Rob Campion of the Window & Glass Association NZ touches on the impacts of the revision to Clause H1 of the Building Code.
It’s here! We’ve been working on parts of this document with the Ministry of Business Innovation and Employment (MBIE) and BRANZ for some time now, so were aware of what was coming — and on November 29 it dropped silently into our inboxes, Clause H1 the Fifth Edition.
It may have taken a couple of months, but as the building industry comes to terms with the impact of the changes, it now appears that drop was more like a silent thermal quake . . .
The revision of Clause H1 brings a new set of regulations governing the thermal performance of our building envelopes, with impact on each of the primary building elements — roofs, walls, floors, and most definitely for windows and doors.
Welcome to the new world. But be aware this revision is only the first step, albeit a significant one!
Changes — overview
So, as you’re all aware, H1 is the Clause of the Building Code that regulates the Energy Efficiency of our built environment. It “Provides for the efficient use of energy and sets physical conditions for energy performance.”
The revision to H1 modifies those conditions in line with, or as a first step towards, the Government’s Building for Climate Change desires, by increasing the minimum required R value for each of the primary building elements.
Previously, glazed elements required a minimum performance value of R0.26, satisfied by a cold aluminium frame with clear double glazing, long recognised as being barely adequate.
The Fifth Edition of H1 has done two things for glazed elements. First, it moved from basing window and door performance on a single standardised window to looking at the weighted average R value of a house lot of joinery, providing a much more holistic view of the contribution to the performance of the thermal envelope.
Second, the minimum R value requirements have increased. We now have two values spread across six climate zones — R0.46 for Zones 1 to 4, and R0.50 for Zones 5 and 6. These requirements kick in for consents lodged from November 3, 2022.
However, there is a slight reprieve for Zones 1 and 2, where 70% of construction is currently happening. The minimum R value required in these zones alone has been reduced to R0.37 for a further 12 months, through to November 2023.
Beginning of the beginning
But how will these changes impact the window and glass industry? For the bulk of our construction, Zones 1 and 2, in the first 12 months it is mostly just a change of glass type.
Using a traditional cold aluminium frame but changing from a clear on clear double IGU, to one that includes a pane of high performance Low E glass, with an argon gas fill, will achieve the required R0.37.
However, to achieve an R0.46 or greater performance value will require a change of frame material to thermally broken aluminium, uPVC, or timber and the clear on clear IGU will vanish for all but timber-framed windows.
Therefore, for consents issued from November 2022 in Zones 3 to 6, and from November 2023 in Zones 1 and 2, cold aluminium frames and clear on clear double IGU’s will essentially be removed from our construction methodology.
Thermally superior frames and Low E glazing will be the new normal and, in my opinion, that is not a bad thing.
The Schedule method and Table E.1.1.1
There are three ways of demonstrating compliance with Clause H1 — the Schedule, Calculation, and Modelling methods, each with their own set of parameters and uses.
However, the schedule method is traditionally the most commonly used, based on a look-up table of window and glass combinations and their respective R values.
With the Fifth edition and the shift in philosophy around the evaluation of thermal performance for glazed elements, Table E.1.1.1 in H1/AS1 was created using the more meaningful weighted average R value of a house lot approach.
The table was developed using windows and door configurations from a variety of current popular house plans to ensure they reflect what is being built today.
The thermal performance of the combinations was calculated using underperforming generic frame types that were further downrated to ensure the product delivered to site actually achieved the requirements of the Code.
Not all Low E glasses are the same, and to help identify this Table E.1.1.1 identifies the variation through the use of terms Low E1, Low E2, Low E3, and Low E4.
Of course, there are other IGU make-ups that will provide differing UCOG values, so architects, designers and builders must work with their suppliers and be clear that their specification reflects the desired outcome.
Impact
The window and glass industry absolutely supports the Government’s initiative around creating warmer, healthier, more energy-efficient homes, and the changes to H1.
However, these changes are not without their impacts, expense, risk, pain and stress for the people and businesses involved.
Aluminium suppliers are redesigning systems and shifting to thermally broken frames, uPVC suppliers are increasing their capacity, timber window manufacturers are adjusting for the changes, and glass suppliers are reassessing their product offerings to align with the new requirements.
These changes have required significant investment in people, machinery and processes as we work towards the time frames afforded us by the MBIE.
But the industry is convinced it will be ready to supply suitable product come the November 2022 and 2023 implementation dates.
