Quick answer
Yes. The exemption asks that the dwelling be intended for a single household, not that the household be your family — MBIE lists a holiday cottage as the same classified use. The day a tenant signs, the Healthy Homes standards attach on top of the Building Code, and in the kitchen that means extraction. The rangehood must vent to outdoors, and for fans installed from 1 July 2019 the fan and all its ducting must be at least 150mm in diameter, or move at least 50 litres per second. A recirculating rangehood alone fails. Run the duct at framing: the exemption caps roof cladding at 20kg per square metre, and cutting into a finished lightweight roof later is the expensive lesson.
Key points
- The exemption never required family occupancy — its condition is a single household, and the classified use expressly covers a holiday cottage.
- Tenanting the flat brings Healthy Homes into force on top of the Building Code, enforced by the Tenancy Tribunal rather than the council.
- The kitchen duty is extraction: vented outdoors, and for fans installed from 1 July 2019 either 150mm across fan and ducting, or 50 litres per second.
- Acceptable solution G4/AS1 already wants 50 L/s including ducting wherever there is a cooktop, so both rulebooks converge on one duct.
- Roof cladding is capped at 20kg per square metre and height at 4 metres, which is why the duct belongs in the framing programme, not the kitchen install.
Two rulebooks. One duct through the roof.
The call usually starts the same way. Someone has a back section in Te Atātū Peninsula, or a wide rear yard in Papakura, and since 15 January 2026 they can put a detached self-contained dwelling of up to 70m² on it with no building consent and no resource consent. They have sketched it. They have priced the framing. Then comes the thing they actually rang about: can I rent it out, and what does the kitchen have to do?
Yes, and more than most expect — though almost all of it lands on one component. This piece covers the kitchen end: extraction, the sink, the cooktop. For the layout itself, making a small kitchen feel bigger applies almost line for line. None of it is legal advice and the settings move, so confirm the current position with your council, your LBP and Tenancy Services.
Renting it out was always allowed
The name has done the damage. People hear "granny flat", picture a relative, and assume the exemption is conditional on housing one. It is not. MBIE’s checklist asks only that the dwelling be intended for a single household or family — a description of the classified use, Housing – detached dwelling. The guidance gives a dwelling, a holiday cottage, or a boarding house of fewer than six people as examples of that use.
Read that list again. A holiday cottage has no family in it. It has guests. The condition describes how the building is used — one household, living independently of the main house — not whose surname is on the letterbox. The exemption does not care who pays you rent. The Residential Tenancies Act cares enormously, and that is what catches people. Two side notes: planning rules for minor residential units are a separate question, and development contributions still apply.
The day a tenant signs, a second rulebook opens
Two regimes, and they do not switch on together. The Building Code applies from the day it is built, tenant or no tenant. The exemption removes the consent process, not the Code — councils may take enforcement action if they become aware a completed granny flat does not comply. You have traded a building official checking your work up front for one who might check it later, with no consent trail and no CCC to point at.
Healthy Homes is the second rulebook, and it attaches to the tenancy, not the building. All private rentals had to comply by 1 July 2025, so a tenancy starting now complies from day one. Landlords must also state the property’s current level of compliance in new or renewed tenancy agreements — your ventilation position goes in writing, signed, before you have collected a cent. Our piece on what the standards ask of a landlord’s kitchen covers the other four.
| NZ Building Code (via G4/AS1) | Healthy Homes ventilation standard | |
|---|---|---|
| When it bites | From construction — the exemption removes the consent, not Code compliance | From the day the flat is tenanted under the Residential Tenancies Act |
| Kitchen trigger | A space in a household unit containing a cooktop | A room with an indoor cooktop |
| Extraction duty | Mechanical extract fan, including associated ducting, flowrate not less than 50 L/s | Fan and all exhaust ducting at least 150mm diameter, or exhaust capacity at least 50 L/s |
| Where it discharges | To the outside | To outdoors — expressly not into a roof space or other space |
| Recirculating rangehood alone | Natural ventilation alone is not adequate for cooktop moisture under this acceptable solution | Not suitable for meeting the standard |
| Who acts on it | The council | The tenant, via the Tenancy Tribunal |
What the kitchen actually has to do
For the ventilation standard, a "kitchen" means a room with an indoor cooktop. That room needs an extractor fan — or certain continuous mechanical ventilation — venting extracted air to outdoors. For fans installed from 1 July 2019, the fan and all exhaust ducting must have a diameter of at least 150mm, or an exhaust capacity of at least 50 litres per second. Either limb will do. Both put the air outside.
