Rock breaking is one of the most common hidden costs in excavation work, and many NZ homeowners are caught off guard when it appears as an extra charge on their final invoice. The short answer is: unless your quote explicitly states that rock breaking is included, you should assume it is not. Here's how to read your quote carefully and protect yourself before the digger arrives.
Why Rock Breaking Is Usually Quoted Separately
Standard excavation quotes are typically priced on the assumption that the ground is normal soil — clay, loam, sand, or loose fill. When a machine hits solid rock, basalt, greywacke, or heavily compacted hardpan, the job changes significantly. Rock breaking requires a hydraulic hammer (breaker) attachment, which is hired or owned separately, uses more fuel, causes more wear on the machine, and takes considerably longer than standard digging.
Because the presence and depth of rock can't always be predicted before work starts, many excavators price rock breaking as a provisional or day-rate item rather than a fixed cost. This is standard practice in the NZ industry — it's not a sign of a dodgy operator.
What to Look for in Your Quote
When you receive an excavation quote, check for the following:
- Scope of works description — Does it say "excavation in normal ground conditions" or similar? This is a strong signal that rock is excluded.
- Exclusions section — Many quotes list rock, tree roots, buried concrete, or contaminated soil as exclusions.
- Provisional sums (PS) — A provisional sum for rock breaking means the contractor has flagged it as a possibility but hasn't priced it firmly. Ask what the day rate or hourly rate would be if rock is encountered.
- Fixed price vs. schedule of rates — A fixed-price quote may include rock only if explicitly stated. A schedule-of-rates quote will list separate line items for different ground conditions.
- Breaker hire costs — Some contractors own their breaker; others hire one in. Ask whether breaker hire is charged to you at cost or with a margin added.
If none of these are mentioned, ask your contractor directly before signing anything.
Questions to Ask Your Excavator
Before work begins, get clear answers to these questions in writing:
- Is rock breaking included in this quote, and if so, to what depth?
- What is your hourly or day rate if rock is encountered?
- How will you notify me before switching to rock breaking, and will I need to approve additional costs?
- Do you own a breaker, or will you hire one in? Who pays for hire?
- Is rock disposal (cartage and tipping) included, or is that extra?
A reputable excavator will be happy to answer all of these clearly. If they're vague or dismissive, that's worth noting.
Ground Investigations: Know Before You Dig
If your project is significant — a new home foundation, retaining wall, or deep drainage — it may be worth getting a geotechnical investigation done before calling for quotes. A geotech report can identify rock depth, soil bearing capacity, and groundwater, giving both you and your contractor much better information to price from.
For building work, MBIE Building Performance provides guidance on site investigations and what the NZ Building Code requires for foundations. Your local council may also have geological maps that give a rough indication of rock types in your area — worth a quick call before you start.
How Rock Breaking Is Typically Charged in NZ
While prices vary widely by region, machine size, and rock type, rock breaking is generally charged in one of these ways:
| Charge Method | What It Means |
|---|---|
| Hourly machine rate | You pay for the excavator + breaker by the hour while rock is being broken |
| Day rate | A flat daily rate for the machine and operator when breaking is needed |
| Per cubic metre | Less common; a rate per m³ of rock broken and removed |
| Provisional sum | An estimated allowance in the quote, adjusted to actual cost after the job |
Always confirm which method applies and ask for a variation approval process — meaning the contractor must get your sign-off before costs exceed a certain threshold.
Rock Disposal Costs
Don't forget that broken rock still needs to go somewhere. Rock disposal is almost always charged separately from breaking. Options include:
- Cartage to a tip — charged by the load or tonne
- Leaving on site — only practical if you have space and a use for it
- Crushing on site — rarely done for residential jobs but possible on larger sites
Ask your contractor to clarify disposal costs upfront, including current tip fees in your area, which vary by region and material type.
When to Call a Professional
Excavation involving rock breaking is not DIY territory. Operating a hydraulic breaker requires a trained and experienced machine operator, and working near existing structures, services, or boundaries carries real risk. WorkSafe NZ sets out health and safety obligations for excavation work, including requirements around underground services — always get a Dial Before You Dig check done before any excavation starts.
If your project requires a building consent (check with your local council — some excavation work may fall under Schedule 1 exemptions, but always confirm), your contractor may also need to work alongside a Licensed Building Practitioner. You can verify LBP status at Licensed Building Practitioners.
For peace of mind, find a qualified, experienced local excavator through tradedirectory.co.nz and get at least two or three quotes so you can compare what's included.
Licensed Building Practitioner (LBP)
