The NZ Building Code has been neglected for a long time and its recommendations have fallen behind the requirements of society. It is only now (in the 2020s) that MBIE is actively pursuing a policy of continuous rolling updates to sections of the Code but even then, we are not yet sure that it will be adequately updated for MDH. The Ministry for the Environment will publish an MDH design guide in 2022.
Some of the new housing being erected in parts of NZ at present may only just be meeting existing Code requirements, and we know that other projects will meet Code on paper but would fail in real life. Remember that achieving Code compliance is a legal minimum, so if your building is not ‘up to Code’ it is therefore illegal – and as the designer, you may technically be only one or two steps away from prosecution, or even jail. That consequence rarely happens, so our building industry continues to churn out poorly designed, poorly detailed, poorly built buildings that don’t meet the client’s expectation of a warm, dry house. Collectively, we need to do better.
In 2021 MBIE consulted on major upgrades for the Building Code, and notice of upcoming Building Code changes were announced on 29 November 2021. Some of the changes include:
- Six new climate zones introduced for NZ (previously only three)
- New R6.6 value for residential roofs, in all six climate zones
- Residential windows significantly upgraded to between R0.37 and R0.50 – double glazing will become mandatory, even in Auckland. Triple glazing may be made compulsory in the deep south of Te Wai Pounamu – the South Island.
- Only R2.0 required for residential walls — only a fraction higher than the current low standards we have
This is very disappointing, largely brought about by people wanting to keep with existing 90mm thick external wall framing. To this, we say “no”. Aim to double the wall insulation.
- Greater weathertightness requirements – always a good thing
- Better requirement for natural light for “higher-density” housing. This is a welcome move.
(MBIE, 2021, Outcome of Consultation)
We all know that building quality needs to improve, including waterproofing and airtightness. Higher quality building wraps will play a part in this – we need our buildings to breathe. Ventilation requirements will also need to be increased and coordinated with the façade/envelope performance as well as occupant actions – we don’t want houses to sweat on the inside. Wall construction systems may need to change, window detailing is well overdue for a change, and construction of walls and floors between adjoining dwellings absolutely must get better. Yes, the NZBC will improve, but the industry needs to move faster and to produce better results. We need to pay closer attention to the circularity of building material re-use (Finch et al, 2021).
Instead of just ‘meeting’ the base minimum of the NZBC, we need to exceed the Building Code for insulation, exceed the minimum values for the acoustic interface between adjoining dwellings, and ensure that the fire separation between dwellings is always constructed as a permanent fire barrier. What will also be required of architects, designers and contractors very soon, will be a far greater focus on the embodied carbon within each of the homes we build.
New Zealand needs to have a new wave of housing that is:
- Energy efficient year round, exceeding NZBC minimums, and staying at the right temperature – not too hot, not too cold
- Dry inside, not damp, exceeding NZBC, easy to ventilate and operate – staying dry, avoiding fungi, rot or mould
- Quiet as well as fire-resistant, allowing multiple families to live near each other without having to hear each other
- Energy efficient or self-generating in energy, to reduce overall life cycle costs and environmental impacts
- Designed and built with embodied carbon and operational carbon front of mind.
- Built far more densely than we build at present – housing that is truly medium density, and offers good living too
This book offers guidance and inspires good building projects. Webb’s excellent book Building Community (2017) offers some inspiration:
“Each of these projects offers valuable lessons in the creation of good living environments. The priorities include well-proportioned interiors with abundant natural light, well insulated to reduce energy consumption and keep noise at bay. Ideally they should enjoy views and cross-ventilation. A balance of privacy and sociability turns proximity to advantage. Residential blocks should be mixed-use so that different activities can mingle. Ground-floor stores stimulate street life and raise apartments above the traffic flow. Plantings provide shade, absorb carbon dioxide, and mediate between the interior and the city. Huge complexes can be humane places for a wide variety of residents, as long as they are well built and maintained, provided with essential services and connections, and softened by generous plantings.” (Webb, 2017).
