THERMAL CONDUCTIVITY (λ). THERMAL RESISTANCE AND TRANSMITTANCE.
The thermal performance of a wall, floor or roof, intended as a calcularion of the heat flow between the environments they serve to separate, is obtained, as we know, by having the thermal transmittance (U) value of each individual component of the stratigraphy, i.e. the thermal resistance (R) of each element.
If properly chosen and proportioned, insulation will make a significant contribution to restricting the flow of heat between two environments. "Choosing well" means using insulation with the lowest thermal conductivity (λ) value.
The following expressions are used (d = insulation thickness):
R = d/λ(m2K/W) U = 1/R = λ/d(W/m2K)
The pentane expanded polyiso foams used in the ISOSTIF range, also due to the fine regular structure of their cells, are insulating materials with one of the lowest thermal conductivity values in the trade: 0.028 W/mK for thicknesses of 20-70mm and 0.026 W/mK for thicknesses of 80-120mm.
The European standard relating to rigid expanded polyurethane foams is UNI - EN 13165, which regulates the method every manufacturer must use to declare the thermal conductivity value (λD) for insulating materials. Such value represents the stable thermic performance of the product for 25 years’ service and is obtained by standardized accelerated aging procedures to which a statistical analysis is applied based on production controls (in-house and external) developed annually by the manufacturer.
WATER VAPOUR RESISTANCE FACTOR (μ)
Hygrothermal tests on walls or roofs by means of the Glaser diagram (or similar method) make it possible to easily detect any critical interstitial condensation in certain climatic conditions inside and outside the dwelling (temperature and relative humidity). The phenomenon of interstitial condensation of water vapours is mainly responsible for the formation of mould on walls and deterioration of thermic performance for the entire structure. Every material of which a wall or roof is composed has its own capacity to transport water vapour and this is expressed in technical terms by the water vapour resistance factor (µ). This is a dimensionless measurement that expresses how many times greater resistance to water vapour is in a material compared to a layer of air of the same thickness.
In principle, an insulating material with a low water vapour resistance factor will transport water vapour very quickly (1-5), whereas one with a high factor (500-1000) will become practically a barrier.
PaneIs in the ISOSTIF range have a water vapour resistance factor that varies according to the type of cover involved. The VERCOP® line (reinforced with glass fibre) has a value of H = 60÷80 whereas COP® and BIVERCOP® panels (bitumen coated) have a value of µ = 100÷150.
The value of insulating material’s resistance factor for transporting moisture, together with the thickness of the chosen insulation, are essential for drawing the Glaser diagram regarding hygrothermal tests on the entire stratigraphy of the wall or roof. According to the degree of criticality, the diagram will lead to establishing the value of the entire stratigraphy, the position of insulation and, if applicable, the use of water vapour barriers to avoid the possible formation of interstitial condensation.
REACTION TO FIRE
European standard UNI EN 13501-1 provides regulations for classifying building products and elements with regard to their reaction to fire. It is well known that pentane expanded polyiso foam has high fire resistance: after the application of a localized flame, even persistent, its surface carbonizes to a depth of a few millimetres, thereby forming a protective char. As a result damage to the foam is restricted, the flame extinguishes itself and the material under the crust is practically whole. This important fact makes this type of foam very different from other insulation of an organic nature and even from the old types of polyurethane foams.
The different reactions to fire of building elements are grouped into several Euro classes: A1 and A2 (non-combustible materials) and B to F (increasingly combustible materials). The reaction to fire of panels with polyiso foam in the ISOSTIF range depends on the reaction of the different coatings, whereas the foam itself is in Euro class E. Therefore, VERCOP® reinforced with glass fibre is in Euro class E, and COP® and BIVERCOP DUO® are in Euro class F due to their use of fully combustible bitumen coatings.
COMPRESSING STRESS
Compressing stress of insulation for the building trade is typically measured at 10% deformation (10% of the panel thickness), a value at which substantial plasticization (yield point) of the material’s first surface layers and a "plateau" response in the load-deformation curve.
Polyiso foams in the ISOSTIF range can achieve compressing stress values of around 140-M60 KPa (1.4-5-1.6 kg/cm2), greatly superior to the overloading found in buildings, including industrial ones, and can therefore be applied with absolute safety under floors, slopes and walkable surface coverings.
DIMENSIONAL STABILITY IN SPECIFIC CONDITIONS OF TEMPERATURE AND RELATIVE HUMIDITY
Dimensional stability is of fundamental importance for an insulating system in the presence of important changes in temperature (as in the case of a roof partially exposed to the sun) or more in general in the case of seasonal changes. In order to check the level of stability for insulating material, standards measure withdrawal or expansion in different conditions of heat and relative humidity.
Insulation in the ISOSTIF range undergoes strict periodic measurements of dimensional stability at -20°C and at +70°C with 90% RH, recording minimum variations along the sides (typically below 1%) and thickness (generally below 2%).
