During the manufacture of EWI Pro’s lime renders, less CO₂ is released into the atmosphere compared with modern cementitious products. This is largely due to the kiln temperatures required in production as they are around 400°C lower when compared with temperatures in excess of 1,000°C for modern portland cement-based materials. EWI Pro's lime range, used in conjunction with wood fibre insulation, is made from NHL lime, marble sand and clay. This means that there's no harmful chemicals, no fly ash or slag and the products are completely at one with traditional construction.
Once applied to the wall, lime-based systems also absorb CO₂ from the atmosphere as they cure, through a natural process known as carbonation. This further contributes to their lower overall carbon impact.
Diffusion-open EWI system to assist with moisture control
Whenever the fabric of a building is insulated, there is potential to alter the way moisture is managed within the structure. Effective moisture control is essential, as without it, internal condensation and dampness can occur. In addition, trapped moisture that condenses within the construction can lead to long-term damage to the building fabric. Guidance on managing moisture risk is set out in BS 5250 ‘Management of moisture in buildings. Code of practice[1]’, which outlines strategies for assessing and controlling condensation.
Both diffusion-open and diffusion-closed insulation systems can be used as part of an external wall insulation solution. As was the case with this domestic retrofit project, solid-wall properties are often constructed from materials that allow moisture vapour to pass through, enabling the structure to breathe. In such cases, diffusion-open insulation systems may be preferred by the retrofit designer, as they more closely align with the existing hygrothermal behaviour of the building fabric.
Wood fibre insulation helps to mitigate overheating
External wall insulation can help to retain heat within a building during the winter and reduce heat gains during the summer. Wood fibre insulation contributes thermal mass to the wall build-up, which can help moderate internal temperatures during warmer weather. Its combination of relatively high density, high heat storage capacity and low thermal conductivity helps to reduce the risk of summer overheating.
These properties enable the STEICO wood fibre insulation to absorb and store heat during the day, slowing the rate at which it is transferred into the internal room spaces of the house. This creates a time delay, meaning peak external temperatures do not immediately translate into peak indoor temperatures.
Importantly, these characteristics can be calculated and expressed as part of a building’s thermal performance. In much the same way that U-values measure heat transfer during winter, summer performance can be quantified using parameters such as thermal diffusivity and time delay.
Thermal diffusivity combines density, specific heat capacity and thermal conductivity to indicate how quickly a material responds to temperature changes. A lower diffusivity means heat moves more slowly, creating a longer time lag between external temperature peaks and internal temperature rise. By incorporating these calculations into design, specifiers for retrofit projects can compare materials not only for winter efficiency but also for their ability to moderate summer heat.
EWI systems can contribute to an improvement in the dwelling’s EPC
EWI systems can help to improve the energy efficiency of a property. As well as helping to lower fuel bills, it can also assist with reducing the dwelling’s carbon emissions when assessed RdSAP[1] for existing buildings. This can improve the Energy Performance Certificate (EPC) of the property, which in turn can help to increase its value[2].
