---
title: "Underpinning Methods Existing Foundations | AVANORTH"
canonical_url: "https://avanorth.ca/blog/underpinning-methods-strengthening-existing-foundations"
last_updated: "2026-03-10T07:34:14.048Z"
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description: "Underpinning guide: mass concrete, helical piles, micropiles, when needed, Ontario building code requirements, and basement lowering process."
"og:description": "Underpinning guide: mass concrete, helical piles, micropiles, when needed, Ontario building code requirements, and basement lowering process."
"og:title": "Underpinning Methods Existing Foundations"
"twitter:description": "Underpinning guide: mass concrete, helical piles, micropiles, when needed, Ontario building code requirements, and basement lowering process."
"twitter:title": "Underpinning Methods Existing Foundations"
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AVANORTH Home
**Construction Tips**·June 1, 2026· 3 min read
# **Underpinning Methods: Strengthening Existing Foundations**
Underpinning deepens or strengthens an existing foundation to support additional loads, increase basement depth, or remediate settlement problems. Understanding the methods helps owners choose the right approach.
**AVANORTH Team**
AVANORTH Construction
Underpinning is the process of extending an existing foundation deeper into the ground or widening it to increase its bearing capacity. It is one of the most technically challenging operations in construction because it involves modifying the structural support of an occupied building without compromising its stability. In Ontario, underpinning is increasingly common as homeowners seek to convert shallow, low-headroom basements into full-height living spaces.
---
## When Is Underpinning Needed?
| Reason | Description |
| --- | --- |
| Increase basement height | Older homes often have basements with less than 6 feet of headroom. Underpinning lowers the floor to create a full-height basement (minimum 6'5" clear for OBC compliance as a living space). |
| Foundation settlement | Differential settlement (one part of the foundation sinking more than another) causes cracking, door/window misalignment, and structural distress. Underpinning transfers the load to deeper, more stable soil. |
| Additional storeys | Adding floors to an existing building increases the load on the foundation. If the existing foundation cannot support the additional weight, underpinning strengthens it. |
| Adjacent excavation | New construction excavation adjacent to an existing building may undermine the existing foundation. Underpinning the existing foundation protects it. |
| Change of use | Converting a residential building to commercial use (higher live loads) may require foundation strengthening. |
---
## Underpinning Methods
### 1. Mass Concrete (Pit Method)
The traditional and most common method for residential underpinning:
1. The existing foundation wall is divided into sections (called "pins"), typically 1-1.5 m wide
2. One section at a time is excavated below the existing footing to the desired depth
3. Concrete is poured into the excavated pit up to the underside of the existing footing
4. The concrete cures, and the next alternating section is excavated and poured
5. Never work on adjacent sections simultaneously; always leave at least one undisturbed section between active pins
| Advantage | Limitation |
| --- | --- |
| Low equipment cost (hand excavation) | Labour-intensive and slow |
| No specialized equipment needed | Limited to moderate depths (typically 1-2 m below existing footing) |
| Well-understood, proven method | Requires careful sequencing to prevent settlement |
| Suitable for most soil types | Not suitable for high water table without dewatering |
### 2. Helical Piles (Screw Piles)
- Steel shafts with helical plates are screwed into the ground beside or below the existing foundation
- Steel brackets transfer the building load from the existing foundation to the helical piles
- Advantages: minimal vibration, fast installation, immediate load capacity (no curing time), works in high water table
- Best for: settlement remediation, supporting new loads, where access is limited
### 3. Micropiles (Mini-Piles)
- Small-diameter (150-300 mm) drilled and grouted piles installed through or adjacent to the existing foundation
- Reach deep, stable bearing layers (can go 15-30 m deep)
- Advantages: can be installed in confined spaces and low-headroom basements, high load capacity for their size
- Best for: difficult soil conditions, deep bearing layers, restricted access
---
## Ontario Building Code Requirements
- **Permit required:** All underpinning work requires a building permit and engineered drawings from a licensed structural engineer
- **Minimum clearance:** 1,950 mm (6'5") clear height from finished floor to underside of floor joists for a habitable basement
- **Drainage:** Interior perimeter drainage and a sump pump are typically required when lowering the basement floor
- **Waterproofing:** Exterior waterproofing of the extended foundation is required where excavation is accessible
> **AVANORTH Underpinning:** We have extensive experience with residential underpinning using the mass concrete pit method. Our crews are trained in the precise sequencing required to maintain building stability throughout the process. Every underpinning project is engineered by a licensed structural engineer. We coordinate the underpinning with new waterproofing, drainage, insulation, and interior finishing to deliver a complete basement transformation. A typical full basement lowering takes 4-8 weeks depending on the size and soil conditions.
#underpinning #foundation #basement-renovation
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