A leaching chamber is a plastic arch that sits in the trench where the stone and perforated pipe used to go, and on the right lot it can make a new septic bed a lot easier to build.
Most leaching beds in Kawartha Lakes are the classic design: a trench, a layer of washed stone, a perforated pipe down the middle, more stone, then backfill. It works, and it’s been the default for decades. But it means hauling a lot of stone to a yard, and some yards are hard to get stone into.
Chambers skip the stone. They’re open-bottomed plastic sections that snap together in a line, leaving a hollow space over the trench floor where effluent spreads out and soaks into the soil. You’ll see them on new builds, bed replacements and cottage lots across Ontario.
They’re not magic, though. They sit in the same soil, follow the same setbacks, and fail for the same reasons a stone bed does. Here’s what they are, what the Ontario Building Code says about them, and when they’re worth asking your designer about.
The Quick Answer
| Question | Short answer |
|---|---|
| What is a leach field chamber? | An open-bottom, arched plastic unit that replaces pipe and stone in a trench |
| Allowed in Ontario? | Yes. The Building Code covers leaching chambers in trench beds, shallow buried trenches, filter beds and Type A dispersal beds |
| Main advantage | No stone to truck in, lighter equipment, faster install |
| Do they shrink the bed? | Only for the wider “Type II” chambers, and the wider spacing eats most of that back in native soil |
| Soil and setbacks | Same rules as any leaching bed |
| Will they fix a bed that failed on bad soil? | No. If the soil was the problem, it’s still the problem |
| Can you drive on them? | No. Treat them like any leaching bed |
| Who decides | Your licensed designer, with the City’s approval |
What a Leaching Chamber Actually Is
Picture a length of culvert pipe cut in half lengthwise and laid over a trench, open side down. That’s the basic shape. Each section is moulded plastic with slotted sidewalls, roughly a metre or so long, and light enough for one person to carry. Sections lock end to end to make a run, with an end cap on each end.
Effluent from the tank (usually through a distribution box or header) enters at one end of each run. Instead of trickling out of holes in a pipe into stone, it lands on the trench floor under the arch and spreads along it. The soil underneath does the treatment, exactly as it does in a stone bed. Our guide to what a drain field is covers that soil side.
Infiltrator is one of the common brands you’ll hear named. There are others, and your designer will specify a product that meets the Code’s requirements rather than a brand for its own sake.
Chambers vs Pipe and Stone
| Pipe and stone trench | Leaching chamber trench | |
|---|---|---|
| Stone | Trucked in, often many loads | None in the trench |
| Equipment | Excavator plus dump trucks to the bed | Excavator; the chambers can come in on a small trailer |
| Install speed | Slower, stone placed and levelled | Faster once trenches are dug |
| Storage | Liquid sits in the gaps between stones | Open space under the arch holds more liquid per metre |
| Soil contact | Stone sits on the trench floor | Trench floor is open under the chamber |
| Bed size | Set by Q × T ÷ 200 | Same for Type I; shorter for Type II, but wider spacing |
| Material cost | Pipe is cheap, stone adds up | Chambers cost more than pipe per metre |
The storage point matters most on busy days. When everyone showers and the washer runs, a chamber has a bit more room to hold the surge while the soil catches up. It doesn’t change how much the soil can take over a day, though.
What the Ontario Building Code Says About Chambers
Leaching chambers are written into Part 8 of the Building Code, which governs septic systems. The details are worth knowing because they explain why chambers don’t always mean a smaller bed.
Where they’re allowed. The Code permits leaching chambers with absorption trenches, shallow buried trenches, filter beds and Type A dispersal beds. They have to meet a product standard for plastic leaching chambers (IAPMO PS 63) and fall into one of two size classes, Type I or Type II. Type I is the narrower chamber, around 40 cm wide; Type II is wider, closer to 56 cm.
How long the runs must be. A standard pipe-and-stone bed needs a total length of at least Q × T ÷ 200, where Q is the daily design flow and T is the soil’s percolation time. We walk through that math in how leaching beds are sized. Under the current Code, a Type I chamber bed uses the same formula. A Type II chamber bed can use Q × T ÷ 300, which is a third less length. The 40 m minimum for a trench bed still applies either way.
How far apart the trenches go. Here’s the catch. In native soil, trenches with Type II chambers have to be centred at least 2.4 m apart, compared with 1.6 m for pipe or Type I. Two-thirds the length at one-and-a-half times the spacing works out to roughly the same bed area. The real footprint savings with Type II show up when the chambers sit in imported leaching bed fill, as in a raised bed, where the 1.6 m spacing applies.
How they go in. The Code requires each run to be level, connected section to section, used full length and uncut, capped at both ends, fitted with a splash plate at the inlet so the incoming flow doesn’t scour the soil, and protected so soil or fill can’t get inside. The header and chambers also have to be locatable after burial, typically with tracer wire.
