Commonly used insulation boards for external insulation

Mineral Wool

Mineral wool refers to a whole family of manmade fibres, some of which are useful Mineral wool being prepared for use as a part of an external insulation system in Kildare insulators. What they have in common is that they are all made in the same way, kind of like candy floss, except they are made from rock or silicates instead of sugar.

Mineral fibres are rated as class zero (Very good) in the UK building regulations for fire safety. It is normally specified for use around chimneys and boilers where there is a risk of high temperatures.
The vapour resistance of mineral fibres tends to be negligible which allows the construction to dry out easily.

Polystyrenes

Polystyrene was discovered in 1839, by isolating the substance from natural resin. In 1930, the scientists at BASF developed a way to commercially manufacture polystyrene. A company called I.G. Farben (now called BASF) is often, incorrectly, listed as the developer of polystyrene, even though it occurs naturally.

Later the Dow Chemical Company invented extruded polystyrene which they called Styrofoam. (Note expanded polystyrene is often incorrectly termed Styrofoam)

Extruded Polystyrene

Extruded Polystyrene in use as a plinth in Dundrum Extruded Polystyrene XPS foam begins as a solid polystyrene resin granule. The granules are fed into an extruder where they are melted additives are mixed with the viscous fluid that is formed. Then, a blowing agent is injected to make the mixture foamable. The foamable mixture is forced through a die, at which time foaming and shaping occurs. The rigid foam is then trimmed to the final product dimensions.

Its excellent resistance to moisture, imperviousness to rot, mildew and corrosion, make XPS foam an excellent choice in places where you expect water, such as a plinth. See here for more information on XPS as an External insulant.

Expanded Polystyrene

Another variation of Polystyrene is Expanded Polystyrene (EPS) Beads of Polystyrene are expanded, which Expanded Polystyrene attached to the outside of a house in Dublin happens in three main stages. First, the beads are heated with hot air or steam until their density is three percent of its original value. The beads are then cooled for 24 hours and moulded. Once inside the mould, they are injected with low-pressure steam, which further expands the beads and fuses them together. When the mould is cooled, the EPS is finished and ready for use or shipment. See the Aeroboard product specification for further details.

EPS comes in two variations, the traditional white EPS and the more modern grey EPS. Grey EPS is also called "platinum" or Graphite Enhanced Expanded Polystyrene. Adding graphite to the EPS enhances the thermal properties of the insulation.

EPS is the most commonly used material in external insulation in Ireland today. Its combination of lambda and cost make it the most popular choice of householders. EPS is also commonly used to create architectural features such as window surrounds or quoins. .

Polyisocyanurate

PIR (Polyisocyanurate) is formed by a chemical reaction between an Isocyanurate resin (Polymeric Methyl Diphenyl Isocyanate, or MDI) and a polyol (usually polyester). Before the reaction takes place a liquid gas is dissolved into one of the components. The reaction produces heat, which makes the gas boil and form thousands of tiny bubbles in the plastic. As the plastic sets the bubbles are trapped, creating the foam.
PIR has the best thermal properties of any insulant in common use today. This means that you can achieve the same thermal properties with a thinner layer of PIR compared to any of the other insulants available.

Lamda values for insulation

The actual measurement of insulation effectiveness is called lambda. The lower a lambda value your insulation has the better it is.

Typical Lambda ranges for commonly used insulants*

Insulant	Lambda range
Expanded Polystyrene (EPS)	0.030 to 0.038
Extruded Polystyrene (XPS)	0.029 to 0.039
Polyisocyanurate (PIR)	0.022 to 0.028
Rock Mineral Wool (MW)	0.034 to 0.042

With thanks to TIMSA for these figures.

*Typical Lambda (W/m.K) for commonly used insulants. 90/90 ranges given, meaning 90% of the products will achieve these ranges 90% of the time.

Another way to look at these properties is to compare thicknesses. For a typical Irish house these are the thicknesses of insulation required to reach the current standard in Irish Building Regulations.

	Lambda (W/mK)	Thickness required (mm)
white EPS board	0.038	125
carbon-enhanced EPS board	0.031	100
mineral wool board	0.036	120
PIR board	0.023	75

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