Picking glass performance values to meet early compliance aspirations seems like a relatively simple task. The reality is that it often culminates in headaches for the design team later in the design process rather than adding value or efficiency.
More often than not, the procurement of glass is based on performance values determined by databases' drop down menus, either online or within software modelling tools. The truth is, these are the absolute last places to make an educated approach to performance design as they are detached from the reality of procurement and architectural intent.
Let’s take a recent mixed 14-storey multi-residential (one and two-bedroom) building in Melbourne as an example. Fairly typical from a design point of view, the façade aspirations were a mix of fixed glazing, awning and sliding door systems with a familiar design remit of transparency and openness.
Entering into the process in support of the façade fabricator looking to provide a suitable, on budget façade system for the main contractor, the first challenge was in this case to enter the performance numbers game inherited during the D&C process. The game is quite simple: to ascertain if and why façade performance values (total glass and frame values) were selected and if they can be matched by the façade fabricator's proposed system.
In this case, a typical NatHERS 5 Star minimum - 6 star average compliance strategy had been set with the underpinning performance set at the façade via the selection of a product in the Window Energy Rating Scheme (WERS) database. Not a product that represented the design aesthetics, not a product that was assessed from a procurable point of view but a product that was deemed to have two numbers to match the ESD compliance strategy, a System (frame and glass) U-value and a SHGC.
Now, so no one is mistaken, WERS is a great system and fit for a purpose - but not for all purposes - pertaining to glass procurement. As a scheme to enable windows to be rated and labeled for their annual energy impact on Australian dwellings (Class 1), it is a great way for consumers to understand the significant impact of glass and frames on the performance of their homes. By gathering data from glass and fabricators, WERS uses typical module sizes to allow consumers to assess performance on a like by like basis, simplifying glass performance for the wider non-technical market.
However, while suitable for the four-bedroom, double garage quickly disappearing from the Australian dream, it has one major flaw. It is not fit for purpose when considering the procurement of specific glazing systems in the high rise multi-residential buildings (Class 2) we are seeing popping up in Australian capitals. Indeed, due the variation in module size of most architectural designs, it is not suitable for 90 per cent of commercial buildings. For example, a WERS system curtain wall system with a typical IGU and frames might have a Total U-value of 3.1 W/m2 based on a two-metre-by-two-metre module. However, the actual module size is two metere by one metre, rendering a lower Total U-value of 3.3 W/m2!
Going back to our example case above, the best option on the WERS menu, a thermally broken high performance frame with a triple low-e IGU glass, was chosen pre-tender to allow the engineer to maximise the façade thermal performance in order to get those NatHERS star ratings in the compliance range.
For those not familiar with the gorgon, this high performing glazing system is uncommon in Australia, particularly in high-rise residential. Sure, from an aspirational point of view, we want to choose great glass and frames on every project to design apartments that are more energy efficient and comfortable throughout the year. However, even at the onset and under the pressure of planning documentation deliverables, the rationale needs to consider: if this goes through Council, will it be procurable and at what cost? Add 10 per cent onto your existing façade costs and you will be in the ball park.
And here lies the issue with this approach; dropdown design to drive façade compliance is commonly sending design teams into a tailspin and not allowing façade fabricators to be engaged so glazing systems can be ordered, fabricated and shipped to site.
Depending on a database of products is oversimplifying the role of façade design and construction. By putting forward a System U-value based on a database of products fails to take into account the complexity of façade design and variation, both of which fundamentally change the performance role of this architectural skin of the building.
The reality of glazing system procurement is not a simple process, but it needs far more focus even at the planning stage to be able to make the process more fluid and to value early design stage. Glass procurement needs to be fundamental to architectural vision, taking into account the representative area of frame to glass, façade system layouts, glass and frame colouration, internal and external reflectivity, transparency, solar control and conduction (U-values) in order for a procurement process to be successful.
The next time you see a specification drop into your inbox, question its relevance and whether it can be procured. With the cost of façade procurement on the rise, the sooner you confirm your façade fabricator and place your order, the better!