Passivhaus retrofit

Dating from the 1860s, 100 Princedale Road in the Holland Park area of London doesn’t, at first glance, look to be much different from any of the other houses in the terrace. But it is. Octavia Housing is aiming to register it as the UK’s first certified retrofit to Passivhaus standards.

Passivhaus buildings are designed to provide high levels of occupant comfort while using very little energy for heating and cooling because space heating requirements are drastically reduced. All this is achieved through meticulous attention to detail and rigorous design and construction according to principles developed by the Passivhaus Institute in Germany.

My past experience of houses built to these standards has been of projects very much in the grand designs mould, indeed I went to visit one house just north of Dublin in Ireland to write it up for Grand Designs magazine. As I walked up Princedale Road I knew that retrofitting a Victorian house to Passivhaus standards was something very different and, in many ways, much more challenging. Indeed the press release asked the question ‘Can a Victorian home reach strict Passivhaus standards?’.

Judging by what I saw the answer appears to be yes. The Passivhaus standard required the home to use less than 15kWh of energy to heat it per m2 per year, compared to the UK average of 130kWh. The refurbished home’s CO2 emissions and energy consumption will be cut by an estimated 83% and 94% respectively through the energy saving works – an estimated £910 a year saving on fuel bills.

This is achieved through a variety of measures including high levels of insulation, air tightness and the minimisation of thermal bridging. The reduction in energy consumption means that there isn’t a conventional heating system. Instead, a self-designed ‘labyrinth’ heat exchanger beneath the insulation in the basement provides pre-heating in winter and cooling in summer. Hot water is supplied by a combination of solar thermal, air source heat pump and waste water heat recovery. Triple-glazed, imitation sash windows were developed in-house to meet strict conservation area requirements.

The question for me is at what cost was all this achieved. And I don’t just mean the financial cost – funding for the project came through the Technology Strategy Board’s Retrofit for the Future competition – but the cost in terms of the potential loss of historic fabric and what might potentially end up in landfill as a result. In the case of Princedale Road, I’m assured that very little of the original remained due to the many alterations that the building had undergone over the years. Even so, the chimney breasts were removed to compensate for the space lost through installing internal insulation and one senses that the gutting of the interior was pretty thorough.

The question of whether this is wrong, and whether it precludes the Passivhaus approach in old buildings, is undoubtedly one that must be considered. Indeed, it brings us to the wider retrofit debate and the degree to which original fabric is dismantled or disturbed. The means of achieving the sort of energy savings being sought are often, by their nature, invasive and there certainly appear to be few easy answers.

Image credit: Octavia Housing


  1. Hilary Grayson on December 21, 2010 at 8:02 am

    This is both interesting and frustrating at the same time. I applaud projects such as this, but have a nagging doubt that the approach is too purist. How do you over come the issues of cold bridging in an older property (tell me – I really want to know as I have my own older property with cold bridges everywhere!); how much did this refurb cost; how do you find a workforce able to manage the level of detail involved; what improvements have the most effect? I could go on. What we really need are examples of improvements that are achievable by the masses or, like the Grand Design buildings themselves, this will just remain a dream and not a mainstream reality.

  2. Roger Hunt on December 21, 2010 at 8:47 am

    Like you I applaud projects like this – we don’t know until we try and we must push the boundaries to discover what is achievable. Implementation of any type of retrofit in the main stream is far more challenging than these exemplar projects and training and funding are key issues, there is a danger that if the process is not managed correctly more harm than good will be done.

  3. Marion Baeli on December 21, 2010 at 9:22 am

    Cost are important to understand. I’ve just written a paper on costs and paybacks of PassivHaus Retrofit (to be published shortly).
    As for the technical aspect, to enable the rolling out of these kind of low energy Retrofit ‘en masse’, we need a lot more research on cold bridges, the effect of internal insulation etc. I don’t think we’re quite ready yet with ‘building physics’ solutions to do anything else than a full-on retrofit similar to what we’ve just done at Princedale. A few people have started their thesis on these issues, I’d say, watch this space, we might have some solutions soon. Marion (architect at pd+p, involved in Princedale Road Retrofit for the Future).

