There are many urban myths surrounding passive solar design and sustainable architecture for our Homes, especially with regards to insulation, glazing, thermal mass and ventilation, to name just a few of the primary influences. (Refer to the EBOSS Detailed Blogs page of this website.) There is no simple formula to objectively calculate the best relationship between just these four; multi-variable inter-related factors are virtually impossible to resolve manually.
Ideally each dwelling, at its site, would be specifically evaluated before construction as a multi-room dwelling by simulation software of the interior thermal performance, and hence the comfort level of the proposed Home. Instead the norm is to undertake a simple calculation of just the in/out energy flow through the thermal envelope (the outer skin) of a single volume building. Preferable a Simulation Tool should be used at the developing design stage of the project when the design is still in a fluid state so that options are easily explored. The AccuRateNZ simulation software I use as a Design Tool, in conjunction with your Architect, was specifically developed for this purpose to evaluate the internal thermal performance of the various rooms within our Homes.
Amongst the requirements to obtain a Building Consent to construct a new house is to demonstrate that compliance with the New Zealand Building Code: clause H1 – Energy Efficiency (NZBC-H1) will be achieved. This is done be applying the equations and methods described within the Code to determine the Energy Balance of the thermal envelope alone. The proposed Building needs to be better than a matching Reference Building. This pragmatic and simple approach is totally sensible given the very large number of Building Consents (around 40,000) being assessed each year. Even so NZBC-H1 includes for compliance to be alternatively demonstrated by dynamic hourly simulation of a multi-roomed dwelling,
Publications by BRANZ describe the benefits of using simulation software to objectively evaluate the interior comfort of houses. In particular refer to: BRANZ’s ‘Level’ resource “Passive Design – Thermal Simulation” dated October 2022, and Bulletin issue BU656 “Designing to Avoid Houses Overheating” dated December 2022. Refer also to my EBOSS Detailed post of April 2026, “Thermal Performance: Comparing Energy Balance and Dynamic Simulation”.
A simple way to illustrate the difference between the AccuRateNZ dynamic hourly simulations, and the Thermal Envelope Energy Balance calculations of NZBC-H1, is to consider a simple “what if” scenario. Take a dwelling with a living space at the North-west corner of the building which needs a large window in one of the walls. Whether it is in the north or west wall makes virtually no difference to the construction R-value of the Thermal Envelope (nor to the window’s installed cost) but a very large difference to the interior thermal performance, comfort level, and feel of the room. Fundamentally different shading and screening solutions are needed for the chosen elevation.
Alternatively, think of rotating a dwelling half a turn (180°). The construction R-values of the various elements of the thermal envelope would not change, but the comfort level of the interior over a year would be significantly altered.
On the other hand the Energy Balanced Thermal Envelope of single-zone calculation methods to show NZBC-H1 compliance are equivalent to the Occupant selecting a puffer jacket and then having to wear it 24 hours per day, every day of the year. A home’s thermal insulation cannot be continually reduced and increased every time the weather changes.
Unfortunately the Occupants of a home do not live at a single monthly average temperature; they live moment by moment in a wide dynamic range of temperatures across the 24 hour daily cycle which itself fluctuates within a month. This then varies cyclically across the 4 seasons of a year. In a home it is this hourly/daily/seasonal cycle which is experienced by the household.
The temperature information produced by a dynamic hourly multi-volume thermal performance simulation allows the objective exploration of moderating design options for specific rooms, or even planning changes if at the Developing Design stage of a project. The data also provide a detailed Brief for the design of heating/cooling requirements to specific rooms and the arrangement of zoning for the ducting/pipework layout. This is especially valuable with the public’s increasing awareness of the summer over-heating problem in new housing.
The dynamic hourly simulations I do use AccuRateNZ software which was brought to New Zealand by Government from Australia after a world-wide search by EECA, BRANZ and Universities in the late 2000s. BRANZ continues to use the AccuRateNZ software (which interfaces to CSIRO’s Chenath computational engine) for their high-level research on housing performance, and carbon-usage.
By working in close co-ordination with your Architect I can, by using AccuRateNZ computational software and my architectural experience, provide an objective measure of your proposed design and so suggest sensible thermal improvements that are practical, buildable and, most importantly, liveable.