Foundations and geotech on a Burnaby slope lot.

Why the geotech comes before the architect

On a flat lot, the soil report follows the design — the architect draws what the owner wants, then the geotech verifies the bearing assumption. On a sloped lot we reverse the order. The geotechnical report tells us what foundation types are practical, and that constrains the structural grid, the basement layout, and the main-floor elevation. Architects who work on slope every day expect this; the ones who don't push back, and the project loses time.

A preliminary geotechnical assessment — done before full design, off a topographic survey and a couple of test pits — costs a fraction of the final sealed report and is enough to steer the architect. The full sealed report is commissioned once the building footprint is fixed and goes in with the permit submission. We walk through how to read a geotech report in a dedicated post.

What's actually in the report

A residential geotechnical report from a qualified Engineer registered with Engineers and Geoscientists BC under their professional practice guidelines follows a predictable structure. The sections that drive construction decisions:

• — Site description and slope history. Topographic context, existing structures, evidence of past slope movement. A previous landslide nearby changes the design.
• — Field investigation log. What was found at each test pit or borehole — soil type, depth, groundwater encountered, organic content.
• — Allowable bearing pressure. The number that drives footing width. Typically expressed in kPa.
• — Foundation recommendations. Spread, stepped, pile, or grade beam — with depth, embedment, and frost-protection requirements.
• — Retaining-wall guidance. Wall heights, drainage requirements, and where the geotech wants the structural engineer to take over.
• — Drainage and groundwater recommendations. Where the water is, where it needs to go, and what the perimeter drainage assembly should look like.
• — Slope-stability assessment. The conclusion the City reads first. A factor of safety of 1.5 is the residential benchmark.

The five hillside foundation types

Almost every Burnaby and North Vancouver hillside foundation we permit falls into one of these five categories — or a hybrid of two adjacent ones. The geotech selects from this menu.

Reading the report as a homeowner

You do not need to be an engineer to read a geotech report, but you do need to know what to look for. Five things every owner should check personally before signing off on the foundation design:

1. The slope-stability factor of safety. Below 1.5 is a problem; below 1.3 is a permit refusal in most cases.
2. The allowable bearing pressure. The structural engineer designs the footings to this number — if the report changes, the footings change.
3. The recommended foundation type. If the report names helical piles and the contractor's quote is for spread footings, the quote is wrong.
4. The groundwater observation. Free water at any depth above the footing changes the drainage design.
5. The slope-monitoring conditions. Some Burnaby permits require post-construction slope monitoring for one to three years — know about it before you sign.

FAQ

What's in a geotechnical report?

A site description and slope history, the field investigation (test pits, boreholes, or both), a logged subsurface profile, allowable bearing pressures, recommended foundation type and depth, retaining-wall guidance, drainage requirements, and a slope-stability assessment. The report is sealed by an Engineer registered with EGBC and submitted with the building permit.

How many investigation locations does a Burnaby residential lot need?

Most Burnaby residential geotech investigations sit between two and four test pits or boreholes, spaced across the building footprint. The number scales with lot size, slope severity, and whether bedrock depth is variable. Lots over 800 m² or with complex grade usually push to four or more.

When are helical piles or drilled piles required instead of strip footings?

When the soil cannot carry the design bearing pressure within a practical excavation depth. Marine clay, uncontrolled fill, and deep weathered material all trigger pile design. Helical piles are common in 60–120 kN loads per pile; drilled cast-in-place concrete piles handle heavier loads or where lateral capacity matters. The geotech specifies which one.

Can I get a single design-build foundation package on a slope?

Yes. Most of our hillside builds use one foundation contractor with in-house concrete, shoring, and pile capability. Splitting the work across multiple sub-trades on a sloped site reliably costs time and creates sequencing problems. The foundation contractor needs to own the work from the dirt up.

Does the foundation type affect the height calculation?

Indirectly. The foundation determines the elevation of the main floor, which determines where the roof lands relative to average grade. A deeper foundation that picks up more downhill grade can give back ceiling height upstairs. The architect and structural engineer should iterate on this together.

What's the lead time on geotechnical work?

Plan for 3–6 weeks from engagement to final sealed report. The field investigation is one day; the lab work on soil samples is 2 weeks; the engineering write-up is another 1–2 weeks. Pre-design preliminary assessments are faster (often 2 weeks) and are usually enough for the architect to start.