BRANZ picked up on these aspects too, describing a potential ‘Liveability’ index, based on work by Bennett (2010). Liveable residential built environments should provide:
- Social capital and interaction
- Access to amenities
- Connection to the outdoors
- Good indoor environment
- Privacy and sanctuary
- Quality buildings
Dwelling liveability is commonly assessed in terms of:
- Space – storage and entertaining spaces, shared spaces (and trade-offs between private and shared spaces, privacy and social interaction), socio-cultural understandings of space, layout of spaces.
- Amenity – natural light/daylight, ventilation and good indoor air quality, safety, privacy (acoustic and visual), ease of use (somewhere to hang washing to dry and to put rubbish and recycling), outlook, connection to the outdoors and outdoor spaces, access (lifts, emergency escape).
- Quality – there is evidence that quality in design and construction is more important than apartment size.
- Building management and maintenance.
The need for a low carbon future
There is another reason why our housing standards need to change: climate change is having a serious, scary effect on the world. We humans are burning far too much fossil-era fuel and creating a huge carbon dioxide (CO₂) surplus that our atmosphere and oceans cannot cope with. Excess CO₂ (and other greenhouse gases) is undeniably causing global warming, with the consequence of changing the world’s climate and altering habitats for humans and other animals all over the world. There is no arguing over that.
Although NZ is only a small player in world terms, we also have a significant effect. We have one of the world’s highest use of cars per capita partly due to our elongated, mountainous country, but also due to our poorly planned, sprawling cities and our habit of buying cheap clapped-out old bangers from richer countries. We have vast numbers of sheep and cattle that produce methane, and we have clear-felled most of our native forests to provide land for us and our livestock. New Zealand really does need to act urgently to reduce our carbon production, in both rural and urban spheres. That means we need to tackle the excess CO₂ being created by our dairy industry, our traffic and our building sector.
Carbon can be considered in two broad phases in housing: during construction and during operation. Construction emissions (or pre-occupation) relate to everything before the owner gets the keys and moves in, with operational emissions being everything once the building is occupied. These emissions may include those from use of energy and water, as well as maintenance and periodic replacement of materials that do not last the service life of the building e.g. IGUs.
Alternatively, you can consider “whole of life embodied emissions” which includes the pre-occupation emissions (manufacture of materials, transport to site, construction waste etc. and post-occupancy emissions that relate to materials, e.g. maintenance, replacement, and ultimately, building end-of-life. In this case, operational emissions tend to focus on energy and water use. The BRANZ website has a useful CO₂MPARE tool where you can see the carbon footprint of an MDH case study. If calculated over a 90 year service life, the operational (energy and water) component is approximately double the whole of life embodied component.
Most of the embodied emissions occur during the year of construction and represent the single largest source of emissions in any year during the building life cycle. Therefore, the carbon dioxide is emitted early and is contributing to climate change from the start. It will then spend several hundred to one thousand years in the atmosphere contributing to climate change.
It’s important to consider when emissions occur as well as the magnitude of numbers. While the period of construction can provide the single largest source of emissions in any year, over the long life of a house, the operational output is approximately double. Therefore, the more we can reduce the use of energy whilst living in the house, the better the house will perform in the long term. A significant amount of energy is needed for water heating and plug loads, both of which are not really addressed by having a high performance thermal envelope. As we head towards a net zero carbon future, designers need to be aware that use of energy is more than just for space heating/cooling.
We need to carefully consider the issue of embodied carbon within all our building materials. Embodied carbon is a moral consideration at present, but it is likely to become a legal requirement to calculate a building's carbon footprint, and an ensuing requirement to try and reduce this as far as possible. Embodied carbon is incredibly difficult to accurately calculate, but there are tools and resources available through the BRANZ website, including a free carbon calculating tool which can be used to calculate the carbon footprint of a building using Life Cycle Analysis. BRANZ also offers free training and support. MBIE published its whole-of-life embodied carbon assessment technical methodology in February 2022.
