We may seem a bit late to the party since Homestar v5 was launched in 2021! However, Homestar v5 is due to come into force in February 2023 so we’d like to share some of our thoughts on it.
Homestar and Passive House – what’s the difference?
First, it’s important to acknowledge that Homestar and Passive House are quite different, but at the same time can be complementary programmes.
- Homestar is a broad green building rating system with many categories created for New Zealand homes that is administered by the New Zealand Green Building Council (NZGBC). Categories include, for instance, daylight, water conservation, appliance efficiency, resource efficiency, healthy materials, VOCs, construction waste, and embodied carbon. Accredited professionals design and certify Homestar projects.
- Passive House is an international standard for comfort, health, and energy efficiency that can be applied to almost all building types, not just homes. The standard is administered by the Passive House Institute in Germany, but accredited New Zealand professionals design, construct, and certify Passive House buildings here. PHINZ advocates and provides education and resources (including software) to promote and encourage the uptake of Passive House in New Zealand.
While Passive House is a standalone standard with many benefits, it also provides an excellent building-science and evidence-based foundation for any sustainable building by ensuring some core fundamentals are rigorously taken care of. This is recognised by NZGBC and a certified Passive House project will gain many Homestar points (mainly energy, comfort, ventilation, and moisture credits) assisting it on the way to a high Homestar rating. Passive House tools have also informed the latest version of Homestar – more on this below.
We were pleased to provide detailed feedback on proposed updates from Homestar v4 to v5 and see some of our suggestions implemented. Here are seven things we love about Homestar v5:
- Greater emphasis on thermal comfort and energy efficiency. These are core fundamentals that every building really should be achieving. It is an indictment of our traditionally poor building standards here in New Zealand that the majority of buildings fail to do so and people have to rely on voluntary programmes like Passive House and Homestar for these to be properly addressed.
- Energy modelling is prioritised. At the core of any high-performance building that achieves high thermal comfort and energy efficiency is rigorous energy modelling. It is a critical tool to guide the design and ensure building science underpins decisions about orientation, thermal insulation levels, glazing areas, configuration and performance, ventilation strategies, etc.
- NZGBC has created its own energy modelling tool, the Energy and Carbon Calculator for Homes (ECCHO), based on the Passive House energy modelling tool, the Passive House Planning Package (PHPP.) The PHPP software has been developed for over 30 years incorporating feedback from the monitored performance of completed buildings and feedback from dynamic modelling tools. It has been simplified enough to make it a highly effective design and certification tool while not losing any of its accuracy and rigour. We expect that the ECCHO tool will be invaluable for assisting Homestar-certified projects to achieve higher energy efficiency and a reduced performance gap, even when they don’t also target or achieve Passive House certification. PHPP can also be used for Homestar, as it can for NZ Building Code compliance (but note the following point.)
- It sets absolute energy intensity caps for thermal performance of the whole building, like Passive House has an annual heating demand limit of 15 kWh/m2. This is in contrast to a “two-model” or “reference model” approach, which the NZ Building Code H1 modelling method currently uses. In the “two model” approach, an improvement over a reference model based on elemental minimum compliance settings is required. This incentivises designing buildings with poor thermal performance as they are easy to show an improvement on. This is a well-established issue and Passive House Canada set it out clearly in this linked article. Setting absolute caps or targets overcomes this issue and it is what we must do if we are serious about reducing energy use and operational emissions from buildings.
- Addresses moisture control at junctions. Surface condensation and mould are prevalent in New Zealand housing, sadly, and often it can be due to thermal bridging at construction junctions or poor window details. Homestar now includes fRsi requirements for junctions, adopting the Passive House (PHPP v9) requirements. The freely available High-Performance Construction Details Handbook provides fRsi values for a catalogue of details, as well as the PSI values for heat transfer.
- Requires pressure testing, aka Blower Door Testing, for 8 Homestar rating and higher. It is good bulding science and widely recognised that reducing uncontrolled air movement (aka infiltration, exfiltration, airtightness) through the thermal envelope is critical for moisture protection and energy efficiency in buildings with high thermal performance. Homestar sets targets as infiltration per square metre of thermal envelope, rather than air changes per hour that Passive House uses. Both results can be derived from the same testing procedure, though.
- Addresses important aspects of sustainability that Passive House doesn’t. Passive House has a relatively narrow focus on the core fundamentals of building performance so there are many aspects of sustainable design it doesn’t cover and we don’t expect it ever will. This is arguably one of its strengths and a reason why it is so successful at delivering what it promises and eliminating the performance gap. This doesn’t mean other aspects don’t need addressing also, though, such as daylight, water conservation, appliance efficiency, resource efficiency, healthy materials, VOCs, construction waste, and embodied carbon, for example. Homestar provides a complementary framework to address these and many other aspects of sustainable design.
Homestar and Passive House crosswalk
NZGBC and PHINZ have worked together on a Homestar and Passive House crosswalk. This provides detailed guidance on which Homestar points and credits a certified Passive House project can acheive to promote and support dual cerrtification. When the crosswalk is published, it will be availabe on our downloads page and a direct link will be added here.
Other green building organisations have also set out how Passive House is complementary with their rating and created crosswalks. We are aware of the following:
- Green Star – Design & As Built (Aus) and Passive House (or download the crosswalk document directly as a PDF)
- LEED and Passive House
- ILFI Zero Energy and Passive House
- Klimaaktiv and Passive House (German language)
The international Passive House Association also maintains a page on crosswalks that may be more up to date.