If your home is built using solid wall or hollow block construction methods, cavity fill insulation is not an option. If, at the same time, the house is on the list of protected structures or for any other reason cannot be insulated externally, there is only one option left. Internal insulation (sometimes referred to as 'dry-lining') involves fixing insulation to the inner surfaces of your external walls. This usually involves fixing an insulation board to the walls and covering it with a vapour barrier layer and plasterboard. The insulation layer can be up to 70mm thick. This also requires all electric sockets, switches and pipework to be relocated once the insulation work is complete.
Applying the insulation internally has the benefit of ensuring that the wall surface and room space warms up quickly. On the other hand, most of the thermal mass is being lost by cutting off an access of the warm air to the external walls. Since there is not much left to retain the heat, temperature fluctuates and might be relatively quickly lost due to natural ventilation or poor doors and windows draught-stripping. Moreover, external structure is exposed to adverse weather condition and can much easier absorb moisture or be penetrated by frost.
Finally, internal insulation by its nature, will always have some points of discontinuity at the junctions with floors and internal walls. This results in cold bridges formation and consequently reduces insulation effectiveness.
The other disadvantage of internal insulation is the loss of room space; this may be minimised by using high performance insulation products that are thinner. While this is often a more affordable option than installing external wall insulation, the loss of space and potential necessity to take out and re-fit fitted kitchens and appliances can result in people choosing the external wall insulation option.
However we do not recommend internal insulation, in some cases this is the only possibility to insulate external walls.