Internal Wall Insulation (IWI) is applied to the internal walls of a building. It typically consists of dry lining in the form of pre-insulated plasterboard or built-up systems using fibrous insulation such as mineral wool held in place using a studwork frame.

• Generally cheaper to install than external wall insulation.
• Will slightly reduce the floor area of any rooms in which it is applied (the thickness of the insulation is around 100mm)
• Can be disruptive but can be done on a room by room basis.
• Requires skirting boards, door frames and external fittings to be removed and reattached.
• Can make it hard to fix heavy items to inside walls – although special fixings are available.
• Needs any problems with penetrating or rising damp to be fixed first.