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Assumptions & references

The possible monetary savings, costs and investments communicated in the Green Family three stage program have been prepared by Natural Strategies Group, an environmental digital publishing business.

Natural Strategies Group advises that the amounts used in the Green Family Case Study are estimates. In most cases, estimates for savings are conservative and estimates for costs and investments are less conservative.

To generate the figures and estimates in the Green Family Case Study, Natural Strategies Group utilised data primarily from the Australian Bureau of Statistics (4102.0 Australian Social Trends, 2006).

The Green family is based on the household expenditure pattern of the “Couple with dependent children only, eldest child 5 to 14” life cycle group.

The expenditure pattern and actual amounts are combined with further assumptions about reduced expenditure to generate the savings listed in the Green Case Study. The following list outlines additional assumptions combined with ABS figures.

Table 1. Assumptions used to generate savings amounts.

Action Assumption Used
Car Pool | Ride a Bike | Use Public Transport (to Work)  Green House Gas Office estimates 33% of car cost relate to getting to work. Used a 3 person car pool as the alternative to generate costs.
Waste Reduction Habits A 2005 paper by The Australia Institute (Wasteful Consumption in Australia) researched and calculated that an average of $1000 is wasted p.a. per person. To be safe we used the individual figure ($1000) for the whole of the Green family.
Slow and Local Travel We assumed that the Greene family would not travel overseas.
Buy Second-hand Goods Buy Second-hand Goods Assume 10% saving through buying second hand clothes where possible
Eat less Meat We combined two assumptions:
1. Reduce meat consumption by 25%
2. Increase Vegetable use to offset "Eat Less meat" by 10%.
Tune your Shopping Radar to the Environment Assume 5% saving through buying in bulk, etc…
Cultivate Energy-saving Habits

We combined several assumptions:

1. Turn down thermostat (1degree = 10% reduction in heating bill)
2. Turn all appliances off at night (assume 25% reduction in appliance part of electricity bill)
3. Turn off lights when not in use (assume 20% reduction in light part of electricity bill)
4. Dry clothes on the line (1/3 reduction in laundry part of the electricity bill)

Buy Local and Seasonal Food Assumed this would reduce Vegie and fruit costs by 20%
Grow your own Food Assumed reduction in Vegetable budget by 10%
Cultivate Water-saving Habits Assume 10% saving. Overall water cost is based on an average water bill for Sydney (most expensive average).
Install Solar Hot Water  Solar Hot water reported to have 75% savings in ABS 1367.5 (June 2007) report on WA water use.
Install Efficient Appliances and Fixtures

Assumes jump from 2 to 5 star efficiency in the following appliances

1. Refrigerator
2. Reverse cycle air conditioner
3. TV
4. Oven

Embrace Energy Efficiency

We combined several assumptions

1. block sun to reduce cooling needs + circulate air (2 degree = 20% from cooling bill)
2. Install Compact Fluorescent globes (75% more efficient)

Use Water Efficiently Assume 30% saving through Efficient showerhead, Faucets, dual flush toilet, grey water use, efficient washing machine., etc…
Harvest and Use your Rainwater Assume 60% saving through all garden and toilet from tank (hence need to supply 60% of 265000 litres = 130000 litres)
Water Efficient Gardening | Grow an Indigenous Garden | Mulch Your Patch Water used on the garden constitutes 60% of household use. Eliminating the need to water the garden.
Reduce & Offset your Car Emissions Assumes that efficient driving (no A/C, serviced car, inflated tires, moderate speeds and acceleration) save 25% fuel bill part of car costs
Generate your own Electricity Assumes a system that would Cover entire electricity bill
Make your Renovations Green Estimated savings derived from Greenhouse Office guide to home sustainability (
Recycle Building and Construction Waste Estimated savings derived from Greenhouse Office guide to home sustainability (

Table 2. Assumptions used to generate investment cost estimates

Action Assumption Used
Install Solar Hot Water Estimated cost for midsized (315 litre, 30 tube) Solar Hot water system (installed)
Install Efficient Appliances and Fixtures 

Cost for

1. 5 star 226/92 Lt fridge/freezer @ $2000
2. 3.5 star energy + 4 star water Asko dishwasher @ $1400

Embrace Energy Efficiency Cost estimate based on 10 new compact fluorescent globes, several new trees and a ceiling fan
Use Water Efficiently Cost estimate based on 1 water efficient showerhead, flow control washes, dual flush toilet refit.
Harvest and Use your Rainwater Based on the installed price of a 10,000 litre water tank.
Generate your own Electricity Based on the price of a 12 panel system that will generate approx 3,000 kWh p.a.
Make your Renovations Green Pure “guestimate” of additional costs to make normal renovation green through improved design, double glazing, heat sinks, etc…