Energy efficiency in different house orientations

As we move towards our target of net zero homes by 2050, it’s important to understand early what is required to meet the higher thermal performance and energy BASIX standards coming into effect from 1 October 2023.

Edgewater Homes and Henley Properties are making a head start. They recently reviewed their standard designs for 2 new houses in Oran Park, south-west Sydney, and explored upgrades needed to meet the higher standards.

The houses

Both houses are on standard rectangular flat blocks of about 350m2. They are typical single-level homes with brick-veneer external walls and timber internal wall structures lined with plasterboard. The slabs are waffle pods on reinforced concrete piers of various heights. The internal areas are between 154-163m2 excluding garages. Both homes have 4 bedrooms, 2 bathrooms and 2 garage spaces.

The key difference between the houses is their orientation. The rear of house 1 faces north-east, while the rear of house 2 faces south-west. The orientation of house 2 requires higher specifications to meet the higher BASIX standards.

House 1

House 2

Key design features to meet higher BASIX standards

	House 1: north-east rear aspect	House 2: south-west rear aspect
Energy	We introduced a solar hot water unit (gas boosted, flat plate) instead of the standard 6-star gas instantaneous hot water system. All bathroom ventilation is sealed and exhausted directly to outside air via eave vents (not into roof space). Kitchen ducting is sealed and exhausted directly to outside air. The air conditioning unit has an energy efficiency ratio (EER) of 3.01/3.68 (cool/heat). The kitchen has an upright gas cooker and electric oven. There is an outdoor clothes drying line and a fixed indoor clothes drying line.	Same as House 1, but no indoor clothesline.
Thermal performance	R2.0 insulation was used in external walls (excluding garage) and internal garage wall. This is an upgrade on the standard R1.5 external wall insulation with a builders wrap. No internal wall insulation. R4.0 ceiling insulation was required – an upgrade on R3.5 standard ceiling insulation. Standard roof material can either be Colorbond or concrete tiles. Roof sarking with reflective side down is required to meet the higher standards. All habitable room windows will require Low E single glazed windows with aluminum frames. This excludes wet area windows.	Same as House 1, except as below: A higher level of insulation was required to meet higher thermal performance standards. R2.2 insulation was used in external walls (excluding the garage) and the internal garage wall. R5.0 ceiling insulation was required, higher than House 1 and standard insulation of R3.5. All habitable room windows will require double glazed argon filled Low E glazing with aluminum frames (excluding wet areas).
Water *	A 2000L water tank is connected to all toilets, a cold water pipe to the laundry and an outdoor tap. A sealed stormwater system with 90mm PVC downpipes is connected to the water tank. Overflow is connected to the stormwater easement at the back of the property. All water from the roof is directed to the tank. Water fixtures include: 3-star showerheads 4-star toilet 3-star kitchen taps 5-star bathroom taps	Same as House 1.

*The water standard is not changing from 1 October.

BASIX scores

House 1

Water: 44 (standard is 40)

Energy: 71 (standard is 70)

Thermal performance: Pass

House 2

Water: 43 (standard is 40)

Energy: 71 (standard is 70)

Thermal performance: Pass

Conclusions

While both houses needed upgrades to meet the higher BASIX standards, House 2 needed more significant upgrades.

Additional costs can be minimised by optimising the orientation of the living areas to be north or north-east facing. Where this is not possible, improved insulation and glazing will ensure the home is more comfortable year-round and less reliant on air-conditioning and other forms of heating and cooling.

For House 1, the estimated additional upfront cost to meet the higher BASIX standards was $10,100. This was based on a cost + builder’s margin model, reflecting real world cost implications.

The estimated additional cost for House 2 upgrades was approx. $13,000 - $15,000. This was to meet the higher requirements for insulation and window glazing.

Comparing the 2 houses shows how orientation affects the upgrades required. Being south-west facing at the rear, House 2 needs higher specifications to meet the thermal performance standards because:

in winter, it receives less sun in the main areas of the house so higher specifications are required to reduce the heating requirements
in summer, it receives the hotter westerly afternoon sun in the main areas of the house, so higher specifications are required to reduce the cooling requirements.

Additional upfront costs for thermal performance will maximise residents’ enjoyment of their home year round. Homeowners and tenants should be able to rely less on heating and cooling and see reduced energy bills.

Energy efficiency across climate zones

How to achieve higher thermal performance and energy BASIX standards in different NSW climate zones.

Increase to BASIX standards

The NSW Government are improving BASIX standards to build more comfortable homes, cut energy costs and contribute to our target of net zero homes by 2050.

Last updated: 29/06/2023