  4. rachel h on December 26, 2010 at 6:36 pm

    The beauty of this project is that it attempts to address those common problems associated with older properties that make up such a high percentage of London homes. Its true that Octavia Housing would not have retrofitted a home to this extent without funding from the TSB competition but the lessons learned from the project could prove very useful for wider scale implementation. It is highly likely that eventually all housebuilders and home owners will need to improve the energy efficiency of homes so we need projects like these to pave the way.

  5. Brian Smith on January 3, 2011 at 2:43 pm

    I was fascinated to read both this article and also the comments. I currently live in a cottage which was built in 1732 (you can see it on my website). Insulation is minimal and the thick stones walls (the same geology as the Cotswolds) leak air and heat very efficiently.

    The reason for my particular and enthusiastic interest is that we’ve just bought a cottage of the same vintage (actually next door) and unlike 1985 when we renovated this cottage, we’d like to be far more eco-friendly. Passivhaus would be the dream but we’re wondering how much – if anything – is actually achievable.

    For example, Ground source/Air source firms will not quote unless the cottage is fully insulated – but that would involve serious compromise of the character of the property. English vernacular cottage interiors are beautiful and precious. Our inglenook with log burner and our open fire with log basket are joys to live with and we would hate to have anything else – even if the listed buildings officer allowed it!

    Any advice or comments would be welcome and I’ll let you know how we get on.

  6. Roger Hunt on January 3, 2011 at 6:26 pm

    I’m delighted that you care so much about the historic fabric of your cottage and it’s vital to find the balance between that and the important aim of making the building energy efficient. Insulating old buildings is difficult and much research is currently being undertaken into their thermal performance. One of the organisations doing this is the Society for the Protection of Ancient Buildings (SPAB) and, since every building is different, I would suggest that you should call their free technical advice line: 020 7456 0916 to discuss how you should move forward with your cottage. Consider other measures as well as insulation such as secondary glazing and draught proofing and keep pursuing the idea of a heat pump. One plus point worth remembering is that a stone built cottage has good thermal mass which will help store heat and stop over heating.

  7. Alan Tierney on January 4, 2011 at 1:40 pm

    I agree completely with Roger’s suggestions for Brian’s cottage.

    In particular continue to pursue the heat pump solution. I have one installed in my C16 timber framed cottage and it works very well. I frequently recommend them as an ideal solution for historic buildings. An enlightened installer should be able to recognise that you, as an enlightened homeowner do not expect to achieve the same results as in a modern, fully insulated building.

    Approach insulation of any traditionally constructed building with caution. As has been said, we really don’t fully understand the implications yet. The best advice is to stick to a limited amount of breathable insulating material, concentrating particularly on reducing air movement / infiltration, and to make the work as reversible as possible while we wait for the results of ongoing and future research.

  8. Brian Smith on January 5, 2011 at 9:01 pm

    Thank you so much, Roger and Alan, for your replies. I feel supported and encouraged.

    My wife and I are very committed to preserving the character of the cottage, yet speaking to eco-professionals had led me to believe it was “all or nothing” – if we couldn’t insulate to current, even future, specs, then we should install oil central heating.

    I’ve argued that if one can harness renewable energy as part of one’s requirements then it has to be a good thing. But the response has been “If we can’t guarantee an internal temperature of 21 degrees from heat pumps alone then we won’t quote”. Advice from all sides, professional and amateur, has been “If you can’t fully insulate, then don’t bother.” Insulation seems to be the holy grail. But Alan’s heat pump is surely evidence that the technologies can be used in traditional buildings. May I ask if it’s ground or air source?

    Clearly, insulation is important and I agree that it must allow traditionally built fabric to breathe but you have reassured me that it’s worth continuing to investigate. And Roger’s point that the stone walls have good thermal mass is a factor which doesn’t seem to have been considered by the professionals i’ve spoken to.

    I suppose the main eco-thrust is inevitably towards new builds or retro-fitting late 20th Century properties. But the fact that listed buildings are different surely shouldn’t rule them out. I’m delighted to hear that research is being conducted.

    My thanks again.

  9. Alan Tierney on January 6, 2011 at 5:47 pm

    Brian, Glad to be of help.

    My heatpump is ground source but in principle air source would be just as well suited to a historic building.

