INSULATION 75
result in damaging moisture problems for two primary reasons.
Adding any internal insulation will reduce the temperature of the existing wall masonry, making it more likely that condensation will occur to the inside as there will be less heat penetrating from the living spaces to warm up the masonry. Secondly, some insulation types – such as rigid foams – can further exacerbate the problem. If not adequately accounted for in the design, this moisture accumulation can continue unchecked, increasing issues with dampness and mould over time and, in extreme cases causing the masonry to degrade due to freeze/thaw cycles. Permeable insulation prevents moisture from being trapped in the construction and minimises disruption of the established balance of moisture flows within the building fabric to the same degree. However, traditional moisture vapour permeable insulation, such as mineral fibre, tends to be very bulky, causing a challenging for preserving interior space.
External or internal insulation? Protected historic listed buildings are often solid wall construction, and a commonly held perception is that it isn’t possible to insulate externally and not practical to insulate internally.
Preserving the external features of the property excludes the traditional approach to solid wall insulation. A traditional external application would be achieved through insulated boards being secured to the external face with a render finish. The drawback of this method is the change in the overall appearance of the dwelling. Internal approaches typically include the application of insulated plasterboard fitted to the walls of each room and then a subsequent plaster finish. The materials suitable for internal insulation can result in an overall reduction of floor space, and therefore the use of these traditional methods can often be impractical due to space constraints. Spacetherm WL is a high-performance laminate specifically intended for use where improved thermal performance is required with limited space. It is fixed to the internal surfaces of existing solid walls without the need for mechanical fixings. At only 13 mm thick, there is often no need to remove skirting boards and cornices, saving time and cost. Typically, a solid wall will have a U-value of around 2.1 W/m2K,
ADF FEBRUARY 2023
however using the product this can be reduced to around 0.8 W/m2K, depending on the wall material and thickness. An internal insulation system using materials such as mineral fibre, wood fibre or natural wool has a relatively high thermal conductivity, and therefore requires a significant depth of insulation to achieve modern thermal standards. Due to the depth required, these materials are typically installed within a freestanding frame, with a cavity to isolate them from the masonry – often resulting in a system depth of over 200 mm. Although this system typically won’t achieve thermal performance in line with Building Regulations, even a small upgrade in thermal insulation can raise the internal surface temperature enough to avoid condensation problems. For example, a solid masonry wall could be prone to surface condensation, particularly around window interfaces. If insulation is added to the main wall surface but omitted from window reveals, although the walls’ surface temperature increases, the reveals’ surface temperature drops, leading to increased condensation risk. Even adding a minimal amount of insulation to the reveals will elevate this temperature enough to mitigate this condensation risk, highlighting the importance of a continuous envelope of thermal insulation.
Callum Anderson is technical advisor for A. Proctor Group
WWW.ARCHITECTSDATAFILE.CO.UK
Protecting listed buildings is much more than preserving the heritage of the past
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