Soakaway & Infiltration System Design — Ontario
Soakaway Design for Ontario Building Permits & Site Plan Approvals
We design P.Eng.-stamped soakaway pits, infiltration trenches, and leaching beds that manage stormwater on-site, satisfy Ontario Building Code requirements, and meet municipal and Conservation Authority approval conditions across Ontario.
Soakaway Requirements
What Is a Soakaway and When Is It Required?
A soakaway — also called an infiltration pit, infiltration trench, or leaching bed — is an engineered subsurface structure that collects roof drainage, surface runoff, or other stormwater and allows it to infiltrate gradually into the surrounding soil. Ontario municipalities, the Ontario Building Code, and Conservation Authorities increasingly require soakaways as a condition of building permit issuance, Site Plan Approval, or Conservation Authority permit approval.
Building Permit Requirement
Many Ontario municipalities require a soakaway or infiltration system as a condition of building permit issuance for new homes, additions, and accessory structures. The Ontario Building Code sets minimum design standards for soakaways receiving roof drainage, including sizing, setbacks from foundations and property lines, and soil percolation requirements.
Site Plan Approval Condition
Site Plan Approval applications for residential infill, commercial, and industrial developments frequently include a condition requiring on-site stormwater infiltration. A P.Eng.-stamped soakaway or infiltration trench design is required to satisfy the condition and obtain Site Plan Approval clearance.
Conservation Authority Permit
Properties within Conservation Authority regulated areas — near watercourses, wetlands, and their buffers — may require a CA permit that includes a condition for on-site stormwater management. A soakaway or infiltration system designed to reduce post-development runoff is a common measure used to satisfy CA permit conditions.
Stormwater Management Plan Requirement
Stormwater management plans for developments with increased impervious area often specify infiltration as the preferred control measure where soils permit. A P.Eng.-stamped soakaway design demonstrates that the required infiltration volume and rate are achieved and that the system is properly integrated with the site grading plan.
Deliverables
P.Eng. Deliverables for Your Soakaway Design
Soakaway Design Report
P.Eng.-stamped engineering report documenting the soakaway design basis, infiltration rate calculations, system sizing, OBC compliance, and design assumptions — the primary submission document for building permit and Site Plan Approval applications.
Infiltration Testing & Soil Assessment
On-site percolation testing and soil assessment to determine the design infiltration rate for the soakaway. Testing is conducted in accordance with OBC requirements and municipal standards, and results are documented in the design report.
Soakaway Construction Drawing
Stamped construction drawing showing soakaway pit or infiltration trench dimensions, depth, aggregate fill specification, geotextile wrapping, inlet pipe configuration, overflow routing, and setbacks from foundations, property lines, and utilities.
Grading Plan Integration
Integration of the soakaway design into the site grading plan, showing inlet grades, overflow routes, and the relationship between the soakaway and the overall lot drainage pattern — ensuring the grading plan and soakaway design are consistent and approvable as a package.
Stormwater Volume Calculations
Pre- and post-development runoff volume calculations demonstrating that the soakaway provides the required storage and infiltration capacity for the design storm event specified by the municipality or Conservation Authority.
Municipal Submission Package
Complete stamped submission package — design report, construction drawing, calculations, and supporting documentation — formatted to the applicable municipal or Conservation Authority submission requirements.
Process
Our Process
Site Review & Requirement Confirmation
We review your property, confirm the applicable municipal and OBC soakaway requirements, check Conservation Authority regulated area mapping, and advise on whether a soakaway is required and what design standard applies.
Infiltration Testing
We conduct on-site percolation testing to determine the design infiltration rate for the soakaway. Testing is performed in accordance with OBC requirements and documented for inclusion in the design report.
Soakaway Sizing & Design
We size the soakaway based on the contributing drainage area, design storm, infiltration rate, and required storage volume, and prepare the construction drawing showing all dimensions, materials, and setbacks.
Grading Plan Coordination
We coordinate the soakaway design with the site grading plan to ensure consistent inlet grades, overflow routing, and lot drainage — producing an integrated package that can be reviewed and approved together.
Permit Submission
We prepare and submit the complete soakaway design package to the municipality, Conservation Authority, or both, coordinating with your architect, builder, or planning consultant as needed.
Comment Response & Approval
We respond to reviewer comments, issue revised drawings and calculations as required, and work with the reviewing authority to achieve approval as efficiently as possible.