    You are right that much of the “eco industry” regards insulation as the holy grail of energy efficiency. However there is a growing body of more realistic and enlightened sustainability experts (Roger among them) who see this as a flawed and potentially problematic approach.

    Stick to your guns and keep looking until you get the right advice to combine your commitment to both your building and the environment.

    There is some good research starting to shed light on this area. The SPAB is always a good point of contact (in fact the latest edition of their magazine, Cornerstone, has an article about the installation of a ground source heatpump at Castle Howard).

  10. Brian Smith on January 12, 2011 at 9:50 pm

    Thanks for your reply, Alan, and forgive my slow reply.
    I’m slowly gaining in knowledge. It’s all very new I’m finding it fascinating. My motivation is partly (and importantly) the environment – I do believe we must change our wholesale plundering of fossil resources. It’s partly to work in sympathy with our traditionally built cottage. But it’s also because oil has increased in price from 10p to 60p in the 25 years we’ve lived here. I do believe it won’t go up another six times in the next 25 – more like 50 times, possibly ! so to become much less dependent on oil really is very important indeed.

  11. Dark Lad Slim on January 13, 2011 at 7:38 am

    Heat pumps are not all that they are cracked up to be. Safely theory and reality have a hard time converging. Both the Energy Savings Trust and Leeds Met in-use studies highlight this.
    The building physics is well understood however it is not broadly appreciated by UK industry. It’s not research that is required but rather it is dissemination. Without exacting levels of airtightness that can be maintained for the long term internal insulation is not a good idea – moisture/mould risks are too high. In a airtight building good balanced ventilation then becomes a prerequisite.

  12. Mike Jacob on January 13, 2011 at 10:36 am

    This is a great site – thanks Roger. Glad to see some caution being put forward re heat pumps: they are not a panacea and anyone considering purchasing one for a new or old property would do well to carry out some simple sums before investing in one. In financial and environmental terms it may be that you are not spending your money wisely.

    There is a slightly pejorative tone in some of the above posts with respect to the ‘eco industry.’ It would be interesting to know what the OP thinks this industry is and who operates within it. Perhaps I have misunderstood, but as someone who is actively involved in helping my clients to achieve significant improvements in comfort and energy consumption on buildings old and new (unlisted and listed) I would be being professionally remiss if I overlooked the importance of addressing fabric enhancements to reduce heat loss through poor insulation, as part of a package of recommendations. It is always advisable in my view to find the best balance of measures that straddles the various needs, encompassing physical and financial constraints.

    I would be disappointed if I thought any of my clients were under the impression that I was an insulation zealot with scant regard for anything else. This is not the ‘eco industry’ if indeed there is such a thing.

    My colleagues and I work in the ‘construction industry’ in one way or another but we are all united by a desire to improve the quality of the built environment in comfort and energy terms. We always pay the utmost respect to the character of any existing building on our books.

    Do not consult with a heat pump salesperson to improve your property – consult with an independent who will provide a holistic assessment of your situation, together with a targeted plan for making it happen.

    I think the broad philosophical approach to exercise caution with regards to moisture in old walls is sensible, as is that to focus on dealing with unwanted ventilation heat losses, however those draughts are probably keeping the building dry by dealing with internal moisture, so a whole house approach needs to be taken whereby the impact of one measure is understood and appropriate action taken if needed to deal with knock-on effects.

    Good luck with it all!

  13. Russell Smith on January 18, 2011 at 10:55 pm

    This is a very interesting discussion. I hope I can add some substance on two counts. Firstly the question of Passive Haus retrofitting. The question we must ask ourselves is whether it will ever be a realistic approach for the entire UK whether in the short or long term. At this time reaching these low levels of energy consumption costs considerably more than say an average 60% reduction on CO2 (and I know this means a variety of things dependent on the baseline). Based on our extensive database of houses that we have modelled in detail over the past 5 years, we have published the resultant costs vs benefits of a range of packages applied to a wide variety of houses.

    You can see that as deeper of energy savings are achieved, there is an exponential rise in the cost of application. Reaching those depths is invariably about expenditure in renewables and tradespeople spending greater time on careful application of insulation and airtightness. The only way to avoid this is a sudden improvement in technology. Will we ever see this?

