Excavation & Site Preparation · Duncan
Footings and Foundations in Duncan
Footings and foundation walls cut to the surveyor's levels, with the water table planned for rather than discovered.
Duncan Excavating digs and backfills footings and foundation walls across the Cowichan Valley. Depth planning carries real weight here: the valley floor is an unconfined sand and gravel aquifer running to about 30 metres, with the water table at a median of 2.4 metres and shallowest from November through January.
A foundation dig is measured work. The levels are not negotiable, the tolerances are tighter than anything else on a site, and the two things most likely to move the number are what the bucket hits and how wet the hole is.
There is no published rate for foundation excavation on Vancouver Island. What moves the figure is depth, whether the material is diggable sand and gravel or rock needing a breaker, how far spoil has to travel, and whether the excavation is deep enough to need shoring.
Depth, water and the 1.2 metre line
Under the OHS Regulation, before a worker enters any excavation over 1.2 metres deep the sides have to be sloped, benched or shored, and excavated material has to be kept back at least 60 centimetres from the edge of a trench and 1.2 metres from any other excavation. Past 6 metres deep, or where a structure sits adjacent to the dig, written instructions from a qualified registered professional are required. That threshold, not the volume of soil, is usually what separates a straightforward footing dig from an expensive one.
Backfill, drainage and what gets signed off
Backfill is where a foundation either stays dry or does not, which is why footing work and perimeter drainage are quoted together more often than not. A Cowichan Valley Regional District building permit application pulls in several separate approvals at once — a riparian declaration where work falls within 30 metres of a stream boundary or the top of a ravine bank, an Agricultural Land Commission Notice of Intent where fill or soil removal is involved, a geotechnical report with a Schedule B where one is required, and a site plan prepared by a BC Land Surveyor.
What a foundation scope usually covers
Building pad preparation
Stripping and preparing the pad to the elevation the drawings call for.
Footing and wall excavation
Cutting footings and foundation wall lines to the surveyor's levels.
Shoring and benching where required
Sides sloped, benched or supported where the dig passes 1.2 metres.
Backfill and compaction
Backfilled in lifts against finished walls and compacted.
How a foundation dig runs
- 1
Levels and layout — Working from the drawings and the surveyor's stakes, with the dig lines set before anything is stripped.
- 2
Locates and access — BC 1 Call locates in hand, and a route onto the pad that a loaded truck can actually use.
- 3
Dig to grade — Cut to the specified elevation, with spoil kept back from the edge and stockpiled or loaded out depending on whether it is going back in.
- 4
Backfill and compact — Backfilled in lifts once the walls and drainage are in, and compacted rather than simply pushed back.
Local conditions
The lower Cowichan sits on three stacked sand and gravel aquifers with median well depths of about 8, 23 and 43 metres, separated by lower-permeability layers of silt, clay and till. For a foundation dig the top one is what matters: unconfined, highly transmissive, and holding water at a median of 2.4 metres below surface. One provincial observation well near Duncan swings about 3.1 metres between its winter high and its summer low. There is a second thing to expect on developed floodplain lots — the provincial aquifer mapping notes fill material where land has locally been built up, which is not the same as undisturbed ground.
In practice
- Situation
- A replacement foundation on a lot near the Cowichan River floodplain, excavated in late autumn.
- Complication
- Groundwater in that aquifer is shallowest from November through January, and the dig was specified deeper than 1.2 metres.
- Resolution
- The excavation was benched rather than cut vertical, spoil was set back from the edge, and the dig was sequenced so the hole stood open for the shortest time the concrete schedule allowed.
People also ask
How deep does a footing excavation have to be?
Depth comes from the structural drawings, not from a rule of thumb. What the OHS Regulation sets is the safety threshold: any excavation over 1.2 metres that a worker enters must be sloped, benched or shored.
What happens if the dig hits rock?
The machine changes. Rock is broken with a hydraulic breaker on a larger excavator rather than dug, which is a different rate and a different timeline. Near-surface bedrock under a metre is mapped across most of the Malahat Ridge area, so it is a live question south of the valley floor.
Is a building permit required before excavating?
For a new building in the CVRD electoral areas, yes — a permit is required before construction, and the application requires the site plan, land title search and any riparian or Agricultural Land Commission confirmations up front. The City of Duncan states that a building permit, when required, must be issued before any work can take place.
Serving nearby communities
Keep exploring
- Compare excavation costsTODO: cost guide blurb.
- Permits and setbacksTODO: permits guide blurb.
- Lot Clearing and GradingBrush, stump and topsoil removal, then grading to drawing levels across the Cowichan Valley. CVRD recycling centres do not accept stumps or land-clearing debris.
- Perimeter Drains and DitchingPerimeter drains, ditching and service trenches across the Cowichan Valley, where groundwater on the valley floor sits at a median of 2.4 metres.
- Duncan Excavating home
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Duncan Excavating quotes excavation across the Cowichan Valley after a site visit.