The 2-metre rule that quietly redraws every granny flat design

Figure 3 from Granny flat Exemption Guidance

Recent Building Act changes introduce a building-consent exemption pathway for certain small standalone dwellings (commonly called granny flats), provided the specific exemption conditions are met (including notification and documentation requirements) and the work is carried out to comply with the Building Code.

Most people focus on the headline (no building consent). In practice, the design conversation usually turns on one condition that can make or break feasibility on a real site:

The exemption guidance commonly describes a minimum separation of 2 metres from any legal boundary and 2 metres from other residential buildings (subject to the definitions and measurement rules in the current guidance).

That single line is what often determines whether a “nice-to-have” layout becomes an awkward compromise—or a clean, buildable solution.

What the rule actually says (and how it’s measured)

In MBIE’s exemption guidance, the separation requirement is stated plainly:

“Two metres or more away from any other residential building or any legal boundary.”

Setbacks are measured from the legal boundary to the building as defined in the exemption guidance—so you shouldn’t rely on fence lines or assumed boundaries where accuracy matters.

This is why the 2 m rule is not just a planning-style “setback”—it’s a practical geometric constraint that affects:

• maximum possible footprint width and length
• where doors, decks, and services can go
• how you thread access around an existing home

Why “2 metres from existing buildings” is the real sting

The “2 m from boundary” part is easy to understand. The real catch on many sites is the second half:

2 metres from any other residential building

In many typical sites, that means maintaining a minimum 2 m separation from the existing dwelling on the same site (and from any other residential building), as interpreted under the exemption definitions.

So even if you have a generous backyard, you can’t always tuck the unit close to the main house to make the site “work” (for example, to preserve a driveway or avoid an easement). In effect, the exemption tends to require a clear separation corridor between the two.

Design consequence: you don’t just draw a boundary setback; you also draw a “no-build halo” around the existing dwelling. On compact sites, those halos collide—leaving an oddly shaped leftover patch that can dictate the plan more than your brief does.

How the 2-metre rule reshapes the configuration

1) It sets the maximum building width before you even start designing

If a site area allows a granny flat “somewhere,” the usable rectangle is still reduced by setbacks.

Illustrative example only:
Say the available “slot” between boundary constraints is 12.0 m wide. Less 2.0 m on the left boundary and less 2.0 m on the right boundary means the maximum theoretical building width becomes 8.0 m—before you account for driveways, turning, services, outdoor living, easements, or other constraints.

If the site is narrower—or you need vehicle access down one side—your workable width can quickly drop into the 5.5–6.5 m range, which heavily influences:

• corridor vs open-plan efficiency
• bathroom/laundry stacking
• whether you can do two bedrooms without a “railway carriage” feel

2) It pushes you toward long, shallow footprints

Because width is often the first casualty, designers typically respond with:

• longer rectangles (e.g., ~9–11 m long)
• tighter service spines
• fewer plan “jogs” (which consume width fast)

This is why many exempt granny flats end up as simple bars: it’s not aesthetic minimalism—it’s setback math.

3) It changes where the front door wants to be

The 2 m separation zone between buildings is tempting to use as:

• a walkway
• a services run
• an access path to keep the backyard functional

But that can also create a “back-of-house” arrival experience unless you deliberately shape:

• entry orientation
• lighting and privacy screening
• a small outdoor threshold that feels intentional

4) It affects decks, steps, and outdoor living (even when the rule talks about the building)

Even where separation is expressed in terms of the building, in practice you still have to think carefully about:

• eaves and gutters
• maintenance access
• overland flow paths and stormwater detailing
• how you keep water and overflow away from tight side yards

The “2 m corridor” quickly becomes multi-purpose: access + drainage thinking + maintenance + privacy buffer.

5) It interacts with other exemption “shape controls”

The exemption isn’t just about distance. It also includes other limitations and conditions that need checking in the current guidance before finalising massing and layout, such as limits relating to height, storeys, and construction approach (refer to the current guidance for the exact values and definitions), along with other construction conditions intended to keep the build “simple.”

That matters because when setbacks squeeze footprint options, people often try to “go up” or add split-level cleverness—exactly the kind of moves the exemption is designed to avoid.

The practical site-planning workflow that works

If you want to avoid redesign loops, start with a blunt feasibility overlay:

1. Confirm the legal boundary (preferably from a survey/base plan where accuracy matters).
2. Draw a 2.0 m offset inside all boundaries.
3. Draw a 2.0 m buffer around the existing dwelling (and any other residential building).
4. Only then test footprints (bars, L-shapes, corner placements), and check whether:
• the access/parking strategy still works
• services can connect sensibly
• outdoor space isn’t reduced to leftover strips

This approach makes the constraint visible early—before anyone emotionally commits to a plan that only works by “cheating” the separation.

Don’t confuse “building consent exempt” with “everything exempt”

Two reminders that stop nasty surprises later:

• The exemption is about building consent only—work still needs to comply with the Building Code, and there are notification/documentation steps to follow under the exemption conditions.
• Resource consent is a separate track. Whether planning approval is required depends on the district plan/NES settings, zoning, overlays, servicing, and site specifics—confirm with a planner or council before relying on any exemption pathway.

The bottom line

The new granny flat pathway is available in principle—and it can simplify delivery—but the 2-metre separation requirement is the condition that most directly shapes what you can physically fit on a site.

Treat it as the starting geometry of the project, not a compliance footnote:

• 2 m to boundaries defines the outer frame
• 2 m to the existing house defines the internal “no-build corridor”
• what remains dictates the plan typology (often long, simple rectangles) more than personal preference does

Footer: General information only, not legal or council advice—confirm requirements with your council/planner and verify boundaries by survey before committing to design or construction.