What price a sustainable home?

The sustainability debate is highly complex. It is founded on difficult and sometimes uncertain, even conflicting, science. Many of its technological solutions carry significant financial implications forcing compromise.

We still lack definitive calculations for embedded energy and so have to act on assumptions rather than fact and the moral and political arguments that sustainability evokes can lead to subjective rather than objective conclusions.

In search of a place to start, the following pages cost and quantify the key energy saving options honestly and objectively. Ultimately, everyone in the housing sector is looking for the best solution to minimise the energy footprint of any given building, though what works for a Victorian semi will not necessarily be the best option for a flat in a 1960s tower block. And what can be built in as infrastructure for a new housing estate may not be affordable or practical as a retro-fit for one already built.

Indeed, we should not forget the 21m existing dwellings in the rush to build new eco homes. Even if the government meets its 2020 target of 3m new homes, they will still only represent 14% of total stock. As Professor Anne Power, a member of the Sustainable Development Commission, has stated: ‘You cannot possibly deliver a 60% reduction in carbon emissions [the government’s 2050 target] by doing nothing to the existing housing stock.’

But what, exactly, should we do? Overleaf we have taken a typical three-bed semi and fitted it with a raft of energy saving devices, from the latest technology to old-school options allowing for easy, but accurate, comparison. However, because one form of energy cannot be converted into another without expending energy, three key considerations must inform these comparisons if we are to harness old and new technology sensibly and effectively:

New technology may be sexy and, if used wisely, can bring enormous benefits, but that doesn’t make it universally practical. An ill-advised and ineffective wind turbine is no more than ‘eco-bling’.

We must ensure that people understand that renewable energy, too, is precious and that it cannot be consumed without restraint.

The quality and precision of policy and its attendant legislation will be key. Because regulations, especially when compliance dictates grants and other funding, are naturally followed to their letter there is no room for unintended consequences. For example, to meet the 10% renewables requirement, bio-mass boilers are being installed that run on a type of wood pellet that can only be sourced from China or Scandinavia not a particularly sustainable solution.

Once built, though, buildings do not consume energy that’s down to the people inside them and consequently our individual and collective behaviour will determine the future far more than technology alone. Perhaps the starkest message from the facts and figures here is that the best energy-saving device you can fit into a building is a responsible occupant. Which is why much of our focus is on the implementation and development of technology, such as motion-sensitive lighting, that makes it easy for homeowners to conserve energy.

1 Wholr house ventilation

Waste heat is transferred from bathrooms, WCs and kitchens, after moisture and smells are removed, and reused to heat living areas.

Can be used with solar, air and water heating to provide good internal air quality and cost savings. It is most effective in air-tight, highly insulated homes where poor ventilation and summertime overheating can be problematic.

Electrical use can be offset by installing photovoltaic (PV) panels on a south-facing roof. However, this will increase capital costs.

Cost: £1,600 increasing to £6,000 if linked to solar panels and water heating.

PayBack*: Medium to long-term, depending on type of system.

Embodied Energy: If grid electricity used: 0.5kgCO2/kWh

2 Ground cource heat pumps (GSHP)

Can also be used for cooling during summer by pumping at a low temperature within the under-floor system.

Cost: £4,500-£8,000, including installation, drilling and laying of either a vertical or horizontal heat collector.

Payback*: Medium to long-term depending on ground conditions.

Embodied Energy: If grid electricity used: 0.5kgCO2/kWh.

3 Solar water heating

The sun’s energy is absorbed by roof-mounted collection panels into a circulating liquid (water with anti-freeze). The heated liquid is then passed through a coil in a hot water cylinder to heat the water. It can be linked with GSHP to offer maximum hot water provision. Typically this will provide the following amounts of the hot water demand:

Summer 50-60%

Spring/Autumn 40-50%

Winter 15-25%

The panels only work efficiently on a south facing roof angled at 40 degrees and are dependent on external conditions. Back-up hot water can be provided by varied sources from biomass and ground source to gas and electricity via PV.

Cost: approx £4,500

Saving: £150 (0.07p/kWh) a year.

PayBack*: Short to medium-term depending on position and shading.

Embodied Energy: If grid electricity used: 0.03kgCO2/kWh.

4 Photovoltaic electricity (PV)

Roof mounted, light-sensitive, solid state semi-conductor cells absorb and convert the sun’s energy into DC (direct current) electricity which is then converted to AC (alternating current) for domestic use. Excess energy can be exported and sold to the National Grid.

Cost: £8,000 for generating 1kWp (1kW of electrical energy at peak operating conditions).

