Underpinning Permit Design
Permit-design coordination for residential underpinning and basement lowering. Because the work directly affects the existing foundation and construction sequence, the design must be based on the actual building and site conditions.
What the permit-design scope can include
Depending on the project and responsible professional scope, the package can include:
- existing and proposed basement/foundation plans
- sections showing existing and proposed basement elevations
- underpinning layout and construction details within applicable design responsibility
- coordination of new slab, foundation, drainage and basement conditions
- coordination with an independent licensed professional engineer where professional engineering is required
- permit submission support and response coordination where included
What we need to understand before design
Underpinning cannot be designed safely from a basement floor plan alone.
- existing foundation type, wall thickness and visible condition
- desired amount of basement lowering and resulting floor/ceiling relationship
- adjacent buildings, party walls and proximity to property lines
- groundwater, drainage or site conditions that may affect the project
- existing columns, beams, stairs and service locations
- whether a basement entrance, structural opening or additional dwelling unit is part of the same project
Construction sequence matters
Underpinning is typically carried out in a controlled sequence so only limited portions of the existing foundation are disturbed at a time. The contractor is responsible for means, methods, temporary support and following the approved sequence/details. The design documents are not a substitute for competent construction supervision.
Common underpinning permit questions
Do I need a permit to lower my basement by underpinning?
Yes. Underpinning changes the support of the existing building and requires a building permit.
Can underpinning be designed without seeing the house?
Reliable existing-condition information is essential. Site measurements, photos and sometimes further investigation are needed before the design can be finalized.
Will I need a professional engineer?
Many underpinning projects involve professional engineering responsibility. The exact requirement depends on the building, design and municipality; when required, the responsible licensed professional must take responsibility for that engineering content.
Can underpinning and a basement apartment be done under one project?
They can be coordinated, but the dwelling-unit design adds separate zoning, exit, fire/life-safety, plumbing and HVAC requirements beyond the foundation work.
What happens if the contractor finds a different foundation than expected?
Unexpected concealed conditions should be documented and reviewed before the affected work continues. Revised design or permit information may be required.
Can I excavate the basement before the permit is issued?
No. Work affecting the foundation should not start before the required permit/design approvals are in place.
During construction
The owner/contractor must arrange required inspections and follow the approved underpinning sequence and details. If site conditions differ from the design assumptions, work in the affected area should stop long enough for the condition to be reviewed by the responsible designer/professional.
What to send for a quote
- property address and municipality
- photos of all visible foundation walls and basement columns/beams
- existing basement floor-to-ceiling height
- desired finished basement height or approximate lowering target
- survey and existing drawings if available
- whether the project also includes a walkout, basement apartment or structural wall changes
Related residential permit services
Basement Walkout · Basement Apartment Permit Design · Building Structural Permit Drawings · As-Built & Measured Drawings
828 Design Inc. — BCIN building design & permit services. Content reviewed for current Ontario permit context: August 2026. Requirements are confirmed for the property, municipality and agreed project scope. Qualifications & responsibility →
Considering basement lowering or underpinning?
Send the address, basement photos and the height you are trying to achieve. We can identify the next documentation and professional-coordination steps.