Alistair Coulstock is a principal at Cundall, a sustainable engineering company operating in the built environment.

His expertise has been called on for such projects as 1 Bligh Street, Central Park Sydney and the Australian Hearing Hub at Macquarie University.

He is a NABERS Accredited Assessor and CBD Accredited Assessor, and has significant experience in green ratings. We caught up with Coulstock to ask him a few questions about the future of façade design in Sydney’s commercial sector and his opinion on full height glazed buildings.


How have recent changes to the BCA and NABERS influenced façade design in the Australian commercial sector?

National Construction Code and NABERS changes are driving higher performance requirements from façades.  One is a minimum standard, regulatory approach, the other is market driven.  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 unless your proposed design uses a reduced amount of glass in its façade.

Glazing performance has increased over the years.  The continual push from architects for unobstructed views with floor to ceiling glass has driven higher performance requirements from the glazing rather than going for smaller window areas.  It is an interesting point to dwell on. 

Currently in the UK, you are no longer permitted to provide full height glazing across the whole of your façade.  Furthermore, our studies show that, generally from energy efficiency, daylight and comfort perspective, punched windows are better performing than full height glazing. In addition, with the tenant quest for floor space efficiency, more and more buildings have desks located against the façade.  This results in an untidy appearance when viewing from the outside in. So the only reason to put it in is aesthetics in the artistic renders as part of the development application and marketing material use for leasing purposes.

For a few years now we have seen thermally broken facades entering the market.  These types of frame, which are common place in Europe, are still a premium in terms of cost.  The uptake of these frames has been slow due to these costs and the regulations have not been tight enough to drive the wholesale change necessary. 

Are these changes having a cultural effect? 

There are a few more parties interested in energy efficient design, but these are driven by other factors.  For example in the commercial office space at the top end of the market, energy efficiency is driven by Corporate Social and Sustainable Responsibility (CSSR) of those prospective tenants who will be moving in to your building.  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.

If you look at the middle and more so lower end of the market then rental income still rules over energy efficiency.  For a building owner it is more important to ensure low vacancy rates. If your grade B or C building has high vacancy rates then this may spur on a refurbishment.  The CBD’s  Mandatory Disclosure scheme is more of a catalyst for energy efficiency upgrades to existing buildings as no one wants to have to market a zero or one star NABERS efficiency rating on their building. These upgrades always go hand in hand with a lobby upgrade or the like.

On the whole, there are more interested parties because regulation is forcing people to take interest.  Energy is generally too cheap to be a standalone driver (as a ratio of energy bills to total outgoings of a company’s running costs) and so the only other way to address the majority of the market is regulation.  Europe has far higher emphasis on energy efficiency for both of those reasons.  Regulation has always been the main driver in the UK and this is particularly important for developers who are going to flip their assets.  Energy costs will drive the remainder of the market if they are sufficiently high enough.

How does the Australian glazing market compare to the rest of the world?

The market is definitely behind the European market and you pay a premium for products which are standard elsewhere.  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. As mentioned before legislation in Europe is ahead driving a better quality of glazing product that is starting to creep into the market place but only for high end buildings.

How should architects best approach the design of a glazed curtain wall in conjunction with National Construction Code (NCC) and NABERS requirements?

It is now commonplace - and has been for a few years - to carry out energy efficiency studies at concept stage in design to ensure your façade will meet compliance.  The obligations are not required under the NCC until Construction Certificate (CC). However, if you get to that stage and you have to make significant changes to the envelope this may drive a resubmission or Section 96 with the council, and subsequent delays to the project.  All but the simplest of buildings these days will require dynamic modelling of the façade (JV3 methodology) to determine compliance rather than the Deemed to Satisfy methodology (DTS).  We carry out these assessments in the early stages to inform the design team whilst the concept is still fluid.  These preliminary assessments can save a significant capital costs to the projects through rationalisation of the glass types and the façade design to ensure the optimum approach is found.

What do you consider the imminent trends for commercial building façade design?

We typically follow Europe in terms of progress in the construction industry.  As mentioned before reduced glazing area is a key factor in the UK for commercial buildings and I expect this will follow in a few years here. 

Leaky buildings in the UK is another focus for current regulation and I expect that façade infiltration testing will become mandatory in Australia over the next few years.. The BCA has an option under JV3 modelling methodology that if you test your façade during the design and construction process then you can vary your infiltration rates in your modelling during design stages. This is only an option, however, and not a compulsory requirement. 

Thermal bridging and thermally broken frames, will be another focus especially for fully air conditioned buildings. A standard aluminium frame in full sun, can get extremely hot.  This heat can be transferred internally and effect not only energy efficiency but also comfort conditions.  I expect that this will also become a focus for future regulations over the coming years.

What would you like to see changed in Australian façade design?

Rather than innovative glazing techniques we would like to see improved daylight modelling in Australia.  The existing method for daylight has been measuring daylight factor on a uniformly cloudy day.  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. Daylight Autonomy assesses useful daylight in the space across the whole year.  In the UK we had involvement in the Education Funding Agency’s baseline designs to ensure good daylight in schools.  We would like to see a similar approach to all building types here in Australia. The GBCA has been taking note of alternative modelling techniques used internationally and subsequently their new Design and As-built tool provides an optional methodology for using Daylight Autonomy as a pathway to achieving credit compliance. 

In addition glare assessments should be used more and more in building design.  The current methodology that is widely used is a direct sunlight assessment, not a glare analysis. It is easy to address direct sunlight entering a façade but this may not result in mitigating glare.  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.

If we are to make the changes necessary across the whole of the construction industry then it will have to be driven by legislation.