Building Consent Site Plan for a Home Extension in New Zealand

A building consent site plan for a home extension in New Zealand needs to show exactly where the new extension will be built, how it connects to the existing house, and how it affects the rest of the property.

For council, a home extension is not just an extra room on the back or side of a house. It can affect structure, foundations, drainage, roofwater, setbacks, site coverage, services, access, floor levels, and existing buildings. A clear site plan helps council understand the proposal before building work starts.

This guide explains what to show on a home extension site plan for building consent in New Zealand, why existing and proposed plans matter, and how to avoid common drawing mistakes that can delay an application.

Do You Need Building Consent for a Home Extension in New Zealand?

In many cases, yes. A home extension usually changes the building footprint, external walls, roof, structure, foundations, drainage, or services. That kind of work often needs building consent.

Building Performance explains that all building work in Aotearoa New Zealand must comply with the Building Code, and that building consent is often needed unless the work is low-risk and exempt under the Building Act. It also notes that local councils can advise whether district or regional plans require resource consent or other permits. Building Performance

Even if part of the work seems minor, a connected extension to an existing house should be checked carefully. Adding new floor area is usually more complex than a detached small structure because the extension must connect safely and weathertightly to the existing building.

What Is a Home Extension Site Plan?

A home extension site plan is a top-down drawing of the property. It shows the existing house, the proposed extension, the property boundaries, setbacks, drainage, driveway, services, easements, and other important site details.

It is different from a floor plan. A floor plan shows the internal layout of the rooms. A site plan shows where the extension sits on the land.

A home extension site plan helps council understand:

• Where the proposed extension will be added
• How it connects to the existing house
• How close it is to boundaries
• Whether it affects drainage or stormwater
• Whether easements or services are nearby
• Whether access, parking, or driveway layout changes
• Whether the plan matches floor plans, elevations, sections, and engineering drawings

What a Building Consent Application Usually Includes

A site plan is only one part of a building consent application. Building Performance says a building consent application must include information such as the location of the building work, a description of the work, any change of use if applicable, estimated value of the work, previous consents if applicable, and subdivision details. Building Performance

For a home extension, supporting documents may also include floor plans, elevations, sections, foundation details, bracing plans, drainage plans, specifications, engineering, and other project-specific information.

Christchurch City Council explains that if building work requires building consent, the applicant needs to complete the application and provide the required information and documents. Christchurch City Council

Why the Site Plan Matters for a Home Extension

A home extension changes the relationship between the house and the site. Council needs to see how the extension fits within the section and whether it affects nearby boundaries, structures, drainage, services, or site constraints.

If the site plan is unclear, council may ask for more information before the application can move forward.

The SIMPLI Guide to Building Consent Application says an incomplete application or lack of supporting information means an application cannot be accepted for processing. SIMPLI Guide to Building Consent Application

1. Property Boundaries and Dimensions

The site plan should show the full property outline. This includes the front, rear, and side boundaries. Boundary dimensions should be included where available.

Council uses property boundaries to check the location of the proposed extension, setbacks, site coverage, height-to-boundary issues, access, and relationship to neighbouring properties.

What to Show

• Full lot outline
• Front, side, and rear boundaries
• Boundary dimensions where available
• Street frontage
• Street name and property address
• Lot and DP number if available
• North point and scale

If the site is irregular, narrow, sloping, on a corner, or has a shared driveway, the boundary layout should be especially clear.

2. Existing House and Structures

A home extension site plan should show the existing house clearly. It should also show other structures that may affect the extension or the site layout.

What to Show

• Existing house footprint
• Existing garage, carport, shed, or sleepout
• Existing deck, patio, veranda, or pergola
• Existing driveway or accessway
• Existing fences or retaining walls if relevant
• Existing paved areas and outdoor living areas if relevant
• Existing stormwater pits, drains, or service locations if known

Showing the existing layout helps council compare what is already there with what will change after the extension is built.

3. Proposed Extension Location

The proposed extension should be clearly labelled. Council should not have to guess which part of the drawing is new.

Use a label such as “Proposed Extension” or “Proposed Bedroom Extension.” If the project includes a kitchen extension, living room extension, side extension, rear extension, second-storey addition, or open-plan living extension, label it clearly.

What to Show

• Proposed extension footprint
• Connection point to the existing house
• Extension length and width
• New external wall line
• New roof area if relevant
• Relationship to existing doors, windows, deck, driveway, or outdoor areas

Use hatching, shading, or a dashed outline to make the proposed extension stand out from the existing house.

