Septic system risers are short shafts that carry a buried septic tank’s access openings up to the surface, so the lids sit at grade instead of under a foot or more of soil. That sounds like a small convenience. It is the difference between a tank that gets opened and checked on schedule and one that gets put off because somebody has to find a shovel first.
I oversee site preparation and excavation on our builds, and the septic system is part of that work. Where the tank goes, how deep it sits and where its lids come up are all decided in the ground, months before anyone thinks about the lawn. Here is what the code asks for, why the townships care, and what I would want an owner to know.
What the Ontario Building Code says about septic system risers
The Ontario Building Code deals with tank access in Article 8.2.2.3, the same article that sets the size and compartments of a septic tank. Three sentences at the end of it are the ones that matter here.
- The lids have to be reachable. Every septic tank is to be installed so its access openings are no more than 300 mm below the ground surface. That is about 12 inches.
- A deeper tank needs risers. Where the top of the tank sits more than 300 mm below the ground, it has to be fitted with risers that run from the access opening to within 300 mm of the surface.
- The risers have a standard. Risers must conform to CSA B66, the standard for prefabricated septic tanks and holding tanks, and they have to leave access openings big enough for regular maintenance.
Read that carefully and you will notice what the code does not require. It does not say the lids must be at grade. A tank can meet the code with its lids a foot down, under sod. That is legal. It is also exactly the situation that makes a tank hard to service.
Why a lid a foot down is still a dig
Twelve inches of soil does not sound like much until you are the one looking for it. The lid is a fixed size and the yard is not. Without a marker, an as-built drawing or a good memory, a buried lid can take an afternoon of probing and digging to find, and then the sod has to go back.
That matters because a tank needs to be opened more often than people expect. The province’s SepticSmart guide says a licensed sewage hauler or onsite sewage system professional should remove the tank cover and inspect the system every three to five years. The building code itself sets the trigger for pumping in Article 8.9.3.4: a tank is cleaned whenever sludge and scum take up one-third of its working capacity. Somebody has to open the tank to measure that.
In cottage country there is a season to think about as well. A lid under a foot of soil in July is a lid under frozen ground and snow in February. If something goes wrong with the system in winter, a tank you can open from the surface is a very different problem from one you have to thaw your way down to.
Township inspections expect you to find the lids
This is where septic system risers stop being a convenience in parts of Muskoka. Several municipalities now inspect private sewage systems on a schedule, and the owner is the one expected to make the tank accessible.
The Township of Muskoka Lakes runs a Sewage System Maintenance Inspection Program. Its program page notes that most septic tanks have two lids, that some are at ground level while others are buried, and that property owners are required to expose them before the inspection: septic tanks, pump tanks and distribution boxes. You do not need to be home for it, as long as every lid is accessible. The township also suggests that if your lids are concrete, an inspection is a good moment to switch to plastic ones.
The Town of Bracebridge works in two phases. Phase I staff will not open lids or dig. Where a Phase II inspection is required, the owner has to uncover the septic tank, distribution box, dosing tank and pumps, and hire a qualified professional to do the inspection at their own expense.
With risers, that obligation is a matter of lifting the lids. Without them, it is an excavation every time your number comes up.
Adding risers to a tank that does not have them
A tank set with its lids below grade can have septic system risers added later. The steps are simple to describe, even if the digging is not.
Finding the tank first
Start with the paperwork. SepticSmart’s Do list asks owners to know where their system is and to keep an as-built diagram somewhere safe. If you have the original permit drawings, they show the tank’s position. If you do not, your township’s building department may hold the records, and Muskoka Lakes invites owners who are unsure where their lids are to contact the township office. SepticSmart also warns against digging without knowing where the distribution pipes run, so find the tank before you start opening ground.
Fitting septic system risers properly
- One riser per access opening. A two-compartment tank usually has two lids, and each one needs its own riser to grade.
- Matched to the tank. The code ties risers to CSA B66, and the riser has to seal properly to the tank opening so it does not become a way in for surface water and soil.
- A lid that locks down. SepticSmart asks owners to keep the tank access lid secured to the riser at all times.
- Finished at grade, not above it. A riser that stands proud of the lawn catches a mower and a snowblower. One that sits flush is easy to find and easy to cut around.
Before you start, ask your township’s building department whether the work needs a permit or an inspection where you are. Rules differ between municipalities, and a phone call is cheaper than redoing it.
A riser lid is a safety device
Bringing a tank’s opening up to the surface also brings its hazard up to the surface, which is why the lid matters as much as the riser under it.
SepticSmart puts one item first on its Don’t list for a reason: never enter a septic tank. The gases and the lack of oxygen in a tank can kill. A lid that is secured to its riser keeps children, pets and curious guests out. A lid that has been left loose after a pump-out is the most dangerous thing on the property.
The same guide asks owners not to drive or park over the tank or the distribution system, and not to plant trees or shrubs too close to the tank. A riser at grade makes the tank visible, and visible is how it stays out from under the trailer, the woodpile and next year’s garden.
Planning septic system risers on a new build
On a new home or cottage, none of this has to be retrofitted. Our site preparation and site development work covers clearing, excavation, grading, driveways, well drilling, and septic system design and installation, and our permits and approvals work coordinates septic permits and inspections with the build. That means the tank, its depth and its lids are being placed at the same time as the house, the driveway and the grade around them.
A few things I would want an owner to think about while that is happening:
- Where the lids land. They should come up somewhere a pump truck can reach, out of the driveway and parking area, and clear of where the deck, the patio or the gardens will go.
- How deep the tank sits. Grading on a sloped or rocky lot can leave a tank deeper than planned. Where it ends up more than 300 mm down, the code calls for risers anyway, and the time to bring them all the way to grade is while the hole is still open.
- The finished grade, not today’s. The lids are set before landscaping, so their height has to match where the topsoil and sod will finish, not the rough grade the machine leaves.
- A record you keep. An as-built drawing showing the tank, the lids and the bed belongs with the house papers, which is exactly what SepticSmart asks for.
Our posts on septic system design and septic tank maintenance cover the rest of the system: how it is sized for your home, and how to look after it once it is in.
Frequently Asked Questions
What are septic system risers?
They are short vertical shafts, fitted to a septic tank’s access openings, that bring the lids up to or near the ground surface. They let a hauler or inspector open the tank without digging down to it.
Are septic tank risers required in Ontario?
Where the top of the tank is more than 300 mm below the ground, yes. Ontario Building Code Article 8.2.2.3 requires risers from the access opening to within 300 mm of the surface, built to CSA B66. A shallower tank can meet the code without them, though its lids may still be under soil.
How deep can a septic tank lid be buried?
Under the Ontario Building Code, a septic tank’s access openings are to be no more than 300 mm, about 12 inches, below the ground surface. A deeper tank needs risers to bring its openings within that distance.
Do I need to uncover my septic lids for a township inspection?
In some municipalities, yes. The Township of Muskoka Lakes requires owners to expose the lids of septic tanks, pump tanks and distribution boxes before its maintenance inspection, and Bracebridge’s Phase II inspections require owners to uncover the tank and its components. Check your own township’s program before your date comes up.
How often should a septic tank be opened and inspected?
Ontario’s SepticSmart guide says every three to five years, by a licensed sewage hauler or onsite sewage system professional. The Ontario Building Code sets the pumping trigger: clean the tank when sludge and scum fill one-third of its working capacity.
