Heat Control / Energy Efficiency

Insulation is the most effective way to improve the energy efficiency of a home. It helps to keep heat in during winter months, heat out during the summer, improves comfort, reduces heating costs, all while reducing the environmental impact of heating.

In winter, when we heat our homes, energy will first go to increase indoor temperatures keeping us warm. A process of heat transfer will then start. Heat will slowly start to flow from the inside to the outside (from warm to cold) through the walls, windows, ceiling and floor. The ARIDON® SMART WALL system wraps around the entire wall frame therefore there are no breaks in the insulation = reduced air movement (cold air entering the home replacing warm air) and heat loss, ensuring the house takes significantly less time to heat up in winter and cool down in summer.

Where should we put insulation to ensure it performs 100%?

If we put the insulation on the inside of the structure the insulation does not protect the structure from heat and cold. Expansion, contraction, corrosion, decay, and almost all bad things all are all functions of temperature. So all the control layers go on the outside1.

The control of heat flow is also important for the control of inner surface temperatures- ensuring human comfort and avoiding cold weather condensation. “Keep the structure from going through temperature extremes and protect it from water in its various forms and ultra violet radiation and life is good”1.

1 Joseph Lstiburek (B.A.Sc., M.Eng., Ph.D., P.Eng) Forensic Engineer and Global expert and authority on moisture related building problems and indoor air quality

Typically 20-25% of each wall in New Zealand buildings is made up of framing. Modern buildings are around 33% – that’s a lot of heat loss through the framing!

That is like imagining one in every four walls is solid timber. Heat flow through a wall, will always take the path of least resistance – any time the insulation is interrupted (such as dwangs/studs), the effective R value of the insulation is significantly reduced below the specified product R value.

Cavity insulation – our favored form of insulating in NZ, performs very well in the stud cavity - however timber is not a good insulator and steel is very poor, so the building suffers from cold and potentially damp spots (thermal bridging).

For Example: In a wall with 26% framing ratio, 10mm plasterboard and an R2.8 Cavity Infill (Glass wool) the R value performance will reduce to R1.85 (Calculations to NZS4214:2006). Building Code guidelines in NZ recommend a Constructed R value = 1.9 for the North Island and R2.0 for the South Island and Central Plateau.

The impact of thermal bridges on energy use, thermal comfort and indoor air quality can be significant.

Traditional NZ New Dwelling - Suffering from Thermal Bridging

The tell-tale signs of Thermal Bridging – Heat loss along the framing members, seen on a chilly Autumn morning. This is also indicative of potential condensation problems within the wall.

An ARIDON® SMART WALL home – No Thermal Bridging

ARIDON® SMART WALL R Value Calculations vs Traditional Systems

In order to know the wall’s true thermal performance, you must calculate overall R-values (unit of thermal resistance for a material) for the entire wall assembly – this is known as the Constructed R Value of the Wall.

Typical Constructed R Values using the ARIDON® SMART WALL system:

ARIDON® Wall Panels


SMART WALL 80mm RIBBED PANELR = 2.0R = 2.45R = 2.48R = 2.49R = 2.52
SMART WALL 80mm RIBBED PANEL + SMART WALL Ribbed Panel Offcuts to cavityR = 2.0R = 3.23R = 3.06R = 3.01R = 2.91
SMART WALL 60mm FLAT PANELR = 1.76R = 2.21R = 2.24R = 2.25R = 2.28
SMART WALL 80mm FLAT PANELR = 2.22R = 2.67R = 2.70R = 2.71R = 2.74
R 2.8 GLASS WOOL CAVITY INSULATION (COMPARISON)R = 2.8R =  1.85 R = 1.65R = 1.58R = 1.42

R4.0 GLASS WOOL CAVITY INSULATION (COMPARISON) *140x45mm framing assumed

R = 4.0R =  2.70 R = 2.38R = 2.27R = 2.05
Note: All values assume non insulated exterior cladding (R = 0.0) on cavity, 10mm plasterboard internal linings and 90 x 45mm timber framing unless otherwise noted. Aridon 80mm Ribbed Panels without any insulation in the framing cavity with exceed the insulation performance of R4 cavity insulation with 140 framing in all walls with framing ratios over 33%. 5mm gap assumed around EPS offcuts to cavity. Perfect fit assumed for Glass Wool calculations. Calculations to NZS4214:2006 "Methods of Determining the Total Thermal Resistance of Parts of Buildings".

