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Green Building News

Remodeling a U.K. Victorian for Passivhaus Performance

A nonprofit housing group leads the way on a deep energy retrofit that aims to meet Passivhaus standards at a reasonable cost

This Victorian-era terraced house is part of London’s social housing stock and the target of a remodeling project designed to bring the building to Passivhaus performance standards on a budget of $234,000.
Image Credit: Octavia Housing (images 1-3), Paul Davis + Partners (images 4 and 5)
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This Victorian-era terraced house is part of London’s social housing stock and the target of a remodeling project designed to bring the building to Passivhaus performance standards on a budget of $234,000.
Image Credit: Octavia Housing (images 1-3), Paul Davis + Partners (images 4 and 5)
A thermal image of the front of the house, which was built in the 1860s. When the remodel is complete, windows like this will have been replaced by custom made triple-glazed windows. Marion Baeli, a Paul Davis + Partners architect working on the project, explains that insulation will be added to the internal faces of the shell only, a process that likely will be followed in most of the U.K.’s historically significant buildings should they become candidates for deep energy retrofits. Paul Davis + Partners architect Marion Baeli notes that window replacement in the Victorian will follow a “to match existing” rule. Triple-glazed replacement windows have been specially designed for the project, which Baeli notes, is a first for the U.K.

There are so many Victorian-era homes still in service in the U.K., it is small wonder they’re among the prime targets for remodelers striving to increase the energy efficiency of Britain’s housing stock. So it’s no surprise the planned remodel of an 1860s Victorian row-house to Passivhaus performance standards has attracted the attention of many of the country’s residential retrofitters.

The renovation proposal for the building, which is part of London’s social housing network — that is, government-subsidized nonprofit housing — was among the 87 winners of a competition called Retrofit for the Future. The competition was an initiative of the U.K.’s Technology Strategy Board, a government-appointed group of executives whose mission is to stimulate innovation in areas that will encourage growth and productivity.

Led by social housing nonprofit Octavia Housing and several partners, the remodel project received $31,200 from Retrofit for the Future to test its strategy for retrofitting to Passivhaus standards and, upon being named a competition winner, another $234,000 to complete the retrofit.

A potential turning point in retrofits of hard-to-heat homes

The level of funding for the project is, of course, of considerable interest. As with many deep energy retrofits, challenges often extend well beyond meeting technical requirements and satisfying guidelines for historic preservation. The recent energy efficient remodel of a 1,075-sq.-ft. privately owned Victorian in London showed that the success of such projects can lean heavily on the client’s financial resources. The house ended up more than 70% more energy efficient than it had been before the remodel, but didn’t quite achieve Passivhaus performance. Still, the Passivhaus ambitions for the project added about $93,000 to standard renovation costs, which for a house of that size, the project architect noted, could fall between $180,000 to $280,000, depending on which luxury amenities the clients might choose.

Nonetheless, with $234,000 to spend, Octavia Housing and its partners sound confident they’ll reach their performance goal and make a case for the affordability of deep energy retrofits. The funding allotment is “not all that much more than a normal whole-house renovation,” Hamish Phillips of renewable-energy and Passivhaus specialist Green Tomato Energy, says in a news update on the Octavia website.

The renovation team – which also includes environmental consultancy Eight Associates, architects Paul Davis + Partners, and energy conservation specialist Ryder Strategies – says it aims to cut the building’s carbon dioxide emissions by 83% and its energy consumption by 94%, which would trim the home’s energy bills by about $1,420 a year.


  1. David | | #1

    Insulation: interior or exterior?
    Richard - Interesting case study. Do you know how the project is planning to insulate the envelope? Wondering if the exterior brick and window trim will be retained by insulating and airsealing on the interior, or if the building will be wrapped with insulation and air barrier on the exterior and re-skinnned.

  2. GBA Editor
    Richard Defendorf | | #2

    Insulation details TK
    David -- Thanks for the inquiry. We've contacted a couple of the partners for more information, and we'll add it to the post soon as they respond.

  3. Marion Baeli | | #3

    Insulation: interior or exterior?
    Dear David

    The envelope is insulated on the internal faces only.

    It forms a continuous and totally air tight box within the existing envelope (sort of a new building within the fabric of an old).

    The house being in a conservation area, installing the insulation on the external fabric was not an option. All external elements are to be replaced 'to match existing'. The team has developed for this effect a special triple glazed sash window (a first in the UK!).

    It is important to note that there is about 1,200,000 buildings located in conservation areas in the UK (source: In total there is 4,766,000 houses built pre-1919 (made of solid masonry walls) with potential aesthetic merit. So the internal insulation approach is going to take a very important role in our aim to reduce the CO2 emissions from existing houses here.

    I would be interested to know which way the US existing housing stock is heading towards in terms of retrofitting insulation measures?

  4. Philip Proffit | | #4

    Word from the technical desig/builder
    Our role has been to design the systems and construction methods for achieving the low energy building in partnership with the architect. We have used common or fairly common building materials and enngineering, but applied in a different way to 'cure' every thermal bridge in the building and combined with a special airtight system running inside the insulation we are able to achieve comfortably the Passive house specification. Air tighness is the most difficult to achieve in a building built in 1840 unless a bulding system and concept are adopted. We have just made an interim test on the building to check that we are on target and have achieved 0.17 against a passive house spec of 0.6. Using our new triple glazed windows whose U-value is between 0.8 and 0.9, we are around 9 Kwh/annum/m2. This is the space heating energy and the passive house spec is 15 so we are reasonably confident in achieving passive house certification.
    We have used some fairly innovative systems for the building industry including the method of separating the floor joists from the external walls, using the cellar floor as a heat exchanger, combined with a habiutable area in the cellar, our window design that is now in production is the first triple glazed system to be approved for a conservation area, a combination of air to water heat pump, built into the ventilation system and combined with an additinal solar powered hot water cylinder to provide a combined storage of 500l of hot water and up about 75-80% power taken from the sun. (the high percentage is gained through the use of drain back technology combined with a large panel area and high storage volume). There is no other additional heating in the building and the gas supply was removed.
    Finally, non of this could have been achieved without a multi skilled dedicated workforce who have been trained and schooled over a long period of time and who have contributed to the building the design and systems. Structure and multi skills minimising external contractors is key in the early days of reto-fit development. We are now waiting to take on our 6th retro-fit.

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