Everyone wants an energy efficient home but what is practical for you depends on your budget. In general there are two approaches to be energy efficiency. Firstly there is efficiency through the building fabric. Concentrating on this aspect of a building is commonly called the "Fabric First" approach. If a building is well insulated and free of draughts with south facing glass to catch the sun then it will not require much energy to keep it warm. This approach is taken to its reasonable limit in the passive house standard. The sustainable energy authority of Ireland has some good introductory guidance here. The key requirement for a new passive house is that it takes a maximum of 15 kWhr/m2 a year to maintain a 20 degree temperature 24 hours a day. This would mean that if you were heating a 200 m2 house with an efficient oil boiler it would cost less than €300-00 euro a year to heat - 24 hours a day for the entire year !
The other way to be energy efficient is in how the energy a building requires is produced. Solar water heating and
Photovoltaic power or heat pump systems are all examples. Under the Irish system for assessing energy efficiency (DEAP) a buildings total energy use is what matters and this can mean a poor standard of building with enough renewable power attached will get a high rating. As an extreme example a stone cottage with single glazed draughty windows and no insulation could be an A1 rated home if it had a hydro electric dam attached that produced all the power it needed.
For new house construction the building regulations standards are now very good with a new house been required to be 60% more energy efficient than a house of the same shape built to 2005 building regulation standards. There are specified minimum levels of insulation and construction detailing and airtightness must be tested to a maximum leakage rate. If your aim is to do the minimum to comply with the regulations meeting the various minimum standards for each element will not be enough to meet the overall energy standard. From our experience and testing of various designs if for a typical detached house you were to meet minimum standards for each element and then add an efficient ground source heat pump to produce your heating and hot water you will come close to meeting the required overall energy target. Alternately if you were to take the "Fabric First" approach and you were increase airtightness to passive house standards and add a heat recovery ventilation system with very good triple glazed windows and perhaps a little more insulation you could meet the passive house standard. You would still need to add solar PV, solar hot water or some other renewable energy source in order to meet regulations requirements for renewable energy contributions.a
When looking at upgrading the energy efficiency of an existing house it can be difficult to know how far to go and measures have to be consistent. For example it would be a crazy waste of money to build an extension to passive house standards while not doing any work to existing uninsulated walls. For most typical houses there are some basic measures that are very effective and I would recommend the following as a starting point. 1. Replace an old boiler with a new efficient condensing boiler and upgrade the heating controls with a programmable timer and temperature sat control and thermostatic radiator valves. Older boilers may be only around 80% efficient (or worse) whereas a condensing boiler might be 95% efficient and improved controls mean you will waste less energy. 2 Insulate the attic with around 300mm depth of mineral fibre insulation. This is very easy to do and cheap. Make sure you do not block the necessary ventilation of the roof space otherwise you could cause damp and rot. 3. If the house has cavity walls investigate having them pumped with blown (grey) bead insulation. The sustainable energy authority of Ireland has a grant system which you can find here.