Compared with many other countries who use nuclear power or have to rely on burning fossil fuels to create electricity, NZ has a remarkable abundance of naturally-renewing energy. Due to this lucky abundance of energy, we have become lax as a country and we waste a lot of electricity. Yet despite our many hydro-electric dams and wind farms, we still turn to gas or coal-fired generation to make up the remainder when there are sudden spikes in electricity usage. Houses in the future will need to be zero-carbon over their lifetime – or even generate more electricity than they use. The journey to the net zero-carbon future starts right now, with low-carbon construction as the first step. It is imperative that we design houses to be as low carbon as possible, so that the amount of offset needed to make them net zero is minimal. If everybody relies on offsetting their carbon emissions to achieve this, we'll very quickly run out of land on which to plant trees, and sending cash overseas in the hope that other countries will plant trees for us is a wasteful plan. We need to solve this for ourselves.
Using fossil fuels as a source of energy is unsustainable, but due to the natural characteristics of trees being an absorber of atmospheric carbon, the use of timber in our buildings is a good thing. For every tonne of (sustainably harvested) timber used, we can be confident that around 500kg of that is carbon, sucked out of the air (from approx. 1800kg of CO₂) by the needles of our fast-growing pinus radiata trees, converted by sunshine into timber logs and locked up for the life of the building as sequestered carbon.
Concrete, on the other hand, is a net carbon producer, as the cement used is created via an exceptionally carbon-intensive process (refer to CO₂NSTRUCT at branz.co.nz). The more concrete you use in a house, the larger the carbon footprint of the house. Steel is even more energy-intensive to create, while the production of aluminium is staggeringly high in energy use. Fresh steel is manufactured in New Zealand from iron sands. Steel is completely recyclable and is continually recycled – albeit overseas. Aluminium is also totally recyclable, easily recycled, and uses far less energy when recycled from scrap. It is crucial to the continuation of our building material supply that we continue to recycle our waste aluminium in NZ. Every fizzy drink or beer can counts – recycle it all.
Variety of housing sizes
A crucial aspect of designing any MDH scheme is to allow for a wide variety of low carbon housing types and housing sizes, to suit any population that may live there. A building with only one size of dwelling restricts the clientele to only one narrow sector of modern Kiwi society. A building is boring if it is all students in single rooms, just as if it was all singles, or retired couples, or for vast sprawling families with multiple children. On their own these may become uncomfortable silos or ghettos, but mixed up they make up an urban village and that brings people together.
The typical London model of one storey half a floor down (a ‘basement flat’) and then walking up two to four storeys on upper floors does not seem to have been taken up in NZ yet, probably due to this being unfriendly to anyone having trouble with stairs. Four storey flats (even five or six storey flats) are common in cities like London, but four floors is the point at which in NZ you need to have a lift as well as the stairs and that can push the price up considerably. So currently our cities are stuck at a three-storey impasse. We need to make a big leap upwards.
Floor to Floor Heights
|Number of Storeys||Height per storey (m) floor to floor||Resulting building height (m)||Height per storey (m) floor to floor||Resulting building height (m)||Density ranking (NZ)|
|6||3.0||18.0 (plus roof)||3.2||20.0 (plus roof)||medium|
|5||3.0||15.0 (plus roof)||3.2||16.8 (plus roof)||medium|
|4||3.0||12.0 (plus roof)||3.2||13.6 (plus roof)||medium|
|3||3.0||9.0 (plus roof)||3.2||10.4 (plus roof)||medium|
|2||3.0||6.0 (plus roof)||3.2||7.2 (plus roof)||low|
|1||3.0||3.0 (plus roof)||3.2||4.0 (plus roof)||low|
How high can MDH cities be?
Heights depend on the limits set in the local District Plan. In the past NZ District Plan settings tended to have an 8m or 10m height limit for most residential zones – tied to the NZS 3604:2011 limit on three-storey, light timber-framed housing being set at 10m max. The change brought about by the MDRS, allowing 11-12m buildings as of right, is likely to have an effect on this height, with MBIE closely examining whether the residential building standards need to change further. Certainly, the NZS 3604 will need to be revised to decide whether an 11m or 12m building will fall within or outside the SED limits. (See Figure 3.1)
Furthermore, the height limit will also be affected by the current need for more stringent building envelope testing for buildings over 10m, thereby encouraging many builders and developers to play it easy and keep their heights below the 10m mark. Will this requirement change too? It seems likely that it will need to change, as our buildings grow in height and setbacks become necessary. (See Figure 3.2)
In Auckland’s Terrace Housing and Apartment Building (THAB) zone, a 16m height limit applies (section H6.6.5), encouraging development at five storeys high (six or seven storeys would still be a push too far at this height) (Table 3.1). Side yards are also still required in THAB, with a stipulated front yard of 1.5m, side yard of 1m, and rear yard of a minimum 1m. These yard requirements do not apply if there is a common wall between dwellings.
