In New Zealand we need to be building housing that is energy efficient and comfortable. Even better if it doesn’t break the budget and the materials are fit for purpose. So when InsideOut was asked to be a part of bringing the Appartamento Il Casino project to fruition, and we found out why, it was an exciting moment.
In 2008 resource consent was granted for an apartment building above the historic Il Casino restaurant in Tory Street, Wellington. For a multitude of reasons the project was not started on site until 2012. In that four years things changed.
The requirements of the building code for energy efficiency had tightened and unfortunately the budget had not sprung elastic sides. A building envelope and glazing that had complied with the requirements of the consenting process at conception now looked like they may be the stumbling block to trip up the entire feasibility of the project. So, the big question was how it might be made to work.
I have described in a previous piece, H1- The Apartment Story, how important it is to pick the right approach to energy efficiency for apartment buildings. In this case each apartment was considered a separate dwelling and the requirement was for each to meet the H1 energy efficiency levels outlined in NZS:4218. The design had a large percentage of glazing and the only valid way to test compliance was through the modelling method.
The good thing about simulating a building with the ability to provide heating or cooling to its occupants, is that the energy to accomplish both is taken into consideration. This means that it is as important to reduce the opportunity for overheating as it is to ensure a cosy and warm home when it’s colder. What that means for the building envelope is making sure that the heat energy we’ve paid so much for can’t easily escape, whilst not trapping the sun’s heat at the warmer times of year which might push us to use the cooling system. Insulation is the obvious response to keeping the building warm but the choice of glass becomes really important year round.
An Engineered Solution
The initial design for Il Casino used single glazing throughout but the world had moved on. Options of double glazing or low emissivity IGUs were under consideration and with the budget in mind the best option needed to be found for each apartment to provide the lowest energy and the best thermal comfort for the occupants. It’s interesting to note that the New Zealand Building Code does not constrain the comfort levels occupants can expect. At InsideOut we think it’s important to know and to respond to evidence for both energy and comfort.
The computer modelling allowed us to investigate the integrated performance of both the transparent and opaque building elements. There were the usual needs for glazing in particular to meet other demands; in this case for acoustics, falls from height and wind loadings. The optimised ‘engineered’ solution we came up with, combining insulation and glazing, was chosen for its many benefits.
Energywise, fitting low emissivity IGUs throughout the building would have been a compliant ‘blanket’ solution for the entire building, but costly. It was important to know how it would impact on the people living in the apartments. If it was going to be the best for them then it might have been difficult to beat, despite the budget.
When we looked at the simulation evidence it seemed that we could do better. In terms of the H1 requirements there was a clear split for compliance:
- Single glazing (some of it laminated) – 20 apartments
- Double glazing – a further 3 apartments
- LowE double glazing – the final 11 apartments
Interestingly some of the apartments which reached the H1 compliance level for energy efficiency would have failed with more insulating glass. Some were helped to reach the level needed by careful calculation of the wall insulation thicknesses.
Although the energy figures had been modelled in line with the requirements of NZS:4218 we wanted to look at how the building would work if for some reason the power was unavailable or occupants chose not to use heating or cooling. Comparing thermal comfort, measured using resultant temperatures, for the engineered solution versus the three whole building options, the figures told us our engineered solution would be more comfortable than any of them.
Given the project hinged upon whether it could be built for the budget, it was important to know what the savings might be for the engineered solution. Costed it out in dollar terms it would have been:
- 47% more expensive than single glazing throughout – but single was non-compliant with H1
- 10% less expensive than double glazing – but even double didn’t reach compliance everywhere
- 27% less expensive than LowE double glazing – which complied but at a cost
A Good Result All Round
- Optimal glazing and insulation specification were worked out together.
- The feasibility of the construction was supported using only that part of the budget which was necessary.
- The energy efficiency was maximised whilst maintaining an earlier design.
- NZBC H1 was complied with for every apartment; the highest level of requirement
- Thermal comfort was demonstrated to be better than the expensive whole building solution of LowE double glazing.
Following construction it was cheering to hear that Il Casino won the GANZ “Best use of glass” award in the WANZ Gala Awards 2014. Well deserved.
Thanks to all who worked with us on the Il Casino project including: Globe Holdings; Peddle Thorp Montgomery; Watts and Hughes; Wellington Council; EcoRate; Architectural Windows; Fletcher Aluminium; Viridian Glass
Author: Ruth Williams – Principal, Buildings That Work InsideOut Ltd