4. Extension Dimensions

The proposed extension needs clear dimensions. A shaded area labelled “extension” may still be incomplete if it does not show the size.

What to Show

• Length of the proposed extension
• Width of the proposed extension
• Total footprint or floor area if required
• Distance from extension to existing house features
• Dimensions that match the floor plan

The site plan should match the architectural floor plans. If the site plan says the extension is 6.0m x 4.0m, the floor plan and elevations should not show a different size.

5. Setbacks to Boundaries

Setbacks are the distances from the proposed extension to the property boundaries. These are among the most important measurements on a home extension site plan.

Missing setbacks are a common reason for council requests for more information.

Setbacks to Show

• Distance from extension to side boundary
• Distance from extension to rear boundary
• Distance from extension to front boundary if relevant
• Distance from extension to other structures
• Distance from extension to easements or services if relevant

Setback rules can vary by council, zone, height, site coverage, fire separation, and district plan controls. Always check the local requirements before submitting.

6. Existing and Proposed Floor Levels

Floor levels can matter for a home extension because the new work must connect to the existing house. Council may need to understand finished floor levels, ground levels, driveway levels, and drainage fall.

What to Show

• Existing finished floor level if available
• Proposed finished floor level if available
• Ground levels or contours if relevant
• Level changes between old and new areas
• Steps, decks, ramps, or access changes
• Cut and fill areas if relevant

The SIMPLI guide says site plans for external or structural work should include items such as finished floor levels, ground contours or levels extending to boundaries, site area, distances to boundaries, and wind zone. SIMPLI Guide to Building Consent Application

7. Drainage and Stormwater

A home extension can add new roof area, new paving, new hard surface, and new drainage requirements. Council may need to see how roofwater and surface water will be managed.

What to Show

• Existing downpipes if relevant
• New downpipe locations if relevant
• Stormwater pits
• Stormwater connection points
• Drainage flow direction
• Drainage easements
• Overland flow paths if known
• Hard surface or paved areas affected by the extension

If the extension changes roofwater, stormwater, wastewater, or site drainage, council may request a separate drainage plan or plumbing and drainage drawings.

The SIMPLI guide lists plumbing and drainage drawings as a plan type for new or altered drainage, including drainage layout, stormwater indication, inspection bends and junctions, on-site drainage, council mains, and calculations for sizing downpipes where required. SIMPLI Guide to Building Consent Application

8. Easements and Services

If your property has easements or services, they should be shown on the site plan. A home extension can create problems if it is too close to drainage, sewer, stormwater, power, gas, water, or access easements.

What to Show

• Drainage easements
• Sewer or stormwater lines if known
• Water, gas, power, or fibre services if relevant
• Shared access areas
• Restricted building areas shown on title or council records
• Distance from proposed extension to easements or services

The SIMPLI guide says site-specific information is required when extending the building envelope, changing the use of a room, or for new builds, and asks whether new or changed connections are required for services such as water, stormwater, wastewater, electricity, gas, and telecommunications. SIMPLI Guide to Building Consent Application

9. Driveway, Access, and Parking

A home extension may affect access, parking, outdoor living space, driveway layout, or paths around the house. If it does, the site plan should show those details clearly.

What to Show

• Existing driveway
• Vehicle crossing
• Parking spaces if relevant
• Pedestrian access
• Access around the side or rear of the house
• Shared driveway or right of way if applicable
• Construction access if relevant

The SIMPLI guide says affected vehicle areas should show crossings, driveway levels, gradients, manoeuvring, parking, and loading areas where relevant. SIMPLI Guide to Building Consent Application

10. Site Coverage and Outdoor Space

A home extension increases the building footprint. Depending on the council and zone, this may affect site coverage, permeable area, outdoor living space, yards, outlook, or height-to-boundary controls.

What to Show

• Existing house footprint
• Proposed extension footprint
• Other structures on the property
• Driveway and paved areas
• Decks, patios, and outdoor living areas
• Site coverage calculation if requested
• Landscaped or permeable areas if requested

If the extension is large or close to a boundary, council may request additional planning information beyond the basic site plan.

11. North Point, Scale, Labels, and Legend

A clear site plan should be easy to read. The reviewer should be able to understand the existing house, proposed extension, boundaries, setbacks, drainage, services, and access without guessing.

