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Existing stock

The UK is working towards a target of reducing CO2 emissions by 60% by 2050 (DTI, 2003b). To reduce CO2 emissions in the domestic sector, the scenarios above clearly show that new build cannot be the only area of focus. To approach the 60% target, existing stock, and measures used to reduce energy consumption in these buildings, need to be taken into consideration.

Scenarios 4, 5 and 6 investigate the effect on total domestic energy demand of making improvements in the energy efficiency of existing houses in the South West. This means looking at measures such as cavity wall and loft insulation, low energy light bulbs and A-rated white goods.

General housing and domestic energy assumptions for existing stock

  • Over 93% of dwellings in the South West have central or programmable heating (ODPM, 2003). The average household replaces its boiler every 10-15 years. Installing a high efficiency condensing boiler and heating controls could save 0.8 tonnes of CO2 per household per year (ESD, 2004). It is likely that it will become mandatory to install condensing boilers from April 2005.
  • Approximately two thirds of households in England have cavity walls (ODPM, 2003). Of these, only one third have been filled to reduce heat loss (DTI, 2004a). It costs about £350 to insulate wall cavities and delivers CO2 savings of 1.3 tonnes per year for the 'average' UK house (ESD, 2004).
  • 85% of dwellings in England have a loft space, and 95% of these have some loft insulation, with only half having over 100mm of insulation (ODPM, 2003 and Utley et al., 2000). At a cost of £200, loft insulation can be increased by 150mm, to achieve CO2 savings of 0.1 tonnes per year per household (ESD, 2004).
  • On average, a householder will replace appliances every 10 years. If all replacement appliances were A-rated, and low energy light bulbs were fitted, the average household could save 0.5 tonnes of CO2 each year. The estimated cost of installing A-rated white goods and low energy light bulbs is £1360 (ESD, 2004).

Scenario 4: Technology improvements, but no energy efficiency measures

What is the impact on domestic energy consumption and CO2 emissions in 2015, if no energy efficiency measures are installed in existing buildings, but technology improvements are implemented, between 2001 and 2015?

The following variables were assumed:

  • Gas, solid fuel and petroleum consumption remains constant in existing properties between 2001 and 2015.
  • Electricity consumption in 2015 is based on a 1% annual increase in consumption in the domestic sector between 2001 and 2015.
  • The CO2 emission factor changes from 0.43 kg CO2 / kWh in 2001 to 0.36 kg CO2 / kWh in 2015, due to a change in the technologies used to generate electricity.

This would mean energy consumption by the existing housing stock will increase, but CO2 emissions will decrease due to a change in the CO2 emission factor. CO2 emissions will decrease from 12.6 million tonnes in 2001, to 12.4 million tonnes by 2015 - a reduction of 230,000 tonnes (2%). Table 6 summarises the findings for Scenario 4.

Table 6
Estimated CO2 emissions generated by existing homes in the South West, based on technology improvements but no energy efficiency measures, in 2015
 
Fuel type Base case 2001 Scenario 4
GWh CO2 (tonnes) GWh CO2 (tonnes)
Total 46,931 12,633,297 49,019 12,405,605
of which…  
Electricity 13,967 6,005,776 16,055 5,778,085
Gas 27,969 5,314,110 27,969 5,314,110
Solid fuel 1,909 572,600 1,909 572,600
Petroleum 3,087 740,810 3,087 740,810
 
Sources: ONS, 2003b and SWRA, 2003

This scenario gives a domestic energy ecological footprint in 2015 of 0.70 gha per person, a reduction of 0.01 gha per person from the 2001 base case.

Scenario 5: Energy efficiency measures

What is the impact on CO2 emissions and the domestic energy ecological footprint if energy efficiency measures are installed in existing buildings between 2001 and 2015?

The following variables were assumed:

  • All householders replace existing white goods with A-rated ones, and fit low energy light bulbs.
  • All remaining wall cavities are filled.
  • All households with less than 100mm of loft insulation increase it to 250mm.
  • All households install a condensing boiler and heating controls.

This means CO2 emissions from the existing housing stock would decrease from 12.6 million tonnes in 2001, to 8.3 million tonnes by 2015 - a reduction of 4.4 million tonnes (35%). Table 7 summarises the findings for Scenario 5.

Table 7
Estimated CO2 emissions generated by existing homes in the South West, based on energy efficiency measures, in 2015
 
  Base case 2001 Scenario 5
Fuel type CO2 (tonnes) CO2 (tonnes)
Total 12,633,297 8,255,297
of which…  
Electricity 6,005,776  
Gas 5,314,110
Solid fuel 572,600
Petroleum 740,810
 
Sources: ONS, 2003b and SWRA, 2003

This scenario gives a domestic energy ecological footprint in 2015 of 0.46 gha per person, a reduction of 0.25 gha per person from the 2001 base case.

Scenario 6: One planet lifestyle

What further measures would be required to reach a one planet lifestyle for domestic energy use in existing buildings by 2015?

This scenario is an attempt to meet environmental sustainability criteria. The criterion used for this scenario is the 'earthshare', taken from the National Footprint Accounts (Redefining Progress, 2002), which assumes the human race lives within the natural limits of the planet. With the current ecological footprint of a South West resident at 5.56 gha/person, an overall reduction of 66% is required to meet the earthshare criterion.

The following variables were assumed:

  • All measures in Scenario 5 are implemented .
  • 80% of householders in the South West install a solar hot water system, offering CO2 savings of 0.3 tonnes per household (ESD, 2004).
  • 10% of householders in the South West fit solid wall insulation, offering CO2 savings of up to 1 tonne per annum (EST, 1999).
  • 25% of householders fit wood burning pellet stoves, offering carbon neutral (but not necessarily ecological footprint neutral) space heating and hot water.

* Wood burning stoves are considered carbon-neutral because the CO2 emitted from burning the wood is equal to the CO2 absorbed by the trees whilst growing. However, the use of wood fuel is not necessarily neutral in ecological footprint terms due to the use of forest land to grow the trees. However, if waste wood was used as fuel, this would have a neutral ecological footprint.

25% of householders fit domestic CHP systems, offering additional CO2 savings of 1.5 tonnes compared to a condensing boiler (ESD, 2004).

CO2 emissions from the existing housing stock would decrease by 66% from 12.6 million tonnes in 2001, to 4.3 million tonnes by 2015 - a reduction of more than 8 million tonnes. Table 8 summarises the findings for Scenario 6.

Table 8
Estimated CO2 emissions generated by existing homes in the South West, based on one planet lifestyle assumptions, in 2015
 
Fuel type Base case 2001 One planet lifestyle scenario
Total 12,633,297 4,255,297
of which…  
Electricity 6,005,776 4,255,297
Gas 5,314,110
Solid fuel 572,600
Petroleum 740,810
 
Sources: ONS, 2003b and SWRA, 2003

Energy saving measures: financial benefits to householders

As well as CO2 savings, householders who install energy saving measures in their homes could benefit from reduced energy bills. For example:

Energy saving measures: financial benefits to householders
 
Measure Installed cost (with no grant funding) Saving (£/yr)
Cavity wall insulation c. £350 £40-145
Condensing boiler (CB) c. £1,200* £20-£50
External wall insulation £3,500-£5,500 £70-£170
Lighting (4 bulbs)   £20
* the additional cost of purchasing a CB rather than a non-CB is approximately £150
 

Various grants and schemes are available to help homeowners to reduce their CO2 emissions.

Sources: EEBPP, 2003 and ESD, 2004