Insulation makes homes cheaper to heat, cheaper to maintain, warmer, drier and healthier. The building code stipulates minimum levels of insulation but these are not necessarily ideal and it is good practice to have more.


Well-insulated homes are cheaper to heat because heat doesn’t escape as fast. It has been shown that a well-insulated home uses around 19% less energy to heat. They are warmer and drier as well, with less condensation, mould and mildew. This makes them much more comfortable and healthier – people living in well-insulated homes have much less asthma and respiratory problems and go to the doctor and hospital significantly less.  Such homes are also cheaper to maintain because there is less damage caused by dampness and condensation.

Insulation works by reducing heat loss through the walls, ceiling and floors of the house. There are two basic types: bulk and reflective.

Bulk insulation

Products such as fibreglass wool, polyester, wool, macerated paper, polystyrene and building materials like AAC block work by trapping still air within tiny pockets and therefore reducing the amount of conductive heat flow.

Reflective insulation

Shiny foil materials are often installed beneath suspended floors. The foil works by creating a physical barrier against wind passing under the floor and by reflecting radiated heat back into the home. In other words, it acts like the “space blankets” commonly found in emergency and first aid kits. When properly installed there should be an air gap between the floor and the foil of about 100 mm. It is not the material that provides thermal resistance but the impact of the reflective, low emittance surface that reduces heat flow across an air space. So, if there is no air gap reflective insulation adds no thermal resistance.

The insulation level (thermal resistance) of a part of a building (say a wall or ceiling), or a particular insulation material, is designated by an “R-value”. The higher the R-value, the better the insulation level.

More is better

Unfortunately, the current New Zealand Building Code provides only minimum requirements for insulation.  So even if you build your home to the current standard your insulation level may not be ideal.

The marginal price difference between installing say R3.5 and R4.6 insulation will be paid back quickly and will make your home that much more comfortable, healthy and energy efficient. A publicly available specification (PAS 4244) provides guidance on the selection of wall and roof insulation and glazing types to achieve “better” or “best” insulation levels.

Wool insulation