Start with the approved system, not the renovation drawing
Locate the permit, filing or registration, approved design/as-built and any later alteration record. Mark the tank, treatment equipment, dispersal area, reserve area where applicable, wells and access points. If the record cannot be reconciled with what is on the property, resolve that uncertainty before placing new construction.
Added bedrooms and changed use can change the design question
Onsite rules often use design flow or occupancy assumptions. Ontario's Part 8 regime applies to qualifying systems with design capacity up to 10,000 litres per day and includes design-flow rules. BC requires plans and specifications to be filed for applicable construction and significant alterations or repairs. A renovation that adds sleeping space, a secondary dwelling or a materially different use can therefore require a fresh capacity/design discussion even if the existing tank is not being replaced.
Do not build over the treatment area by accident
Garages, additions, pools, driveways, retaining walls, patios and grade changes can interfere with the approved layout, access or treatment area. Heavy equipment can compact soil. Stormwater changes can saturate areas that need to manage effluent. Show the onsite professional the full site plan—not only the plumbing fixtures being added.
The building permit and septic approval can be separate
In Alberta, private sewage is part of the Safety Codes system and the permit issuer can differ by jurisdiction. In BC, health-authority filing is separate from municipal zoning/building decisions. In New Brunswick, provincial Technical Inspection Services approves onsite installation, repair and replacement while municipal development approvals address other parts of the project. Confirm both tracks early so one approval does not arrive after the design has already boxed out the other.
Waterfront and constrained lots need earlier review
Setbacks, soil, groundwater, property boundaries, wells and water bodies can limit the usable treatment area. Saskatchewan's private-sewage rules are changing effective November 1, 2026, including additional documentation and designer-certification requirements for many new private sewage works. A project spanning that date should confirm which version of the requirements will apply before submission.
Repairs discovered during a renovation
Do not assume an existing defect can simply be covered up or replaced in kind. The authority may need to review a significant repair or alteration, and the present site may not support the same layout under current requirements. Ask what record, inspection and design documentation is needed before excavation.
What to hand your designer or contractor
- confirmed sewer/onsite service status;
- permit, filing or registration and approved plan;
- maintenance and repair history;
- current site survey if available;
- proposed floor plan and bedroom/use changes;
- proposed building footprint, driveway and grading changes; and
- wells, water bodies and other known site constraints.