How Do I Make Sure My New Home is Cheap to Run?

First of all, the good news: compared to the home you currently live in (assuming it was built before about 1990), the new home you’ll end up building – practically however you do it – will be significantly warmer and cheaper to run (assuming it meets the Building Regulations). These regulations have tightened significantly over the past 20 years and knowledge of energy efficiency best practice has become more commonplace – so much so that you could do just the bare minimum and be amazed as to how warm your new home feels compared to your older one. Not to mention how much cheaper it will be to run.

By far the most important – as well as the easiest and cheapest – element of ensuring low future running costs is to concentrate on the amount of energy that your home requires in order to run. That’s a factor of several different factors: its size, the number of occupants and so on, but the element you have some control over is your home’s ability to hold on to the energy it generates.
 

There are many things to consider here – not least the way the house is designed and built, minimising so-called ‘thermal bridging’ which ensures materials that face the outside don’t conduct cold air into the house. Insulation is also critical – ensuring that heat isn’t lost through the roof, walls and floors. The main indicators here are the U-value and the PSI-value.
 
As you compare different build systems and suppliers, all will list the U-value of the walls, roof, and floors they sell. It’s a measure of the heat loss through the system or window, and the lower the number, the better. It is designed to help you compare the different choices. Although there isn’t a universal building regulation requirement for U-values, the notional target is 0.18 for walls. To offer some context on this, the requirement in 2006 was 0.3; most poorly insulated old homes (i.e. most of them) will have U-values in excess of 0.2. From a thermal bridging perspective, PSI-values measure the heat lost along a metre of junction between two thermal elements. Look at how your system designs it out.

Because it’s relatively cheap and easy to install extra insulation at the construction phase, most experts agree it’s the first thing you should do if you really want to minimise your long-term bills – certainly much easier and more effective than fitting insulation after you’ve finished. Different types of insulation have different levels of performance, of course, but in general terms, the more the better. Modern forms of insulation such as those with phenolic cores perform far better for each inch of thickness than traditional forms such as expanded polystyrene or mineral wool.

 

As modern homes tend to have a bigger window to wall ratio (as opposed to traditional cottage-style homes, which have more walls and smaller windows), it’s important to consider the U-values of the windows, too.
 
It’s redundant to have highly insulated walls only for the windows to leak heat. Your window supplier will outline the performance, with triple glazing being the best available, its U-values siting around 0.8; double glazing can achieve around 1.6.
 

The other element of minimising the amount of heat loss from the building is to concentrate on airtightness- now a requirement under building regulations. The more airtight a house, the fewer draughts and gaps for warm air to depart and the cold to get in. As insulation performance gets to a stage where marginal gain is minimal, airtightness is a significant way you can improve the energy efficiency of your home.
 
Generally speaking, leaky homes usually occur because of poor building system choice (i.e. the system could never be airtight) or poor site practice, such as a lack of attention to detail on the part of the builders primarily using blockwork, not finishing around windows properly, and so on. Factory-built panellised systems such as Kingspan TEK and Kingspan ULTIMA clearly reduce the capacity for things to go wrong in this area.
 

Having minimised your heat requirement by concentrating on the four core areas of energy efficiency – thermal envelope design, insulation, window performance and airtightness – you have mastered the ‘fabric first’ approach, and can then decide on how you generate your energy. Simply put, the conventional choices have limited upfront costs but an element of uncertainty about future running costs.
 
The main options for renewable systems include (but are not limited to) biomass (wood pellets or logs); heat pumps (air or ground source); and solar (creating hot water or electricity as PV panels). They tend to have lower long-term running costs but a higher upfront investment, ranging from £5,000 to £15,000 in most cases, depending on the particular system and its size. There are a range of government incentives designed to mitigate the burden of these high-capital costs.
 
Building your own home is all about making decisions. For most people who want to do the sensible things to invest in low running costs, the best approach is to get the basics right – the things you can’t change later. And that is the compelling case for a fabric-first approach.
 

U-value
A measure of the heat loss through a square metre of thermal element such as a wall. The U-value (the lower the number, the better) calculation accounts for the thermal resistance of each of the materials concerned, along with an assessment of the repeating thermal bridges that exist.
 
PSI-values
A measure of heat loss along a metre of junction between two thermal elements. PSI-values are concerned with non-repeating thermal bridges and are based on standard construction details. The default PSI-values can be enhanced by thermally modelling the junctions.