We’re summarizing, and the Code gets updated, so don’t treat this as the final word for your lot. Which chamber type, which formula and how the bed lays out is the designer’s call, checked by the City of Kawartha Lakes Building Division at permit and inspection. The province publishes the Code through Ontario’s Building Code page.
Where Chambers Make Sense in Kawartha Lakes
Chambers earn their keep where stone is the hard part of the job.
Tight cottage lots. Many waterfront lots around Bobcaygeon and Fenelon Falls have one narrow lane, a steep drop, and mature trees you’d rather keep. Getting loaded dump trucks to the bed can mean tearing up the driveway or the lawn. A few trailer loads of plastic is much easier.
Rock country. On Shield lots near Norland and Coboconk, beds are often raised on imported fill because there isn’t enough soil over the granite. You’re already trucking in sand, so cutting the stone from the order helps, and a Type II chamber in leaching bed fill can use the tighter spacing.
Hard-to-reach sites. Water-access properties, lots behind other buildings, and yards where the only route crosses a septic tank or a well line all favour lighter materials. Spring load restrictions on some rural roads can also make heavy stone deliveries awkward to schedule.
On an open rural lot with good access and a quarry nearby, the difference is often small, and a stone bed is perfectly good.
What Chambers Don’t Fix
This is where people get oversold. A chamber is a different way to spread effluent over soil. It is not a different soil.
- Same percolation limits. In-ground trench beds still need soil between 1 and 50 min/cm, chambers or not.
- Same separation. The trench bottom still needs 900 mm of unsaturated soil above rock or the high water table.
- Same setbacks. Distances to wells, the lake, the house and the lot line don’t change.
- Same biomat. The layer of slime that forms where effluent meets soil builds up under a chamber just as it does under stone. That layer, not the plastic, is what eventually limits the bed’s life.
So if your old bed failed because it sat in tight clay or a spring water table, rebuilding it with chambers in the same spot won’t save it. That calls for a proper redesign, often a raised bed or a treatment unit. Our drain field repair page covers how we sort out what actually failed.
Driving Over Chambers and What Goes on Top
Some manufacturers publish load ratings for their chambers, and those are about construction and cover depth, not parking. A leaching bed is never a driveway, whatever is in the trench, and compacted soil around the chambers chokes off the air the bed needs. Grass is the right cover. Our list of what can go over a leaching bed applies to chamber beds exactly as it does to stone.
Maintenance and Lifespan
A chamber bed needs the same care as any leaching bed. Pump the tank every 3 to 5 years, clean the effluent filter if you have one, keep roof water and sump discharge away from the bed, and don’t flush wipes or grease. Solids that escape the tank clog the soil under a chamber just as fast as under stone.
The plastic itself doesn’t rot, but the soil interface sets the lifespan. We don’t assume a chamber bed will outlast a well-built stone bed on the same soil. Treat it like the 15 to 25 years we’d expect from a conventional bed that’s pumped on schedule, and be pleasantly surprised if it goes longer.
Cost: Chambers vs Stone
Chambers cost more than perforated pipe per metre. The savings come from what you don’t buy: stone, trucking, and some machine hours. On an easy lot, those roughly cancel out. On a hard-access lot, chambers can come out ahead.
Either way, a chamber bed falls inside the same ranges we publish for any bed: $10,000 to $25,000 to replace a leaching bed, with raised systems higher. The leaching bed replacement cost guide breaks down what drives that number, and septic bed installation walks through the job itself. The easiest way to compare is to ask for both options priced on the same design, or start with a ballpark from the septic replacement cost estimator.
Frequently Asked Questions
Are leach field chambers better than gravel?
Not better, just different. They’re lighter to install, need no stone, and hold more liquid in the trench. On good soil with easy access, a stone bed performs just as well. The soil does the treatment in both.
Do septic chambers need gravel under them?
Not in the trench. Chambers sit directly on the prepared trench floor. The designer may still call for imported sand or leaching bed fill under the whole bed if the native soil isn’t suitable.
Are septic drain field Infiltrator chambers allowed in Ontario?
Leaching chambers are permitted under the Building Code if they meet its product standard and dimension classes. Infiltrator is one of the common brands. Your designer confirms that the specific product fits the design and the Code.
Can you drive over septic leach field chambers?
No. Load ratings exist for installation and cover, not for regular traffic. Parking or driving on any leaching bed compacts the soil and can damage the system.
Does a septic chamber system make the leach field smaller?
Sometimes. Type II chambers are allowed about a third less total length, but in native soil they need wider trench spacing, so the overall footprint is often similar. The bigger savings show up in raised beds built on imported fill.
Thinking About Chambers for Your Bed?
If your designer has offered chambers, or you’d like to know whether they’d help on a tight or rocky lot, call (705) 702-5526 or Book A Pump. We install and service beds across the county, including Bobcaygeon, Fenelon Falls, Norland and Coboconk, with no travel surcharge anywhere in Kawartha Lakes.