A LOT – When you consider that an average home of 100 square meters has about 80 square metres of exterior walls, its no surprise that external walls lose a significant amount of heat. The large range of construction types and styles of home in New Zealand mean that it’s difficult to state an exact percentage of heat loss lost through walls. However, it’s typically it’s between 25% – 35% Since the mid 80’s it’s been mandatory to build new homes with wall insulation, so the benefits have been recognised for many decades.   Read more information here: