There are instances where early cavity walls can be insulated. However, such work should only be carried out by a certified installer and after a thoroughly detailed assessment has been made of the particular building
and its performance characteristics. Any solutions may need to be varied to take account of the location, orientation, exposure, construction and condition of an individual section of wall.
The aesthetic, practical and technical impacts of insulating an early cavity wall externally or internally are comparable with those of insulating a solid wall. Where the tie between the two leaves of a cavity wall is of a porous material, cavity insulation is not usually a suitable option although it could be used in conjunction with external wall insulation and further weather protection to increase the thermal insulation value of a wall.
Monitoring should be undertaken before, during and after any such insulation to ensure that the work is not only done on an informed basis but that lessons can be learned from any successes and failures. This will enable future practice to be made more robust and effective.