BUSTING EXTERNAL WALL INSULATION MYTHS

We often hear claims about external wall insulation that are completely untrue so we thought we’d round them up to prove why we believe in it so strongly as an energy saving measure.

1. EXTERNAL WALL INSULATION STOPS BUILDINGS BEING ABLE TO BREATHE

It is certainly true that properties need to allow moisture to escape. If you live in a solid wall or system built property, when choosing External Wall Insulation materials it is very important to select a ‘breathable’ render, such as silicone or mineral render – as opposed to a non-breathable render such as acrylic render – as these will allow water vapour to escape through the walls, therefore allowing the building to ‘breathe’.

Unfortunately, many installers only use acrylic render, as it is the cheapest available render. The problem of using acrylic render is that it can prevent water vapour from escaping through the walls, thus leading to problems with condensation. This is why many people have heard stories of External Wall Insulation causing condensation problems.

Therefore, we strongly advise you to request a ‘breathable’ render when having External Wall Insulation installed.

Figure 1: Before and After photo of External Wall Insulation – installed with a ‘breathable’ render.

2. EXTERNAL WALL INSULATION LEADS TO MOULD

Kind of the opposite – Mould occurs from damp, often caused when warm, moist air in a room condenses on cold walls, causing condensation to form. External Wall Insulation raises the surface temperature of walls, reducing the temperature difference between the inside and outside and meaning condensation is less likely to settle on walls.

As mentioned above we recommend that you have a breathable render installed and also recommend that the mechanical fixings are coated with plastic, to keep thermal bridging to a minimum.

So there’s no reason why EWI with a breathable render would cause mould. As always, it’s important to ensure adequate ventilation through opening windows and using extractor fans in areas of the home where steam is present, such as kitchens and bathrooms.

3. IT USES MORE ENERGY TO MANUFACTURE EWI - EXTERNAL WALL INSULATION THAN THE MEASURE SAVES OVER ITS LIFETIME

This is categorically untrue. While there’s no denying the energy used in manufacturing chemical-bases insulation products such as XPS, the payback in terms of the energy you save through installing them makes it worthwhile in almost all cases. The manufacture of foam, glass, PU or XPS insulation is estimated at 1,3000kWh/m3. Based on these figures, the payback in terms of energy saved can be as little as 1-2 years.

For example, 90mm of EPS attached to a traditional 9-inch solid brick wall will reduce the U-value (which is a measure of how much energy is lost) from 2.2 down to just 0.3 per m2K, bringing it in line with a brand new wall built today. Even with the most expensive insulating materials installed at a high thickness, the energy amortisation period will generally be less than 5 years.

4. EXTERNAL WALL INSULATION IS A FIRE HAZARD

All building and insulation materials should be British Board Agreement (BBA) approved http://www.bbacerts.co.uk/

We advise you to check with the installer to ensure that the materials that they use are BBA approved – if so the materials will have been tested to ensure that they are fire retardant.

5. EXTERNAL WALL INSULATION CAN DAMAGE HEALTH

The insulation materials are manufactured in solid blocks and do not contain any loose fibres. They are also sealed with an impermeable coat of render.

6. EXTERNAL WALL INSULATION ENCOURAGES THE GROWTH OF ALGAE

Algae can be seen growing on some cheaper renders – while normally only a cosmetic problem, algae growing on walls can be an annoyance to the homeowner.

We advise you to request a hydrophobic render (such as silicone render) which will repel water and is also resistant to the growth of vegetation. It will keep your home looking new – probably more so than standard brick.

7. EXTERNAL WALL INSULATION DOESN’T LOOK VERY NICE

External Wall Insulation can be installed with almost any decorative finish that you desire including render (hundreds of different colours are available), pebbledash, timber cladding, stone cladding and brick. Please see our EWI photo gallery for examples of the different finishes that are available. We are sure that you will agree that External Wall Insulation enhances the appearance of almost any property.

Figure 2: Before and After photo of External Wall Insulation – installed with brick render and pebbledash finish

8. A LIVING ROOF WILL INSULATE JUST AS WELL

Green roofs and walls, planted with grasses and flowers, have a minimal effect on heat transfer through solid surfaces. Although living roofs can help with air pollution in densely populated areas, the only way they affect temperature is that they can help keep walls cool in summer, because sunlight cannot shine directly on the facade.

Conversely, External Wall Insulation has an impact in both summer and winter – and a much bigger one at that. It can prevent up to 40% of heat lost from a property.

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