Shoring holds back the earth so the sides of your excavation don't collapse — needed when you can't slope the dig back because a property line (or a neighbour's house) is right there. Underpinning extends your neighbour's foundation deeper, in small sequenced pits, so your deeper basement doesn't undermine it.
The trigger rule is simple: whenever your excavation poses a risk of undermining the neighbouring foundation, you underpin. Old Toronto houses often sit within 2 feet of the property line with footings far shallower than a modern basement. If your dig goes below their footing level — very common — underpinning isn't optional, and an engineer designs and stamps the underpinning drawings.
| Item | How it's measured | 2026 GTA planning range |
|---|---|---|
| Underpinning | Per linear foot of party wall + soil disposal (yd³) | $400–$800/lf typical pits |
| Shoring | Per sq ft of shored face; carried by the excavation sub as its own line | Highly site-specific |
| Single-faced foundation forming | Walls poured against shoring cost ~2.5× normal two-sided forming | Ask your forming sub how they price it |
| Engineering & monitoring | Design, review engineer, movement monitoring | $10,000–$25,000 |
Depth of the existing neighbouring foundations is almost always "TBC on site" — nobody knows until test pits expose them. Budget with contingency.
Get the geotechnical report early — soil type drives everything. Ask your excavator whether shoring is included or a separate TBD line (it's usually separate). And if your design can raise the basement slab even a foot, you may dig above the neighbours' footing level and avoid underpinning entirely — worth a conversation with your architect before permit.
When is underpinning required in Toronto?
Whenever your excavation risks undermining a neighbouring foundation — in practice, whenever your new basement goes deeper than their footings and you're within the zone of influence. An engineer designs the underpinning; existing footing depths are confirmed on site.
How much does underpinning cost per foot?
Planning range for typical sequenced-pit underpinning in the GTA is roughly $400–$800 per linear foot of wall being underpinned, plus soil disposal, engineering and monitoring. Complex or deep conditions cost more.
What's the difference between shoring and underpinning?
Shoring retains the soil on your own excavation faces; underpinning strengthens and deepens the neighbour's foundation. Tight infill builds often need both.
Who pays if the neighbour's house is affected?
You do — which is why pre-construction condition surveys of neighbouring homes, monitoring, and proper insurance are non-negotiable on party-wall-adjacent digs.