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 or exterior 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 solid wall insulation
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.
2. 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.
Considerations
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.
Further information
'Energy Efficiency Best Practice in Housing 'publications provide information and advice on all aspects of energy efficiency in domestic dwellings. These can be obtained free of charge by calling 0845 120 7799 or visit the Energy Saving Trust website.
The publications concerned with the internal insulation of solid walls are:
- GPG138: Internal Wall Insulation in Existing Housing
- GPG297: Refurbishment site guidance for solid walled houses – walls
External solid wall insulation
External solid wall insulation wraps the masonry exterior walls of the building within insulation so that rooms will cool down more slowly after the insulation is installed and hence is more suited to buildings that are heated all day rather than those that are heated intermittently.
Although the work can be completed whilst the occupants remain in the building this type of insulation is worth considering if the exterior walls are in need of repair or if major internal renovation is planned as there is a significant amount of disruption involved. Furthermore if the work is not carried out in conjunction with other repairs this form of insulation will have a very long payback period.
Materials and installation
External wall insulation is usually installed as a composite system consisting of insulation material protected by render, cladding or tiles and the use of proprietary systems with British Board of Agrement certificates are recommended. . The installation of proprietary systems must be carried out by a specialist contractor. The Insulated Render and Cladding Association maintains a register of proven systems and installers and further information can be obtained on their website.
The overall thickness of the insulation and render or cladding is often quite substantial so care must be taken around rainwater down-pipes, window sills and where the walls meet the roof. Certain finishes may be vulnerable to impact damage and hence may require additional protection at ground level. A specialist contractor will employ the latest approved techniques and materials to deal with these problems.
Planning considerations
Additional restrictions on the installation of external solid wall insulation may apply in certain local authority areas and particular care must be taken when considering installation within a conservation area or to a building listed as being of special architectural or historic interest. It is therefore highly advisable to check with the planning department before proceeding with any work. It is also recommended that approval is sought from building control before work commences.