• Fabric First

NCC 2019: J1.5 Walls and Glazing - Facade efficiency but at what cost?

Updated: Feb 19, 2019

Last week, after jumping around on stage at Zak World of Façades – Brisbane, I had the chance to wrap my head further around another element of the National Construction Code (2019) - Section J - J 1.5 Walls and Glazing.

After finishing a quick 20-minute summary of Section J 2019, rushing to the end without really hitting the high notes and as clear a conclusion as I would have liked, I failed to raise a vital observation. When the changes come into force in May 2020, by the virtue of building simulation modelling in the draft consultation period, they are deemed to render a ‘30% increase in energy efficiency while being cheaper to build than under NCC 2016’.

With such bold statements out there about cost neutral improvements to Section J, have the ABCB found the energy efficiency silver bullet, that balances the challenges of buildability, aesthetics and performance against cost? Will these updates combine to establish a natural stepping stone for building envelope energy efficiency to elevate our minimum compliant landscape or represent a disruption to how we design and construct buildings?

This is an extended read, so you may need a coffee, distraction or time to kill to get through to the end!

What’s new?

Section J - J 1.5 Walls and Glazing is now a one stop shop for your glazing and wall performance requirements for Class 2 (multiple dwelling unit) common area, a Class 5 (Office), 6 (retail or restaurant), 7 (carpark or warehouse), 8 (laboratory or manufacturing facility) or 9b (school) or 9a (health-care) and Class 3 (hotel or student accommodation), 9c (aged-care) or a Class 9a (health-care) ward areas.

Introducing new metrics and concepts to the Australian construction industry, it establishes both the minimum performance requirements for wall and glazing components of a wall-glazing construction and the methods needed to illustrate compliance against them.

As usual, not happy playing the tick box approach to compliance, you can always take a punt on one of the 4 verification pathways now available. More on these in another post.

Wall-Glazing Performance Requirements

Staying true to the NCC 2019 definition, a wall-glazing construction is deemed to combine wall and glazing components of the envelope, excluding display glazing which is treated separately and opaque non-glazed openings. So, in other words, we combine the performance for 1) glazing and 2) walls to get single values for a ‘wall-glazing construction system’.

With various levels of stringency set as a function of when the building is typically occupied, the wall - glazing performance requirements are broken up by Climate Zone and Building Class. Total System U-Value and Total R-value are the metrics of choice, creating an unnecessary complication for industry as one is the inverse of the other!

Thermal Performance Requirements

In all Climate Zones, for a Class 2 common area, a Class 5, 6, 7, 8, 9a or 9b building other than a ward area, we now need to have a Total System U-Value ≤ U2.0 for a wall-glazing construction.

Expanding on the existing definition of Total System U-Value, a revised 2019 definition now states that thermal transmittance allows for the effect thermal bridging. While it was already implied in 2016 but not categorically stated, when combined with the definition for glazing and that ‘supporting frames located in the envelope’ are to be included, this lays the foundation for an important change to the way we approach the thermal bridging associated to frames.

Today, using a protocol provided by the Australian Fenestration Rating Council (AFRC), we only need to include part of the framing elements, excluding sub sill details which have a major impact on the Total System U-Value performance for glazing as installed. As a ‘supporting frame located in the envelope’ that must ‘allow for the effect of thermal bridging’, we will now formally include such sub-sills or other elements in 2019 without debate, rendering the AFRC protocol subject to revision.

This is great news for those familiar with this debate and the back door it has left open on the subject of glazing system energy efficiency given that WERS values don’t accounts for such losses and are based on standard module sizes that are non-typical in construction. Well done to the ABCB for plugging this performance gap and accounting for all thermal bridging!!!! Anyhow, a slight tangent, back to the post….

For Class 3, 9c or a Class 9a ward area building, our performance requirements vary by Climate Zone, from the most stringent requirements in alpine areas (Total System U-Value ≤ U0.9), less stringent requirements in warm temperate climates such as Sydney, Brisbane and Perth (Total System U-Value ≤ U2.0) to somewhere in between for all other climates (Total System U-Value ≤ U1.1). The Total System U-Value of display glazing falls outside the wall-glazing construction definition, is unambitious and set to be not greater than a Total System U-Value U5.8.

As for the wall components of the wall-glazing construction, the ABCB have had the foresight to allow for backstops to the performance of wall systems, whether they are spandrels within a curtain wall system or a more typical precast, timber or masonry wall build-up.

