Why external wall insulation is beneficial
With a long winter behind us, I am thinking of investing in external wall insulation for my house. Why is external wall insulation becoming so popular and how do I know it is suitable for my house?
External wall insulation (EWI) is a proven method for effective improvement of heating energy performance of houses and apartments.
It involves the application of insulation and a new render coat on the outer face of the existing external walls of the building. Extremely high performance insulation standards can be achieved.
It is usually possible to achieve comprehensive coverage of external wall surfaces. Careful detailing will minimise heat leakage at 'thermal bridges' – the heat leakage points (such as around window openings) that are difficult to insulate using other insulation methods.
The building will also be made more airtight, reducing heat loss due to draughts. The installation can be completed with minimal disruption to life indoors.
The surface skin of the building is renewed, thereby extending the life of the building.
The EWI installation consists of insulation board fixed with adhesives and pins to the existing wall, covered with a basecoat render that contains a reinforcing mesh and topped with a decorative finish.
In Ireland most houses built with brick or concrete walls are suitable for EWI. Single skin walls of brick, solid / hollow blockwork or stone are generally ideal for EWI. Cavity walls (two separate leaves of brick or block with a gap between) should first have the cavity filled by injection of insulation to prevent air movement reducing the insulation effect of EWI.
Timber frame houses are generally not suitable for EWI. If there is rising damp in walls, careful analysis should be undertaken.
Various other factors should be considered prior to installing EWI. There must be adequate ventilation to maintain good air quality in rooms for occupants.
Planning permission will be required if the building is a protected structure listed by the local authority or if the appearance of the building will be changed significantly from the original appearance or the appearance of neighbouring buildings.
If in doubt, get advice from an architect or your local planning officer. As the installation of EWI adds about 120mm – 200mm to the outside thickness of the walls, you must be sure you are not intruding on public footpaths or neighbouring property without formal permission.
About 22 separate systems of external wall insulation are certified by the National Standards Authority of Ireland (NSAI).
There are significant differences in the components approved for the different systems, such as the insulation (chemical type and performance), window sills (aluminium, factory made polystyrene, resin) and finishes (acrylic paint, cement type render, stone dry dash, brick effect).
Each system has a panel of trained and approved installers.
EWI is quite expensive. Installation costs will vary significantly according to site conditions and specification but are generally between €80-125/m2 of wall surface area.
Grants from €1,800 to €3,600 are available from SEAI for approved installations.
Advice and information is available from www.riai.ie; www.nsai.ie and www.seai.ie
William Scott of Scott + MacNeill, Architects, specialises in sustainable design and construction and is a consultant in external wall insulation