1. Passive House for Medium Density Housing in
NZ
Elrond Burrell
elrond.burrell@via-architecture.net
1 Introduction
The Passive House standard is often associated with single-family homes. In NZ, only single-
family homes (and a two-family home) have been certified to the standard to date. In fact, the
standard can be applied to most building typologies and sizes. Scaling up to medium density
housing (MDH) actually makes it easier to achieve the standard. This is due to the inherent
efficiencies (good thermal envelope to floor area ratio) of multi-unit housing.
Housing densification is an important topic in NZ due to the increasing population and a
notable housing shortage in the main centres. This has been reflected in the government,
official bodies and the construction industry giving more attention to MDH in recent years.
With these different factors at play, it seems like there is a good opportunity for Passive House
MDH uptake in NZ. And it is hoped that this study can contribute in a small way towards the
development of Passive House MDH in NZ.
At the time of writing, the author is aware of two Passive House MDH projects being developed
in NZ but neither has started construction yet.
2 Study Description
Given this interest in MDH in NZ and the opportunities and benefits that Passive House MDH
offers, it was considered worth doing a short study on the subject. The purpose was primarily
to check what changes from the basic NZ Building Code (NZBC) requirements would be
needed in order to meet the Passive House standard. The specific focus was on the opaque
thermal envelope R-values as these are often equated with building performance and energy
efficiency.
The study comprised the following steps:
1. Establish what is defined as ‘Medium Density Housing’ in NZ.
2. Survey examples of Passive House MDH from around the world
3. Identify an example (real) MDH project in NZ
4. Model the example MDH project in PHPP in basic form

2. 5. Test the PHPP Model in a range of scenarios
6. Analyse the results
3 Discussion
‘Medium Density Housing’ is defined by BRANZ (Building Research Association of NZ) as
“multi-unit dwellings (up to 6 storeys)” (Bryson and Allen, 2017) and broken down into three
categories as follows;
Category 1: 1 – 2-storey attached houses
Category 2: 2 – 4-storey attached houses
Category 3: Apartments (up to 6-storeys)
International examples of each of these typologies were found in the Passive House
Database (http://www.passivhausprojekte.de) and reviewed.
A proposed development in Auckland that was being advertised and about to start
construction was identified as a suitable example of Category 3 MDH. Building plans, unit
plans and some building elevations were readily available from the developer’s website
(Figure 1, Figure 2.) making it possible to model in PHPP with a fair degree of accuracy.
Figure 1 (North is vertical up the page)

3. Figure 2 (North elevation)
The project was entered into PHPP with basic geometry and NZBC compliant U-values but
no thermal bridges. The building was oriented facing north. Windows and doors were
modelled as fixed glazed units, except entrance doors that were modelled as solid doors.
Shading from the building geometry and interior blinds on the north elevation were modelled
but no other shading effects. Ventilation was left as a default HRV unit with 75% efficiency
and 0.6 ach infiltration air change rate was assumed.
The form of the building has a Heat Loss Form Factor (External surface area / treated floor
area) of 1.4 which in inherently very efficient. A form factor below 3 is considered efficient.
4 Results
The NZBC has only three identified climate zones in contrast to the 19 climate zones
identified for Passive House purposes. A city in each NZBC zone was chosen for modelling
purposes, starting with Auckland where the real building is being constructed.
NZBC Zone City Required R-value
Roof Wall Floor Windows*
1 Auckland 2.9 1.9 1.3 0.26 / 0.35
2 Wellington 2.9 1.9 1.3 0.26 / 0.71
3 Christchurch 3.3 2.0 1.3 0.26 / 0.71
* For modelling purposes, the window R-value had to be improved as R0.26 (U-value 3.85
W/(m²K)) does not meet the Passive House comfort criteria. Instead, R-values of 0.35 (U-
value 2.87 W/(m²K)) for Auckland and 0.71 (U-value 1.4 W/(m²K)) for Wellington and

4. Christchurch were used. These were the minimum whole window values required to achieve
the comfort criteria.
NZBC Zone City Results
Heating
Demand
kWh/(m²a)
Heating
Load
W/m²
Overheating
%
Passive
House?
1 Auckland 13 10 7 Yes
2 Wellington 13 12 3 Yes
3 Christchurch 21 10 2 Yes
These results are heavily caveated due to the basic nature of the modelling undertaken.
It should be noted also that the Auckland results indicated a very high frequency of high
internal humidity (29%). However, more detailed modelling of the ventilation and possibly the
introduction of some cooling may resolve this.
Varying the orientation of the building was tested and rotating it within +/- 30º of north only
has a marginal effect in each case.
5 Conclusions
While this is a very basic study, it can be concluded that for the three main cities, each
representing a climate zone in the NZBC, the opaque thermal envelope R-values required in
the NZBC are a reasonable starting point for designing Passive House Medium Density
Housing.
The conclusion is heavily dependent on the specific building design and incorporating other
elements needed to meet Passive House requirements. By concentrating on the opaque
thermal envelope R-values, the study actually highlights the elements where there is a gap
between the NZBC and Passive House.
This is an important discovery because industry proponents of improving the NZBC often
advocate increasing the required R-values. For MDH in the main cities, such as the apartment
building studied, this isn’t the case and the focus needs to be on other elements of building
performance.
These elements are; high performance windows and doors, a thermal bridge-free
construction, an efficient heat recovery ventilation system, and an airtight building envelope.
1. High performance windows and doors. The R-value required for windows in the NZBC is
not adequate anywhere in NZ to meet the Passive House comfort criteria. This implies that
NZBC compliant windows are likely to be a source of uncomfortable convection draughts,
condensation and mould. (Most people that have lived in NZ can attest to this being the
unfortunate reality.) It should be noted also that a single R-value figure is very crude and
unlikely to accurately reflect the installation situation in most cases. It lacks the detailed
consideration given to window performance in PHPP.
2. Thermal bridging. While none was modelled in the study, the author’s experience suggests
that thermal bridging could easily add 2 kWh/(m²a) to the heating demand thereby causing

5. a design to fail the Passive House requirements. There is also a question about whether
or not repeating thermal bridges within opaque elements of the thermal envelope are
adequately accounted for in the NZBC.
3. Ventilation. A combination of window ventilation and intermittent mechanical extract that
would comply with the NZBC does not meet Passive House requirements for comfort or
energy efficiency.
4. Infiltration. There is currently no requirement to test or meet a specified value for infiltration
in the NZBC.
The successful development of Passive House Medium Density Housing in NZ is critically
dependent on these elements.
6 References
Bryson, K. and Allen, N. (2017). SR376 Defining medium-density housing. Porirua, NZ.
BRANZ