G-05 Draft guide · review pending
How to build a complete granny flat budget in New Zealand
Build a whole-project budget from dated property-specific quotes, explicit exclusions and the professional, council, site and owner costs around the building contract.
Representative design only.
Source: Ready to Build
Build the budget from the whole project
A useful budget combines the building quote with the property, council, network, professional and owner-side costs needed to reach a documented finished dwelling. Use dated written figures for the actual property and keep uncertain items visible.
Compare the same whole-project scope
Record the property, council, floor area, dated design version, specification, quote date, programme and GST treatment. Then mark every cost as included, excluded, provisional or not yet quoted.
Whole-project quote comparison
| Cost group | What to compare | Status |
|---|---|---|
| Plans and design | Licence, drawings, engineering, revisions and as-builts | Confirm |
| Property investigations | Title, survey, ground, hazards and service capacity | Confirm |
| Council and infrastructure | PIM, extra processing, connections and contributions | Confirm |
| Professional services | Design, engineering, surveying, QS and monitoring | Confirm |
| Site preparation | Access, excavation, retaining, remediation and temporary work | Confirm |
| Foundations and building | Specification, finishes, preliminaries, margin and GST | Confirm |
| Utilities and drainage | Capacity, provider fees, trenching, meters and certification | Confirm |
| Owner-side work | External works, legal, finance, insurance and moving costs | Confirm |
| Contingency | Set only after known exclusions and risks are visible | Confirm |
Property and council costs
Allow for site investigations, the PIM, extra council processing, service connections and any development contribution. Ask the relevant council and providers for written property-specific figures rather than treating one council example as a national allowance.
Design, construction and evidence
Define the foundation, structure, envelope, finish level, utilities, external work, professional monitoring and records included in the price. Council does not carry out routine inspections for exempt work, so agree who checks the work and what evidence they supply.
Finance, insurance and contingency
Speak to the lender and insurer early and keep contingency separate from known quotes and provisional sums. Borrowing, cover, contracts and universal contingency percentages require appropriately scoped professional advice.
Next step
Check the cost drivers on the actual property
Ground, access, hazards and service connections can change the project scope before construction starts.
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