Can I Do a Basic Feasibility Study for a Minor Dwelling Myself?

Yes, you can absolutely do a basic feasibility study for a minor dwelling yourself — and it's a smart first step before spending money on architects, engineers, or consents. A DIY feasibility study won't replace professional advice, but it will help you quickly assess whether your project is worth pursuing and where the major hurdles might be.

What Is a Feasibility Study for a Minor Dwelling?

A feasibility study is simply a structured way of asking: "Is this project viable — financially, physically, and legally?" For a minor dwelling (sometimes called a granny flat, secondary dwelling, or sleepout), that means checking whether your site, budget, and goals actually line up before you commit serious money.

A basic DIY version covers four key areas: site and planning rules, physical site constraints, rough cost estimates, and financial return (if applicable).

Step 1 — Check Your District Plan and Zoning Rules

This is the most important starting point. Your local council's district plan sets the rules for what you can build on your property, including:

• Whether a minor dwelling is a permitted activity in your zone (many residential zones allow them, but rules vary widely across NZ councils)
• Minimum site size requirements (often 400–600 m², but check your specific council)
• Setbacks from boundaries, maximum site coverage, and height limits
• Whether the dwelling must be for a family member or can be tenanted

Most councils publish their district plans online — search your council's website or use their GIS mapping tool. Ring the duty planner if you're unsure; most councils offer a free initial chat.

Also check whether your project needs a building consent. Minor dwellings almost always require one. Some very small structures may qualify as Schedule 1 exemptions under the Building Act, but always confirm this with your council before assuming — the rules are specific and getting it wrong is costly. MBIE Building Performance has clear guidance on consent exemptions.

Step 2 — Assess Your Site's Physical Constraints

Walk your section with fresh eyes and note:

• Available footprint: Where could the dwelling physically sit while meeting setbacks?
• Slope and ground conditions: Steep or unstable ground significantly increases foundation costs
• Access: Does the site have (or can it get) a compliant vehicle access point for the new dwelling?
• Existing trees or covenants: Protected trees or title covenants can block or complicate development
• Flood or hazard overlays: Check your council's GIS maps for any natural hazard designations

For anything beyond a flat, straightforward section, you'll want a geotechnical assessment or surveyor's input before going further.

Step 3 — Rough Cost Estimate

This is where a DIY study has real limits, but you can still build a useful ballpark. As a broad guide only, minor dwellings in NZ typically range from around $150,000 to $350,000+ depending on size, specification, site difficulty, and region — but costs vary enormously and have shifted significantly in recent years. Treat any figure you find online as a starting point only.

Break your estimate into categories:

For a more reliable number, a quantity surveyor (QS) can provide a preliminary cost plan at an early stage — this is money well spent before you commit to design fees. You can find local QS professionals on tradedirectory.co.nz.

Step 4 — Financial Return and Viability

If you're building to rent, compare your estimated total project cost against likely rental income. Check current rental market rates in your area via Trade Me Property or similar. A simple calculation:

• Gross yield = (Annual rent ÷ Total project cost) × 100
• A gross yield of 5–7% is often considered reasonable in NZ, though this varies by location and your financing costs

If you're building for a family member or to add value for resale, the calculation is different — consider getting a registered valuer's opinion on the likely uplift in your property's value.

Also factor in ongoing costs: rates, insurance, maintenance, and if tenanted, property management fees and compliance with the Healthy Homes Standards.

Step 5 — Identify the Showstoppers Early

A good feasibility study surfaces the deal-breakers before you spend money. Common showstoppers include:

• Wastewater capacity: Your existing system may not handle an additional dwelling. Check with your council and a licensed drainlayer
• Title covenants: Some titles prohibit additional dwellings entirely
• Easements: Services or access easements may limit where you can build
• Heritage or character overlays: These can restrict design and add cost

When to Call a Professional

A DIY feasibility study is a great filter, but bring in professionals before making major commitments:

• Quantity surveyor: For a reliable cost plan and value management advice
• Architect or designer: To test what's physically possible on your site within the rules
• Licensed building practitioner: For construction advice — find one at LBP
• Licensed drainlayer or plumber: Wastewater and water connections are restricted work under the Plumbers, Gasfitters and Drainlayers Act and must be carried out by a licensed professional registered with the PGDB
• Registered electrician: All electrical connection work is restricted work and must be done by a registered electrician — check EWRB
• Registered valuer: For an independent view on value uplift

For a project of this scale, a qualified QS or project manager found through tradedirectory.co.nz can save you far more than their fee by catching cost blowouts early.

Sources & Further Reading

• MBIE Building Performance — Consent Exemptions
• BRANZ — Building Research
• Tenancy Services — Healthy Homes Standards
• Licensed Building Practitioners
• Plumbers, Gasfitters and Drainlayers Board
• Electrical Workers Registration Board