create a new independent connection to the sewer main.
Is it cheaper to plan ADU plumbing during a renovation instead of afterward? Yes, significantly. On one of our jobs, stubbing out water and drain connections during an open basement renovation added about $1,200 to $1,500. A similar connection dug separately later cost about $4,500 plus tax on another project.
Do I need a gas line and duct work for an ADU if I want heating? A properly sized cold-climate heat pump can heat and cool an ADU without gas lines or duct work. It can also help you avoid a crawl space foundation.
Does a crawl space foundation add cost to an ADU beyond just construction? Yes. A crawl space with a floor drain usually requires a code-mandated sewage ejector pit. If the pit isn’t used for any fixtures, this adds cost a slab-on-grade foundation would avoid.
How do I know where a stubbed-out water or drain line is located years later? Ask your plumber to bring the connection up to grade with a visible clean-out. Tag any valves clearly. This helps prevent the connection point from being lost or mistaken for something else.
Aron Oretan owns Triton Home Service. He is a Licensed Red Seal Plumber and Steamfitter with 26 years in the trade. His coverage includes London, St. Thomas, and Oxford County.
