Energy efficiency, airtightness and the environment

The reason why energy efficiency is a pre-design consideration is because it is far more difficult and expensive to reverse engineer an energy efficient home into a design than it is to design it in at the start.

This is especially a concern in ROI where, in simplified terms, the building regulations require that you build a house with an energy rating in the A band; if you do not comply with the regulations the house cannot be lived in. The current energy rating average for a new build in NI is around a C, which is relatively easy to achieve with reasonable attention to detail.