Choosing the Right Insulation
Insulation is one of the most important elements of a building’s energy and comfort performance, and New Zealand builders have a wider range of insulation products available than ever before. Understanding the performance characteristics, installation requirements, and appropriate applications of different insulation types is practical knowledge that helps builders specify and install insulation that achieves the design intent and meets the Building Code.
The primary performance measure for insulation is its R-value — a measure of thermal resistance, where higher values indicate better insulating performance. The R-value of an insulation product depends on its material type and thickness, and increasing insulation thickness increases R-value in a broadly linear relationship. New Zealand’s H1 requirements specify minimum R-values for different building elements (ceiling, wall, floor) in each climate zone.
Glasswool (Fibreglass) Batts
Glasswool — sold in New Zealand under brands including Pink Batts and Bradford Gold — is the most widely used insulation material in residential construction. It’s available in standard R-value grades for ceiling, wall, and underfloor applications, is non-combustible, and is cost-effective for standard framing depths. Installation requires personal protective equipment (gloves, mask, protective clothing) as the fibres cause skin and respiratory irritation during installation.
Polyester Batts
Polyester insulation batts are increasingly popular for wall and ceiling insulation, offering similar R-values to glasswool without the skin and respiratory irritation of glasswool fibre. Polyester is also more dimensionally stable than glasswool and easier to handle in tight spaces. The main limitation is cost — polyester is typically more expensive than equivalent glasswool — but for installers who work extensively with insulation, the handling advantages can justify the premium.
Rigid Foam and Spray Foam
Rigid foam insulation (PIR, EPS) is used where very high R-values per unit thickness are needed — in exterior insulation layers, under-slab insulation, and in assemblies where framing depth is limited. Spray polyurethane foam (SPF) provides both insulation and airtightness in a single application, and is used in specific situations including cathedral ceilings, underfloor insulation, and airtightness detailing in high-performance building. SPF application requires specialist training and equipment.