Type A Dispersal Bed in Ontario: What It Is and Why Your Designer Picked One

What a Type A Dispersal Bed Actually Is

If the drawing your designer handed you says “Type A dispersal bed,” you are not getting an ordinary septic bed. You are getting a treatment unit that cleans the effluent first, followed by a wide, shallow pad of sand with a stone layer on top that spreads that cleaner water over a big patch of ground.

Here is the mechanism in two sentences. A conventional leaching bed asks the native soil to do most of the cleaning, so it needs decent soil and plenty of it under the pipes. A type a dispersal bed lets a machine do the heavy cleaning up front, so the bed’s main job is getting the water into the ground without it showing up on the surface.

Think of it like a roof. On a conventional bed the soil is the roof deck doing the structural work. On a Type A, the treatment unit is the deck and the sand layer is the eavestrough, spreading the water out to where the ground can take it.

The rules live in Article 8.7.7.1 of Part 8 of the Ontario Building Code (read the article). The 2024 Building Code took effect January 1, 2025 and kept Type A beds in the same article, with one clarified rule for slow soils (Tillsonburg’s Part 8 change summary). Older paperwork will cite O. Reg. 332/12; newer paperwork cites the 2024 Code. Same bed.

Type A vs Leaching Bed, Filter Bed and Type B

Homeowners get these four mixed up because designers use them like everyone already knows. Here is the plain version. The sizing rules are the Code’s; Q is your daily design flow in litres and T is the soil’s percolation time (the T-time) in minutes per cm.

The line that matters on most hard lots is the separation. A filter bed needs 900 mm of clearance under the stone. A Type A needs 600 mm. On a lot with a high water table, that 300 mm is a foot of fill you are not trucking in, spreading and paying for.

Type B is the less common cousin. It also needs Level IV effluent, but it is always pressure-dosed through small-hole pipe and laid out long and narrow along the slope. If your designer chose B over A, it is usually because of slope or lot shape. Ask them.

When the Code Allows a Type A Dispersal Bed

The Code only lets you build one behind a treatment unit that meets the Level IV effluent limits in Table 8.6.2.2. You cannot put a Type A bed after a plain septic tank and call it good. No Level IV unit, no Type A.

The Code does not force a Type A on anyone either. It is one of the permitted leaching bed options, and your designer picks it because the site makes the cheaper options awkward or impossible. Final say belongs to your approval authority, which is the township building department or the health unit depending on where you live.

In our experience, a designer reaches for Type A when the lot looks like one of these:

1. High water table. The 600 mm separation beats a filter bed’s 900 mm. See our high water table guide.
2. Shallow bedrock. Same logic: less vertical room needed. See shallow bedrock septic options.
3. Tight clay. Slow soil that would need a huge conventional bed. The cleaner effluent is easier on it.
4. Small or waterfront lot. A raised conventional bed needs room for its side slopes, and its setbacks grow by twice the height it is raised. That eats a small lot fast.
5. Replacement on a crowded lot. The old bed failed, the house and well are not moving, and there is no room for a big new bed.

How a Type A Dispersal Bed Is Sized

You can check these numbers yourself. Two areas get calculated: the stone layer on top, and the sand layer under it.

The stone layer

Article 8.7.7.1 sets the stone area at A = Q/B, where B is 75 when the daily design flow is 3,000 L or less and 50 when it is more. The stone layer has to be rectangular, run its long side parallel to the contours, be at least 200 mm thick, and sit with its bottom at least 600 mm above the high water table, rock, or soil with a T-time of 1 or less or over 50.

The sand layer

The sand has to be at least 300 mm thick, with a percolation time of 6 to 10 minutes and no more than 5% fines passing a 0.074 mm sieve. Sand and stone together must be at least 500 mm thick. Durham Region Health’s Part 8 sizing form (Schedule A) lists the sand area as QT/850 where T is 15 or less, and QT/400 where T is over 15, with T capped at 50.

Here is what that does on two lots with the same house. This is a planning example only; your daily design flow comes from bedrooms, floor area and fixtures (see how design flow and tank size work).

The stone pad stays the same. The sand footprint goes up more than sixfold on clay, and then you add the 15 m extension. That is why two quotes for “a Type A” can be thousands of dollars apart. One lot is sand and one is clay.

What a Type A System Costs

Set your expectations now: a Type A system is not the cheap option. You are paying for a treatment unit, its electrical, often a pump, a load of spec sand and an annual service contract. What you save is fill, height and lot space.

These are planning estimates from Ontario jobs, not quotes. Our septic replacement cost guide breaks the ranges down, and the treatment unit comparison covers the brands designers usually pair with a Type A bed.

Where homeowners go wrong on price:

1. Comparing it to the neighbour’s bed. Their 1990s trench bed on sand is not your lot. Compare Type A to a raised bed or filter bed on YOUR soil.
2. Forgetting the yearly contract. The cost varies by brand and servicer. Get the annual price in writing before you pick a unit. It runs as long as you own the house.
3. Letting the sand get swapped. The Code calls for 6 to 10 minute sand with 5% fines or less. “Close enough” pit sand is how a bed fails an inspection or fails early.
4. Pricing only the bed. The electrical run, the alarm and the pump chamber are real lines. Ask in writing what is in and what is out.

What the Inspector Looks For on a Type A Bed

Every inspector has their own habits and some want to see the bed open at more than one stage. Ask at permit time which stages they want to see before anything gets covered. These are the items straight out of the Code that they are checking:

Setbacks trip up more jobs than anything else. Measure from the edge of the stone layer, not the middle of the bed. Our well and septic setbacks page has the distances people most often get wrong.

Living With a Type A System

Here is the part the brochure skips. Under Article 8.9.2.3 of the Code, no one may operate a treatment unit other than a septic tank without a maintenance agreement in place, and conservation authorities such as the Rideau Valley CA treat that as a yearly obligation. Budget for it like you budget for insurance.

1. Keep the service contract current. If your township runs a re-inspection program, expect to be asked for it.
2. Pump the septic tank when the servicer says so. Pumping runs about $300 to $600 (planning estimate), usually every 3 to 5 years.
3. Treat the alarm like a smoke detector. If it sounds, cut water use and call your servicer the same day.
4. Keep traffic off the bed and the sand extension. No parking, no paving, no trees close by.
5. Keep the paperwork. As-built drawing, unit model, sand ticket and service records. The next buyer’s inspector will ask for all four.

For the rest of the routine, see our septic maintenance guide. A Type A bed that gets its yearly visit is a quiet, boring system, and quiet and boring is exactly what you want buried in your yard.

Sources: Ontario Building Code, Article 8.7.7.1 (Type A dispersal beds); Durham Region Health, Part 8 sizing form, Schedule A; Town of Tillsonburg, 2024 OBC Part 8 changes; Rideau Valley Conservation Authority, annual compliance for treatment units. Costs are planning estimates only. Final approval belongs to your local building department, health unit or approval authority.