Retrofit with factor 4
Factor 4 also for sensitive (listed) buildings: Passive Components + interior insulation
Exterior insulation has a whole series of technical and practical advantages. Even on old buildings (apart from a few details), it provides a thermal-bridging-free, highly effective construction and insulation thickness so that (except for ground floors) Passive House standard can also be achieved in modernized old buildings.
However, a significant amount of existing buildings are not suitable for thermal insulation on the outside. This mainly applies to listed buildings, but also to buildings with high-quality visual facades (special features) or other durable exterior surfaces that will require no work apart from cleaning every now and again. In the latter cases, the reasons against external insulation are mainly economic.
Good insulation and sensitive facades – can these two come together? As has been shown during the 32nd meeting of The Working Team for Cost-effective Passivhaus’ (Arbeitskreis kostengünstige Passivhäuser) and with five actual examples, the use of internal insulation in nineteenth century buildings and half-timbered houses provides an improved level of thermal protection, without altering the exterior view.
When used together with well-known Passive House components and methods, the heating requirements of a building can be reduced to less than one quarter (hence the title ”Factor 4”) of their previous levels. In order to avoid unpleasant surprises, the project must be carefully planned and executed.
Interior insulation can be installed without long-term damage providing that important conditions are fulfilled. Driving rain, air leakage and thermal reduction, as well as rising damp must be avoided and controlled ventilation of the dwelling must be incorporated.
Both insulation methods require good vapour barriers on the inside as well as breathable, capillary-proven insulation. It is crucial that the chosen approach is consistently maintained and adapted to site and buildings.
In-depth studies on the parameters of moisture balance in walls insulated from the inside, supported by the humidity and heat flow calculation program ’dolphin’, have been carried out. They showed, among other things, the importance of the performance of the vapour barrier to actually achieve the desired vapour retarding effect. Even a convective influx of moisture by ventilation of the insulation must be avoided. On the other hand it was shown that the often discussed edge diffusion, e.g. in the including interior walls, for hygroscopic materials such as masonry or wood is usually straightforward.
With well-installed interior insulation and passive house components, the energy consumption of listed buildings can be brought to below the level required for new buildings. With external insulation however, even higher savings are economically feasible.
Contact the Scottish Passivhaus Centre if you are planning to upgrade a sensitive or listed building.
Source: PHI
