Minor Dwellings: What To Think About When Creating A Welcoming Second Residential Unit

There are many reasons that you may want to build a second residential unit on your property. Until recently, this was very restricted and only permitted as a ‘family flat’ that had to be occupied by a family member.

This changed in Christchurch after the earthquakes, when the new Christchurch District Plan made allowance for a minor dwelling on most sites. A minor residential unit is essentially a second dwelling on the site with a floor area between 35-80m², and the family member restrictions don’t apply.

New planning rules that have been proposed in Christchurch and other large cities in New Zealand can allow for up to 3 dwellings on most residential-zoned properties. While this rule change is designed to allow for larger-scale medium-density dwellings, it also provides much more freedom for Christchurch architects when designing secondary dwellings on a site.

Note that in the wider Christchurch area, the medium-density dwelling rules may vary slightly differently between areas covered by the Christchurch City Council, Selwyn District Council and Waimakariri District Council, each of which has its own rules relating to multi-unit development. Before embarking on a residential dwelling build project, always make sure you understand the rules in your area. Overall though there is a move to make it much easier to build new houses in Christchurch and other large centres around the country, and make better use of existing residential-zoned land rather than allowing cities to keep expanding into the countryside.

What Opportunities Could Building A Secondary Dwelling Offer You?

There are plenty of opportunities that you can grasp with a secondary dwelling, such as:

A smaller home, or granny flat, for elderly parents.
A house for your children.
An investment in rental accommodation.
Short-term visitor accommodation.
Development for resale.

In this article we will discuss specific considerations for each of these types of development, as well as the most important factors you should consider when planning to build a secondary dwelling. For more information, we’ve also written about good design and construction principles for higher density housing in the past, and those principles could also be applied to secondary dwellings.

What Is Causing The Push For Increased Housing Density?

The driving factor behind the push for increased housing density is that it is a way to address several problems associated with urban sprawl, such as:

Cities that continue to spread require costly new infrastructure, such as drainage, roads and so on.
Land is a scarce resource. Land costs will remain high if rules require large minimum lot sizes for stand-alone developments.
A spreading city places new development further from the centre. This increases reliance on cars as the public transport network coverage reduces.

Medium density development can have the following positive effects that can help make new developments more sustainable:

Making better use of existing infrastructure reduces the cost of establishing new developments.
Fitting more residential units on properties allows the cost of land to be spread between several units, allowing for more affordable home ownership and promoting more sustainable use of scarce urban land.
Allowing more development in existing residential areas reduces travel times for people travelling to work, school, shops and visiting friends and family. It also allows better use of the existing public transport network.

Exploring The Different Uses For A Secondary Dwelling

As mentioned before, there are plenty of different opportunities that you can explore when creating a minor dwelling on your property, such as:

A Smaller Home, Or Granny Flat, For Elderly Parents:

This isn’t a new idea of course, and has for many generations been a popular way to support ageing parents who need to downsize and may appreciate living close to supportive family members.
Building a new unit allows for a purpose-designed home that exceeds building code requirements and is warm and dry. This is much more appealing than downsizing into an older house that often requires alteration work and maintenance to bring it up to an acceptable level.
By considering accessibility, ease of maintenance and designing for the sun, it is possible to create a beautiful home that is safe and easy to live in.

A House For Your Children:

Younger generations are faced with increasing barriers to home ownership, with many people wondering if they will ever be able to get onto the property ladder.
Building a secondary dwelling on your site can make housing much more affordable by removing the cost of a new section from the equation. This can be a very affordable way to achieve a new build house.
By building new, your children will be able to live and raise their families in a modern house that is warm and comfortable, rather than being stuck with an older home that is expensive to heat and requires costly maintenance. This allows them to enjoy the cost-saving features of sustainable design, which may otherwise be unaffordable in a first home.
It is also a good idea to design for future expansion – perhaps having in mind where additional bedrooms or living areas could be located.
You could consider a rent to own option for your children.
A secondary dwelling on your property would provide your children with excellent privacy.
A secondary dwelling is an excellent alternative to a tiny home – it’s something that can increase in value with the property market.
It could also act as a sleepout.

Investment In Rental Accommodation:

Building a new unit to generate rental income can be a great way of earning some income from your existing property.
By building new, you will also be able to be fully compliant with current building code requirements for insulation, double glazing and ventilation. Not only does this make the property more desirable for tenants, but it also saves you money on costly upgrades to existing homes.
By building new you can select materials and finishes that are durable and will require minimal ongoing maintenance.

Short Term Visitor Accommodation:

Airbnb and similar short-stay accommodation are good ways to generate income from your property.
Short-term accommodation is a great opportunity to do something striking and a little bit quirky that catches attention, and you can often get away with something that might seem too small or unusual to be a permanent home but is just perfect for a short stay.
The new medium-density rules allow for a unit like this to be fully self-contained, so you needn’t worry about sharing bathrooms or cooking facilities with guests.

Development For Resale:

Developing a secondary dwelling for resale can help you generate income.
By building a new dwelling, you can pay attention to current market trends and advancements to create a structure appealing to modern buyers.
This will allow you to make use of space on your property that you may not be using.

Top Considerations For Building A Minor Dwelling

Whatever the reason that you are building a minor dwelling, many of the same issues need to be considered. It is important that the project is carefully designed from the outset to maximise your use of the available land and minimise some of the downsides of building at a higher density.

