BCA 2010 - ABCB - Australian Building Codes Board

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BCA ENERGY & INDUSTRY EFFICIENCY NEWS IN THE BUILT ENVIRONMENT Comparative Stringency of Elemental Glazing Provisions For BCA 2010 Volume Two Written by Bruce Lightfoot, Consultant, Australian Building Codes Board Key points: 1. Glazing Provisions for BCA 2010 use a somewhat different approach than BCA 2009, which prevents a direct comparison of stringencies in simple terms of percentage area change. However, examining the types of glazing needed at typical glazing ratios (ie the proportion of glazing to floor area) is a practical means of comparing outcomes. 2. The BCA 2010 provisions allow for minimal changes of glazing systems although glazing ratios may be constrained in some cases. 3. Glazing ratios under the BCA 2010 provisions, nevertheless, remain comfortably within the typical range (20-30%) identified by an ABCB Office survey in 2002 and found in practice. 1. Elemental glazing method for 2010 Provisions for BCA 2010 extend the BCA 2009 calculation method to produce outcomes closer to those achieved by simulation. In particular, the provisions assess wintertime solar access in detail to reward good orientation and glazing selection. Stringency has been increased by changes to the glazing constants (in Table 3.12.2.1) and flexibility has been improved by adding winter exposure factors for the calculation of conductance requirements in climate zones 2-8 (in Table 3.12.2.2a). The new exposure factor is applied in a revised conductance calculation for climate zones 2-8 in Part 3.12.2.1(a)(ii)(B). Although slowing heat conduction into or out of a dwelling can be beneficial year round, the stringency is set by ensuring that the rate of heat loss in winter does not exceed the rate of heat gain that can be supplied by wintertime solar radiation. Winter gains can be at risk from shading or glass tinting to control summer gains unless good orientation and beneficial shading geometries are used. The new winter exposure factors take account of these opportunities to balance the competing summer and winter requirements. 2. Table of glazing types needed for similar dwellings The extended calculation method for BCA 2010 means that 2009 and 2010 stringencies cannot be compared simply in terms of percentage changes. Comparing requirements for similar dwellings, however, can illustrate their relative impacts. The table on the following page shows how the 2009 provisions and the 2010 provisions affect dwellings with similar glazing layouts in each BCA climate zone. Two configurations are compared. The first configuration assumes that the total glazing area is distributed equally between the four faces of the dwelling which are oriented to the North, East, South and West. The dwelling is therefore “orientation neutral”, meaning that there is no advantage in rotating it through any 90° step. A typical level of shading by eaves is assumed for each climate zone and the table shows the glazing system needed if the same system is used throughout the dwelling. The glazing system needed may vary 20 • Australian Building Regulation Bulletin
under the 2009 and 2010 provisions. The table also shows the permitted glazing ratio (the proportion of total glazing area to the dwelling floor area) in each case. The second configuration slightly skews glazing distribution to the favourable North orientation. 33% of the glazing faces North and 22% to each of the remaining cardinal orientations. The same glazing system is applied to this configuration but shading is increased in some cases to take advantage of opportunities for larger glazing areas. The effects of this favourable orientation are most obvious in climate zones 7 and 8. The examples shown are for houses with concrete slab on ground floors and Standard air movement levels. As in BCA 2009, the requirements are more demanding for houses with suspended floors but less so for houses with high air movement levels. Table 3.12.2.1 now allows ceiling fans to be used to meet the “High” air movement requirements. The “Standard” air movement provisions in Part 3.12.4.1 have reduced the minimum opening area needed for some situations in climate zone 1 from 15% to 10%. This change prevents the opening requirements driving glazing areas to unhelpfully high levels. The assumption of a consistent glazing system throughout both example configurations is conservative because, in practice, North orientation in most locations will permit simpler and cheaper glazing systems than nominated for the whole dwelling. 