19 Jan 2011  – FAVOURITES – The energy efficiency requirements in the Building Code of Australia became more stringent for commercial buildings on 1 May 2010.  With the exception of Tasmania and the Northern Territory, the revised measures have been adopted nationwide.

In this revision to BCA 2010, Section J, the Australian Building Codes Board has increased the stringency of the measures so the net financial benefit in operational savings is around twice that of the additional investment required in energy efficient technologies.

While changes to many of the minimum energy efficiency requirements are incremental and industry has adjusted, the building envelope performance requirements have undergone the biggest revision. Increasing the insulation performance of walls, roofs and suspended floors is relatively straightforward, but architects’ biggest challenge is adjusting to the new facade glazing requirements.

Why target glazing?

A sizeable component of the demand for heating and cooling energy results from the thermal performance of a commercial building’s facade. While some heating and cooling energy is required to compensate for heat lost or gained through insulated walls, roofs and suspended floors, heat lost or gained through windows, glazed doors and roof lights can be a greater contributor to a commercial building’s greenhouse gas emissions.

In a nutshell the four major changes in the BCA2010 stringency of the deemed-to-satisfy glazing requirements for the building’s thermal envelope are as follows:

  • Non-residential commercial facade glazing energy allowances have been reduced by between 17 per cent  (climate zone 2) to 51 per cent (zones 7 and 8 ) in the Method Two calculator;
  • Residential commercial (hotel and aged care) facade glazing energy allowances have been reduced significantly with the deletion of the Method One calculator and replacement with a more stringent version of the Method Two calculator;
  • Minimum energy performance of internal fabric glazing is now specified and assessed in the same way as if it were south-facing external glazing; and
  • The total area of roof lights must not exceed 5 per cent of the floor area of the room or space served (previously it was 10 per cent).

It should be noted that the requirements for retail display glazing remain unchanged as the existing requirements in BCA2009 already posed a significant design challenge.

What do these changes mean for designers?
The facade glazing energy allowances have been reduced in BCA2010. Therefore a barely compliant design with the deemed to satisfy glazing requirements in BCA2009 (the glazing area compliance ratio is 100 per cent for all orientations in the 2009 glazing calculator) would need to be altered to comply with BCA2010. Depending on glazing orientation and location, the design may need glass with a higher insulation performance, a deeper tint, wider external shading overhangs, reduced glazed area or a combination of these.

Much of Australia’s commercial building activity occurs in the major coastal cities of Brisbane/Gold Coast, Sydney, Melbourne, Adelaide and Perth. The relevant climate zones are zone 2 (Brisbane/Gold Coast), zone 6 (Melbourne, Adelaide Hills and western Sydney) and zone 5 for the rest. The greatest challenges to architects designing commercial buildings in these locations are posed in zones 5 and 6. In zone 5 the glazing energy allowances have been reduced by a third and in zone 6 the allowances have been halved.

What are the implications for the design process?
Essentially the changes have been significant enough that an architect developing a building concept for development/town planning approval can no longer afford to draw a highly glazed building without investigating whether it complies with the new glazing requirements, either by deemed to satisfy or through a performance-based approach. The easiest way for a concept architect to develop a design is with a basic understanding of acceptable window-to-wall area ratios  on the various major glazed orientations for their preferred glazing type.

Design charts such as those in figures 1a and 1b (excerpts from an upcoming Environment Design Guide  note) enable architects to quickly understand what extent of glazing is possible on various orientations and what levels of shading and glass thermal performance are necessary. The charts for climate zone 6 explore the relationship between allowable WWR, glazing insulation value (U-value of 6.5 and 3.7 W/m2.K), Solar Heat Gain Coefficient (SHGC of 0.7 and 0.3) and external horizontal shading ratio (P/H of 0 and 0.4).

P is the horizontal distance from the window sill to the shadow casting edge of the sunshade and H is the vertical distance from the window sill to the shadow casting edge of the sunshade.  A national series of training seminars is being organised by the Australian Institute of Architects to assist architects with developing compliant glazing designs. Details are presented at the end of this article.

