You have several possible routes: change the existing house, add a self-contained home on the same property, or plan for two separately titled properties. Each solves a different problem. This guide helps you compare them, test your site and avoid decisions that are hard to undo.
Chester brings planning, surveying and engineering together to assess what your property can support. Use this guide to form a clear brief before you spend money on a building design or order a prefabricated home.
01
Choose the outcome before the building
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| If the family needs… | Start by testing… | Keep in mind… |
|---|---|---|
| More bedrooms or an accessible bathroom within one household | An alteration or extension | One connected home can be easier to share, but less private. Work to the existing structure may be substantial. |
| Independent daily living close by | A second self-contained dwelling on the same property | A separate front door and kitchen do not create a separate title. |
| Separate ownership, or the ability to sell one home independently later | Subdivision as well as the dwelling design | The proposed boundary, access and service routes should shape where the new home goes. |
| A temporary solution | A design and ownership arrangement that can adapt | “Portable” does not remove the need to consider lawful use, site access, foundations and services. |
Two questions clarify most family conversations: Does each household need its own kitchen and bathroom? And does either household need to own or sell its home separately? If the answer to the second question is yes, investigate subdivision before fixing the position of the new building.
02
Three ways to make space
1. Alter or extend the existing house
This can work when everyone is comfortable sharing a single home but needs more room or better accessibility. A ground-floor bedroom and bathroom near the main living area may serve an older parent better than a large new bedroom upstairs. A second living area can give an adult child privacy without duplicating an entire home.
Before choosing an extension, walk through a normal week: Who uses the kitchen in the morning? Will someone need a quiet entrance after night shifts? Can a parent reach the bathroom without steps? Will the new space have enough daylight and ventilation? Check whether the proposed addition takes away the garden or parking that makes the existing home work.
An alteration also needs to connect safely to the existing building. Have a designer and builder examine the structure, roof, drainage and construction access before comparing its cost with a standalone home.
2. Add a separate home on one property
A self-contained dwelling can give each household its own kitchen, bathroom, living space and front door while keeping family nearby. This may be the simplest ownership arrangement if one person will continue to own the land and independent sale is not a goal.
Its layout must still work as two homes. Give each household a clear route from the street, a place for bins and deliveries, outdoor space it can use comfortably, and enough distance or screening for privacy. Plan who pays for power, water, internet, insurance and shared maintenance. If costs will be split, decide how they will be measured before anyone moves in.
In 2026, some new, standalone, single-storey dwellings up to 70 m² can be built without a building consent if every exemption condition is met. A Project Information Memorandum (PIM) is required before building work starts, licensed professionals must do or supervise the relevant work, and completion records must be supplied to council. The building must still comply with the Building Code. Separately, the national environmental standards may allow a qualifying detached minor residential unit without resource consent. The two tests are independent. Neither exemption gives the home its own title. Read MBIE's homeowner guide and the Ministry for the Environment's national standards before assuming a particular model qualifies.
The exemption is a route for qualifying designs, not a reason to compromise the home your family needs. For example, if a parent needs a particular level-entry shower, a different design or the building-consent route may be more appropriate: some shower designs with waterproof membranes fall outside the exemption's conditions. MBIE's detailed exemption guidance explains the conditions.
3. Create a separately titled property
Choose this route if a family member needs to own their home independently, borrow against it separately, or have a straightforward option to sell it later. Subdivision involves more than building another dwelling. Each proposed lot needs a workable relationship with the road, services, boundaries and any existing buildings, followed by the applicable approvals, survey, condition-compliance work and title registration.
If you build first and think about title later, the new house may be in the wrong place for a future boundary. A shared water line might cross the wrong lot. The driveway may be too narrow for the arrangement you later want. Show a surveyor the possible future boundary while the building location can still change. See our subdivision guide for the full route to new titles.
03
Put two homes on the plan, not just one
Take an aerial image or site plan and mark these eight things before selecting a floor plan:
- Both front doors. Can visitors find each home without walking through the other household's private space?
- The everyday paths. Draw routes for groceries, mobility aids, a pram, rubbish bins and emergency access. Consider how they work after dark and in rain.
- Windows and outdoor areas. Which bedroom or living-room windows would face each other? Where could a fence, planting or a different orientation improve privacy without blocking daylight?
- The existing home's necessities. Mark the parking, washing line, garden, storage, access and views you want to retain. Do not use the same piece of land twice in the plan.
- Water and wastewater. Find existing connections and consider the route, capacity and levels for a new home. A nearby pipe on a map is not proof of a usable connection.
