Insulation materials and their thermal properties
Thermal insulation is the reduction of heat transfer
(the transfer of thermal energy between objects of differing temperature) between objects in thermal contact.
- Reducing the amount of energy used from fossil fuels is the most important factor in promoting sustainability.• Insulation has the greatest potential for reducing CO2emissions.• Energy conserved through insulation use far outweighs the energy used in its manufacture.
Only when a building achieves a ‘Low Heat’ standard does insulation’s embodied carbon become significant.
The most important aspect of an insulation material is its performance – that it consistently provides the designed-for resistance to the passage of heat throughout the lifetime of the building (Wall insulation Types). Though the insulation manufacturer’s published performance expectations will be an essential guide, other factors associated with the ‘real-life’ installation of the material need to be considered as part of the design process:
• Ease of installation
– the ultimate performance will be determined by how effectively a builder can install a material using conventional skills. For example, insulation slabs need to be installed so that no gaps result either between adjoining slabs, or between the slabs and other construction components that form part of the overall insulation envelope, such as rafters or joists. Any gaps left over will enable the passage of air and result in a reduction in performance.
• Shrinkage, compaction, settlement
– Some materials are likely to suffer a degree of dimensional instability during their installed life. In many instances this is anticipated and can be overcome through careful design and installation methods. In all other instances, the specific should seek guidance concerning associated risks from the insulation manufacturer – particularly where materials have not had an established record of installed performance.
• Protection against moisture
– some insulation materials will suffer a degradation of performance when moist or wet. The designer should, through careful detailing, ensure that vulnerable insulation is protected from moisture. If moisture is a high risk (ingress or over 95% RH), then a suitably resistant material should be specified.
Below we take a look at performances exhibited by a range of common and increasingly common construction insulation materials.
Insulation materials, particularly where ‘green’ specification is concerned, divide into so-called ‘natural’ materials and ‘man-made’ materials.
When considering how to specify an insulation material in terms of environmental impact, it is often the case that the ‘natural’ material is the most beneficial in terms of environmental attributes. However, in some cases, the inherent efficiencies of man-made materials can be included into the environmental equation to provide a wider environmental benefit eg where space for insulation is at a premium such as in retrofit.
What are the performance terms and what do they mean?
Thermal conductivity measures the ease with which heat can travel through a material by conduction.
Thermal Resistance (R)
Thermal Resistance is a figure that connects the Thermal Conductivity of a material to its Width.
Specific Heat Capacity
The Specific Heat Capacity of a material is the amount of heat needed to raise the temperature of 1kg of the material by 1K
The density refers to the mass (or ‘weight’) per unit volume of a material.
Thermal Diffusivity measures the ability of a material to conduct thermal energy relative to its ability to store thermal energy.