Retrofitting to six stars
in Architecture and building on 15 November 2011
HOUSE energy ratings are on the rise again. From May, the regulations in the national building code were lifted from five to six stars. Within a year, the new rules will be in place throughout the country (except New South Wales, which uses BASIX instead).
The rating system is based on predicted heating and cooling requirements for your home. Depending on your location, a six-star rating means you’ll need up to a quarter less energy to stay comfortable than you would under the old five-star rules. With utility prices on the march, that equates to a hefty saving on your bills.
So how much does it cost to convert five-star plans to six stars?
In a recent study, Timothy O’Leary and Dr Martin Belusko from the University of South Australia analysed a dozen house designs offered by volume builders. Using standard materials and without any major redesigns, they found it would cost an average of $3900 to lift the plans to the new standard (PDF).
But Alison Carmichael, CEO of the Association of Building Sustainability Assessors, says it’s possible to build to six stars at no extra cost, so long as you include passive solar design techniques such as good orientation and cross-ventilation.
“You need to involve someone who understands thermal comfort right from the beginning,” she says.
If you wait until you’ve settled on the design, moving to a higher rating can get expensive. “By then, there’s usually been so much blood, sweat and tears put into the plan that you’re loathe to change anything,” Carmichael says. “To get it up to six stars, the building sustainability assessor is left with little option than to recommend expensive inclusions such double glazing.”
Retrofitting existing homes
Although the timing and details are still unclear, the federal and state governments have agreed that a dwelling’s energy efficiency should be disclosed when it is put up for sale or lease. That’s sure to provide a big incentive for homeowners to lift their green game. But is possible for every home to hit six stars?
The researchers surveyed each dwelling and calculated its energy rating. Then they modelled a series of upgrades to the building fabric: ceiling, wall and floor insulation, draught proofing, drapes and pelmets, external shading and double-glazed windows.
Govind Maksay, from MEFL, says that without major renovations, six stars will be very difficult to achieve in most homes.
The average upfront rating of the houses they examined was just 1.7 stars. With a full suite of retrofitting measures in place, the average jumped to 5 stars. But out of the 45 dwellings studied, only half a dozen were able to reach or exceed six stars.
In Maksay’s initial study, the full retrofitting package landed at an average cost of over $22,000. However, the changes weren’t all equal, in either impact or cost.
“On average, over 80 per cent of the rating improvement came from the insulation and comprehensive draught proofing,” he says, “but that constituted just 20 per cent of the total upgrade cost.”
In contrast, double-glazing proved highly expensive for more limited benefit.
Although these findings vary according to the dwelling and the modelling undertaken, Maksay says householders can learn important lessons from the study: focus on the fundamentals before going for trendy upgrades – seal gaps and insulate walls and ceilings.
“To really improve your star rating you have to tackle wall insulation, whether that’s with blow-in granulated mineral wool, or by removing the weatherboards or plasterboard and inserting batts.
“Insulating your ceiling and ignoring your walls is like trying to stay warm wearing a beanie, but no clothes,” he says. “The other message is that there’s a difference between wimpy and comprehensive draught sealing. You need more than just door snakes.”
Maksay adds another important caveat: all-out blitzing your home’s star rating probably isn’t the smartest way to spend your money, or save energy, because it only takes into account the building fabric. “You can reduce your energy costs cheaply in other ways, with efficient lighting, appliances and hot water systems, and by reducing standby power,” he says.
“Also, if you’re renovating, think about how you can more effectively heat and cool your house – for example, you could put a super-efficient reverse-cycle air conditioner into your living room and limit the total area you need to keep at the right temperature.”
RETROFITTING CASE STUDIES
From Sustainability Victoria’s On-Ground Assessment of the Energy Efficiency Potential of Victorian Homes.
Construction type: 1970s single-storey, detached brick veneer, 175 m2. Suspended timber flooring.
Rating before upgrade: 1.5 stars
Rating after full upgrade: 5.3 stars
Cost for full upgrade: $45,724 (including double glazing worth $26,288, which added 0.4 stars to the rating, after drapes and pelmets)
Comments: “This home was orientated well,” Maksay says. “The long axis of the block is east-west, so it has a long northerly aspect and the living areas are situated to the north. All the utility areas are on the southern side, with a small amount of glazing. It had very good sub-floor access so it would be possible to insulate the ceiling, walls and floor to a high level.”
Construction type: 1930s single-storey, detached weatherboard, 108 m2. Flooring partially suspended timber and partially concrete slab on ground.
Rating before upgrade: 1.2 stars
Rating after full upgrade: 3.7 stars
Cost for full upgrade: $18,376 (including double glazing worth $11,455 which added only 0.2 stars to the rating, after drapes and pelmets)
Comments: “This house is not oriented very well,” Maksay says. “It only has a couple of windows to the north and one of them is in a bedroom. Wall insulation made a significant impact here – more than doubling the star rating of the house – but there wasn’t sufficient access to install floor insulation.
“But this house is ideally suited to using an efficient gas heater in the kitchen and living space only, because that area is thermally isolated. The Vermont house is centrally heated, so even though it reached a higher star rating, it would have a much larger overall annual heating and cooling bill.”
This article was published in Sanctuary Magazine