- Stormwater. Identify where rainwater currently goes, including any slope or overland flow path. A new roof, driveway and retaining wall can change that pattern.
- The build route. Could a truck, crane or excavator reach the proposed location? Where would materials be stored and how would the existing household enter its home during works?
- A future boundary, if it might matter. Sketch how access and services could be separated later. You may decide against subdivision, but an early check can preserve that option.
The first drawing does not need to be accurate enough to build from. Its job is to reveal conflicts while moving a rectangle on paper is still easy.
04
Make an arrangement the family can live with
Good family relationships are helped by clear expectations. Have a conversation before design starts, then write down the answers. A designer can use the living arrangements; a solicitor can advise on the ownership and occupation documents.
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| Decide together | A concrete question to answer |
|---|---|
| Privacy | Can either household invite people over without seeking permission or interrupting the other? |
| Shared land | Who uses which part of the garden, driveway, garage and storage? |
| Money | Who pays for the build, rates, insurance, utilities, repairs and eventual removal or replacement? |
| Control | Who decides on changes to the home or land? |
| Change of circumstances | What happens if someone moves, needs care elsewhere, separates, dies or wants to sell? |
If a parent or adult child pays for a home on land owned by someone else, do not leave the contribution described only as “helping out.” Tell your solicitor whether it is intended as a gift, loan, ownership stake or payment for a right to live there, and how any repayment would work. Involve your lender if the property is mortgaged. Those decisions affect what arrangement you should build for; a building invoice does not create a separate title.
05
Compare the complete costs, not catalogue prices
A displayed price for a small home usually cannot tell you the total cost on your land. Compare options using the same end point: a lawful, finished, connected home that your family can occupy.
Swipe or scroll sideways to see every column.
| Cost area | What can be missed |
|---|---|
| Site investigation | Survey, planning advice, ground or flood assessment, locating existing services |
| Building | Design changes, foundations, delivery, crane access, decks, steps or accessible paths |
| Connections | Water, wastewater, stormwater, power, communications, trenching and reinstatement |
| Approvals and charges | PIM or consent processes, service-provider fees and any applicable development contributions |
| Existing home | Changes to the driveway, drainage, landscaping, fencing, parking or utilities |
| Living through the build | Temporary access, storage, service interruptions, accommodation or insurance changes |
| Future ownership | Survey, subdivision works and legal costs if separate title is a goal |
For an extension, allow for the condition of the existing building and the cost of joining new work to old. For a detached home, allow for reaching the site and supplying a complete second household. For subdivision, include the work after consent that produces new titles. See our project cost guide for a broader budget framework.
06
A practical order for the work
- Write a one-page family brief. Who will live where? What independence, accessibility and future ownership do they need? What must remain usable in the existing home?
- Test the land and the options. Review title, boundaries, planning, access, levels and services. Compare an extension, a same-title dwelling and separate-title route only where each could meet the brief.
- Choose a layout and approval path. Develop a concept that shows both households, then establish the relevant resource, building, PIM, service and subdivision requirements. Decide whether the 70 m² exemption genuinely fits the home you want.
- Agree the family and financial arrangement. Document contributions, occupation, shared costs and what happens when circumstances change. This should happen before major deposits are paid.
- Price and programme the whole job. Include site works, connections, changes to the existing home and the finishing milestone you actually need. If you need a separate title, programme through title issue rather than stopping at consent.
- Build and keep the records. Confirm who manages access and safety while the existing home is occupied. Keep the design, approvals, professional records and completion information together for future owners, insurers and lenders.
COMMON QUESTIONS
Questions families actually need answered
Can my parent live in a second home on my property without subdivision?
Potentially, yes. A second lawful dwelling and a separate title are different things. If you will keep one owner for the whole property, you may not need subdivision just to have a parent living independently next door. The proposed dwelling still needs to meet the applicable planning and building requirements and have workable services and access.
Start with three decisions. First, will the parent have a fully self-contained home, or share the main house's kitchen and facilities? Second, who will own and pay for the new building and running costs? Third, what happens if the parent later moves into care or the property is sold? A same-title arrangement can meet the immediate living need, but it will not let the parent sell their home as a separate property. If that matters, investigate subdivision now.
Can I build a granny flat without consent in 2026?
Some new standalone homes can avoid a building consent, and some can avoid resource consent, but you must qualify for each route separately. The building exemption is for qualifying new, standalone, single-storey dwellings of up to 70 m². It has design, siting, professional-work and documentation conditions. You must obtain a PIM before building work begins. Under the national environmental standards, a qualifying detached minor residential unit may be a permitted activity, but other applicable planning requirements still need checking. The national standards were updated in September 2026 to clarify how setbacks are measured.