By contrast, in Auckland’s H5 Residential - Mixed Housing Urban (MHU) zone, an 11m height applies, in order to achieve a three-storey height limit. (Refer to AUP Figure H126.96.36.199). Yards requirements are front 2.5m, side 1m, rear 1m, but again these do not apply if there is a common wall. The new MDRS brings Tier 1 cities into line with this.
Other factors that affect the height limits are more subtle but have huge influence. The maximum height at which the Fire Department can control fires with their standard Type 4 appliances (fire engines) is just 18m. Fire and Emergency NZ is therefore comfortable with MDH being a maximum of only 18m tall – but that’s just six storeys high. Type 6 (heavy aerial appliances) are fire trucks with ladders and a pump that can have 32m (ten storeys) of reach to attack fires in multi-level buildings such as apartments. But these heavy aerial appliances are rare – there are only two of these in the Auckland/Hamilton region and two type 5 units in Wellington. It’s therefore not surprising if Fire and Emergency NZ has serious concerns about buildings taller than 10 storeys. (See Table 3.2)
Despite the Government issuing NPS-UD which stipulated minimum height limits in certain areas to be ‘at least’ six storeys high, that’s not often an achievable height in New Zealand, primarily due to cost. The two key cost factors that come into play here are lifts (elevators) and structural systems. Having a lift on a project is compulsory on any multi-unit housing projects that have their entry door four or more storeys high. As lifts are expensive to install and maintain, there’s a natural tendency for developers to want to build to only three storeys high: no lift required. Any building project proposed to be five or six storeys high will be saddled with a commercial lift cost to be spread over relatively few units.
Materials used for the structural skeleton of the building also have considerable effects. While it is simple for housing to be readily erected up to three storeys high using low-cost, light timber structural framing, the move to more floors will require a structural frame of greater strength. A simple low-cost timber house may only have one or two steel beams, but a full steel structure of steel beams, steel columns and concrete floor slabs will add significantly to the cost, the weight, and the carbon footprint. Therefore, many developers will push for many more storeys, perhaps ten or twelve, to better offset their development costs. But are buildings this high good for the city or for the people living there?
Reinforced concrete structures have similar cost issues, with the more commercial-scale use of composite concrete floor slabs, reinforced concrete beams and columns, and tilt-slab or precast concrete wall panels as cladding or dividing walls. Plus, concrete buildings are slow to build, forcing up labour costs. All these extra costs must be absorbed somewhere, which is again why taller buildings of ten or more storeys are often preferred by developers. But are these appropriate or really needed?
We need to consider the environment around the buildings, from both near and far, and select a responsible height that works best for people’s lives and does not destroy the neighbourhood. So, do we have to accept the developer’s word that ten storeys is their minimum height? In many cases, a ten-storey building is simply too big for the street that it sits on (see Figure 3.2). Are there any other options, or are we stuck in a three-storey vs ten-storey world forever? (See Table 3.2 and 3.3)
We are in luck – new materials like cross laminated timber (CLT) and laminated veneer lumber (LVL) are a very real possibility to radically change our construction prospects, with great strength at a much more manageable weight, and great accuracy because they are fabricated in a factory. Already being avidly used in some cities overseas, CLT is the great game changer, still in its infancy in NZ construction circles. With this NZ-made, lightweight, lower carbon, seismically stable structural solution of CLT, we can now construct six or eight storeys without the mass and inertia of a big heavy concrete building (see Table 3.3). In later chapters CLT solutions are explored in more depth.
