Internal wall insulation, also called dry lining or internal insulation, adds an insulated lining to the inside face of external walls. It is used where external insulation is not possible, for example on protected structures or where the façade must be retained, but it reduces room size and needs careful moisture detailing.
Internal insulation is applied as insulated plasterboard, or as insulation between battens or a stud frame with a lining board. It can be installed room by room, which suits phased renovation, and it does not change the external appearance of the building.
The complication is that the existing wall becomes colder because it is now outside the insulation. That raises the risk of interstitial condensation within the construction and of surface condensation at junctions where insulation cannot be continuous, such as at intermediate floors and internal partitions.