Solid wall insulation (SWI)

What is solid wall insulation?
Houses built before 1930 and some in later years typically have solid masonry walls. Heat loss through the external walls is on average 35%. Solid wall insulation is a way of preventing energy waste and cutting up to 25% of the fuel bills. In addition to its weatherproofing benefits, where the building fabric of older houses is in a poor state of repair, solid wall insulation can deal with both the structural and aesthetic issues.

Solid wall insulation is generally a composite system made up of three basic layers - an insulant, a fixing, and a protective, decorative finish.

The two main types of solid wall insulation are external and internal. The typical U-values of 2.10 W/m2K can be reduced up to 0.30 W/m2K.

External wall insulation
The design and installation of external wall insulation is a specialist job. It is strongly recommended to use certified materials and components. The typical method includes attaching standard size insulation boards to the wall and finishing with a reinforced render or cladding. The boards are between 40-90 mm thick, fixed to the wall with adhesive and mechanical fixings. The total thickness of the insulation is 50mm to 150mm. For most cost-effective results this should be done as part of other renovation work.

Internal wall insulation
Also referred to as dry-lining, this type of insulation involves applying a 25-50 mm insulation layer on the inside of external walls covered with plasterboard fixed with adhesive and possibly metal fasteners. The thickness is 40mm -100mm.

Planning permission



The Oxford Solar Initiative (OSI) has secured financial incentives for properties in Oxford:
The following fixed grants are available for both internal and external type of solid wall insulation through London Energy:

The figures are based on gas central heated properties. The grant will depend on the U value achieved.

Additionally the Oxford Solar Initiative offers £500 cash back for any full property external solid wall insulation


  • External wall insulation - it is preferable to employ an approved installer in order to ensure professional work especially in the detailing (finishing around external services, pipework, windows, etc.). Insulated render and cladding systems can be applied on average in about three working days. Because it is applied to the outside of external walls, there is less disturbance to the household in the process.
  • Internal wall insulation - can be done either using a qualified installer or as a DIY job. Only part of the house can be done at one time. Nevertheless, comfort in the chosen rooms is very likely to be disturbed and therefore it is best to coordinate with a redecorating job.

What are the benefits of solid wall insulation?

Further information on products and installers:
- Insulated Render and Cladding Association (INCA) Ltd., Surrey, tel: 01428 654011; fax: 01428 651401; web site:

- Celotex Litd., Suffolk, tel: 01473 822 093; fax: 01473 820 880; web site:

- PermaRock Products Ltd., Leicestershire; tel: 01509 262924; fax: 01509 230063; web site:

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