The word carrying the weight is "all". Meeting it by size means the diameter must be maintained throughout, including through cornering or any change of direction. A 150mm fan feeding a 125mm elbow at the roof is not a 150mm system. If you cannot meet the size requirement you must meet the capacity requirement instead, unless an exemption applies — and capacity is measured in the real world, where advertised flow rates assume minimal ducting and fall away with length and bends. That is ducted versus recirculating rangehoods, compressed into one small building.
A quieter requirement gets missed. The living room, dining room, kitchen and bedrooms each need openable windows, doors or skylights totalling at least five per cent of that room’s floor area. In a 70m² flat the kitchen usually is the living room — one open volume. Read literally, the 5% measures against that whole combined space. Confirm the reading with Tenancy Services before the joinery schedule locks.
The Building Code got there first
Here is the part that reframes the exercise. MBIE lists G4 Ventilation among the Building Code clauses applying to granny flats built under the exemption. Acceptable solution G4/AS1 says spaces in household units containing cooktops must have mechanical extract fans installed, and those fans — including associated ducting — must have a flowrate not less than 50 L/s for cooktops. Natural ventilation alone, it adds, is not adequate.
So the Code asked for 50 litres per second, ducted out, before any tenant existed. Healthy Homes asks for 150mm or 50 litres per second, ducted out. They meet on the same duct. Build to the acceptable solution and the honest answer to "what do I have to do for Healthy Homes?" is usually: nothing extra, you already did it. The landlords who get hurt never satisfied the Code, and find out when a tenant files at the Tribunal.
One honesty about G4/AS1: it is an acceptable solution, one route rather than the only one. An alternative solution is open to you, but somebody qualified must stand behind it — and with no consent and no building official signing it off, the risk sits with you and your LBP.
| Option | Meets the 150mm size limb? | Meets the 50 L/s limb? | Verdict for a tenanted granny flat |
|---|---|---|---|
| Recirculating rangehood, carbon filter, no duct | No — nothing vents outside | No | Fails both rulebooks |
| Ducted rangehood, 150mm rigid duct, short straight run | Yes, if the diameter holds through every bend | Usually clears it comfortably | The default for a rental |
| 150mm fan reduced to 125mm at the roof penetration | No — the reduction breaks the size limb | Only if measured capacity still clears 50 L/s | The classic accidental fail |
| 150mm flexible duct, long run, several bends | On paper yes; the diameter is nominal | Often not — flow drops with length and bends | Passes a glance, fails the tenant |
| External-wall extract fan, no rangehood canopy | Depends on the unit and the duct | Depends on the unit and the duct | Legal if it meets a limb; catches less steam |
| Recirculating unit ducted outside later | Only if fan and every duct section hold 150mm | Only if rated capacity survives the run | Workable, but you are now retrofitting |
Why the duct is a framing decision
Look at what the exemption permits and the timing writes itself. Roof cladding is capped at 20kg per square metre, framing is light steel or timber, and maximum height is 4 metres above floor level.
A 20kg per square metre roof is a lightweight roof — long-run steel, most likely. That is a gift while the roofer is up there with the sheets still loose: the penetration gets cut, flashed and sealed in one visit by the person who owns the weathertightness. It is no gift afterwards. Retrofitting means opening a lined ceiling, cutting and flashing a finished roof, re-stopping, repainting, and manufacturing a leak risk on a building with no consent behind it. The 4 metre cap tightens it further.
The duct is a framing decision, not a kitchen one.
I have never once been called back because the duct was too big. It is always the other way round — 150 at the fan, 125 at the roof, and a tenant with black mould on the ceiling by the second winter.
The sink has to fall to the drain
The exemption’s plumbing conditions are less famous than the 70m² and they reshape kitchens harder. Total fixture units must not exceed 30. The main drain must be at least DN100 at 1:60 grade, branch drains at least DN65 at 1:40, upstream vents at least DN65. And the one that matters at the drawing stage: no pumped systems inside the building.
That last condition removes the escape hatch. Float the sink on an island mid-plate, find the fall is not there, and you cannot solve it with a pump and stay inside the exemption. Gravity decides where the sink goes — usually the wall nearest the outfall — and that one constraint drives the cooktop, the duct route and the whole layout. Get the drainlayer and the kitchen designer talking before the slab, the same discipline behind standard cabinetry sizes.
