H1 Compliance Case Study: Residential Building with over 40% Non-Thermally Broken Aluminium Frame Windows in Auckland
January 12, 2024 By Anthony Broatch
Introduction
Over the last 2 years the government has made large changes to the minimum insulation requirements in buildings, significantly increasing construction costs and proposing new challenges in the industry. The changes are covered in the New Zealand Building Code, Clause H1 for Energy Efficiency (H1/AS1, H1/AS2, H1/VM1, H1/VM2, and H1/VM3) and are described in more detail in the appendix of this article.
Reshape recently worked on 2 seperate residential project in Auckland, where we faced an interesting challenge. The design of both projects had a lot of windows - they covered over 40% of the walls and both owners only wanted to use non-thermally broken Aluminium framing to save construction costs.
Windows can let a lot of heat in or out, and the new minimum H1 schedule method requirements for residential buildings don’t allow the use of non-thermally broken Aluminium framing. This is because the R value is too low meaning they are not as effective at keeping heat in or out.
So, this was the dilemma on our hands. The windows and the % of glazing our client wanted to use would not comply using the schedule or calculation method. But to keep the design of the building the same while still using non thermally broken windows, the only way forward was the modelling method with some innovative ideas.
The Project
The client wanted to use non-thermally broken windows, which have a R-value of 0.36, with is lower than the minimum schedule method required. And the glazing area was over 40% which exceeds the maximum requirement of both the schedule and calculation method. This choice posed a notable challenge.
The lower R-value meant that these windows were not as good at preventing heat loss in winter or heat gain in summer, compared to the thermally broken framing option. So, by using non thermally broken glazing framing, and having a large percentage of glazing area, it could potentially lead to higher energy consumption to maintain a comfortable indoor environment, thus making the path to achieving H1 Compliance more difficult.
As with all of our H1 Report projects, we aim to meet the clients’ needs and goals as our number one priority. There will always be compromise but our main aim is to retain the original design that the architect has supplied us with while staying within the material budget for the client. To date, Reshape has never had to go back to an architect to request reduced glazing areas – even when it has made up 70% of the total wall area!
Figure 1: Reference Building Model Without Solar Shading
Innovative Insulation Solutions
The key to balancing out the thermal performance was to consider solar shading strategies already existing in the design, looking at the glazing type for the amount of solar heat it lets through, and enhance the insulation in other parts of the building.
To determine compliance for the above we used the H1 modelling method (H1/VM1) which allows us to consider both space heating and cooling energy use. This allowed us to consider the solar shading in the existing design and also the glazing types for solar performance. This would not have been possible using the H1 schedule or calculation methods.
In addition to the existing solar shading strategies, entered high R-value insulation solutions - a pivotal player in our strategy to meet the H1 Compliance standards.
For one of the projects we employed R 7.3 Skillion High Performance insulation in the roof between timber framing, this resulted in a total roof R value of R6.4 which slightly lower than the R6.6 minimum requirements in the schedule method, and R 5.26 200m EXPOL Thermaslab S concrete slab insulation in the floor, with no slab edge insulation, resulting in a total R value of R3.26. The walls were 90mm timber framed and had approximately the same R values as R2 minimum requirements in the schedule method.
For the second project both the roof and floor R values were lower that the minimum requirements in the schedule method however the wall R values were increased as that was the optimal solution for the design.
So why were these specific insulation materials chosen? Several factors contributed to this decision:
-
Exceptional Thermal Performance: The insulation we suggested offered excellent thermal resistance, which was paramount in compensating for the lower R-value of the windows used in the project.
-
Compatibility with Existing Design: These insulation solutions could be integrated seamlessly without necessitating any changes to the wall thickness or the overall design, thereby preserving the architectural aesthetics and floor area.
-
Long-Term Energy Efficiency: By significantly enhancing the insulation in certain areas, we could ensure long-term energy efficiency, thus contributing to lower energy costs over the lifespan of the building.
-
Ease of Installation: Both insulation solutions presented a straightforward installation process, minimising any potential disruptions to the construction timeline.
The selection of these high R-value insulation solutions, in addition to solar shading strategies already existing in the design and look at the glazing type for the amount of solar heat it lets through, not only addressed the thermal performance challenge but also upheld the original design integrity of the project. By increasing the insulation to make up for the energy loss from the non-thermally broken windows, we were able to achieve compliance for our client.
Conclusion
Faced with the design intricacy of over 40% glazing using non-thermally broken windows, the narrative could have veered towards compromise. Yet, it steered towards innovation.
This project is a narrative in Reshape’s ethos of client-centric, innovative solutions. It's an exemplar that even when design aspirations tread an unconventional path, achieving compliance is very much possible while not compromising on energy efficiency or aesthetics.
Engage with us at Reshape, where your architectural visions are nurtured towards compliance without compromising aesthetic elegance. Let’s embark on a journey from conceptual sketches to compliance certificates, navigating the complexities with innovative solutions. Reach out to us to discuss your next project and discover how we can reshape the narrative towards achieving exceptional, compliant, and aesthetically pleasing built environments.
About the author
Anthony Broatch
Director, H1 Specialist, Chartered Senior Mechanical & Hydraulic Engineer
BE(Mech), CEng, MCIBSE, MEngNZ
Reshape Consulting Ltd
I have had been involved in a energy efficency and energy modelling in buildings for the the last 15 years and have worked on countless H1 complaince reports, building performance analysis projects, and energy audits.
