Heat Losses

[Barrie Christian]

For dwellings, heat is lost through the external envelope (walls, floors and roof, as well as windows and doors), and ventilation. Which of these sees most heat loss is affected by how old the house is, and the size and type of windows. It is only relatively recently that insulation has been required for houses (about 40 years) and the minimum thickness required by Building Regulations has increased by several times.
Most houses in the UK have poor insulation - inevitably so. In 2010, just over 100,000 homes were built in the UK - to current energy saving regulations. Compare that with the 23 million total number of dwellings which had been built when energy saving was either not required, or the standards were substantially less.
Many houses have had insulation improvements - loft insulation, cavilty wall insulation, and windows replaced with double glazing.
Current Government policy towards saving energy in dwellings places emphasis on raising insulation levels - "Fabric First".
By building in measures which will endure over the lifetime of a dwelling, this will ensure that the energy savings will persist. But there are ways to save significant amounts of energy which, by complying with the Building Regulations, are simply wasted.
The Building Regulations require that "wet-rooms", ie kitchens, bath/shower rooms, utility rooms and WCs, have extract ventilation. If this is mechanical extract, the this method discharges heated air directly to the outside.
For a semi-detached house I designed recently, to 2010 Regulations, the energy usage is shown in the attached chart.Energy Usage 2.jpg
Extract ventilation is the second largest energy usage, and a significant part of that could be saved. By installing heat recovery on the extract system a very large part of the wasted heat could be returned to the house.

[Barrie Christian]

There is an organisation called Insulated Render and Cladding Association (INCA) dedicated to supporting external wall insulation contractors and suppliers.
Insulating the outside of walls is an option in some instances, for example with solid external walls.
INCA provide slightly different figures to those above.
They say that "at least 80% of the country's 26 million homes expected to be still standing in 2050, including around 7 million un-insulated solid wall properties ...".
I suspect that for the majority of those 7 million dwellings, external render would not be appropriate. They are likely to have walls whose external appearance is highly attractive (eg stone walling, old brickwork), and many will be Listed.
For me, and possibly many others, adding extra thickness to the outside of the wall, and it must be in the order of 30 - 50mm at least, makes detailing around windows and doors awkward, and often not attractive.
But if it can be done carefully, it is worth considering to save energy.
This form of remedial insulation is eligible for government subsidy.