Regulatory Context
Regulatory Context
Soakaway design in Ontario is governed by a layered framework of provincial, municipal, and Conservation Authority requirements.
Ontario Building Code (OBC)
Division B, Part 8 of the Ontario Building Code sets out minimum requirements for soakaways receiving roof drainage, including minimum pit dimensions, aggregate fill specifications, setbacks from foundations and property lines, and soil percolation requirements. A P.Eng.-stamped design is required where the OBC prescriptive requirements cannot be met or where a municipality requires an engineered design.
Municipal Engineering Standards
Many Ontario municipalities — including those in the GTA, Ottawa, Hamilton, and Simcoe County — have their own soakaway or infiltration system design standards that supplement or exceed OBC requirements. We prepare designs to the applicable municipal standard and coordinate directly with municipal building and engineering reviewers.
Conservation Authority Requirements
Conservation Authorities across Ontario — including TRCA, CVC, LSRCA, NVCA, and others — may require on-site stormwater infiltration as a condition of a CA permit for development in regulated areas. We check regulated area mapping for your property and prepare the CA permit application where required.
Low Impact Development (LID) Policy
Provincial policy and municipal official plans increasingly require Low Impact Development measures — including soakaways, infiltration trenches, and rain gardens — for new development and redevelopment. A P.Eng.-stamped soakaway design is the standard method of demonstrating LID compliance for building permit and Site Plan Approval applications.
FAQ
Frequently Asked Questions
What is the difference between a soakaway pit, an infiltration trench, and a leaching bed?
All three are subsurface infiltration structures that collect stormwater and allow it to infiltrate into the surrounding soil, but they differ in shape and application. A soakaway pit is a compact excavated pit filled with clean aggregate, typically used for roof drainage from a single downspout. An infiltration trench is a long, narrow excavated trench filled with aggregate, used where a larger footprint is available or where a linear layout suits the site. A leaching bed is a broader, shallower infiltration area, sometimes used for surface runoff or where soil conditions favour a larger infiltration footprint. We select the appropriate system type based on your site conditions, drainage area, and municipal requirements.
Do I need a P.Eng.-stamped soakaway design for a building permit in Ontario?
It depends on your municipality and the size of your project. The Ontario Building Code includes prescriptive soakaway requirements for roof drainage that do not require an engineer. However, many Ontario municipalities require a P.Eng.-stamped soakaway design as a condition of building permit issuance — particularly for new homes, additions, and infill development. We confirm the applicable requirements for your municipality during our initial consultation.
How is the size of a soakaway determined?
Soakaway size is determined by three factors: the contributing drainage area (the roof or surface area draining to the soakaway), the design storm event (typically the 1-in-5-year or 1-in-100-year storm, depending on the municipality), and the soil infiltration rate (measured by on-site percolation testing). We calculate the required storage volume and infiltration area, then size the pit or trench to meet the design requirements while respecting setbacks from foundations, property lines, and utilities.
What happens if the soil on my property has poor infiltration?
If on-site percolation testing reveals that the soil infiltration rate is too low to support a soakaway, we assess alternative stormwater management measures — such as a cistern with controlled release, a rain garden, or a connection to the municipal storm system — and advise on the most appropriate solution for your site and the applicable municipal requirements.
Can a soakaway be used near a foundation or property line?
The Ontario Building Code and most municipal standards require minimum setbacks between a soakaway and building foundations, property lines, wells, and septic systems. Typical OBC setbacks are 1.8 m from a foundation and 0.6 m from a property line, but municipal requirements vary. We confirm the applicable setbacks for your municipality and design the soakaway to comply.
Do you design soakaways across Ontario?
Yes. We design soakaway pits, infiltration trenches, and leaching beds for properties across Ontario, including the Greater Toronto Area, Ottawa, Hamilton, Simcoe County, Muskoka, and rural municipalities. We are familiar with the OBC requirements, municipal engineering standards, and Conservation Authority requirements that apply across the province and coordinate directly with municipal and CA reviewers.
Need a Soakaway Design for Your Permit?
Contact our team for a free consultation on your soakaway or infiltration system design requirements.
Contact Us
Start Your Soakaway Design
Tell us about your property and project. We'll confirm the applicable OBC and municipal soakaway requirements, check Conservation Authority regulated area mapping, and advise on the design approach for your site.