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Retrofit of Victorian terrace house reduces energy bills by 89%

Posted by Cathy Debenham on 20 April 2012 at 7:38 am

Described as a "labour of love" by designers Green Tomato Energy the conversion of a Victorian mid-terrace, built in approximately 1870 with solid brick walls, to PassivHaus standard has significantly improved comfort and reduced energy bills.

Due to planning restrictions in the local conservation area, the exterior of the house had to be kept unchanged in appearance. As such, all insulation was applied internally on floors, walls
and ceilings, with floor joists rehung to avoid penetration of the insulation. The renovation works were used as an opportunity to redecorate the interior, remedy structural defects in the fabric and extend the house at ground and third floor levels. 

Special features

- Ground-to-air heat exchanger below existing basement floor
- Integrated solar thermal system for hot water, backed up by air-source heat pump
- Exhaust-air heat pump inside ventilation system for all space heating
- Green roof
- Specially designed triple-glazed sash imitation windows for conservation area
- Thermal bridges cut off by extensive detailing and rehanging of floors

Metered energy use for the first six months of occupation was 1.78MWh (including space heating, DHW, auxiliary and household electricity). Projected forwards, this gives an annual energy consumption of approximately 5.35MWh, or a saving of 89% against the most recent metered energy consumption from the house before the
renovation works.

The values above correspond to a PassivHouse specific primary energy demand of 54.8kWh/m2a. This is well below the predicted energy consumption, despite the presence of a baby and young child (and hence very intensive use of the washing machine). Close monitoring of the house continues.

The user experiences are overwhelmingly positive and the owner describes the house as a “fabulous living environment… exceptionally comfortable”.


If you have a question about anything in the above blog, please ask it in the comments section below.

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3 comments - read them below or add one


utility-exchangeComment left on: 25 April 2012 at 11:53 am

Interesting and the end result is superb - but many Victorian terrace houses are just two up two previous property was tiny - built in 1868 - and any insulating on the inside would drastically reduce living space....every cm was used! There was no cellar so no space for a mechanical ventilation system. Nice idea though if you have a big house and money to spend!

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Green Tomato Energy

Green Tomato EnergyComment left on: 23 April 2012 at 4:16 pm

Hi Simon, 

The cost of a passivhaus renovation will vary by project, but on this particular project it constituted 25% of the total build cost. This could increase to 30%, or decrease to 15%, depending on the geometrical complexity and orientation of the property. The expected financial (including income from the feed-in tariff on the small solar pv system and HotROCs from Good Energy) on this project is anywhere between £2,000 - £3,500 per year, depending on which neighbour the occupant talks to - i.e. varying behaviour of those in unaltered buildings. In linear payback terms at today's energy prices, this equates to anything between 18-30 years.  This period will shorten if energy prices rise.  It is also important to note that this payback analysis assumes that the works have added no capital value to the house.

I hope this helps


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violetlightComment left on: 20 April 2012 at 8:46 am

Hi Cathy,

Is there an estimate of costs, ROI and payback time for the PassivHaus conversion?  I'd be wary of doing something this radical to my victorian terrace without an estimate of payback time...



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