Why asking the right questions matters
A retaining wall can look straightforward from the outside, but in New Zealand it often involves drainage, excavation, soil conditions, site access, and sometimes council approval. A wall that is poorly designed or built can fail under pressure, create drainage problems, or affect neighbouring properties.
Before you sign anything, use the questions below to check whether a retaining wall builder is experienced, properly insured, and realistic about what your project needs. The aim is not just to find the cheapest quote, but to find a builder who can deliver a wall that is safe, compliant and fit for purpose.
1. What retaining wall projects have you done recently?
Start with experience. A builder who regularly works on retaining walls is more likely to understand soil movement, drainage, excavation and the practical challenges of NZ sites.
Ask:
- What types of retaining walls do you build most often? - Have you built walls similar to mine in height, length and site conditions? - Do you work on new builds, renovations, sloping sections, or boundary walls? - Can you show photos of recent completed jobs? - Have you worked in my suburb or area before?
Why this matters in NZ: many sites are exposed to heavy rain, soft ground, clay soils or steep sections. A builder who understands local conditions is better placed to spot issues early and recommend the right solution.
2. Do I need council consent or engineering sign-off?
This is one of the most important questions to ask early. In New Zealand, some retaining walls need building consent from the local council, and some may also need a chartered professional engineer to design or certify them.
Ask the builder:
- Do you think this wall needs building consent? - Will you help me work out what the council requires? - Will you provide or arrange the drawings and engineering documentation if needed? - Have you built walls under consent before?
As a general rule, retaining walls over 1.5 metres high usually need building consent, but there can be other triggers too, especially if the wall is supporting a load, close to a boundary, or affecting drainage or nearby structures. Councils can also have local rules, so don’t rely on a general rule of thumb alone.
If a builder tells you consent is not needed, ask them to explain why and check with your council yourself if you’re unsure.
3. Are you licensed or qualified for the work involved?
Retaining wall construction itself is generally building work rather than restricted trade work, so there is no national licence specific to retaining wall builders in the way there is for electricians or gasfitters. However, the people working on your project may need other qualifications depending on the job.
Ask:
- Are you a Licensed Building Practitioner (LBP), if the work requires it? - Who will actually be on site each day? - Will any electrical, plumbing, gasfitting or drainlaying work be done by separately licensed tradespeople? - If drainage, stormwater or wastewater connections are needed, who will handle those?
If the project includes electrical work, it must be done by an appropriately authorised person. Plumbing, gasfitting and drainlaying are restricted trades under the Plumbers, Gasfitters and Drainlayers Board (PGDB). Make sure the builder is not offering to do work outside their scope or handing it to unqualified subcontractors.
4. Are you insured, and what does your insurance cover?
Insurance is a key protection if something goes wrong during the job.
Ask for the details of:
- Public liability insurance - Contract works insurance, if applicable - Vehicle and equipment insurance - Any professional indemnity cover, if design advice is included
Ask them to confirm:
- What the policy limits are - Whether subcontractors are covered - Whether the cover is current - Whether you can sight a certificate of currency
Don’t assume a builder is insured just because they say they are. A reputable contractor should be able to provide proof. If the wall is being built near a driveway, neighbouring property, or existing structures, insurance becomes even more important.
5. What exactly is included in your quote?
Quotes for retaining walls can vary a lot because one builder may include excavation, drainage, disposal, materials and engineering, while another only prices the labour.
Ask for a written quote that clearly sets out:
- Wall length, height and type - Materials to be used, such as timber, concrete blocks, gabions or concrete - Excavation and site preparation - Drainage system and backfill details - Disposal of spoil and rubbish - Any retaining wall consent or engineering fees - Labour, equipment hire and delivery charges - GST, if applicable - What is excluded
A good quote should make it easy to compare “apples with apples”. If something is unclear, ask for it to be broken out separately.
6. What assumptions have you made about the site?
Retaining wall builders often need to make assumptions if they haven’t fully investigated the site yet. Those assumptions can affect the final price.
Ask:
- Have you inspected the site in person? - Have you allowed for excavation in hard ground, clay or rock? - What happens if you encounter unexpected fill, wet ground or buried services? - Have you checked access for machinery and deliveries? - Is the quote based on the site being clear and ready to work on?
On NZ sections, access can be a big factor. Tight driveways, steep slopes, narrow side access and wet winter ground can all affect labour, equipment and timing. If the builder hasn’t seen the site, the quote may be too vague to rely on.
7. How will drainage be handled?
Many retaining walls fail because drainage was overlooked. Water build-up creates pressure behind the wall, especially during heavy rain, which is common in parts of New Zealand.