Height to Boundary
The missing middle
There is a phenomenon in the housing industry known as ‘the missing middle’, a term originating from the USA (Parolek 2020). This describes cities that have single family houses at one end of the scale and large apartment buildings at the other end but are missing all the interesting MDH housing types in between. The American Institute of Architects (AIA) list the types of housing missing in the middle of Austin, Texas, as:
Du – Duplex
Tr – Triplex
Co – Courtyard Apartment
Gc – Garden Cluster
Rh – Rowhouse
Mu – Multiplex
Lw – Live Work
Until very recently, New Zealand had a missing middle as well, but we are now starting to get some of these types of housing in our cities. Taking our traditional post-war 100m² house on a 1,012m² section, our ‘traditional’ density equates to just four houses per acre, or ten houses per hectare (10du/ha). Densification from removing one house on that section and replacing it with two townhouses gives us only a small increase. Even going from 10 du/ha to 20 du/ha is not going to urbanise our cities enough to make a difference – and will have the effect of locking in place inadequate housing for the next 50 years. To be fully effective, our density intensification needs to be aiming at the top end of our MDH scale, achieving around 60 du/ha. We are already underway, section sizes have not been produced at quarter-acre sizes for decades. Sections are now around 350-400m² each, which leaves us with a density 2.5 greater than we had in the 1950s. But that’s still not enough – we need to go much further. Not just two-storey townhouses, or sausage flats, but building a minimum of three storeys, everywhere. This is where the art of the missing middle, multi-storey, multi-unit design comes into play. Get it wrong and all we have is wall- to-wall terraced houses – Coronation Street all over again. Get it right and we have great cities in which to live, work and play.
Design Factors to Consider
|Density level||Storeys||Approx. height||Lifts||FRR without sprinklers||FRR with sprinklers||Fire Engineer||Wind Report||Urban Design Report|
Design Factors to Consider
|Density level||Storeys||Approx. height||Light timber frame||Concrete block masonry||Insitu and precast concrete||Structural steel frame||CLT||Plywood panels||SIPS|
What types of MDH are there?
As noted by the ‘missing middle’ there are several types of MDH that are possible:
Apartment living generally describes a building of at least three storeys in height, where people live both next to each other (with adjoining walls) and above/below each other (with fire compartment breaks at each floor). In recent years apartment living has become more common in the larger cities of New Zealand. It is generally more upmarket than other forms of MDH, due in part to the associated greater costs generated by the concrete and steel construction methods. Taller apartment buildings, of course, provide high density housing, while low-rise apartments (three to six storeys) fall into the MDH range. For more on this subject, refer to my other book Modern Apartment Design (Marriage, 2022).
The term flat is often used interchangeably with the word apartment, typically a self-contained dwelling unit, usually all on one level (i.e. having a flat floor). A ‘block of flats’ often implies properties for rent rather than for purchase.
Terraced houses are houses linked by common adjoining side walls. They can be small scale, cosy, and rather intimate (think of Coronation Street, set in Manchester), or large scale and somewhat grander (like the Georgian designs of London’s Bedford Square, installed by the Duke of Bedford). In Britain terraced houses may combine to construct a continuous wall around the street space: all the brick front walls become one giant piece of urban wallpaper. On the less fancy terraced houses the façade may be rather flat, with perhaps just a small projecting front entry porch, while on the larger or more grand schemes such as in London’s Kensington, columns and projecting bay windows are more common.
In NZ, terraced housing is likely to be none of these things. Terraced housing is a huge boom area in the Auckland housing market, generally just two or three storeys high and with moderate variation in street elevation.
Much the same as terraced houses, a row house is an American term, implying a number of identical dwellings in a row, all linked by common vertical walls. In New Zealand, we tend to call all these Townhouses, including the Duplex and Triplex mentioned below.
While in Europe a townhouse may imply that the owners also have a grand house elsewhere in the country, in New Zealand a townhouse is a smallish dwelling, with two or more floors. Often townhouses are built as a terrace of similar dwellings. Typically, the amount of garden space outside is rather limited.
Duplex / Triplex house (horizontally adjoining i.e. side by side)
Duplex in the traditional NZ terminology means two houses adjoining side by side, either side of a common boundary wall. Triplex is similar, but with three dwellings. Much of the terraced housing we are building in Auckland is duplex houses, while a much smaller proportion is triplex.
