Property Size and Type and its Effect on Energy Usage and Your EPC

EPC

Energy usage by property size and type

It’s a simple fact that large old detached houses have a lower EPC score than modern flats.

Logic suggests that, on average, larger properties will generally use more energy for heating than comparable smaller ones. However, there are many variables involved in such a calculation, not least of which will be the type of property. Flats tend to have fewer external walls and roofs than terraced houses, which in turn have fewer than semi-detached or detached houses. The larger the external surfaces, the greater the expected loss of energy. Other variables such as the age of the property, building materials and the effectiveness of energy efficiency measures that have been installed also confuse the picture.

So although there are a lot of things you can do to influence the score of your EPC, some things you can’t.

A large sample of households would be needed to make an analysis of energy need by dwelling type statistically reliable. The Government’s Home Energy Efficiency Database (HEED) provides such a data set. While not freely available to individuals, the information is available to researchers and organisations planning and monitoring progress in home energy efficiency. It includes information collected between 1995 and 2012 on some 13 million dwellings in the UK, almost half of the country’s housing stock. The data includes property age, type, tenure and energy use, and details such as glazing type, wall type, heating systems and energy efficiency measures.  All of which are fundamental to EPC calculations too.

Researchers at the Energy Institute of University College London were given access to the database to undertake a wide range of analyses, including an evaluation of average energy usage by dwelling type and number of bedrooms.  Their research is reported in the journal Energy Policy (Energy efficiency in the British housing stock: Energy demand and the Homes Energy Efficiency Database. Hamilton I.G. et al, Energy Policy 60 (2013) pp 462-480).

The researchers analysed the data to provide an overview of the statistics for gas and electricity use in 2006 by different types and sizes of dwelling. The following tables summarise their findings, giving the median value in each case (i.e. the mid value when all data are set out in increasing order of size), as they showed this to be a more representative ‘average’ than the mean. The figures for gas and Economy 7 tariff electricity are likely to be most representative of energy demand for heating.

Median energy use for different types of property

Type

Normal tariff  Electricity (kWh/yr) median

Economy 7  tariff  Electricity (kWh/yr) median

Gas (kWh/yr) median

Flat

1,967

4,309

10,242

Bungalow

2,784

4,828

16,129

Terraced house

3,038

4,845

14,983

Semi-detached house

3,310

4,765

16,571

Detached house

4,023

5,135

20,992

Median energy use for different numbers of bedrooms

Number of bedrooms

Normal tariff  Electricity (kWh/yr) median

Economy 7  tariff  Electricity (kWh/yr) median

Gas (kWh/yr) median

1

1,934

4,685

11,137

2

2,554

4,662

13,541

3

3,357

4,637

16,590

4

4,358

5,390

21,560

5+

4,890

6,171

24,246

As expected, the results confirm that detached houses and bungalows have the highest energy usage. The figures show a clear decrease in demand as the level of detachment declines, so that flats, with the highest number of party walls and ceilings, show least energy usage.  Something which EPC scores also make clear too.

The median gas demand increases on average by 22% for every additional bedroom over one in any property type. Overall electricity use also generally increases with additional bedrooms, though not as clearly and steeply as gas.

Loft Insulation

Loft Insulation

Roof insulation

Modern houses are built with loft insulation, but older properties may be losing a quarter of their heat through the roof. Installing or topping-up insulation in a standard loft is an easy and cost-effective way of making a home more energy-efficient. 

Types of loft insulation

For an accessible loft, the most straightforward method is to lay loft rolls of mineral, glass or sheep’s wool between and over the ceiling joists to a depth of 270mm. A layer is placed between the joists then another is laid at right angles to cover them.  For topping up, the appropriate depth of loft roll is simply laid on top of the existing material.  The loft door can be insulated, but it is better to replace it with an insulated trap door.

The second method, blown installation of fire-retardant mineral wool or cellulose, is for roof spaces with difficult access. The process usually takes no more than a couple of hours.

Finally, for flat roofs, expanded polystyrene insulation boards can be attached on or beneath the roof. These can be a bit more expensive and complicated to install, and can lead to condensation problems, so installation is best left to a professional.

Storage

If the loft is used for storage and there is insufficient joist depth to accommodate the insulation, there are two solutions. The first is to infill between the joists with loft roll and then lay insulation boards and chipboard loft boards across the top. Alternatively, the level of the loft floor can be raised to accommodate two layers of loft roll, by fitting battens across the joists and nailing chipboard loft boards on top.

For either method, a gap should be left between the loft insulation and the boards to prevent condensation and compression of the loft roll, which will reduce its efficiency.

Loft conversions

The floor of an existing loft conversion can be insulated to keep the rest of the home warm, with loft roll added between pitched roof rafters and insulation boards to false ceilings, walls and dormers to keep the loft room itself cosy. A 50mm gap is needed between insulation boards and roofing felt for ventilation.

Other things to remember

For DIY, choose products with an ‘Energy Savings Trust Recommended’ logo, insulate pipes and tanks and do not install loft roll beneath the cold water tank. Remember to wear protective clothing and a mask.

If the space is used to store perishables like photographs or clothes, the roof should also be insulated to keep more heat in the loft.

An insulated loft needs to be adequately ventilated around the eaves to prevent damp. If there is an existing damp problem it is best to get professional advice.

Costs and savings

270mm of new loft insulation could yield annual savings of £225 for a detached house or £135 for a three bedroomed semi-detached. The cost would be £395 or £300 respectively. It may be possible to get grants through the Energy Company Obligation (ECO) towards the costs. Check with your energy supplier.