Do You Need a Geotechnical Engineer for Your New Build or Renovation?

Kyle Nicholson - Team Leader

We get asked this all the time by homeowners, architects, and developers, usually just before submitting for building consent:

“Do I actually need a geotechnical report or soil test?”

If you’re planning a new build or major renovation in Wellington, Lower Hutt, the Kāpiti Coast, or Wairarapa, the answer is often yes.

In many cases, councils will require a geotechnical report — sometimes called a site investigation report or foundation soil test — before they’ll approve your plans.

The requirements aren’t always straightforward. Some sites only need a desktop review of existing information. Others require a full on-site investigation with soil sampling and strength testing. The right approach depends on your site’s specific conditions, which often can’t be confirmed without a visit from a geotechnical engineer.

In this guide, we’ll explain:

• When a geotechnical engineer or soil test is required

• Why councils care about ground conditions

• What can go wrong if you skip the process

• What’s included in a geotechnical report

It's not just about soil. It's about risk

A geotechnical engineer looks at what’s happening under the surface. Things like:

• Soil strength and type

• Risk of liquefaction or settlement

• Slopes and landslide potential

• Groundwater conditions

• Bearing capacity for your foundations
  

That information goes into a geotechnical report, something councils often require before they’ll issue consent for new builds, major renovations, subdivisions, or retaining walls.

Checking the soil conditions is vital for any new build or house addition

When is a Geotechnical Engineer / Report required in New Zealand?

In Wellington and much of New Zealand, your project will likely need a geotechnical report if it falls into any of these three key categories:

Sloping sites over 5°

If your site has a slope greater than 5 degrees (roughly 1:11), you’re officially in geotech territory. This is especially true if you’re:

• Building near the edge of a slope

• Excavating into the hillside

• Planning a retaining wall

• Adding a deck, extension, or second storey

Sloping sites increase the risk of ground movement, landslips, and differential settlement — all of which must be accounted for in both foundation and retaining wall design.

Wellington suburbs like Brooklyn, Karori, Ngaio, Wadestown, and Northland often trigger this requirement automatically.

Liquefaction-prone zones

Many parts of the Wellington region sit on soils that may liquefy during an earthquake. These areas include:

• Petone and Seaview

• Lower Hutt Valley

• Porirua Basin

• Lyall Bay and Kilbirnie

• Parts of Paraparaumu and Raumati

Councils will require a geotechnical report for most new builds or additions in these areas. The risk is too high to ignore — and if your LIM flags it, your engineer will need to respond with foundation design that mitigates those risks.

Filled or reclaimed land

If your site is on old fill, demolition rubble, or reclaimed coastal land, the strength and consistency of the soil is unpredictable. This can lead to:

• Uneven settlement

• Increased earthquake risk

• Unexpected foundation costs during construction

Red flag areas in Wellington include parts of Lyall Bay, Kilbirnie, Petone, and many older subdivided sections.

Liquifaction potential of the Greater Wellington Region, including Wellington, Waiarapa, Kapiti Coast, and Lower Hutt

While the three above are the most frequent and serious, you’ll also likely need a geotech report if:

• You're adding new foundations or a basement

• You're subdividing your section or adding multi-unit housing

• You're building retaining walls over 1.5m, or closer than 1.5m to a building

• Your builder or architect flags soft, wet, or unusual ground on site

• Council specifically requests a “site-specific geotechnical investigation”

What happens if you skip the geotech report?

You could delay your consent. Or worse, get declined until the report is submitted.

Even if your consent goes through without one, not doing proper ground investigations upfront can lead to:

• Foundation problems later (e.g. cracking, movement)

• Unplanned cost blowouts during construction

• Expensive redesigns if the soil isn’t suitable
  

And if you’re planning to sell one day, buyers (and their lawyers) will want to see that geotechnical risk has been properly managed.

What is included in a Geotechnical or Site Investigation Report?

We tailor our reports based on what’s needed — no more, no less. But typically they include:

• Desktop study (history of the site, previous investigations)

• On-site investigation (hand auger or cone penetrometer)

• Soil classification and bearing capacity

• Foundation recommendations

• Slope stability or retaining wall advice (if needed)
  

And we design it with building consent in mind — meaning your council reviewer doesn’t have to come back with lots of questions.

A Typical Site Soils Investigation with Dynamic Cone Penetrometer Test

Typical costs for Geotechnical report and Soil Testing in Wellington

We get this one a lot. It really depends on what the council requires and how complex the site is.

Typical ballpark:

• $1,000–$1,500 for a basic desktop report

• $1,500–$6,000 for a site soils investigation with hand auger or Dynamic Cone Penetrometer

• $6,000+ for large or complex hillside/multi-unit projects

We’ll always give you a fixed-fee quote before we start — no surprises.

Are Wellington councils stricter?

Sometimes, yes , and for good reason! Wellington has some of the most geotechnically complex land in the country. Many council zones are flagged for:

• Liquefaction

• Slope instability

• Flooding or poor drainage

• Fill or reclaimed land
  

Each council has their own maps and overlays (e.g. Wellington City, Hutt City, Porirua, Kapiti Coast), and they’ll often require a geotech report even for minor projects if your site falls in a flagged zone.

Why working with a team that does both Structural and Geotechnical Engineering helps

A big advantage of working with us?

We do both geotechnical and structural engineering. In-house or through long-standing partnerships , which means less back-and-forth for you, and a much smoother consent process.

Here’s what that looks like in practice:

• We know what geotechnical details your foundation designer will actually need

• We can align site investigations with the structural scope from day one

• If the soil requires adjustments to the design, we can make those changes quickly and in-house

• We often pre-empt council questions by coordinating both reports upfront
  

In short, it’s more efficient, and more cost-effective, to have the same team handle both parts of the equation. You get aligned advice, faster turnaround, and fewer surprises later on.

Need advice before you apply for consent?

If you’re unsure whether your project needs a geotechnical report, it’s best to ask early, we can usually give you a straight answer in one quick phone call.

We’ve delivered structural and geotechnical design across Wellington for decades. Whether you’re working with a sloped site, building near the coast, or just need to meet council consent requirements, we can help, and we can often handle the entire engineering package in-house.

Email us now!

Give us a call on 04 475 7933

About the Author

Kyle Nicholson is a senior chartered professional engineer with over 15 years of experience in New Zealand, particularly in retaining wall design and slope stability assessments. He has collaborated with architects and building owners on providing comprehensive geotechnical reports