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A wonderful day learning about how Nigel and Marta made their home so warm and cosy … and low carbon

Nigel and Marta bought their new home in Acocks Green in 2016.  The house was built by Birmingham City Council in 1958; Nigel and Marta were only the third occupiers of the house.  The house had cavity wall insulation but apart from that it had little in the way of energy saving measures.  On October the 15th 2022 they opened their door to visitors through Birmingham Green Doors.  There were three two-hour slots throughout the day.  That’s their home on the left in the image.  Spot the difference!

Nigel and Marta had previously lived in a house in Nottingham with external wall insulation, and it had made such a difference that they decided to have it in the new house, even though it already had cavity wall insulation.  They converted the loft into a bedroom, with a new insulated roof.  Their builder discovered that the uninsulated solid concrete floor on the ground floor contained fly ash (power station residue) and that this had caused the concrete to deteriorate.  Nigel and Marta saw this as an opportunity not only to have an insulated replacement floor.  but to have low-temperature under-floor heating at the same time.  This was a wet underfloor heating system connected to a new condensing combination boiler.  Nigel and Marta hope that in the not-too-distant future, there will be a shared ground source heat pump connected to theirs and neighbours houses, which will provide space heating to their under-floor heating and radiators on the first and second floor – although the radiators are scarcely needed most of the time.  This is not only due to the insulation but also to the airtightness of the house and the additional heat input from a MVHR system – mechanical ventilation with heat recovery.  This provides a steady background heat that reduces the need for input from the gas boiler.

I was particularly impressed with the way the contractor, Jericho Foundation, designed the under-floor insulation to include an additional vertical layer of insulation where the floor slab meets the external walls.  This stops heat escaping horizontally through the floor slab; a detail often overlooked in replacement solid floors, where thermal imaging often shows dramatic heat loss horizontally through the floor slab.

MVHR also means that the house does not have air bricks in the walls.  Normally air bricks are essential for ventilation.  But MVHR has sophisticated sensors which mean it can provide ventilation exactly when it’s needed, as well as recovering heat from stale air to provide background heating.  Most houses lose heat through cold air infiltration – Nigel and Marta, who are also founders of Acocks Greener, have virtually eliminated this due to not needing air bricks; removing the chimney; and having continuous insulation to prevent thermal bridging.  Insulation of the walls, roof and floors are the most important factors in preventing heat loss – but the importance of air tightness in Nigel and Marta’s house cannot be underestimated.  Air tightness is often overlooked in “measures-led” retrofit – i.e. where the retrofit is designed around the availability of a particular measure, or the availability of government funding.  Nigel and Marta’s green makeover is a good example of a whole-house approach.  That means you consider the home as a whole system and not as a series of individual components.  That doesn’t mean you have to do all the measures all at once; quite the opposite; a whole-house approach involves planning for medium and long term improvements as well as immediate ones.  In Nigel and Marta’s case this involved treating the difficult bits of building fabric (wall insulation, loft conversion, floor insulation) before they moved in.  Their medium and long-term plans involve not only a heat pump but also addressing the performance of the windows, which is good, but where thermal imaging shows that some of the rubber seals have deteriorated, allowing heat to escape.  Window replacement is disruptive and expensive, especially when you have just had wall insulation, but Nigel and Marta have a medium term plan – which is to replace the rubber seals.  This is a simple and cost effective measure that often gives better value for money energy saving than window replacement.

I was also impressed that Nigel and Marta had insulated the party cavity wall with the neighbouring property.  This is an essential measure on semi-detached and terraced houses where there is a cavity party wall with the neighbours.  Failing to do so can allow heat to escape up the cavity in the party wall.

Another example of having a short, medium and long-term retrofit plan is Nigel and Marta’s approach to solar.  While understanding that energy saving measures come first, Nigel and Marta decided to put in solar on their new roof – both on the south-facing pitched roof and on the north-facing flat roof.  The solar output from the flat roof is almost identical to the solar output from the pitched roof.  Some people think that solar on a flat roof doesn’t work.  Nigel and Marta have proved that this is a fallacy.  Just before Covid broke out, Nigel and Marta installed a small electric battery.

Big isn’t always better when it comes to solar batteries.  An incorrectly sized battery is not a good use of anyone’s money.

Nigel and Marta’s battery was sized appropriately to make best use of not only the solar panels, but the availability of cheap off-peak electricity through Octopus Energy’s agile tariff.  This is a bit like the old-fashioned Economy 7 tariffs that are good for people with storage heaters, only designed for the digital low-carbon age.  Nigel and Marta will add further battery capacity in the future when they have a heat pump, but they don’t need it yet.

If you install energy saving measures, how do you know if they are working?

I meet a lot of householders and businesses who have had energy saving or renewable energy measures fitted, or have moved into buildings that have them, and aren’t sure if they work.  It can be quite difficult to evaluate this but it is one of my favourite bits of helping people to decarbonise buildings.  It’s possible to design a monitoring strategy that is as simple or as sophisticated as you want.  One of the reasons I am so in favour of smart meters is because they make it easy to do this.  Nigel and Marta have done this and produced evidence of how much energy, carbon and money they have saved.

I was blown away by the range of people that attended this Birmingham Green Doors event.

This was the second Birmingham Green Doors event and was attended by a wide variety of people including:

  • Concerned citizens who want to make their homes more energy efficient
  • Community workers who are encouraging Birmingham residents to participate in energy saving schemes
  • Professionals working in architecture and energy saving who are keen to learn from real-life practical examples.

The community workers raised some vital questions during the course of the day about what happens when residents sign up to government funded energy saving programmes.

  • What handover information is given to residents about the measures?  How is it delivered?  Verbally?  In writing?  What about people who have limited literacy or have limited written English (including people who are fluent in English and a community language such as Mirpuri but who have limited written English)?
  • What aftercare is available?  What guarantee is there?  What do I do if something fails?  What happens if the installer goes out of business?  Will the render on external wall insulation need painting?

These are vital questions that local authorities need to be able to answer.

There was also a discussion about the quality of work done on the now-defunct Green Homes Grant in Birmingham, with reference to one particular neighbourhood where there had been a lot of external wall insulation done.  It was agreed that the quality of work was poor; the insulation was not continuous; there was already evidence of render cracking (either due to applying render during wet weather, or by lack of attention to detail around edges of insulation).  We looked in detail at Nigel and Marta’s insulation and saw how the contractor, Six Star Group, had ensured that the edges of the insulation were protected from the risk of cracking).

The discussion highlighted that where retrofit can go wrong, the problem isn’t the kit that gets installed, it’s the lack of attention to detail in design.  Nigel and Marta used contractors that understood this and they are looking forward to many years in a low-carbon, warm home with minimal maintenance issues.  One problem they have had is finding people to service their MVHR – now resolved – but showing the continuing lack of capacity in the energy saving supply chain caused by many years of inconsistent government policy leading to a stop-start retrofit economy.

One final point about Nigel and Marta’s floor.  In 1958 building materials and labour were still in short supply following the war.  So material re-use was widespread, and the use of ash in concrete floors was an example of this, albeit one that would lead to long-term problems.  It seems to me that there must be many thousands of homes built by councils in the 1950s and 1960s that have floors like Nigel and Marta’s, that will need replacing at some point.  Councils could see this as an opportunity to plan for the replacement of these floors when homes become void, to replace these floors with insulated floors with under-floor heating.

Click here to read about forthcoming Birmingham Green Doors events.  We look forward to seeing you!

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