What to Include

• North arrow or north point
• Scale or scale bar
• Street name
• Clear labels for existing and proposed work
• Legend for boundary lines, proposed work, drainage, easements, and setbacks
• Drawing title and date
• Revision number if the plan has been updated

Simple labels can prevent confusion. Use labels such as “Existing Residence,” “Proposed Extension,” “Existing Driveway,” “Stormwater Pit,” “Drainage Fall,” and “Boundary Line.”

12. Existing and Proposed Plans

For a home extension, council may need both existing and proposed drawings.

The existing plan shows the house and site as they are now. The proposed plan shows the house and site after the extension is added.

Existing Site Plan Should Show

• Current house footprint
• Existing driveway and access
• Existing structures
• Existing drainage features if known
• Existing easements and services if known
• Boundaries, north point, scale, and street name

Proposed Site Plan Should Show

• Everything important from the existing plan
• Proposed extension clearly labelled
• Extension dimensions
• Setbacks to boundaries
• Drainage and stormwater changes
• Service changes if relevant
• Access, driveway, or parking changes if relevant

The SIMPLI guide lists drawings and plans showing existing and proposed modification or new build as documentation that should be supplied for applications. SIMPLI Guide to Building Consent Application

Other Drawings Commonly Needed for a Home Extension

A site plan is important, but a home extension usually needs more than a site plan. Depending on the project, the building consent package may include several drawings and supporting documents.

Common supporting documents include:

• Existing floor plan
• Proposed floor plan
• Elevations
• Sections
• Foundation plan
• Bracing plan
• Roof plan
• Drainage plan
• Engineering drawings
• Specifications
• Product information
• Energy efficiency information if required
• Fire or accessibility information if applicable

Building Performance explains that applicants altering existing buildings need to provide information showing the proposed alteration complies with the Building Code, and that the building’s compliance with other Building Code clauses is no less than before the alteration. Building Performance

Common Home Extension Site Plan Mistakes

Home extension applications can be delayed when basic site plan details are missing or unclear.

Common mistakes include:

• Proposed extension not clearly labelled
• Extension dimensions missing
• Setbacks to boundaries not shown
• Existing house footprint unclear
• Existing structures missing
• Drainage and stormwater changes not shown
• Easements or services missing
• Floor levels or contours missing on a sloping site
• Driveway, access, or parking impacts not shown
• No north point or scale
• Site plan does not match floor plans, elevations, or engineering drawings

Home Extension Site Plan Checklist Before Submitting

Before submitting a home extension site plan for building consent, check that it shows:

• Property boundaries
• Boundary dimensions where available
• Street name and frontage
• North point
• Scale or scale bar
• Existing house clearly shown
• Existing structures shown
• Existing driveway and access shown
• Proposed extension clearly labelled
• Extension length and width
• Connection point to existing house
• Setbacks to boundaries
• Distances to other structures where relevant
• Finished floor levels, levels, or contours if relevant
• Drainage and stormwater details
• New or changed services if relevant
• Easements and restricted areas if applicable
• Driveway, access, and parking details if affected
• Clear labels, legend, and notes
• Plan matches all other submitted documents

When a Site Plan Alone Is Not Enough

A site plan helps show where the extension sits on the land, but it does not prove every part of the extension complies with the Building Code.

Council may also need detailed information about:

• Structure and bracing
• Foundations
• Roof framing
• Cladding and weathertightness
• Insulation and energy efficiency
• Fire separation
• Accessibility, if applicable
• Drainage and plumbing
• Ventilation
• Natural hazards
• Engineering or geotechnical matters

If council asks for engineering, drainage design, sections, specifications, or other documents, a basic site plan will not replace those requirements.

Final Thoughts

A building consent site plan for a home extension in New Zealand should clearly show the existing house, proposed extension, boundaries, setbacks, dimensions, floor levels, drainage, stormwater, easements, services, driveway access, north point, and scale.

The site plan should also match the floor plans, elevations, sections, engineering drawings, and written application details. A clear site plan does not guarantee building consent, but it helps council understand the proposal and can reduce requests for more information.

References

• Building Performance – Check if you need consents
• Building Performance – Apply for building consent
• Building Performance – Meeting the requirements for altering existing buildings
• Christchurch City Council – Building and renovation projects
• Christchurch City Council – Apply for a building consent
• SIMPLI – Guide to Building Consent Application