    By aiming for a fabric focussed reduction in CO2 towards a 60% saving we could consider that by providing greater controls on heating, and improve lifestyles to minimise internal temperatures through better feedback (smart meters may help this) followed by grid decarbonisation, we simply may not need to event think about Passive Haus retrofit. Lots of assumptions here maybe, but before we spend huge buckets of money on one off house, consider how many others houses we could have renovated with that money to a perfectly adequate standard…….

    On a second count – heat pumps. We’ve also published more analysis following repeated analysis results showing that any kind of heat pump will not give the ‘advertised’ benefits for any house on the gas grid and in fact might lead to rise in fuel bills.
    Anyone happy with a COP of 225?

  14. Alan Tierney on January 20, 2011 at 3:20 pm

    Some very good points made by Russell.

    You are absolutely spot on to point to lifestyle & how we use buildings as key to this issue. In fact there are indications that many fabric improvements are negated by changes in lifestyle which follow from them. e.g. rebound effects (maintaining a higher room temperature because it can be done at a lower cost after retrofit); spending extra disposable income (derived from lower heating costs) on carbon intensive activities, such as flying.

    This just goes to show how complicated the subject is. It’s hard to swallow, but it is entirely possible that reducing domestic energy costs will actually make things worse rather than better.

    How do you influence behaviour and lifestyle on the required scale?? The only convincing suggestion I’ve seen so far is the elimination of the winter time change to GMT, which is forecast to deliver massive energy savings.

    I also agree that, as things stand, for anyone on the gas grid conventional heating is likely to be the best solution. Of course future gas prices and fuel security may become significant issues in time.

  15. Brian Smith on January 23, 2011 at 4:51 pm

    These discussions have been fascinating. Thanks to everyone who has contributed.

    My wife and I have become increasingly despairing. We seriously want to break away from dependence on fossil fuels, partly because the price of all of them will incase dramatically – far more than the odd doubling we’ve seen in recent years – but also because if we don’t, then the future for the human race is a litle less certain.

    However, whichever technology we look at the results are the same: you can spend £10-£20 thousand on equipment but your savings will be about £50 a year if you’re lucky.

    The energy saving trust website gives figures for our house for a variety of scenarios and all are dreadful. Just not worth doing unless one has a lot of spare money or strong green motives.

    The RHI might sway the figures but not by an enormous amount. Not really enough to make oil less of an option. So it looks as if we’re going to have to just bung in oil-fired heating because we’re not made of money. Having said that, my worst-case scenario is that oil could double in price every year for the foreseeable future.

    Even wood pellets, which sound very Eco-friendly, and are carbon neutral (they release the CO2 the trees absorbed, they tell me) turn out to be dearer than oil to buy. And as oil prices rise, you can bet that wood pellets will mirror the rise – because they can.

    So we feel trapped.

  16. mike jacob on February 2, 2011 at 2:22 pm


    I feel your pain. Not wishing to use this as an overt opportunity to solicit for work but perhaps you might want to contact me for an informal chat about your situation in more detail?


  17. Philip Proffit on February 19, 2011 at 4:08 pm

    As a director of Ryder Strategies I was responsible for the design and retro-fitting of 100 Princedale Rd.
    I hear a lot about the economics of this project, the fact is that the spend was not massively more than the total refurb cost that this building needed anyway.

    There seems to be too much focus on cost and payback. I would like to make the point that the comfort levels of a passive house such as no. 100 are enough of a reason to justify such a retro fit. The well ventilated atmosphere and warm tranquil atmosphere experienced inside the property are a direct contrast to my own victorian house not far away.

    The useable space inside the house is much greater, I could not think about sitting next to the window with minus temps outside in my own house and the massive reduction of outside noise experienced, especially at night would be shear luxury.

    We should remember that the passive house specification does provide many advantages and I am sure that a 94 o/o reduction in energy costs is just one.

    We should remember that while we question whether passive house is what we want in this country many mainland European countries have now adopted this as their normal standard for not just housing, but also public buildings as well. They are now enjoying an improved quality of life that these buildings bring not to mention the reduced energy benefits that are strategically important to their countries.

    We have shown that victorian buildings in conservation areas can be made into passive houses, Princedale is one of two Victorian Houses that we have retro fitted. The economics are not at all bad, our next stage is to develop our solution to make them easily repeatable for mass refurbs.

    Philip Proffit