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Mid-victorian end-terrace house
Ours has been a somewhat challenging house type. Located in a conservation area, it is a two storey terraced house built in the mid 1860’s as part of the wholesale speculative development of Osney Island in central Oxford.

The house was poorly constructed for a working class and rental market, although (as with the ironies of modernity) it has since become highly desirable due to its central waterfront location.

The house faces east, but, as an end terrace house, enjoys an unobstructed southern aspect along its side. This aspect and the close proximity to the Thames were the main inspirations for our renovation, which we have endeavoured to make a showcase for renewable and low energy systems.

Our renovation combines insulation, photovoltaics, solar thermal and a highly innovative heat pump heating system taking its heat from the river Thames.
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When we first moved in, in 2000, the house was in poor condition requiring a thorough renovation. It also became clear that the building was structurally unsound: the side gable wall was only four inches thick and was skewing dangerously under the weight of the roof. This along with other structural problems led to a decision to rebuild both roof and floors within the strengthened shell of the original house. The renovation also included a new kitchen extension at the rear of the house and a self contained office at the end rear of the garden.

Vital Statistics

This property was built between 1700-1920. It is a end-terrace house with 2 bedrooms, located in a suburban area in the South East. The household is a multiple occupancy shared house, with an average occupancy of 2 all year round. Planning is restricted due to the location being within a conservation area.

Annual Energy Use

(No energy use data is currently available for this ecovation.)

About us and why we did it

We are Barbara and David Hammond. David is an architect with a long and passionate interest in renewable technologies and space heating using low grade heat sources such as solar collectors and heat pumps. Whilst Barbara has a PhD in Sustainable Development and works in Central Government in these areas.

David has been interested in renewable energy systems since the 1970s when he did a thesis at college in which he explored the possibility of using a heat pump in conjunction with solar collectors to deliver low grade heat to underfloor heating. The vehicle he used was a sheltered housing scheme.

We share interests in sustainable issues, and when we bought this house in 2000 we thought this was an opportunity to see how some of these ideas might work in practice. Through experience of architectural practice we are both well acquainted with and have been frustrated by the slowness of developers, planners, and clients to adopt these new technologies. As a result we wanted to show what could be done using our own house. We both harbour the deep commitment to the environment which has inspired this project.

Heating and Power

The heating system is a particular feature of our house, which along with a south facing 'sun trap', ensures highly effective space and water heating in the winter and summer.

The space and water heating are both fed by a large water thermal store tank (provided by Chelmer Heating), which is maintained at a temperature of 45°C by a combination of solar and a heat pump.

The five Viessmann thermal flat plates with a total area of 7.5 m2 provide the initial heat. A clever (and money saving) feature is that the large area of panels fully replaces the roof of the south facing roof above the side and rear kitchen extension. They were installed by a Viessmann recommended contractor at a cost of £3,600.

The additional ‘top up’ heat is provided by the heat pump. Heat pumps are electrically powered compressors that extract heat from the local environment and concentrate it at the temperatures needed for heating purposes. Most conventional heat pump systems have a ground source - either from a closed circuit of piping laid in trenches or in a single deep bore. A ground source was not practical on this restricted site and our system draws its heat from the River Thames. A pump lowered into the river pulls the water at a rate of 35 lites per minute through a filter and into the 1.5 inch diameter pipe which carries the water under the road and the ground floor of the house, through the heat pump, and then back into the river. The river has a higher and more stable temperature than a ground source and the high flow levels possible with an open loop system of this kind further enhance efficiency. The main costs for using the river was £600 for a section 50 license from Oxfordshire County Council and £1500 for the specialist contractors to dig up the road.

The 6Kw heat pump cost £3,100 and is a simple and standard model from Kensa Engineering. Because of its slight operating noise it is housed in the back garden in a box the size of a small fridge. In three years the entire system has only once required maintenance - a relatively straightforward operation to clear the water inlet of leaves.

The space heating is provided through an underfloor system. On the ground floor the heating pipes are set into screed under the solid wood floorboards. On the first floor the pipes are laid between the floor joists and set into sand and cement ‘pugging’.

The combination of heat pump and underfloor heating is a perfect marriage. Because an underfloor heating system requires a lower operating temperature than conventional radiators, the combination minimizes the temperature gradient- the differential between the input and output temperatures - which is the main limitation on heat pump performance.

There is a 1.1 Kw PV array installed by Solar Century on the roof of the office, which supplies the domestic demand and exports any surplus to the grid. It has generated 1101kwh since it was installed in October 2004.

The passageway along the south side of house was glazed over to create a sun porch, and sliding doors installed along most of the kitchen wall which faces onto it. The doors are closed during cold periods so that the space traps any additional solar warming and acts as an extra south facing skin for the building. This absorbs heat on sunny days and improves overall thermal performance. On sunny days, the double glazed doors of this single glazed unheated space are opened up to the main house, particularly during the summer months, letting warmth into the house.


The loft and external walls were insulated, the latter internally, and our windows were replaced with new, high performance double glazing.

The existing external walls were battened out to approximately 100mm and insulated internally with rockwool held between the batons and dry-lined with Fermacell. This seems superior to plasterboard due to its strength and environmental performance. The loft was fully insulated and windows replaced with high performance (low emissivity, argon filled) double glazing in wooden frames.

Obstacles and How we Overcame Them

Installation and maintenance did on occasion prove problematic, though with regard to local government and planning restrictions we experienced few problems.

We faced difficulties finding skilled and committed installers and were further frustrated by the difficulty of getting installers back for minor adjustments to the solar panels. This is, no doubt, in part due to a lack of competition in the market for renewables.

On the other hand we had a resoundingly positive experience when dealing with the local planners. Although we live in an Article 4 conservation area, we kept within planning regulations because the solar panels were not installed on the street face of the house. The Environment Agency and the Council were very helpful with the paperwork and logistics of digging up the road to lay the piping for the heat pump system.

Unfortunately, anyone wishing to replicate the heat pump system will face a new obstacle: negotiating terms with the government’s Clear Skies programme. The programme, which was launched after the completion of our project, awards substantial grants for domestic solar and heat pump systems. However, due to bureaucratic oversight, it has only issued grants to closed loop systems and does not recognise ‘open loop’ heat pump systems despite their higher efficiency.

Low Carbon Lifestyle

What were the improvements in energy performance or the carbon savings?

From October 2004 to October 2005, the heat pump has used just over 4000kwh of electicity. This is supplied at a green tariff from Good Energy at a cost of approximately £300/year for both heating & hot water. Even if this had been supplied from conventional grid electricity it would still equate to only 2 tonnes of Carbon Dioxide emissions.

Top Tips

Three top tips:

1. Work with your house - as this project shows, working with an existing property can inspire new and creative solutions. There are far more possibilities and opportunities in any house than most people realise.

2. Hire builders and workers who have the necessary skills and have sufficient support for your vision that they will acquire the additional information or skills they may need.

3. Chimneys are perfect for mounting wind turbines, providing both support and a duct for the cabling. A small wind turbine is the next planned addition to the house. It does now seem plausible that one day wind turbines could be as common on chimneys as television aerials.

© Climate Outreach Information Network, 2006-2007
Design - AHG