External Wall Insulation

External wall insulation (EWI) has become increasingly popular over the last 10 years due to increased awareness and focussed government funding.

If your property was built before 1930, its more than likely a solid wall construction. An easy way to ascertain whether  your property is solid wall is by looking at the way the bricks are laid.  The photos below will help.  Measuring the thickness of the wall is another indicator–  if the external wall is under 27cm it is more than likely solid and if over, it is likely to be cavity wall (on very old properties in colder areas thickness of wall  is less reliable)

The installation method for EWI comprises of mechanically fixing a form of insulation board to the external façade and then finishing with a special render coat or weatherboarding.  Any fixtures and services like gutters, downpipes and lights that are fixed to the wall need to be removed and refitted after or extended to accommodate the new insulation depth.  An average EWI system will add an additional 9-10cm to the thickness of the walls so window sills normally need to be extended and the roofline may need to be extended out too if there isn’t enough overhang at the soffit to butt up to.  You may also require groundwork’s if your damp proof course is too close to the external ground level.

EWI may not be the top choice for some period properties. Planning permission may be needed if you’re changing the look of the property, for instance from original brick to a new render finish.  There may already be existing planning constraints in place if the property lies in a conservation area or is otherwise protected.  We strongly recommend speaking to your local planning department  if you are unsure. A good rule of thumb is if the external appearance is relatively unaltered, and you are in a protected area, it will be difficult if not impossible to install EWI on the front facade. It may also be that an unprotected property has interesting brickwork or other features that you want to retain–this will be very difficult with EWI, which is best for simple facade treatments.

However, EWI does bring benefits compared to Internal Wall Insulation (IWI), mainly that there is less disturbance to the internal fit out and features, also losing no internal floor area. It can be suitable to install EWI on the rear facade even in a conservation area (again, check!). The EWI insulation, in order to be effective, must overlap with internal insulation used on the front portion of the building and a hybrid system has to be correctly detailed. 

As with any other method of insulating your home, choosing an incorrect system can have detrimental effects on the building and on your health.  As most traditional buildings were built to “breathe” and construction materials were vapour permeable, the system to insulate these buildings would need to breathe as well otherwise it could exacerbate existing moisture-related problems or create new ones. 

Heat loss through the walls can be dramatically reduced once EWI installed. However, since heat travels through the path of least resistance, it is important to insulate ceilings and floors at the same time and to address the junctions where they meet to avoid any thermal bridges.  The ideal is to create a continuous uniform thermal envelope around your property.

With all fabric insulation measures, it is vital that ventilation is maintained or improved.  Insulation reduces passive air flows so it reduces natural ventilation. However insulating in a coordinated way will greatly reduce condensation and mould, thereby  improving internal air quality.

If installed correctly external wall insulation can dramatically change the dynamics of your property, making it a cosy, energy efficient home. It can improve the appearance of your home if the exterior is looking tired and without losing valuable internal dimensions.

You can add significant  value to your home and in some cases, it can be the difference between making it lettable or unlettable with the new requirements for EPCs of C or higher coming into effect soon.

Hearth can assess your property for suitability for external wall insulation as well as holistically looking how your home can be more energy efficient, and if eligible we can direct you to possible government funding towards installation.  We perform our  assessments according  to PAS 2035,  the new robust government trustmark standard for domestic properties.