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External Wall Insulation (EWI)

Rising energy bills mean that it’s no longer just our more forward thinking clients asking for an efficient home as well as light bright family spaces. 20 years on the Green Register have taught us that comfort and low bills starts not with photovoltaics or heat pumps, but in the less glamourous, more difficult and detail intensive process of cutting down the energy used to keep you comfortable, nowadays hand in hand with avoiding overheating in the summer.

Most 19 and 20 Century homes by now already have the loft well wrapped (if not start there), although the exception to this is often older loft extensions, and probably double glazed windows. What’s next? Draughts, floors and walls. Floors deserve a separate article. Treating your external walls may seem impossible, but it’s not. Filling a cavity wall (if you have one – unknown before about 1930) helps, but that’s only 50mm (2 inches) of insulation and we’re probably looking for 150mm. That leaves a choice between inside, hugely disruptive and costly in space, or outside = External Wall Insulation.

EWI is the most efficient in terms of the physics, and relative ease of application. But in most cases you will need planning permission for the ‘extension’. That’s getting more acceptable too. Right now we have one freshly finished EWI project in a Wimbledon conservation area, and another on site in a CA in Putney. Time to take another look at your house?

Pictured are two we did (much) earlier. At no 6 (ten years of savings) the bay is insulated inside to line up with the neighbour, but the right hand side is EWI. Heat recovery ventilation keeps the air fresh whilst saving even more energy. At No.2 (30 years of lower bills) what you see is all EWI, including the cornice. Note the external shutters here keeping the house cool in summer.


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