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Seven tips for a low energy retrofit

Posted by Alberta Congeduti on October 13, 2016

I am in the middle of retrofitting an 1880s house, including fully redesigning the existing 1990s extension to get better energy, light and comfort standards. One year on from the start of the project, which is now in the construction phase, I have some tips to share, for those about to start their own project…


  1. Get the daylight design right! My house is south facing and, in spite of this, it was incredibly dark and cold before the refurbishment. It is very important, both for solar gains and daylight purposes, to maximise the south facing glazing and have an intelligent design of skylights. South-facing vertical glazing can provide a great amount of solar gains in winter, whilst triple glazed skylights can be used to bring daylight in the more internal parts of the house, which are not reached by window light.
  2. Consider timber frame for the extension. This allows obtaining a high thermal performance within a relatively small wall thickness and is also one of the most sustainable building techniques, especially from a life cycle perspective.
  3. Keep the old part of the house as close to the original as possible. It is very tricky to retrofit an old building to low energy standard. Many of the modern building products and techniques can actually produce more damage than improvement to an old structure. In the old part of our house we are restoring sash windows and we are internally rendering the red brick façade with a lime plaster mixed with cork, thus replacing the existing modern gypsum plaster. Breathability and capillarity of the lime plaster, together with its alkalinity, contribute to reduce the risk of mould growth.
  4. Ranelagh RetrofitWork hard on project management. If you spend time in project managing you can keep the project within budget. In our project we made an extensive use of glazing on the south-facing side and we managed to keep it within budget by mean of a very wide and detailed research of the providers of highly efficient windows. For every building component there are a lot of different options and different providers. Choosing the cost effective option for each of them will save you a lot of money.
  5. Get a good builder! Choose a contractor who has experience in low energy building techniques and, also, who is very well organised. Ask for references and check with previous clients and/or with professionals who have already worked with that contractor. And then… be on site every day! Your builder will ask you to make a lot of decisions, sometimes from one day to another. Make clear from the beginning that it is his responsibility to give you enough notice (two weeks could be a good time…)
  6. Define your project in fine detail before the start of the building phase! Before you know it, you will need to provide the exact position of your kitchen appliances, radiators, lighting, switches, sockets, bathroom fittings, tiles, stove, boiler, flues, ventilation unit… and this is just a very short list! You could easily find yourself with a pipe in the middle of a room where you didn’t want it at all, unless you have everything clear from the beginning. Moreover, changes during work in progress never come without an extra cost!
  7. Time-schedule your shopping list. Make a very detailed list of all the items you will need to provide, which could include windows, floor, tiles, kitchen, bathrooms, stove and so on, each with the date it is needed on site. Then, for every element of the list, get the lead times from the manufacturers. Work back from that by putting everything on a calendar and give yourself a good couple of weeks to choose every item. And good luck with it!


You will find more information about my retrofit project on the NZEB Magazine.

5 thoughts on “Seven tips for a low energy retrofit

  • Simon Moynihan
    on October 14, 2016

    Are you leaving the Windows single or fitting double glazed panes?
    What u value is your lime mortar with cork mix, is there a max thickness you plan to apply?
    I enjoy and appreciate your tips.

    • Alberta Congeduti
      on October 14, 2016

      Hi Simon, thank you for your comment. I didn’t use single glazed windows. The sash windows, at the front of the house, are double glazed. In the new extensions at the rear all the windows are triple glazed, a part from the south facing ones which are double glazed, as the PHPP model gave us a better energy efficiency in that case.

      The thermal conductivity of the cork lime plaster is 0.045 W/mK. The thickness I am using is about 40mm, but it is very irregular due to the very irregular brick wall I am applying it on.

  • Liam
    on October 15, 2016

    Have you any issues on rising damp on old external walls and how are you dealing with it. Thanks for the tips keep them coming.

  • Stephen
    on November 12, 2016

    How did you consider air tightness considering the likely air leakage of the old house, did you replace the whole roof and reinsulate (assuming it was not converted) and was the south facing aspect just luck or was it a purchase criteria as many houses are east-west as they are North-South. Are you working to a standard (Enerphit/BER rating/PassiveH). I presume you were not able to insulate the front of the house so was the focus internal (and the loss of space)

  • Alberta Congeduti
    on November 14, 2016

    Hi Stephen, thank you for your comment. The airtightness in the old house is achieved with plaster on the walls and a membrane at the ceiling level. The roof is insulated at the ceiling level, cold attic. We bought a south facing property in purpose. The house is A3 EnerPHit standard. For the front insulation it is described in this article, where you could find also some other information:

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