Beware of unintended and costly consequences when upgrading houses

This week Tony Trobe talks to Peter Overton,an architect and vice-president of the Australian Solar Council (ACT Chapter)

TT: Do renovations and extensions in the ACT need to have energy ratings provided for the building applications, as is the case for new houses?

PGO: Yes they do. While the Building Code Energy Provisions are aimed at new buildings, the ACT government introduced an appendix to the Building Act in 2011 which sets out various ways in which the Energy Rating software (intended for new houses) can be adapted for use with extensions and renovations. If an extension is more than 50 per cent of the original gross floor area, the legislation requires that the whole house is rated, exactly the same as a new house. It must pass the mandatory 6 Star level under the NatHERS scheme, or meet the mandatory Building Code measures. If the extended area is less than 50 per cent of the original, only the extended part needs to meet the Building Code measures. Purely internal refurbishments will not generally require energy efficiency assessment. Things can get complicated, however, in situations where there may be substantial refurbishment to the original house in addition to a small extension, or if the extension itself faces away from north.

TT: That sound like a problem what happens then?

PGO: If the refurbished part is judged to have a significant effect on the thermal performance of the house or extension, the building certifiers may request that some, or all, of the refurbished area is included in the energy-rated part of the house. In all cases, the extended area needs to pass the current Building Code requirements, and that means the windows must also be assessed against current requirements.

TT: That could make life difficult in older houses which may not have been set up with good orientation or insulation.


PGO: Exactly. It can mean that all the assessed parts (both extension and refurbishment) of the house need to meet the current Building Code measures, just as a new house would. In theory, this is a good outcome, however, in practice, it can lead to situations where satisfying the Code, particularly the requirements for windows, becomes a difficult and very expensive undertaking. The simple spreadsheet calculator provided for use with the Building Code does allow assessment to be made without using simulation software, however, in a house with windows largely facing away from the north, compliance can be extremely difficult without resorting to very expensive, high-performance windows, or lots of retro-fitted insulation in roof, floors or walls.

TT: Do you think the ACT government compliance pathway offered to consumers works as it was intended?

PGO: Not in the case of smaller projects with a lot of refurbishment. We have seen many budget-oriented projects where, despite small size of the extended area, the current code has been applied to much of the house floor area, reflecting the level of refurbishment. This can effectively present a disincentive to making improvements to parts the house, even though the improvements will generally lift the thermal performance of the house and reduce energy use. In reality, some improvement is always going to be better than no improvement, even if, overall, the house may not meet 6 Star level.

TT: If the system isn't working well what would be your suggestion as to how it could be improved?

PGO: I think it should allow for comparative assessment against the level of the existing house in an unimproved state. Rating software could be easily used to assess a "before & after" case. If the house showed a useful improvement after modification (the exact level of improvement would need careful consideration), then it would be deemed to satisfy the code. While some might see this as accepting a "lower bar" for small extension projects, at least there would be a sustained, incremental improvement in the housing stock without so much of a cost impost for the budget-conscious renovator.

Tony Trobe is a Canberra-based architect.