R-Value is a measure of how well a material resists the flow of heat. In essence, the higher the R-Value, the better the material is at slowing heat transfer. Insulation materials with higher R-Values have better insulating properties—helping to keep homes warmer in winter and cooler in summer.
How Does Insulation Work?
Most of the insulation materials used in New Zealand today slow the transfer of heat by incorporating tiny pockets of still air in their structure – air is a poor conductor of heat. These bulk insulation materials include:
- segments or blankets of glasswool or polyester
- rigid sheets such as EPS (expanded polystyrene), XPS (extruded polystyrene) or PIR (polyisocyanurate)
- structural insulated panels (SIPs) – sandwich panels made of two face layers and an insulating inner core
- loose-fill insulation such as glasswool, mineral fibre, or cellulose fibre
- spray foam insulation
How is it relevant to Insulation?
R-Value directly indicates how effective insulation will be in reducing heat loss or gain through building elements like walls, floors, and ceilings. A higher R-Value means the insulation is more efficient, which can lead to improved comfort and lower energy bills.
In calculations of the thermal performance of a house, two types of R-Value are considered – the R-Value of the insulation material or product itself, and the Construction R-Value of the building element.
In New Zealand, the Building Code specifies minimum construction R-Values for floor, wall, ceilings and glazing.
The construction R-Value is the total thermal resistance of all the physical elements that make up or impact on a building element. For example, the total thermal resistance (R-Value) of a wall includes the wall lining, wall framing, insulation, underlay, exterior cladding.
Understanding R-Value
R-Values aren’t fixed—several factors influence them:
Factors that affect R-Value
- Material type: Different insulation materials (like glasswool, polyester, or foam) have different thermal properties, and therefore have different R-Values.
- Thickness: Increasing thickness generally increases R-Value—though the relationship isn’t always perfectly linear. Compressing insulation will generally reduce the materials R-Value so it is important to understand the insulation materials thickness and ensure it can fit un-compressed in the space available.
- Density and condition: Factors such as moisture, ageing, and settlement can reduce effectiveness of insulation over time.
Insulation materials with high-density often provide higher R-Values.
How R-Value is measured
Insulation products in New Zealand must meet specific labelling requirements which state the materials R-Value as tested in a Lab setting. This ensures that products and performance can be compared.
The insulation materials nominal thickness must also be displayed on the product label. The nominal thickness is the minimum space required for the insulation to meet its R-Value. Compressing an insulation material below its nominal thickness will reduce the insulation R-Value.
What is the difference in R-Values on insulation?
Different insulation types offer different R-Values per unit thickness. Materials such as polyisocyanurate (PIR) foam offer significantly higher R-Values compared to traditional options like fibreglass or polystyrene.
Importance of R-Value In Energy Efficiency
R-Value is a key indicator of thermal performance. High R-Values in insulation reduce heat flow, keeping homes cosier in winter and cooler in summer. That translates to reduced reliance on heating and cooling systems, lower energy demand and cost savings. It’s not just about comfort—it’s about smarter, more sustainable use of energy.
A well insulated home is warmer, drier and healthier for occupants.
What Is The Minimum R-Value For Walls?
Current New Zealand building regulations specify a minimum R-Value of R2.0 for wall insulation. This baseline ensures homes maintain sufficient thermal resistance to meet energy efficiency and comfort standards.
It’s a very good idea to exceed the minimum requirements to get a warmer home which is healthier and easier and cheaper to heat.
Summary
- R-Value measures how well a material resists heat flow; higher is better.
- R-Values vary by material, thickness, and installation quality.
- In New Zealand, wall insulation must meet a minimum of R2.0, though higher values enhance efficiency and comfort.
Understanding and selecting the right R-Value means choosing insulation that delivers real-world benefits for comfort, energy use and long-term performance.