Saving: £63 (0.07p/kWh) a year.

PayBack*: Long-term, depending on position and shading.

Embodied Energy: If grid electricity used: 0.05kgCO2/kWh.

5 Roof-Mounted wind turbine

Turbines convert wind power into DC, which is then converted into AC for domestic use. Turbulence from the supporting structure and surrounding buildings will decrease output. Turbines need to be rotating continually for several minutes before the energy is recorded and allowed to be counted as energy exported (sold) to the grid.

Cost: £1,600 for a direct drive turbine with generation potential of 800W at a wind speed of 12.5m/s. Plus additional costs for structural requirements and vibration protection.

Saving: Approximately 480kWh a year dependant on external conditions and turbulence, equating to £33.60 a year (0.07p/kWh).

PayBack*: Short to medium-term.

Embodied Energy: If grid electricity used: 0.03kgCO2/kWh.

6 Rainwater harvesting

Rain is collected from the roof(s) via down pipes and stored in an underground tank (1200 litres upwards) for garden irrigation, toilets and other non-potable water appliances such as washing machines. Water butts can be used as an alternative for garden irrigation.

Cost: £2,800 for below ground rain water storage.

Saving: Based on a 60m2 roof area and an annual rainfall of 850mm, approximately 34m3 will be saved per year, or £44.

Pay Back: Medium to long-term, depending on installation and water use.

Embodied Energy: N/A

7 Combined heat and power

Two types of CHP predominate, either fuelled by biomass (wood chip/pellet) or by natural gas. Power generated is DC and connected to the grid through an inverter allowing conversion to AC for exporting/importing in either direction. The ‘generate-and-resell’ model allows surplus power to be sold back to regional electricity companies. While biomass CHP installations require large plant and storage space, gas-fired installations require less space. Both systems have a very high coefficient of performance ratings as the energy consumed is produced at the point of consumption.

CHP generates large quantities of hot water requiring long-term storage. This can be deployed as low energy consumption absorption cooling.

Cost: £4,500-£5,500 for a micro CHP (run on gas, biomass versions are not yet available).

Saving: Generation of electricity gives free heating as a by-product of operation.

PayBack*: Medium term, depending on system size.

Embodied Energy: N/A

8 Low Energy Equipment

To minimise CO2 emissions, provision should also be made for the integration of low energy and low water use appliances. These include:

• 6/4 dual-flush WCs
• Flow reducing/aerating taps
• 6-9 litre per minute showers
• Shallow baths
• AAA-rated dishwashers with maximum volume of 18 litres
• AAA-rated washing machines with maximum volume of 60 litres
• AA-rated fridges and freezers

Cost: Dependant on manufacturer.

PayBack*: Short-term, depending on use.

9 Waste management

Recycling, composting and education for waste reduction are all low-cost options. When developed with education and in conjunction with facilities offered by the local authority, wider savings in both cost and environmental impact are achievable.

10 Traditional measures such as double glazing, roof lagging...

The Energy Saving Trust recommends you consider the following to make savings:

• Turning the thermostat down by 1oC could save 10% on average heating bills = £40 a year.
• Using energy-saving lamps. Just one can save up to £100 over the lifetime of the lamp.
• Insulating a loft space with a typical installation cost of £240-£270 will save between £180-£220 a year in energy bills.
• Draughtproofing around doors and windows with a typical DIY installation cost of £75 will bring annual energy savings of around £20 and a payback in five years.
• Double glazing a typical house will give an annual energy saving of around £80-£100. With a typical installation cost for a semi detached house of £5,500, payback is around 55 years.
• Additional insulation on a hot water tank with a DIY cost of around £5-£10 and an annual energy saving of around £20, payback can be in as little as six months.
• A+ or A++ ratings give an annual energy saving of £45 for fridge freezers or £20 for refrigerators.
• A-rated washing machines give an annual saving of £10 and dishwashers £20.

11 Green energy tariffs

The use of green energy tariffs, even though they are not included in current renewables calculations, should still be considered within the design philosophy. When linked with energy-saving technology and a commitment to a ‘low-energy lifestyle’, it will reduce long-term emissions.

Cost: Now comparable with standard tariffs.

Pay Back*: Short term as tariffs are similar to normal use.

*Payback is defined thus: short-term: 5-25 years; medium term:

25-45 years, long-term: 45+ years.

Unless stated, costs are exclusive of VAT and installation. Figures are costed on a ‘typical’ two or three-bedroom semi. Embodied energy figures are taken from the Green Register and are for manufacturing and day-to-day use.