External / Exterior Wall Insulation

External / Exterior Wall Insulation

Exterior Wall InsulationOne of the most effective ways to insulate your home is by installing external wall insulation. However before proceeding with such works make sure there are no rising or penetrating damp issues with the existing walls. It there are then these damp issues must be rectified before proceeding with the exterior. Exterior insulation requires a layer of insulation material to be attached to the walls using mechanical fixings and adhesive. It is then covered with protective layers of render or cladding.
Existing structures such as concrete window sills may need to be removed prior to fixing to avoid any preventable thermal bridging. Also, all external pipework and other fittings will have to be removed and replaced.
After fixing the insulating layer the next step is the finished appearance. There are a variety of different finishes to choose from such as smooth, textured, tiled, panelled, pebble-dashed, or real masonry brick finish.
To prevent condensation, recessed areas around windows must be insulated as well as the walls – with the depth of insulation depending on the width of the window frame.

External wall insulation should be fitted by a by a specialist installer trained by an approved system designer.

Up to half of the heat loss from a house occurs through the walls. This can be reduced by two-thirds by insulating the walls.

Most houses built before about 1980 have no wall insulation. Many (though not all) houses built during the 1980s have some wall insulation. Houses built since the 1991 Building Regulations came into effect are required to have wall insulation.

Insulation may be placed on the outside, in the cavity or on the inside of a wall, without altering the overall insulation properties.

External or cavity insulation allows the internal wall to act as a thermal store, absorbing heat during the day and releasing it at night-time, reducing fluctuations in room temperature throughout the day. Internal insulation isolates the thermal mass from the room. This reduces both the response time of the heating system and the energy required to reach comfort levels in the room. Occupancy patterns, the response time of the central heating and its controls, and the optimal thermal mass of the building will determine the appropriate action.

When considering wall insulation, first you should find out whether your house has cavity walls or solid walls. A building contractor or architect will be able to tell you if you have cavity walls in your new or older house. If you have cavity walls, then cavity insulation is likely to be the most cost- effective insulation method. If cavity insulation is not an option, then the more expensive options of either internal or external insulation may be considered. It is not possible to fill the cavity in a wall constructed simply of 9-inch hollow blocks.

Prior to the scheme starting Ms S had a lot of draughts, condensation and mould growth in the kitchen and also in her bedroom which were both located at the rear of the property.  The tenant reported she had to clean condensation off the windows on a daily basis.

Whilst the scheme work was in progress this tenant had minor issues with the scheme;

  • As a result of cutting the insulation boards on-site there was an accumulation of insulation beads in the outside drains. This resulted in investigation work having to be carried out into a drain blockage and overflow of the storm water outlet in the flat roof. The result of which was a combination of bead build up and a 50+ year old soak away no longer draining correctly.
  • Scaffolding was erected in February 2013 and remained for the duration of the scheme and for the three weeks when the contractors could not work because of poor weather;
  • Ms S uses a walking stick at times and there was concerns about the existing state of the rear yard where the tarmac had sunk, after a trench had been dug to place the oil line. After the works were complete the District Office undertook to resurface the rear yard.
  • External wiring under the fascia boards had to be disconnected by NIE during the scheme. NIE insisted the cables were replaced underground, requiring some excavation work to the rear of the property. This made access by the back door difficult for this tenant and added to scheme costs.

Learning point:

  • Cover gutters and downpipes to prevent blocked drains with insulation beads
  • Scheme designers should plan for any existing overhead electricity cables having to be replaced underground.

After insulation was installed Ms S provided valuable feedback by indicating;

  • Problems with draughts and condensation had been resolved.
  • The house heated up quicker and retained heat better.
  • Her oil lasts longer. She normally puts the heating on for an hour every morning and then uses the ‘boost’ switch if she needs the heat on throughout the day. She finds she needs to use this less often. Previous to this scheme Ms S kept very good records of expenses, she was able to tell us that on average she bought 1500 litres of oil per annum. We will continue to monitor oil usage with her over the next three years.
  • She has been able to turn her room thermostat down from 25°C to 20°C. (The Energy Saving Trust estimates that turning your room thermostat down by 1°C could save you up to £75 per year). Before the work was completed Ms S slept in an upstairs bedroom. She has since been able to move her bed downstairs as the spare room downstairs is now much warmer. This has made life much easier for her and removed any potential risk of falling on the stairs Ms S also commented that the external wall insulation had made a big difference to her home, both in terms of comfort and appearance.


Energy performance assessments were taken before the scheme started and again on completion which results in an Energy Performance Certificate (EPC) being produced.  These Energy Performance Certificates show an overall energy efficiency rating for your home from ‘A’ to ‘G’.  ‘A’ represents the most energy efficient properties and ‘G’ the least. The EPC also contains advice on how to cut carbon emissions and fuel bills by making home improvements. If a dwelling does not have insulation installed the EPC will recommend the type and level of insulation required to improve the dwelling performance.

Energy efficiency rating of dwelling (SAP):

  • Before insulation it was D
  • After insulation it was C


(Source: Northern Ireland Housing Executive Project)