Ask:
- What drainage system will you use behind the wall? - Will there be drainage pipe, drain coil, free-draining backfill or geotextile fabric? - Where will water go once it is collected? - Will you connect to stormwater, and if so, is that approved? - How do you prevent blocked drains or saturated soil?
A builder who cannot explain drainage clearly may not be the right person for the job. Good drainage is not an optional extra; it is part of making the wall last.
8. How long will the job take, and what could delay it?
Timelines matter, especially if your wall is holding up a driveway, garden, or boundary area.
Ask:
- What is your expected start date? - How long will the wall take to complete? - How many people will be on site? - What weather delays could affect the programme? - Will you keep me updated if the schedule changes?
In New Zealand, winter rain can slow excavation and make some sites unsafe or too wet for machinery. Spring and summer are often busy for builders, so booking early can help. If the builder promises an unrealistically quick turnaround, treat that as a warning sign.
9. Who will manage the project and communicate with me?
Good communication often makes the difference between a smooth build and a stressful one.
Ask:
- Who is my main point of contact? - Will the person quoting the work be the one supervising it? - How often will you update me? - How do you handle variations or unexpected issues? - What decisions will need my approval before work continues?
Make sure you know how changes are handled. For example, if the builder discovers poor ground conditions, they should talk to you before doing extra work that increases the cost.
10. Can I see recent references or talk to past clients?
References help confirm whether the builder is reliable, tidy, and able to deliver on time.
Ask for:
- Two or three recent references - Projects similar to yours - Before-and-after photos - If possible, addresses of completed work you can drive past
When talking to references, ask:
- Was the quote accurate? - Was the site left tidy? - Did the builder communicate well? - Were there any unexpected costs? - Would you hire them again?
You can also check online reviews, but don’t rely on them alone. A real conversation with a previous client is often more useful.
11. What guarantees or workmanship warranty do you offer?
A retaining wall should be built to last, but it’s still worth asking about guarantees.
Ask:
- Do you provide a written workmanship warranty? - What does the warranty cover? - How long does it last? - Does it cover movement, cracking or drainage issues? - What voids the warranty?
Be careful with vague promises. A warranty is only useful if it is written down and explains what is covered. Also remember that product warranties on materials are separate from the builder’s workmanship guarantee.
12. Who is supplying the materials, and what quality are they?
Material choice affects price, appearance, maintenance and longevity.
Ask:
- Are you supplying all materials? - What brand or grade of materials will you use? - Are the timbers treated for outdoor ground contact, if timber is used? - Are blocks, posts or steel components suitable for retaining applications? - Can I choose from different material options?
If the builder suggests a cheaper material, ask why it is suitable for your site. Some walls are better built in timber, others in concrete or engineered systems. The right choice depends on height, loading, drainage and appearance.
13. What could change the price after the quote?
Unexpected extras are one of the biggest frustrations for homeowners. Ask the builder to be specific about what could cause a variation.
Common cost drivers include:
- Hidden rock or unstable ground - Extra excavation or spoil removal - Changes to wall height or length - Additional drainage or engineering requirements - Restricted access requiring smaller machinery - Damage to existing structures or services
A fair builder will explain these risks clearly and tell you how any variation will be approved.
14. Compare quotes using a simple checklist
When you have several quotes, compare more than the total price.
| What to compare | What good looks like | |---|---| | Experience | Relevant retaining wall jobs, recent photos, local knowledge | | Compliance | Clear advice on consent, engineering and council requirements | | Insurance | Current proof of cover for public liability and contract works | | Scope | Detailed inclusions and exclusions in writing | | Drainage | Proper drainage design and disposal of water | | Timeline | Realistic programme with weather and access considered | | Communication | One clear contact person and written variation process | | Warranty | Written workmanship guarantee | | References | Recent clients you can contact |
A cheaper quote is not necessarily better if it leaves out consent, drainage, excavation or disposal. Missing items often become expensive variations later.
15. Red flags to watch for
Walk away or ask more questions if a builder:
- Won’t put anything in writing - Gives a quote without visiting the site - Says consent is never needed - Can’t explain drainage clearly - Pressures you to pay a large deposit upfront - Refuses to show insurance or references - Suggests doing electrical, plumbing or drainlaying work without the right licensed tradespeople - Won’t explain who is responsible for council paperwork
Trust your instincts. If communication feels vague at the quoting stage, it is unlikely to improve once work starts.
Final checks before you hire
Before you commit, make sure you have:
- At least two or three written quotes - A clear scope of work - Confirmation of any consent or engineering requirements - Proof of insurance - A realistic start date and programme - A written warranty or guarantee - Contact details for references
Asking these questions upfront takes time, but it can save thousands of dollars and a lot of stress later. A well-chosen retaining wall builder will welcome careful questions and give you straight answers.