Why is The ARIDON® SMART WALL system so energy efficient? Because it wraps around the entire wall frame therefore there are no breaks in the insulation. This means that much higher Constructed Wall R Values are achieved with the SMART WALL system than with traditional cavity insulation systems, which are limited to the spaces between framing. In areas around windows and corners particularly, there is usually very little room for cavity insulation thereby lowering the effective R value of the wall (R Construction).

The Critical Questions

Will increasing insulation in my ceiling and floor stop heat loss?

No, physics dictates that warm air rises and therefore ceiling insulation has a large impact. However heat also escapes through walls and this is the next most critical area to address. In addition, we typically live closer to walls than to the ceilings as does our furniture. Therefore the coldness of a poorly insulated wall has much more impact on the comfort of the occupants than a cold ceiling.

If the ceilings, walls and windows are properly insulated, only then does the underfloor become a significant area for heat loss

I have very expensive, thermally efficient windows – I therefore have a thermally efficient wall – do I need better wall insulation?

Heat always flows from hot to cold – if the window is less resistant to heat flow the heat will bypass the window and escape through the studs around the window. Large windows = significant framing = heat loss.

How does the ARIDON® SMART WALL perform if exposed to moisture?

Typically when insulation gets wet it needs to be replaced as mould and mildew forms and the material has degraded in terms of performance. EPS is one of the most resistant products to the adverse effects of moisture.

Moisture gained during the installation or after accidental leakage will only marginally influence the thermal performance of EPS. This results in lifetime durability.

Interesting Fact: After almost 30 years in the ground, samples of EPS retrieved from locations as little as 200 mm above the groundwater level all showed less than 1% water content by volume, whilst blocks which are periodically entirely submerged show less than 4% water content - performance notably superior to other foamed plastic materials. EPS is used for floating decks as a base for river buildings and is not affected by salty water if used for sea pontoons.

How much power does the SMART WALL actually save?

An independent BRANZ energy efficiency study we commissioned identified that in a typical group builder/volume built home the replacement of the ARIDON® SMART WALL system showed “Very good reductions” in space heating requirements.

Excellent benefits were seen in the case of the passive solar house examined, with the space heating energy required for comfort provision dropping by over 40% in the 80mm panel and nearly 50% with the ARIDON® 80mm Ribbed Panel combined with ARIDON® in-frame offcuts.

Does the SMART WALL shrink when it gets wet?

EPS is one of the most resistant products to the adverse effects of moisture. Other board type systems can suffer from shrinkage which means that gaps might open up between the boards. The stable qualities of the EPS material in the ARIDON® SMART WALL system combined with the unique overlapping jointing system means that long term thermal perform is assured.

Are K values more accurate than R values when measuring insulation?

Thermal Conductivity (K Value) is the property of the material to conduct heat. Heat transfer occurs at a higher rate across materials of high thermal conductivity than across materials of low thermal conductivity – for insulation you want a low k value.

Thermal Resistance (R value) is the ability of a material to resist the flow of heat and is inversely proportional to its k value. There are a number of ways to measure thermal conductivity. Each of these measurements are suitable for insulating materials, depending on the thermal properties and the medium temperature. Rather than argue – which is the correct way to present this information, – the discussion we should be having is: How does your insulation perform in real world conditions versus a measurement on the bag? How is it’s resistance to air penetration, to water and to vapour drive?

How does the long term thermal performance of EPS compare to other foams?

The ARIDON® system is a homogenous material – meaning what you see is what you get. The insulating gas contained within the bead structure is air. Other insulation foams may appear to provide higher R values initially however they suffer degradation of the R Value (or thermal drift) as the insulating gases contained in those products leach out. Foils and other facing materials attempt to slow this process but it is impossible to seal these products sufficiently for thermal drift not to occur. It is important to consider the likely R value of your insulation in 10-15 years’ time to ensure that energy efficiency is maintained and that condensation will not become an issue in the future.