If there are only two dwellings sharing a wall, the British would refer to this as a ‘semi-detached’ house. What we would just call a house (standing on its own), is known in the UK as a detached house, showing perhaps just how wedded the British are to the idea that houses should be joined together.
Duplex / Triplex apartment (vertically adjoining i.e. one above the other)
A duplex apartment is slightly different and means a two- storey apartment within a larger apartment development. Triplex means the same, but with three-storey dwellings. A two-storey apartment or townhouse is sometimes also called a maisonette (French for ‘little house’) when it is within a larger building.
An infill development built in parts of Auckland in the 1960s with a series of adjoining dwellings, typically four to six single storey two-bedroom units built in long thin terraced blocks at right angles to the street. Living conditions are hence a little extruded, like a string of sausages. It is a “characteristically small scale of development that matched the capabilities and organisation of the building industry at the time, with limited financial risk to relatively small investments” apartment block (Turner, 2010, p214). There is little common space except for the extensive long driveway down one side.
Three Floor Walk-up
Houses where there is a single dwelling on the ground floor, and stairs up to the floors above for more vertically adjoining units. This has become a very popular housing form recently, allowing for a rentable unit/granny flat on level access downstairs, and a larger unit or two above for those who can handle the stairs. The phrase ‘walk-up’ denotes that there is no lift. At present this is the most affordable form of low/medium density development. The key difference between a terraced house and a walk-up is that the walk-up is designed from the start to be in separate units. If terraced housing is carefully designed, it can be readily converted to walk-ups instead – all the more important after the 2022 raising of the height bar.
Courtyard housing is a classic housing type, once common in China, Europe and the Middle East. It is a housing system unlike anything we usually have in NZ – like a house turned inside out. There are no front yards, or rear yards, and certainly no side yards. Instead, the house
is built up to the property boundary on all four sides. Rooms face into the centre rather than out to the neighbours, assuring a remarkable level of physical and acoustic privacy. Public street noise is reduced to a minimum, while security is maximised. Courtyard housing can
be a single home designed around an atrium or can be a group of double or triple height dwellings all wrapped around a common central courtyard.
In Morocco, the old cities still accommodate thousands of people in courtyard housing, concentrated around delightful airy central courtyards with fountains and palm trees cooling the air in the centre. Large courtyard blocks still exist in northern European cities like Berlin or Stockholm with arrival off the street into a central courtyard, and four or five storeys of apartments facing inwards. And in Wellington, there is an MDH development in Seatoun that features a series of 13 single courtyard homes, arranged like a checker pattern, with common boundary walls and carefully designed small courtyards to shelter from stormy weather (Studio Pacific, 2003). There is still a lot of scope for NZ to explore the world of courtyard housing, as it can be a very efficient use of land (Marriage, 2014).
Perimeter Block Housing
If housing is permitted to be built right up to the side boundaries in a coordinated manner, then eventually an entire block may have a perimeter of housing around the edge. This is known as perimeter block housing (PBH), a logical combination of Terraced housing and Courtyard housing.
The Manor house is a concept which is rarely seen in NZ. It is used in parts of Britain and the USA, where numerous dwellings are constructed in a manner that makes them look like they are all part of one grand big house. An apartment block in all but name, the Manor House concept allows the designer to treat their architectural ambitions on a grand scale.
Multi-dwelling or multi-unit development
All of the above are multi-units developments of some variety: there are many overlapping names or concepts in the housing industry. Nearly all multiple- dwelling construction in NZ falls under the very broad umbrella of MDH.
In Auckland, under the new Unitary Plan, Terrace Housing and Apartment Buildings (THAB) have become a big part of solving the housing crisis. Indeed, THAB is now the largest part of the NZ residential construction industry, with terraced housing in particular hitting record highs.
The new Medium Density Residential Standards (MDRS) require minimum sizes to yards, but do not mention interior living space standards – that is left to individual councils. All Tier 1 city District Plans will have to be essentially rewritten due to the introduction of MDRS.
Material Factors to Consider
|Studio (m²)||One-bed (m²)||Two-bed (m²)||Three-bed (m²)|
Australian system of Setbacks for narrow urban streets. Australia understands the importance of getting sunlight and daylight into inner-city urban housing.