What are the most important factors you and your architect should consider when thinking about building more than one residential unit on your property in Christchurch?

General Site Layout:

Where can each unit best be positioned to enjoy the best sunlight and minimise shading to other units?
Are there any existing buildings or landscaping elements on the site that you will need to work around?

Legal Requirements:

Check building covenants, which may restrict what you are able to build on the site even where it is otherwise compliant with planning rules. For example, some subdivisions may not permit secondary dwellings at all, or they may have other restrictions on building height or location that are more restrictive than the district plan rules.
It is worth discussing with your architect how you could subdivide the new unit(s), even if you’re not planning to do this right away. It will be much easier to do this down the track if you have thought about how services and access can be provided to rear units through easements.
It is useful to engage a land surveyor at an early stage so you know the best way to set up subdivision boundaries, unit titles, easements and other constraints that may affect the design.

Council Approvals And Consents:

The proposed medium density residential rules have been established with the intention of allowing many developments to occur without requiring resource consent. This may cover many minor issues such as height limits, recession planes and site coverage. Some other issues may still trigger a requirement for Resource Consent, particularly on hill sites where excavation is needed. In Christchurch, an architect is generally able to manage the resource consent process for residential projects, though input from other consultants such as geotechnical or structural engineers may be required for more complex sites.
Your project will require building consent. In many cases, this isn’t any more complex than a stand-alone dwelling, and this can be coordinated by your architect in conjunction with other specialist consultants if required. While some smaller accessory buildings may be exempt from building consent, generally, this doesn’t apply where there will be new plumbing work for kitchens or bathrooms.
Where you are increasing the number of residential units on a site this will usually trigger Development Contributions. This is a one-off payment to the Council to contribute towards the cost of infrastructure. There are calculators on Council websites that will provide you with an estimate of these costs for your actual property, but as a rough guide, this may be around $10,000 – $12,000 for each additional unit. If you are demolishing an existing unit then the Development Contribution applies to the net increase in units. One unit demolished and two new units built only counts as one new unit.
You will also notice an increase in your total rates bill to cover any new units. This varies depending on factors such as whether the property is subdivided, how many sets of bins you have for collection and the total rateable value of the property.

Fire Protection:

This is a specialist area, may warrant some closer investigation at the design stage to ensure you are aware of any requirements that may apply.
In some cases, preventing the spread of fire may simply be achieved by maintaining sufficient separation. Where buildings are very close together, it may be necessary to use fire-rated external walls and/or non-combustible materials.
Fire alarm systems – Standard domestic smoke alarms will be sufficient for most stand-alone units and minor dwellings. For larger or more complex units there may be a need for specific fire alarm systems.

Acoustic Performance:

This is a very important factor in the quality of life of people living in close proximity to other units. This always requires careful consideration to achieve the best outcome and avoid noise complaints.
The Building Code requires a minimum level of sound isolation between connected units. Some of the systems and products that can be used to achieve this include concrete walls and floors, using two layers of staggered framing, acoustic batts, noise control linings and specially designed products that can be used as a barrier between framed walls. Usually, these intertenancy systems will double as the fire-rated wall and ceiling elements
The layout of units can also affect noise transfer between units. It is a good idea to separate noisy spaces such as living rooms and bathrooms from the sleeping areas in attached units. Garages can also be positioned to create more distance between adjoining units.
It is also becoming common to utilise noise-controlling elements such as acoustic-rated glass, higher-density wall cladding materials and roof underlays. This can help quieten external noise sources like traffic or neighbours, and such measures are often mandatory near busy roads.

Outdoor Living:

It is important to make sure every unit has access to functional outdoor spaces.
The quality of a space is often more important than its size. A small space that is sheltered and sunny will be much more useful than a large area that is shaded for most of the day.
Ensure direct access from living areas. Outdoor areas won’t get much use if they’re not easy to get to – even if you’re building a rental property, you’ll be better off if your tenants have spaces they enjoy using.
Consider privacy from other dwellings on your site and from the street. Even if you plan to have a communal outdoor area, it is still a good idea to have private spaces for each unit.

Parking And Vehicle Access:

Parking and vehicle access are always challenging when increasing the density of housing development, as there will usually be more occupants competing for the same number of on-street parks and often a reduction in space available for off-street parking.
There is typically no requirement for on-site parking or garages per unit in many residential zones. This can give much more flexibility in developing a site. In contrast, in the past, the scale of many residential developments has been limited by the number of parking spaces that can be achieved.
Ensure that each unit has access to the parking area, and that any shared driveways are designed with safety of all residents on mind.

Utilities:

Make sure there is ample space for the storage of bins, and a clear path to wheel them out to the street.
There should be access to water meters, drains and other utilities for inspection and maintenance work.

Creating A Welcoming, Comfortable Minor Dwelling On Your Christchurch Property

Designing and building a minor dwelling on your property can be very rewarding for a multitude of reasons. Regardless of whether you want to build a home to support your parents or children, or you’re interested in development opportunities, at Chaplin Crooks Architects we are here to help.

To get in touch, you can call us on or reach us through our website.

Create the perfect minor dwelling for your needs with help from our Chaplin Crooks Architects team.