Internal Insulation

Internal Wall Insulation or Dry Lining

This is a cheaper alternative to exterior insulation. The most common form of retrofit interior insulation is dry-ling. This entails fixing an insulation board to the interior walls of your home and covering it with a vapour barrier layer and finished with plasterboard.
The main downside though is that decreased room volume. Existing radiators have to be removed and re-installed away from the finished insulated walls. Therefore you will need to commission a plumber as well as the insulating contractor. It is normal practice to insulate only the interior of the exterior wall. Make sure you get a price for both works before proceeding with the works. The insulating contractor may well engage his own plumber.
Interior wall insulation should significantly reduce your heating bills. In addition to the insulation make sure that any draughty areas such as badly fitted doors or floorboards are sealed airtight as part of the overall contract.


For solid walls, insulation must be applied either internally or externally. Internal insulation involves fixing a layer of insulation to the internal surfaces of external walls, usually with a plasterboard finish. This is also referred to as dry-lining. Care must be taken to install a vapour check (e.g. polythene sheeting) to seal the insulation against humid air penetration from within the house.

The insulation of solid walls is considerably more difficult than the insulation of cavity walls. Due to the lower potential savings and higher cost of undertaking the work it is best to incorporate the insulation of solid walls into major internal repair of the interior of the dwelling. Furthermore the work, although it can be done whilst the occupants remain in residence, is substantially more disruptive than the process of insulating cavity walls.

Internal wall insulation is also known as insulated dry lining and consists of a layer of insulating material installed behind a layer of plasterboard. It is applied from the inside and necessitates the removal of all fittings affixed to the walls - radiators, skirting boards, architraves etc.

Materials Used and Installation Methods

Insulated dry lining can take the form of a composite 'thermal board' or a built up system using insulation behind timber battens fixed behind conventional plasterboard. For both systems the surface of the wall must be carefully prepared and all cracked or damaged plaster must be either repaired or removed. Bare brickwork or blockwork should be pointed with mortar to eliminate air paths to the exterior.

  1. Thermal boards

Made of plasterboard bonded to an insulating material.

Incorporate a vapour control layer to prevent water vapour passing through the board and condensing on the cold masonry behind.

Boards are available incorporating a variety of insulants, e.g. polystyrene, polyurethane and mineral wool.

Usually 25mm - 50mm thick, with the thicker boards being the most insulating.

Should be fixed to the wall using a continuous ribbon of plaster or adhesive, and not individual 'dabs' of plaster, unless the wall is particularly uneven.

  1. Built up systems

Conventional mineral wool Insulation is placed between vertical timber battens fixed to the wall

A polythene sheet is fixed over the insulation and battens beneath the plasterboards and acts as the vapour control layer.

Joint edges and services (electrical cables and wiring) which penetrate the polythene sheet must be thoroughly sealed using tape to exclude water vapour and subsequent condensation formation behind the lining.

Whichever system is installed it is very important to ensure that moisture cannot penetrate behind the plasterboard as condensation and dampness will result. Additional insulation will be required around the sills and reveals of openings and adjacent to where internal masonry partitions meet external walls in order to prevent thermal bridging. The installation of internal wall insulation will result in a slight reduction of the floor area of the rooms concerned. Rooms will heat up more quickly after insulation and hence this form of insulation is particularly suited to dwellings that are heated intermittently, such as in the morning and evening. Special fixings must be used to affix pictures and small items to plasterboard lining. Heavy items must be fixed through the dry-lining into the masonry wall behind the insulation.

There are primarily two wall types in the domestic residential sector, solid walls and cavity walls and both can be insulated to improve the energy efficiency of a property. There are also non-traditional or hard-to-treat types which can also usually be insulated but may require more specialised preliminary works.

Solid walls may sound like they should be better at keeping in heat but unfortunately the opposite is true. Un-insulated solid walls can lose heat twice as fast as un-insulated cavity walls, but insulating them externally could save over £490 each year* and insulating them internally could save over £460 each year* (Source: Energy Savings Trust). Put simply, the better insulated a property is, the less money will be spent on heating it. The good news is that solid walls and hard-to-treat properties can be insulated – from the outside or the inside. This will cost more than insulating a standard cavity wall, but the savings on heating bills can be larger too, because more insulation can be used on the inner or outer walls.

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.

External Wall Insulation (EWI) involves fixing a layer of insulation material to the wall, then covering it with a reinforcement and a special type of render. The finish is usually a textured render, pebble-dash or sometimes a brick slip or a brick effect render finish could be used.

These solutions can be used in conjunction with each other, known as a Hybrid solution, where there may be restrictions (i.e. listed building, conservation areas, etc) that meant an IWI or EWI systems on their own would not be suitable.