3. ABCB Office survey of typical glazing ratios Before energy efficiency measures for housing were introduced into the BCA, the ABCB Office conducted a survey of residential glazing ratios (the proportion of glazing to floor area) and published the findings on the ABCB website in 2002. The principal findings reported were: • Glazing ratios ranged from 14% to 30% and averaged 22%. • The highest average value for any one location was 27% in Hobart. • The lowest average value was 16% in Alice Springs. • The populous centres of Brisbane, Sydney, Adelaide, and Perth had location averages lower than the national average of 22%. • Melbourne had a higher location average of 26%. The 22% national average glazing ratio identified by the survey coincided exactly with the average figure found by the original developers of the Nationwide House Energy Rating Scheme (NatHERS). ABCB Energy Efficiency project - 2010 elemental glazing proposals printed 10/2/10 ENERGY EFFICIENCY BCA + IN iNDUSTRY THE BUILT NEWS ENVIRONMENT Comparison of glazing systems needed for similar dwellings in 2009 and 2010 The examples shown are for houses with concrete slab on ground floors and Standard air movement levels. Requirements are more demanding for houses with suspended floors but less so for houses with High air movement. Calculations assume half of all glazing is 2100mm high and half is 1200mm high. Shading projections shown can include the depth of any window reveals (recesses). Equal glazing on all four sides One third of glazing facing North shading (mm) glazing / floor area glazing system shading (mm) glazing / floor area glazing system Climate zon e 1 2009 24% single clear glass in improved aluminium frames No change 990 990 (eg. Darwin, Townsville) 2010 23% single toned glass in improved aluminium frames Wintertime solar heat gain is not considered in this climate Climate zon e 2 2009 33% single clear glass in improved aluminium frames 39% single clear glass in improved aluminium frames 660 990 (eg. Brisbane) 2010 27% single low-e glass in improved aluminium frames 34% single low-e glass in improved aluminium frames Climate zon e 3 2009 21% single clear glass in timber or UPVC frame 25% single clear glass in timber or UPVC frame 660 660 (eg. Longreach) 2010 22% single low-e glass in improved aluminium frames 23% single low-e glass in improved aluminium frames Climate zon e 4 2009 660 30% double clear glass (6mm air gap) 660 30% double clear glass (6mm air gap) (eg. Wagga Wagga) 2010 24% double clear glass (12mm air gap) 25% double clear glass (12mm air gap) Climate zon e 5 2009 660 35% single clear glass in improved aluminium frames 990 35% single clear glass in improved aluminium frames (eg. Sydney, Adelaide, 2010 28% single clear glass in improved aluminium frames 34% single clear glass in improved aluminium frames Perth) Climate zon e 6 2009 33% double clear glass (6mm air gap) 35% double clear glass (6mm air gap) 165 330 (eg. Melbourne) 2010 27% double clear glass (12mm air gap) 31% double clear glass (12mm air gap) Climate zon e 7 2009 38% double clear glass (12mm air gap) 38% double clear glass (12mm air gap) 0 330 (eg. Canberra, Hobart) 2010 28% double clear glass (12mm air gap) 39% double clear glass (12mm air gap) Climate zon e 8 2009 40% double low-e glass (12mm argon gap) in timber frame 40% double low-e glass (12mm argon gap) in timber frame 0 660 (Alpine) 2010 40% double low-e glass (12mm argon gap) in timber frame 73% double low-e glass (12mm argon gap) in timber frame Australian Building Regulation Bulletin page 3 of 3 • 21
Page 1: BULLETIN AUSTRALIAN BUILDING REGULA
Page 4 and 5: CHAirMAN’S ADDrESS Mr graham huxl
Page 6 and 7: BCA & INDUSTRY NEWS BPIC MAINTAININ
Page 8 and 9: ific metal screens in buildings wit
Page 10 and 11: BCA & INDUSTRY NEWS New Safety Stan
Page 12 and 13: BCA & INDUSTRY NEWS Report on Devel
Page 14 and 15: BCA 2010 NOW AVAILABLE... Energy ef
Page 16 and 17: A STATE PERSPECTIVE Building a bett
Page 18 and 19: COVER STORY Climate Change Adaptati
Page 20 and 21: COVER STORY Damage to houses in Inn
Page 24 and 25: INDUSTRY Perspective Four Decades o
Page 26 and 27: INTERNATIONAL Perspective manufactu
Page 28 and 29: BAF 2009 OVERVIEW Building Australi
Page 30 and 31: BAF 2009 OVERVIEW Construction haza
Page 32 and 33: EGULATOrY DEvELOPMENT DrAFT STANDAr
Page 34 and 35: INTERNATIONAL Regulatory Developmen
Page 40 and 41: Client Feature PRODUCT Innovation B
Page 46 and 47: CONFErENCE + Events Calendar CONFEr
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