Caring for the ageing

In the 1960s the first rules appeared in the UK Building Regulations aimed at limiting heat loss in new buildings. With our climate more energy is required to keep buildings warm in cold weather than to cool them in hot weather. This is the case particularly in housing where houses have been built with central heating since the sixties but air conditioning is still the exception. With global warming this balance may be starting to change. To give ourselves a feel for the scope of the issue, here are some (approximate) numbers...

Number of houses in England: 25M of which (to the nearest half-million)...
<20 years old: 2.5M
20-30 years old: 2M
30-40 years old: 2M
>40 years old: 18M

Only 10% of houses can be described as new. Around 60% are owner-occupied, the rest rented or shared ownership. This ratio seems not to change much with the age of the house.

Maximum allowable U-value (rate of heat loss) for external walls and typical heating load (for a 3-bedroom house) for new houses built in...

1970:     1.6        9.1kW
1980:     1.0        6.8kW
1990:     0.6        5.5kW
2000:     0.45      3.6kW
2010:     0.3        2.2kW
2020:     0.18      1.4kW

Simplifying a little, if all 25 million were similar three-bedroom houses then, from the broad-brush numbers above, new houses - those built since 2000 - use less than 4% of the total energy needed to keep our homes warm.

A house built before 2010 typically needs twice as much heating as one built now, and by 2050 houses already around in 2010 will be at least 40 years old and will comprise more than 70% of the housing stock.

That's enough statistics for now. The lesson is that older houses use more energy and houses last a long time so most of them are relatively old. So even if all new houses were required to be 'zero carbon' from tomorrow (which begs the questions 'What exactly does that mean?' and 'How can it be done?') by 2050 less than one-fifth of houses would meet this standar, saving relatively modest amounts of energy compared with leaving the requirements at today's levels.

To make a big difference, quickly, then we must address the energy needs of older houses. In the 1960s this was done by levelling whole districts of terrace houses and replacing them with tower blocks and maisonettes. This is not going to be repeated and nor should it: making things well and making them last is more sustainable in housing in other areas. A far better strategy is to improve old buildings, reducing their energy needs, making them more comfortable and cheaper to run while increasing their value and helping save the planet.

The energy-saving regulations mentioned above were mainly concerned with fabric heat loss - through walls, roofs, floors and windows and doors - and this is still what most people think of: loft insulation and double glazing. But there are other equally important aspects. The shape and orientation of houses and positions of windows can make big differences to both heat loss and passive heating. And as increasing levels of insulation reduce fabric losses, ventilation losses - throwing energy out of the extract fan or draughty door - become increasingly significant. Warmer summers already seem to be making overheating more of a problem and if this continues we may see air conditioning more widely used. Here too, factors like orientation,  shading and ventilation can lessen problems without having to use even more energy for cooling.

Reducing a house's carbon footprint means not just reducing its energy needs but ensuring the minimum CO2 emissions associated with that energy. Back in the 1960s again, most houses were heated by burning coal, but central heating was the coming thing and to this day, the vast majority of even the newest houses have hot-water radiators and gas boilers. Switching to electricity can reduce carbon as an ever-increasing proportion is renewable, and including photovoltaic solar panels on every new house would increase the renewable ratio.

To make a significant mark on the carbon footprint of our housing stock in the short-to-medium term we need to devise ways of improving existing houses so how do we do this?

Planning

With existing houses we cannot pick them up and turn them round to face south, but if significant alterations are planned, we can plan extensions or demolitions to make them more compact with the minimum external envelope for their internal space, while adding or enlarging south-facing windows will provide more cool-weather passive heating and shading windows from full summer sun with roof overhangs or deciduous trees will help avoid overheating. If roofs are being altered, south-facing slopes are best for adding solar panels.

Insulation

This is the classic approach to energy saving. Most older houses will already have loft insulation, double glazing and, often, cavity-wall insulation. We need to double down on this: when replacing windows go for argon-filled triple glazing; converting lofts, max out on roof insulation; for old houses with solid brick walls add internal or external insulation; if possible, insulate below timber ground floors and always below new concrete floors.

Ventilation

Insulation reduces fabric heat losses so ventilation losses become more significant. Pay attention to sealing gaps, draught-proofing and air leakage through wooden floors. Building Regulations require air-tight houses but also extract fans to through heated air out! Whole-house mechanical ventilation with heat recovery (MVHR) or extract air heat pumps (EAHP) recover all the heat from extracted air and feed it into the heating and hot water systems.

Photovoltaics

Solar panels, preferably on south-facing roof slopes, generate free electricity and any spare goes into the grid, reducing the need for power stations. If you have an electric car or a 'solar' battery you can use the energy you generate even when you're not using any in the home.

Heat pumps

Most houses have gas or oil-fired boilers or burn solid fuel for heating. Fossil fuels are far too valuable to simply burn and should be reserved for when there is no practical alternative andwhere valuable byproducts can be extracted. Even wood-burning stoves or wood-pellet boilers are constantly pouring CO2 into the atmosphere. If the house is well enough insulated its energy needs might be met by a small heat pump extracting heat from ventilation air. In other cases a dedicated heat pump (air-sourced ones are cheapest and easiest to install though ground-source heat pumps are more efficient) will heat a house using renewable electricity.

low U-values means less heat loss thanks to high levels of insulation
doors and windows lose more heat so triple-glazing helps
photovoltaic solar panels reduce the load on power stations
roof overhangs limit summer overheating 
south-facing windows warm the house in colder months
heat-recovery ventilation reclaims the heat from extracted air
heat pumps are efficient and use renewable electricity

All these measures should be incorporated into every new home built but some may be difficult to implement in existing houses. They all cost money and naysayers will say the energy saved will never cover the costs, but the technology is getting cheaper in real terms all the time, while energy costs rise relentlessly, and £10,000 spent this year will seem like a bargain in five years time, so payback time calculations need to take these inflationary effects into account. Plus, improvements like this will enhance property values. Look at all the options and do as much as you can to care for your ageing home.