The kitchenette loophole, and why it fails
Someone always spots it. The ventilation standard defines a kitchen as a room with an indoor cooktop. No cooktop, no kitchen, no extract duty — fit a microwave and a jug and the problem evaporates. It does not survive contact with the exemption, which requires the dwelling to be self-contained: Code-compliant for the classified use Housing – detached dwelling, with G3 Food preparation among the clauses that apply. MBIE is explicit that sleepouts and sheds are not dwellings precisely because they lack facilities like a kitchen. Dodge the rangehood and you may argue your way out of the exemption you relied on. Bad trade.
What goes wrong
- 150 at the fan, 125 at the roof. A reducer at the penetration breaks the size limb silently, and nobody measures capacity to see if the other limb saves them.
- Flexible duct, coiled long, four bends. The advertised flow rate assumed minimal ducting; what reaches the roof is a fraction, and the shortfall shows up as condensation.
- Ducted into the roof space rather than through it. Expressly non-compliant, and a reliable way to rot your own framing.
- The appliance pack picks the rangehood. The recirculating unit is cheapest because it has no duct, and no duct is the entire problem.
- The duct is left to the kitchen installer. By then the roof is on and the ceiling lined, so you are paying trade rates to undo finished work.
- Nobody owns the penetration. It falls between the roofer’s scope and the kitchen contract, so it is in neither, and gets cut by whoever is on site when it turns urgent.
What to ask before you sign
- Is the rangehood ducted to outside, and what is the internal diameter at the fan, at every bend, and at the roof penetration?
- If we are relying on capacity rather than diameter, what is the rated figure, and what do you expect after this duct run and these bends?
- Who cuts and flashes the roof penetration — the roofer’s scope, or the kitchen contract? Get it in writing.
- Where does the kitchen waste fall to, and does it get there without a pump inside the building?
- Is the extract fan in the kitchen contract or the building contract — and if it is neither, who is buying it?
Frequently asked questions
Can I rent out a granny flat built under the consent exemption, or must it house family?
You can rent it out. The exemption’s condition is that the dwelling is intended for a single household or family — a description of the classified use, Housing – detached dwelling, not of the occupants’ relationship to you. MBIE gives a holiday cottage and a small boarding house as examples, and neither houses family. Planning rules under the Resource Management Act are a separate question for your council.
Does a recirculating rangehood meet the Healthy Homes standards in a granny flat?
No, not on its own. Tenancy Services states that recirculating extractor fans, or fans that do not ventilate to the outdoors, are not suitable for meeting the healthy homes ventilation standard. Such a unit can comply if external ducting is added so it vents outside and meets either limb. Doing that after the roof is on costs far more than ducting at framing.
What size rangehood duct do I need for a rental kitchen in New Zealand?
For fans installed from 1 July 2019, the fan and all exhaust ducting must have a diameter of at least 150mm, or an exhaust capacity of at least 50 litres per second, venting to outdoors. Relying on the size limb means holding 150mm throughout, including through corners — a reducer at the roof breaks it. Acceptable solution G4/AS1 separately asks for a mechanical extract fan, including its ducting, of not less than 50 L/s for cooktops.
If I fit a microwave and no cooktop, do the kitchen ventilation rules still apply?
The ventilation standard defines a kitchen as a room with an indoor cooktop, so a cooktop-free room falls outside that trigger. The catch is that the exemption requires the dwelling to be self-contained and Code-compliant for a detached dwelling, with G3 Food preparation among the clauses that apply. MBIE says sleepouts and sheds are not dwellings precisely because they lack facilities like a kitchen — so removing the cooktop to avoid a duct risks removing your basis for the exemption.
Can I vent the rangehood out a wall instead of through the roof?
Yes — the requirement is that extracted air reaches outdoors, not that it goes through the roof. A short run straight out an external wall is usually better engineering, since fans vented directly through a wall or with minimal ducting are likeliest to achieve their advertised flow rates. Whether the wall works depends on where gravity puts your sink and therefore where the cooktop lands.
Get the kitchen priced before the framing is booked
A granny flat kitchen is a short kitchen. A galley or a compact L, no scullery — which is why the numbers sit at the bottom of the range: a durable rental-grade fitout lands in the lower five figures plus GST, supplied and installed. The duct is not what makes a kitchen expensive; cutting it in afterwards is. For the wider picture, what a kitchen costs in Auckland sets the bands, and materials that survive a rental covers what survives a tenant.
We build in East Tamaki, 23 years and 2,000-plus kitchens in, turning out ten-plus a week — so a 70m² galley is a comfortable week’s work. Supply and install come under one contract and one invoice, which on a consent-exempt build matters more than usual: there is nobody to arbitrate a gap between two contracts. Send the scope — a rough sketch is enough — and you will have a trade-priced number back inside 24 hours. Tell us where the duct is going while you are at it.