Use MBIE's homeowner checklist with the actual model, foundation, services and site plan. If a condition does not fit, design for the ordinary consent path. A small prefabricated home is not automatically exempt; a sleepout without self-contained facilities is not the same thing as a dwelling.
We want to keep living in the main house during construction. How can we plan that?
Often you can, but make an occupied-site plan before the contractor starts. Draw a fenced construction zone and a separate daily route to the house. Check whether the driveway will be blocked during deliveries, whether vehicles can still reach the property, and how rubbish collection and emergency access will work. Ask for dates and notice before water, power or wastewater interruptions. Plan where pets and children will be during excavation and deliveries.
Also check whether trenching will cross the current entrance, whether a new connection means temporary changes to existing plumbing, and where noise or dust will be worst. Put temporary access, service reinstatement and damage to gardens or paving in the contractor's scope. If keeping the home liveable is essential, those are design and budget requirements, not minor details to decide once work begins.
What if my parent needs step-free access or may need more care later?
Set that requirement before selecting a kitset or compact floor plan. Look at the whole route, from parking or drop-off to the front door, bathroom, bedroom and outdoor space. A level floor inside does little good if the path from the driveway is steep or has steps. Allow room to turn with a walking aid, reach the shower and use the kitchen safely. Consider lighting and how someone could call for help.
Check the proposed bathroom against the chosen approval path. Some level-entry shower designs requiring a waterproof membrane do not meet the granny-flat building exemption conditions. If the accessible design you need calls for a building consent, follow that route rather than trading away a useful bathroom to fit an exemption. An alteration to the main house may also be a better answer if close daily support matters more than a separate front door.
Could our adult child pay for the new home and own it later?
They can contribute money, but payment for construction does not itself create a separate Record of Title. If separate ownership is the aim, test subdivision before placing the building. A future boundary needs to leave both homes with appropriate access and services, and the title process has costs and conditions beyond the build.
If you plan to build now and transfer ownership later, put the financial arrangement in writing before spending: is the contribution a gift, loan or proposed purchase? What if subdivision is refused or costs more than expected? What if either party wants to move before titles issue? Ask your solicitor and lender to structure the arrangement around the actual property and mortgage. The practical design task is to preserve a viable separate-title layout if that is the agreed goal.
Can we rent the second home to someone else later?
Often that is worth keeping as an option, but design and document it as a genuine independent home now: safe access, privacy, usable outdoor space, clear utility arrangements and sufficient services. Check any consent or title conditions that affect occupation. A future rental will also need to meet the legal requirements that apply to rental homes, including the healthy homes standards.
If rental income is part of the financial case, do not assume an informal family arrangement gives a reliable market rent. Ask a property manager for a realistic rental view based on the finished design and its access, size and location. Keep the family decision sound even if you never rent it out.
Is an extension cheaper than a small standalone home?
There is no reliable answer from floor area alone. An extension can become expensive where it requires new foundations beside old ones, roof changes, structural alterations, or substantial work while the family lives in the house. A standalone home's advertised shell or package price can leave out delivery, foundations, drainage, power, landscaping and changes to the driveway.
Create two like-for-like budgets that end at the same outcome: a finished, occupied space meeting the family's brief. Have a designer or builder test the extension and a site professional test where the standalone home and services could go. If one option lacks a key feature, such as step-free access or independent living, it is not a cheaper version of the same solution.
Can we put a portable or prefabricated home in the backyard first and deal with the paperwork later?
Treat the home and the site as one project from the beginning. Check whether the proposed unit is a dwelling, how it will be founded and connected, whether a truck or crane can deliver it, and which approvals apply before paying a deposit. The word “portable” does not resolve those questions. Nor does a promise that the home is “granny flat compliant” establish that your particular site and installation qualify for an exemption.
Ask the supplier for plans, dimensions, weight, foundation assumptions, service requirements and the exact scope of its price. Check those against the property. If the preferred model needs a change that takes it outside the exemption, allow for the appropriate consent route before ordering.
YOUR NEXT STEP
Start with the family arrangement you want to protect
Send Chester your address, who the space is for, whether you need one or two titles, and anything that must remain in the existing home. If you have a preferred plan or prefabricated model, include it with the supplier's specifications. We can help identify the site and approval questions that should be settled before detailed design or a deposit.
Discuss your family housing optionsContinue with building or extending, understanding your site and subdividing your property.
