By the Orangeville Pre-cast Team | Last updated: August 13th, 2026
Concrete septic tanks hold up better than plastic for most Ontario properties because they resist the frost heave, clay soil pressure, and high water tables that cause plastic tanks to shift or float. Plastic tanks cost less and install faster, but the trade-off shows up in long-term durability. Your septic tank material affects the tank’s lifespan, Ontario Building Code compliance, and how well it performs underground for decades.
What Is the Difference Between Concrete and Plastic Septic Tanks?
A concrete septic tank is a precast, reinforced structure built from dense, poured concrete, typically manufactured off-site and delivered ready for installation. A plastic septic tank is a lightweight, single-piece tank rotomolded from high-density polyethylene (HDPE). Both tanks perform the same core function, separating solids from wastewater before it moves to the leaching bed, but the material changes how each one handles Ontario’s ground conditions.
TL;DR
- Concrete lasts longer. Precast concrete septic tanks are engineered to last 40 to 50 years or more with proper maintenance.
- Plastic weighs less. Lighter tanks are easier to transport and install but can float in high groundwater or flood conditions.
- Ontario’s climate favours concrete. Frost heave and clay soil put more stress on lightweight tanks than on heavy precast concrete.
- Code compliance matters. All septic tanks sold in Ontario must conform to CSA Standard B66 and the Ontario Building Code’s compartment and capacity rules.
Why Material Matters in Ontario’s Climate and Code
Frost Heave and Clay Soil
Ontario’s underground conditions are demanding. Frost heave, soggy clay soils, and seasonal flooding put constant pressure on buried structures. Heavy, dense precast concrete tanks stay in place under this pressure, while lighter tanks are more prone to shifting.
Floating Risk in High Water Tables
Properties with high groundwater levels face a specific risk with lightweight tanks: floating. A tank that isn’t heavy enough to stay anchored can shift out of position when the surrounding soil becomes saturated. Concrete’s weight keeps it seated in the excavation regardless of water table changes.
CSA B66 and Ontario Building Code Compliance
Every septic system in Ontario with a daily flow under 10,000 litres falls under the Ontario Building Code, and every tank sold in the province must conform to CSA Standard B66, confirmed by a CSA certification label or CPA red dot logo. The Code also sets minimum compartment sizing: a septic tank’s first compartment must hold at least 1.3 times the daily design flow, with a minimum working capacity of 2,400 litres, and total tank capacity can’t fall below 3,600 litres. Confirming a tank meets these specifications, regardless of material, protects your investment and keeps your system inspection-ready.
Concrete vs. Plastic: Side-by-Side Comparison
|
Factor |
Concrete | Plastic | Best For |
|---|---|---|---|
| Typical lifespan | 40-50+ years | 15-25 years | Concrete: long-term ownership |
| Weight / floating risk | Heavy, stays anchored | Lightweight, can float | Concrete: high water table sites |
| Performance in clay soil | Resists shifting under soil pressure | More prone to shifting | Concrete: heavy clay properties |
| Code compliance | Meets CSA B66 | Meets CSA B66 | Both, if properly registered |
Common Mistakes to Avoid When Choosing a Septic Tank Material
- Choosing on price alone. A lower upfront cost can mean a shorter replacement cycle and higher lifetime cost.
- Ignoring your water table. Skipping a site evaluation before choosing a lightweight tank raises the risk of floating.
- Assuming all tanks are code-compliant. Only tanks bearing a CSA certification label or CPA red dot logo have confirmed CSA B66 conformance.
- Overlooking compartment sizing. A tank that doesn’t meet the Building Code’s minimum compartment capacity can fail inspection regardless of material.
How to Choose the Right Tank for Your Property
Start with your soil and water table, not the price sheet. Properties with clay soil, a high water table, or a history of spring flooding are better matched to concrete’s weight and structural margin. Confirm the tank carries CSA B66 certification and meets your household’s design flow before you order. Orangeville Pre-cast has manufactured precast concrete septic tanks since 1966 and is a registered manufacturer with the Concrete Precasters Association of Ontario, so every tank leaving our yard is built to these standards. Review our septic tank drawings to compare compartment sizes before you order, or contact us to talk through your site conditions.
Frequently Asked Questions
How long do concrete septic tanks last?
Precast concrete septic tanks typically last 40 to 50 years or more with proper maintenance and regular pumping. Plastic tanks generally last 15 to 25 years under the same conditions.
Can a plastic septic tank float?
Yes. Plastic tanks are lightweight enough that high groundwater or flooding can cause them to shift or float out of position, especially before backfilling is complete. Concrete’s weight prevents this because the tank stays anchored regardless of water table changes.
Is concrete or plastic better for clay soil?
Concrete performs better in clay soil. Heavy clay expands and contracts with moisture and frost, and dense precast concrete resists that shifting pressure better than a lightweight plastic tank.
Does Ontario require septic tanks to meet a specific standard?
Yes. Every septic tank sold in Ontario must conform to CSA Standard B66, and the Ontario Building Code sets minimum compartment sizing and capacity requirements for tanks with a daily flow under 10,000 litres.
Is a concrete septic tank more expensive than plastic?
Concrete tanks typically cost more upfront because of their weight and manufacturing process. Over a multi-decade ownership period, the higher upfront cost is often offset by a longer service life and fewer replacements.
Action Steps
- Get a site evaluation before choosing a tank material, especially if your property has clay soil or a high water table.
- Confirm CSA B66 certification on any tank you’re considering, either a CSA label or CPA red dot logo.
- Compare compartment sizing against your household’s daily design flow to avoid an undersized tank.
- Talk to a local manufacturer who can confirm your tank meets Ontario Building Code requirements before you order.
For most Ontario properties, especially those with clay soil or a high water table, concrete’s durability and code margin outweigh plastic’s lower upfront cost and easier installation.
About the Orangeville Pre-cast Team: Orangeville Pre-cast has manufactured precast concrete septic tanks and supplied masonry and landscape products since 1966, and is a registered manufacturer with the Concrete Precasters Association of Ontario. Learn more at orangevilleprecast.ca.