System classes

Ontario septic system types, explained

Ontario rules · CAD pricing · Reviewed October 2026

"Septic system" is a family of technologies, not one product. Ontario's Building Code Part 8 recognises several classes — conventional beds and trenches, raised beds, filter beds, and treatment units including aerobic systems — and each exists because a different kind of lot demanded it. Understanding the family tree is the fastest way to make sense of the quotes in your inbox, because most price differences between installers are really disagreements about which class your lot needs.

Conventional leaching bed or trench

The classic: a septic tank settles and digests solids, then effluent flows by gravity (or a simple pump) into a network of perforated pipe laid in gravel-filled trenches or a single wide bed, where soil organisms finish the treatment. Conventional systems are the cheapest class and the easiest to maintain — but they need enough depth of permeable, unsaturated soil to work, plus room to meet every setback. On deep till, moraine sand or gravel, this is the right answer and everything fancier is a waste of money.

Raised bed / area bed

Where native soil drains too slowly (heavy clay) or sits too close to bedrock or groundwater, the bed is built up: a mound of imported granular sand placed on the existing grade, with the leaching pipe inside it. Raised systems trade fill-hauling costs for usable treatment. They are the mainstream answer across Ontario's clay belts — Essex, Chatham-Kent, Prescott-Russell, the London area — and on Shield lots where rock refuses excavation. Expect a larger visible footprint and a correspondingly larger price band.

Filter bed

A filter bed pressurises effluent through small-diameter distribution pipe into a sand-filter medium, delivering more consistent treatment in a smaller area than a conventional bed. Classed as its own system type in the Code, it suits constrained lots — narrow waterfront properties, infill replacements, anywhere setbacks squeeze the geometry. It also suits owners who want strong treatment performance without the higher service rhythm of a mechanical unit.

Treatment units, including aerobic (ATU) systems

A treatment unit is a powered device — an aerobic treatment unit being the common example — that actively treats effluent before it reaches a smaller leaching facility. Because the unit does much of the work, the discharge area can shrink dramatically, which is exactly what rock-limited Muskoka and Haliburton lots, tight cottage laneways and high-setback shoreline properties need. The trade: annual professional servicing, electricity, and component warranties to track. If an installer proposes one, ask what the service contract costs per year — that line follows the system for its life.

Side-by-side comparison

Matching the class to the lot

Three questions usually decide it: how fast does your soil accept water, how deep is it to rock or groundwater, and how much clear space do setbacks leave? The site evaluation answers the first two; the designer's layout answers the third. If two quotes propose different classes for the same lot, the honest resolution is to ask each installer to explain their class choice from the site evaluation data — not from inventory convenience. Our cost calculator lets you price the classes side by side.

Servicing differences in practice

Budget the class, not just the build. Conventional, raised and filter systems share the same light rhythm — pump the tank every two to five years and keep surface water away. Treatment units add a service relationship: annual visits, electricity for the aerator, and parts that eventually wear. Owners in Muskoka, Haliburton and Bruce County who accept that trade deliberately are the happiest advanced-system customers; owners who learn about the service contract after moving in are not.

Questions Ontario owners ask about system types