Figure 1a: BCA2010 Allowable window-to-wall area percentages for climate zone 6 single glazed

As the deemed to satisfy glazing rules must be complied with on all levels of the building on all orientations, the higher stringency in BCA2010 means that there is now a greater likelihood that these deemed to satisfy measures will be exceeded in some areas of any building design. The performance-based JV3 energy modelling compliance method allows the design team to demonstrate compliance with BCA2010 even if there are some areas of glazing that do not comply with the deemed to satisfy requirements. Effectively energy modelling permits the

Figure 1b: BCA2010 Allowable window-to-wall area percentages for climate zone 6 double glazed

trading of glazing energy allowances between facade orientations or levels, thereby providing the architect with greater flexibility to incorporate external glazing into the building’s design. Complying with the JV3 method still requires that the proposed design has the same building envelope thermal performance as one complying with the deemed to satisfy measures throughout. The input of an experienced energy modeller will assist any architect developing a compliant design concept that will exceed the deemed to satisfy requirements in some areas.

Passive design and the glazing regulations
Good commercial building passive design principals underpin the Method Two glazing rules. In most climate zones shading (external overhangs and tinted glass) is rewarded highly, recognising that direct solar radiation places large loads on the cooling plant. In some but not all climate zones and orientations, increased glazing insulation performance is rewarded. North facing glazing with appropriately sized external shading and south facing glazing (shaded in climate zones 1, 2 and 3) generally offer the highest WWR values for architects. As direct sun entry is harder to control on east and west facades, these orientations typically have lower WWR allowances. These are a simple reflection of good passive design and should be born in mind when an architect develops building massing concepts for their chosen sites.

As the new regulations generally encourage lower glazed areas on the facade, more external shading and more tinted glass than the 2009 regulations, opportunities for visible light entry diminish. Architects will need to pay careful attention to effective day lighting design principals by locating facade glazing more strategically in their designs. This will be particularly important for building classes 3 and 9c which are residential accommodation uses where deeply tinted and/or externally shaded glazing may not be acceptable from a day lighting point of view.

In summary
Designers are encouraged to develop their awareness of the Section J deemed to satisfy requirements in BCA2010, particularly in relation to facade and roof glazing allowances.  As these requirements are generally more stringent than those in BCA2009, the performance-based JV3 compliance method involving energy modelling will be used more regularly to offer greater design flexibility to architects. Depending on the complexity of the design the time to undertake this modelling could vary from a minimum of three days up to a maximum of three weeks. It is recommended that designers incorporate passive design principals and establish that their designs can comply with the glazing rules prior to submitting for development/town planning approval.

Michael Shaw

Michael Shaw is a senior environmentally sustainable design engineer in the Melbourne office of Norman Disney & Young. He has been educated in both engineering and architecture and has significant experience in the application of environmental rating systems. His analysis of the draft BCA2010 Section J glazing requirements informed the Australian Institute of Architects‘ response to the public consultation process.

In February and March the Australian Institute of Architects will run nation-wide training on energy performance requirements for façade glazing. Entitled, All the way with Section J, the seminars will address key design considerations for architects arising from the latest changes to the BCA’s Section J.

Mr Shaw will explain how architects can develop building design concepts informed by the new more stringent glazing requirements for both non-residential and residential commercial buildings. Architects can learn ways to document their designs without adding unexpected expense in glazing or redesign at the end of the design process.

All the Way With Section J are:

Melbourne    Monday 21 February
Hobart          Tuesday 1 March
Launceston  Wednesday 2 March
Perth              Monday 14 March
Adelaide        Tuesday 15 March
Gold Coast    To be announced
Brisbane       Wednesday 23 March
Canberra      Monday 28 March
Sydney          Tuesday 29 March
Newcastle     Wednesday 30 March

Go to https://www.architecture.com.au/nss to register.

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