Floor-to-ceiling glass in large-scale commercial buildings has been on trend for the last ten years and doesn’t appear to be slowing down anytime soon.
This trend is seemingly in direct competition with the sustainability movement that also has interest from a variety of parties including developers, investors, government and consumers because in general increasing glazing means an increase in potential space for solar heat gain and glare and therefore more money spent on mechanical cooling, better glass and frames, or shading devices.
This paradox has resulted in better glazing products entering the Australian market such as low-e glass, double glazed units (DGUs) and thermally broken framing, particularly as buildings are increasingly being marketed on their energy performance as well as their looks.
Although studies do show that from an energy efficiency, daylight and comfort perspective, punched windows perform better than unshaded full height glazing, market demand will see floor-to-ceiling glass continue to be specified for Australia’s high-rises.
The Westpac building in Adelaide (left) with punched windows and Sydney (right) with full height glazing with a low Visible Light Transmittance glass.
Alistair Coulstock of Cundall Australia says that both regulation and the market are the driving force behind higher performance requirements from facades and points to increased stringency in the NCC, “Section J Façade Energy Efficiency Requirements” as well as voluntary rating systems such as NABERS and Green Star.
“Over the last 10 years improved Section J efficiency regulations have meant that no longer can you get away with specifying a single glazed clear façade on a commercial building unless your proposed design uses a reduced amount of glass in its façade,” explained Coulstock.
“Also, if you are building a new commercial building in any of the capital city CBD’s the market expects a minimum of 5 Star Green Star and 5 Star NABERS Energy. This ties in with the PCA’s Guide to Office Quality, which states a Grade A asset should be a minimum of 4 and 4.5 Green Star and NABERS energy respectively and Premium Grade asset should be 5 and 5. Both Green Star and NABERS are voluntary schemes but the market has driven the uptake of both.”
But meeting these ratings with a completely glazed curtain wall poses its own problems, namely, but not solely, cost.
“The Australian market is definitely behind the European market and you pay a premium for products which are standard elsewhere,” explains Coulstock.
“Part of this is because of the general rules competition. Australia is a small market compared to Europe (22 million versus 731 million) and therefore not a sufficient amount of competition to drive the costs down.”
Even though better products are being shipped to Australian shores, Coulstock predicts that Australia’s predilection for completely glazed commercial buildings will suffer a blow when UK style regulations board that boat as well.
“Currently in the UK, you are no longer permitted to provide full height glazing across the whole of your façade,” he said.
“We typically follow Europe in terms of progress in the construction industry and as mentioned reduced glazing area is a key factor in the UK for commercial buildings and I expect this will follow in a few years here.”
Daylight Modelling and Glare Assessments
1 Bligh Street Sydney by Ingenhoven and Architectus adopts a double skin façade. A clear exterior pane of glass and a double glazed interior unit are separated by a cavity with venetian blinds. The blinds control daylight penetration and glare. Image: Architectus.
Coulstock is also largely concerned with improving daylight modelling and glare assessments in the design of Australian commercial buildings, concepts which he feels are overlooked and undervalued because of rudimentary testing.
He would see the uptake of Daylight Autonomy assessments for building’s which assess the useful daylight in the space across the whole year.
“The existing method for daylight has been measuring daylight factor on a uniformly cloudy day,” he explains.
“This rudimentary method for measuring daylight only takes into account the low light scenario, when there are plenty of occurrences during the year that daylight is too bright resulting in blinds down for long periods.”
Coulstock would also see a glare analysis complement the current direct sunlight assessments of facades, and believes that considering glare also leads to a more energy efficient building.
“It is easy to address direct sunlight entering a façade but this may not result in mitigating glare,” he says.
“Glare can be present in a number of forms; discomfort glare, reflection ‘glare’ or veiling luminances. The most common, discomfort glare is a function of contrast. If the contrast between the light source and its’ surrounding surfaces is too great then discomfort will be sensed. Simple glare modelling can eliminate issues in design that may cause ongoing problems for tenants. Poor glazing and shading selection that do not address these glare issues result in tenants putting blinds down for long periods. This subsequently has a detrimental effect on energy efficiency as the tenants will need to use lights in the space. This has a twofold effect not only from the power from the lights but also the additional heat load on the air conditioning system.”
Coulstock takes a holistic outlook on interior comfort and believes punched windows put the architect in better stead to provide this in comparison to full height glazed windows.
There are exceptions which we can expect to see creeping into the higher end commercial office market which allows for full height glazing and complete control of glare. One is closed cavity facades and we’ll have more on that system in the coming days.
So if Coulstock is correct and we do follow UK trends and begin to see glare assessments and daylight modelling incorporated in Section J, NABERS and Green Star façade testing can we expect to see the popularity of full height glazing decline in Australia?
If the market demands commercial buildings meet a minimum NABERS and Green Star performance, would glare assessments and daylight modelling make it impossible for developers to ignore the benefits of punched windows versus full height glazing?