Where the wall is less than 80% of the area of the wall-glazing construction, we get a Total R-value performance requirement in all Climate Zones and Building Classes of R1.0. Given that most spandrels will not meet this value without being thermally broken, this is a game changer!More than 80% wall area, then we are again subject to variable requirements as set by Climate Zone and Building Class. Again, the 2019 definition now includes thermal bridging. Are you seeing the trend? Thermal bridging folks!

In all climates except sticky ol’ Darwin, for a Class 2 common area, a Class 5, 6, 7, 8, 9b or 9a building other than a ward area, we now need to have a Total R-value ≤ U1.4 while the constant heat of Top End gets a significant jump up to a Total R-value ≤ U2.4.

As for Class 3, 9c or a Class 9a ward area, we get more variable Total R-value performance requirements that broadly align to that set by the Total System U-Value performance requirement. So, alpine regions along with Darwin remain the most stringent (Total R-Value ≥ U3.8 and U3.3), Sydney, Brisbane and Perth are the most lenient (Total R-Value ≥ U1.4), while Melbourne, Canberra, Hobart are somewhere in between (Total R-Value ≥ U2.8).

Putting aside the accuracy or potential impact of the performance requirements set out above, I think it is fair to say that those Climate Zones and Building Classes that are deemed to be conditioned and occupied during the day have the most stringent wall-glazing construction performance requirements. This makes 100% sense and is in line with 2016 requirements.

Solar Performance Requirements

By recreating the approach to wall-glazing construction discussed above, it was also required to take a similar approach for solar control for vision and wall areas. As such, solar admittance or the fraction of incident irradiance on a wall-glazing construction, has been added as a new metric to account for this total heat load.

As we have seen above, Climate Zones and Building Classes set the performance requirements with various levels of stringency set as a function of when the building is typically occupied. Speeding this up, in all Climate Zones and Building Classes, different performance requirements are set for only north, east, south and west aspects with a view to simplifying the impact of a more thorough stipulation of all cardinal directions.

Incredibly, in most cases, the performance requirement for each aspect are deemed to be the same so the southern side of the building would ‘benefit’ from shading and reduced SHGC? While an allowance for southern and western aspects is provided in Class 2 common area, a Class 5, 6, 7, 8 or 9b or 9a for alpine regions, it does not carry over to Class 3, 9c or a Class 9a ward areas? Through such simplification, you can be sure that eye brows will be twitching in the engineering community, as this is a fundamentally flawed approach and difficult to understand as to how this has sneaked in to NCC 2019.

More Calculations? Afraid so....

Luckily, the ABCB will be providing a glazing calculator of sorts, this time for the wall-glazing construction. So, while the ol’ DTS Glazing tool may have been put out to pasture, and long may it rest there, we have something new on the horizon that will speed up the calculation process. Put simply, Specifications J1.5a and J1.5b set out the methods for compliance for wall-glazing construction and determine the performance of spandrel panels, respectively.

For Specifications J1.5a, we are provided 2 methods for U-value and solar admittance compliance, Method 1 (based on a single aspect) and Method 2 (allowing for trade-offs between multiple aspects). With clear boundaries set by AS/NZS 4859.2 for accounting for thermal bridging and clear formulas to follow, Specifications J1.5a is unsurprising in its methodology or intent.

Specifications J1.5b, however, begs more questions, as its methodology is less clear. Responding to the unequivocal fact that poor spandrel performance has been ignored for years, spandrel panels are now deemed to have either default Total System R-Value if they match a very specific configurations description (Method 1) or Total System U-Values are calculated by an equation (Method 2). Yes, that is two different units that fail to make this process as simple as it should be!

For example, of the 4 generic default configurations provided, configuration 2 consists of a thermally unbroken (bridged) frame and a centre of spandrel panel consisting of a double-glazed opaque face with a 50mm air gap and a back pan with no performance specifications provided. So, if the stars are aligned, the gods are smiling and you can manage to describe your spandrel as per configuration 2’s generic labels, you can then pull a performance value from a table based on the proposed R-value of the insulation. In this case, if we assume an insulation R-value of 1.5, we can then nominate a Total R-Value of 0.44! The limitations of this approach are abundantly clear and render it as a largely pointless exercise as we simply don’t have enough information provided to ever truly match up to a configuration.

Of course, we can always take Method 2, where we calculate our way to more accurate representation of what will be installed. For those not familiar with the Total System U-Value of spandrel systems, assume a value of 1.5 is typical for a standard spandrel system, but this of course is subject to its dimensions. Convert this back to a Total R-Value renders a value of approximately 0.65 and a failure to meet the minimum backstop. The only way to truly deal with the poor performance of spandrels is to ensure that the frame is insulated from the interior. Thermally breaking the spandrel is of course an advantage but ensuring a thermal line that is not made of aluminum has its benefits!

How will this impact buildings?

Will this DTS provision lead to better buildings and at what cost? Well, it is certainly going to lift the minimum performance requirements, along with some the other parts of Section J, creating a higher performing reference building and an industry shift in how we value, design, procure and construct buildings.

But there is nothing like a wee case study to produce some easy to read graphs, so let’s have a look at Sydney, Brisbane and Perth as they have identical performance requirements and a generic office building wrapped in a curtainwall with varying levels of industry practise.

Creating 3 specifications aligned to 1) Standard Industry Practise (Non-thermally broken and fails R-value backstop), 2) Industry Leaders (thermally broken) and 3) Next Generation (thermally broken advanced), the graphic below allows us to summarise the expected Total System U-Value of the wall-glazing construction and the resultant step change required to catch-up with minimum performance requirements.

With the orange line representative of our target performance, we can see today’s Standard Industry Practise of curtainwall delivery fail on all glazing to façade ratios. Simply put, today’s typical options will not be a solution for those on the horizon as they are too thermally inefficient for NCC 2019.

However, it’s not all bad news as our Industry Leaders in design and fabrication, although few and far between, are ahead of the game and able to meet Method 1 performance requirements for glazing to façade ratios up to 60%. Crystal balling but the evidence is already available, Next Generation systems may even be able to really hit the high notes and go beyond minimum performance requirements by some degree.

However, before we get too excited and move onto the next challenge, noting this is for the easier climates of Sydney, Brisbane and Perth, we are not quite out of the woods yet. We still have solar admittance to get over the line and limiting factors of high solar loads.

Going back to our 3 specifications, Standard Industry Practise has been assumed a 0.30 SHGC, Industry Leaders has assumed 0.26 SHGC but needs to be spectrally selective to retain high Visible Light Transmittance (50%) and our Next Generation has assumed 0.24 SHGC, with ultra high spectral selectivity.

What we can begin to appreciate is that while we can get things across the line thermally, accounting for Standard Industry Practise to transition in Industry Leadership and even Next Generation, Solar Admittance is a real limiting factor that begins capping out glazing to façade ratios @ circa 50%. This is not a bad thing, as we have too much glass often driven by developer requirements for increased floor areas and maximising views, but the cost uplift is becoming apparent. But what about Method 2, is that not a solution?

Keeping it quick, the answer is, about the same! Given in this example, where we are assuming the building is wrapped in standard to very high-performance curtain wall on all aspects, the results are not expected to be too different, which is evident below.

What does this all mean?

A post way too long for most, but the facts are slowly revealing themselves. If there is a silver bullet here, it is very difficult to see. Based on a like for like scenario, between NCC 2016 and 2019 requirements, cost uplifts are evident within the case study provided, which is the ‘best-case scenario’, as all other climates have higher performance requirements.

Façades are not cheap, and it would be fair to say that this new compliance landscape is in the region of pushing per m² rates of façade procurement between 7.5 and 10%, based on efficient façade investment strategies and overseas glass procurement. Keeping things local and including the increased performance of the spandrel, this might kick up into a 15% premium or more for Next Generation systems and have a very negative impact on the competitiveness of local suppliers.

Benefits will be seen from an energy efficiency point of view, as J 1.5 Walls and Glazing establishes performance requirements that will push façade design hard, even if you chase a verification pathway, such as our ol’ friend JV3. But this will all come at a cost uplift, that cannot be ignored and needs to be understood as soon as possible.

However, it is also the stepping stone required to push forward and improve our buildings, so they are more resilient and energy efficient. So, as difficult as some of the challenges industry will face in terms of overcoming cost hurdles, lets reduce glazing to façade ratios to improve design outcomes and begin to embrace these changes as our minimum compliant landscape sets how our buildings perform, not just the lucky projects chasing certification and accolades. A game changer it is and an opportunity to remove some of the dead wood for sure, but planning will be critical for those ready for change!


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